research questions about the great barrier reef

Frequently asked questions

Background information and frequently-asked questions about coral reef restoration and the approaches taken by RRAP to develop tools to enhance the natural resilience of the Great Barrier Reef.

Climate change is widely recognised as a key threat to the Great Barrier Reef. The accelerating negative impacts of climate change threaten to overwhelm natural rates of reef adaptation. These threats include:

increasingly frequent and severe coral bleaching

increasingly frequent and severe and weather events, such as cyclones and floods

ocean acidification.

Corals have a mutually-beneficial relationship with microscopic photosynthetic algae (zooxanthellae) that live in their tissues.

Corals provide the algae with a protected environment and compounds needed for photosynthesis. In return, the algae provide much of the nutrition for the coral.

When the water temperature exceeds that normally experienced on the reef, algae are lost from stressed coral, leading to the white appearance that is termed bleaching.

If the heat stress is not too extreme, and water temperature returns to normal, it is possible for the corals to regrow their algae, and for the bleaching to be reversed, although health effects can be felt several years following recovery in some species.

With prolonged or extreme temperature stress, bleached corals will die.

The ocean’s chemistry is significantly changed when carbon dioxide is absorbed by the ocean: CO 2 reacts with seawater, producing acid, which reduces coral’s capacity to build skeletons.

There are already some very promising reef restoration and adaptation measures, which may help buy time for the Great Barrier Reef – and other coral reefs in Australia and around the world – while the nations of the world reduce carbon emissions to sustainable levels, and global temperatures stabilise.

These are at different stages of development, and most need further research. In addition, methods to affordably scale up the technology for a significant, positive impact on the Reef ecosystem need developing. Building the Reef’s resilience to increasing water temperature, and other stresses, is complex and challenging.

The Reef Restoration and Adaptation Program is working with different groups with a stake in the Reef – as well as Australians generally – to better understand how they see the risks and benefits of restoration and adaptation actions.

This will inform planning and prioritising of reef restoration measures, to ensure the proposed actions meet ecological and community expectations. The aim is to create a suite of acceptable measures that can be used for medium to large-scale reef restoration and adaptation.

Coral reefs are in decline worldwide. Climate change has reduced coral cover and surviving corals are under increasing pressure. Rising ocean temperatures and marine heat waves led to mass coral bleaching on the northern and central Great Barrier Reef in 2016, 2017 and 2020, compounded by cyclones and outbreaks of coral-eating crown-of-thorns starfish.

The frequency and severity of bleaching events is forecast to increase, in line with climate change predictions. Many corals already live close to their temperature tolerance limit and their ability to naturally adapt to increasing temperatures may not be sufficient given the magnitude and rate of global warming.

Despite the alarming outlook, the Great Barrier Reef still has high biodiversity, natural beauty and resilience. Commitments by governments to the targets of the Paris Climate Agreement could limit global warming to between 1.5°C and 2°C above pre-industrial levels (noting the Reef has already warmed by ~1°C). This gives us a window of opportunity to develop additional actions to support the resilience of coral reefs and to sustain their values and services.

RRAP is investigating ways to assist the Reef’s capacity for recovery and adaptation. The ultimate aim is to help protect coral species that provide critical habitat for 35 percent of the world’s fish, thousands of other marine species, and support livelihoods and economies worth hundreds of billions.

RRAP aims to take an integrated three-point approach to intervention to help the Great Barrier Reef resist, adapt to and recover from the impacts of climate change:

• cooling and shading the Reef to help  protect it  from the impacts of climate change
• assisting reef coral species to evolve and  adapt  to the changing environment, to minimise the need for ongoing intervention
• restoring  damaged and degraded reefs.

The program’s focus will be on protection and adaptation to prevent or minimise degradation and thus the need for restoration.

More information

Global emissions reduction remains the most important action to minimise the impact of climate change on the Great Barrier Reef and other coral reefs of the world. However, even if global warming can be kept within 1.5 degrees Celsius above pre-industrial (the most optimistic goal of the Paris Climate Agreement),  the world is set to warm another 0.5 degrees Celsius in the coming decades .

Because corals already live close to their temperature tolerance limit, this amount of warming will likely be too much for many sensitive coral species, including those that build important fish habitat. Emissions reduction, on its own, is no longer enough to guarantee the survival of the Great Barrier Reef as we know it. Safeguarding the Reef requires new interventions in addition to strong carbon mitigation and best-practice conventional management.

The additional warming the Reef will experience will depend not only on the latent warming already in the system,  but also future emission trajectories . RRAP has evaluated the costs, feasibility and risks across multiple scenarios: climate change trajectories and social/economic futures.  The Reef will have its best chance of maintaining biodiversity and ecological value if additional warming can be minimised and if people continue to care about the Reef and support its management . If global warming exceeds 2°C above the pre-industrial level,  we will need to consider more radical interventions and measures of adaptation to build resilience. RRAP is evaluating a range of potential interventions including large-scale cooling and shading techniques and  developing enhanced, heat-resistant corals to help increase reef adaptation to the changing conditions. Taking these approaches to protect key species in key target locations could maintain critical Reef values under less favourable climate scenarios. Importantly, CO 2 mitigation and continued water quality management, crown-of-thorns starfish control and no-take areas will be more important than ever, and the prerequisite for a successful reef adaptation program.

RRAP interventions would aim to harness the Reef’s natural processes of larval dispersal to help spread resilient species or populations to reefs that urgently need climate tolerance. Where possible, we would help the Reef help itself. A small subset of the Reef’s 3000 individual reefs can help colonise corals on large areas of the Reef in a short time . RRAP research includes understanding and designing strategies for when and where RRAP interventions would be most effective. RRAP is focused on the recovery and survival of coral species that serve key ecological functions and underpin multiple Reef values. These include species that build important fish habitats. In addition to using natural Reef processes to help us scale up interventions in key areas, RRAP is working closely with engineering and technology sectors to develop innovative deployment solutions that can be delivered cost effectively at scale.

Corals have adjusted and adapted to their environment over decades to millennia. For example, corals in the Persian Gulf survive temperatures that are too extreme for coral species elsewhere, while certain coral species naturally tolerate more acidic (lower pH) water. On the Great Barrier Reef, temperatures vary by several degrees from north to south, and large temperature differences also exist within reefs between habitats and depths. The thermal tolerance of corals reflects their local temperature environment. This means corals in the northern Great Barrier Reef bleach at higher temperatures than those to the south. With rapid global warming, the key question is whether rates of natural adaptation are fast enough to keep up.

Adaptation can occur through a variety of ways and can be fast under the right conditions. Genetic adaptation occurs through changes in the organism’s DNA. Epigenetic changes involve modifications to the chemical switches on the DNA and can sometimes be passed from parents to offspring. RRAP aims to understand how adaptation in stress tolerance can be harnessed and enhanced over short time frames to help coral become more temperature tolerant.

The current rate of environmental change, and back-to-back bleaching events in 2016, 2017 and 2020, raised concerns that most reef-building coral will not be able to adapt fast enough. Recent research has found the Reef’s resilience may already be impaired with significantly reduced rates of coral recruitment and recovery following the bleaching events. Ultimately, this could result in a catastrophic loss of coral. Because corals build habitats and reef structure, they are foundational for much of the Reef’s biodiversity. Losing coral therefore means losing functions, and consequences could be devastating for all reef life and the people and economies who depend on it. The result could be a Reef with few ecological, social and economic values intact.

The Great Barrier Reef is home to around 600 different species of corals, many of which serve different functional roles. For example, some coral species are important as fish habitats, while others promote reef recovery after disturbances. Loss of coral means loss of habitat and food for fish, themselves potentially also directly impacted by climate change. This can lead to changes to the ecosystem, for example an increase in seaweeds that make it difficult for coral larvae to recruit to the reef and for adult corals to survive and recover. RRAP will explore solutions that will assist the recovery and survival of coral species that serve both key ecological functions and underpin multiple Reef values.

Conventional coral reef management on the Great Barrier Reef is currently focused on protecting reefs through zoning, managing and improving water quality and managing the populations of coral-eating crown-of-thorns starfish . These efforts remain critical to support reef recovery between bleaching events and storms. However, the gain in reef resilience from conventional efforts, even if they are intensified, cannot compensate for the stress caused by more frequent and severe bleaching events. In short: climate change will increasingly affect the Reef’s natural resilience despite the best conventional management efforts.

Keeping the Reef healthy in the future will require a multi-pronged strategy that combines:

• climate mitigation
• best-practice conventional management to minimise multiple, cumulative stressors
• additional interventions designed to boost climate tolerance and resilience .

The Great Barrier Reef and all other coral reefs in the world are changing as a result of impacts from human activities including climate change – with or without our best interventions. RRAP aims to provide solutions to help the Reef help itself, to maintain the ecological functions and species that support biodiversity, tourism and fisheries and give the Reef the best chance of survival in the future.

The Great Barrier Reef is home to many thousands of species, so the challenge will be to identify the species that most urgently need help while considering what species provide values for the ecological health of the Reef and society. Some species of coral that are homes for fish are also the most sensitive to climate change so they should be considered a priority.

Some species are seen to play more important roles in ecosystems than others. This importance is of course judged by people and relate to whether species support functions that underpin biodiversity and ecosystem services. RRAP will work with Reef stakeholders to develop a set of criteria against which we will develop strategies and alternatives for interventions. This includes the evaluation of “ecosystem engineers” (e.g. coral species that build structure and habitats), “keystone species” (which impact on other species), and species that have high aesthetic, recreational or commercial values.

Genetic engineering of corals or their symbionts is one of many ways we might help corals become more tolerant to bleaching in the future. Genetic engineering provides a way to precisely edit specific genes that regulate for heat resistance or to insert genes that increase heat tolerance or disease resistance. However, the application of genetic engineering solutions for the Reef will require extensive research and development, assessments of benefit and risk, plus legislative approvals that do not currently exist. RRAP will consider all options that meet the criteria of providing a net benefit for the Reef at acceptable levels of risk, scale and cost. Most of the currently proposed interventions will not involve gene technology. For example, we can consider to move warm-adapted corals or their offspring to naturally cooler places or we can use other assisted evolutionary processes to promote heat tolerance in corals. Starting the research and development and rigorously testing these tools soon gives us the best chance to use them safely and effectively in the future if or when we need to.

The right time to start any new intervention is when the risk of inaction is greater than the risk of action. As climate change intensifies, so do impacts on the Reef. Delaying the use of new interventions means foregoing opportunities to save species and values. But acting too fast with untested intervention can also pose risks from unknown side effects. To strike the right balance of minimising risk and maximising opportunity, RRAP must begin researching and development of the most promising interventions now. The longer we wait, the more expensive and difficult it will be to successfully intervene at any scale, and the greater the risk the window of opportunity will close. All new interventions will be rigorously assessed and tested, in close consultation with partners and stakeholders. The result will be an expanding set of interventions that can be ready for safe implementation if or when they are needed.

The interventions being investigated by RRAP aim to enhance the resilience of coral reefs but vary in their associated risks. For example, enhancing corals using assisted gene flow and assisted evolution represent manageable risk because they use genetic material already present on the Reef. Assisted colonisation that involves importing coral species from outside the Great Barrier Reef may carry greater ecological risk than other approaches. A full understanding and evaluation of risks is a key component of RRAP and will be evaluated from ecological, social and economic angles. They will be assessed against the risk of ‘doing nothing’ or delaying interventions. Predicted benefits will be evaulated against the chances of any potential negative outcomes. These analyses will provide clarity for all, inform a prioritisation of techniques for technological development, decision-making, facilitate a license to operate, and promote stakeholder engagement.

Our vision is that RRAP will help protect values that are critical for the health and ecosystem function of the Great Barrier Reef – its rich biodiversity, continued status as a World Heritage Area, and a place that continues to support recreation, culture and a multi-billion dollar economy. The Reef is a natural asset valued at $56 billion, an ecosystem of global significance and a critical part of the Australian national identity. By working closely with partners and stakeholders to identify interventions that sustain both ecological functions and social and economic values, RRAP will help sustain this asset for Australia and the world.

An essential part of the planning and feasibility assessment phase will be to understand not only the likely benefits and costs of possible interventions but also the ecological, economic and social risks. To do this requires a collective effort of all Reef stakeholders. RRAP will actively engage and consult with all people connected to the Reef. It will build strong partnerships between researchers, government agencies and the wider community, including Traditional Owners.

A range of reef restoration approaches have been applied on reefs around the world for decades. They have been successful in, for example, increasing coral cover or reducing algal cover on very small scales. Many projects have included gardening of corals in land-based or marine nurseries, and more recently laboratory reared coral young have been used. Despite positive reports of many restoration efforts, the cost and effectiveness of many interventions remain unclear.

RRAP is capitalising on existing knowledge and aiming to provide a step-change in the cost and scale by which active interventions can be delivered on coral reefs. To achieve this we will be working closely with the engineering and technology sectors to develop innovative deployment solutions that can be cost-effectively delivered at the required scales.

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Impacts on the Great Barrier Reef

Our scientists are working hard to understand and find innovative ways to improve the quality of water reaching the Great Barrier Reef World Heritage Area (the Reef).

The challenge

An icon under threat.

The Great Barrier Reef is under threat from a range of pressures with a major one being deteriorating water quality due to pollution from adjacent land use.

Rising water temperatures, increasing ocean acidification, Crown of Thorns Starfish (COTS), fishing, and coastal development are also impacting the Great Barrier Reef.

CSIRO has a long legacy working on the Reef and we continue to collaborate with a wide range of partners to find novel ways to preserve, protect and improve this international treasure.

Our response

Improving land management.

Many areas of the Reef still show resilience, which presents a window of opportunity to act now, while there is still enough diversity to preserve and restore.

The Reef 2050 Long Term Sustainability Plan provides the framework that can guide policy responses, but it needs to be supported by a harnessing of Australia's world-class research capability across multiple organisations, so that we can capitalise on the Reef's resilience and ability to recover.

Preserving the Reef's ecological function by 2030 is not just about its coral reefs, but of all its ecosystems.

Between 2008 and 2017, the Australian and Queensland governments spent an estimated $600 million on improving land management with the aim of enhancing the quality of water reaching the Great Barrier Reef World Heritage Area (the Reef). About half of the investment was allocated to reducing river loads of fine sediment and nutrients through improved land management.

We continue to work with rangeland ecologists and the grazing industry to develop practical and effective land management solutions for the Reef.

With our partners, we have defined the system of erosion and sediment transport processes connecting agricultural land with receiving water bodies. We have assisted the Australian Government to be more targeted in their programs to reduce sediment and nutrient delivery.

This research supports the current Reef 2050 Long-Term Sustainability Plan, through the draft Reef 2050 Water Quality Improvement Plan 2017-2022.

[Music plays and an image appears of bushland and the camera pans over the bushland and the CSIRO logo appears in the centre of the screen]

[Image changes to show a school of fish swimming and text appears: Water Quality and the Great Barrier Reef]

[Images move through to show a tortoise swimming above the reef, a colourful fish swimming amongst coral, and then a school of fish swimming in and out coral]

Dr Rebecca Bartley: We now know that climate change is the biggest threat to the Great Barrier Reef but we all need to work together on all of the elements that are impacting on the Reef including water quality.

[Image changes to show Dr Rebecca Bartley talking to the camera and text appears: Dr Rebecca Bartley, CSIRO Research Scientist and Group Leader]

We’re working in the Burdiken Catchment. The Burdekin Catchment is one of the largest catchments draining on the east coast of Australia out to the Great Barrier Reef.

[Image continues to show Dr Bartley talking to the camera and then the image changes to show a school of colourful fish swimming above the reef]

It drains just south of Townsville near Aire into the marine system and it’s enormous.

[Camera pans over an aerial view of the Great Barrier Reef]

It’s 130,000 square kilometres or the same size as England.

[Images move through to show Dr Bartley talking to the camera, Brett Abbott standing in bushland collecting samples, and then the camera pans over an aerial view of bushland]

CSIRO is focussed on understanding what some of the remediation strategies are where we can actually improve land management and reduce the amount of sediment and nutrients getting out to the Reef.

[Image changes to show Dr Bartley talking to the camera then camera pans over a catchment area amongst bushland]

So, with James Cook University we’re collaboratively linking the research between solutions in the catchment and responses in the marine system.

[Image changes to show Dr Steve Lewis talking to the camera and text appears: Dr Steve Lewis, Research Scientist, TropWATER, James Cook University]

Dr Steve Lewis: We saw the floodwaters from the Burdekin River move a long way offshore in this year’s floods.

[Image shows Dr Lewis talking to the camera and then the image changes to show an aerial view of bushland and the camera pans over the bushland]

That impinged over coral reefs and also influenced sea grass meadows within the Great Barrier Reef.

[Camera pans over an aerial view of the Great Barrier Reef and then images move through of Aaron Hawdon labelling sample bottles, holding them up, and then putting them in a locked cabinet]

During these floods we were able to take a lot of samples of the sediments in the water where we were able to do some detailed experiments on those sediments to characterise them and trace them back to a source within the Burdekin Catchment.

[Image shows Aaron putting the samples in a locked cabinet and setting a pin code while out in bushland area and then the image changes to show Dr Lewis talking to the camera]

Our project really aims to characterise the sediment that causes the most harm in the Great Barrier Reef to both coral reefs and seagrass meadows. So, we can understand where that sediment is coming from in the catchment.

[Image changes to show Aaron talking to the camera then the image changes to show Brett surveying a bushland area and text appears: Aaron Hawdon, Senior Instrumentation Specialist, CSIRO Townsville]

Aaron Hawdon: We’re using laser scanning and other survey methods to measure the change in the shape of the gullies and when we look at this over time we’re actually able to investigate where the erosion is coming from.

[Image changes to show Brett surveying a bushland area and then the image changes to show Aaron talking to the camera]

We’ll also have a suite of sensors set up inside the gullies that measure how much water flows through as well as how much sediment is actually in that water.

[Image changes to show Aaron taking samples out from the locked cabinet in a bushland area and camera zooms in on the sample bottle being turned in Aaron’s hands]

So, today we’re collecting samples from our auto sampler from a gully that we’ll later take back to the lab for analysis.

[Camera zooms out on Aaron looking at the sample bottle and then turning and talking to the camera]

So, we’ll actually find out exactly how much sediment is in this water as well as how many nutrients are in there which we can then use to determine whether our treatments are working.

[Image changes to show Brett collecting data on soil and vegetation conditions while standing holding his Smartphone in a bushland area]

Brett Abbott: On the hill slopes above the gullies we measure soil surface condition and vegetation components.

[Image changes to show Brett kneeling down in long grass while talking to the camera and then the image changes to show Brett standing looking at his phone in a bushland area and text appears: Brett Abbott, Rangeland Ecologist, CSIRO Townsville]

Data we collect here is taken back to the lab and analysed against the water quality data to look at changes over time due to the landscape management.

[Image changes to show Dr Bartley talking to the camera while seated next to Dr Lewis and then the image changes and the camera pans over an aerial view of a Landcruiser moving through bushland]

Dr Rebecca Bartley: We’ve set up a very strong team of people who have expertise in collecting real time data to support decision making about where investment about remediation to improve water quality to the Reef should be placed.

[Images move through to show Aaron typing on a laptop at a testing site, using surveying equipment, and Dr Lewis talking to the camera while Rebecca listens]

Dr Steve Lewis: And it also allows us to observe the processes that are happening in our environment so we can see where the sediment’s coming from for the major tributaries as well as where the sediment and floodwaters are moving into the Great Barrier Reef where we’re able to better target our measurements, better target the investments

[Images move through to show Aaron and Brett inside the car driving through bushland, taking samples, and the car driving through the bushland again]

and it also allows us to engage with industry to be out, physically out in the field taking these samples and engaging with different landholders to show what we’re collecting and where we’ve collected that sample from and the different processes that’s involved to process those samples.

[Images move through to show an aerial view of bushland, Dr Bartley talking to the camera, a school of colourful fish swimming through the reef, divers looking at the fish, and a school of striped fish]

Dr Rebecca Bartley: When we work with people living in the regions, working in the regions, the regional bodies, state government, federal government, and the landholders themselves I think we actually have a chance of making that difference for the Great Barrier Reef into the future.

[Music plays and sponsors’ logos and text appears: CSIRO’s water quality work is conducted in partnership with James Cook University, the Australian Government’s Reef Trust and National Environmental Science Programme (NESP), NQ Dry Tropics and Queensland Government]

[Text appears: Additional footage supplied by Matt Curnock, Josh McJannet, and the Great Barrier Reef Foundation]

[Music plays and the CSIRO logo and text appears: CSIRO Australia's innovation catalyst]

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Besides improving water quality and land management practices, there is a range of CSIRO research underway to address all of the impacts on the Great Barrier Reef. View the extent of our Great Barrier Reef research.

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‘ Wake-up call to humanity’: research shows the Great Barrier Reef is the hottest it’s been in 400 years

Lecturer, School of Agriculture, Food and Ecosystem Sciences, The University of Melbourne

Professor, Environmental Futures & Securing Antarctica's Environmental Future, School of Earth, Atmospheric and Life Sciences, University of Wollongong

Professor, School of the Environment, The University of Queensland

Disclosure statement

Ben Henley receives funding from the Australian Research Council.

Helen McGregor receives funding from the Australian Research Council.

Ove Hoegh-Guldberg does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

University of Melbourne provides funding as a founding partner of The Conversation AU.

University of Wollongong and University of Queensland provide funding as members of The Conversation AU.

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The Great Barrier Reef is vast and spectacular. But repeated mass coral bleachings, driven by high ocean temperatures, are threatening the survival of coral colonies which are the backbone of the reef.

Our study, published today in Nature , provides a new long-term picture of the ocean surface temperatures driving coral bleaching. It shows recent sea surface heat is unprecedented compared to the past 400 years. It also confirms humans are to blame.

The results are sobering confirmation that global warming – caused by human activities – will continue to damage the Great Barrier Reef.

All hope is not lost. But we must face a confronting truth: if humanity does not divert from its current course, our generation will likely witness the demise of one of Earth’s great natural wonders.

One-of-a-kind ecosystem

The Great Barrier Reef is the most extensive coral reef system on Earth. It is home to a phenomenal array of biodiversity , including more than 400 types of coral, 1,500 species of fish and 4,000 types of molluscs, as well as endangered turtles and dugongs.

However, mass coral bleaching over the past three decades has had serious impacts on the reef. Bleaching occurs when corals become so heat-stressed they eject the tiny organisms living inside their tissues. These organisms give coral some of its colour and help power its metabolism .

In mild bleaching events, corals can recover. But in the most recent events, many corals died .

The Great Barrier Reef has suffered five mass bleaching events in the past nine summers. Is this an anomaly, or within the natural variability the reef has experienced in previous centuries? Our research set out to answer this question.

A 400-year-old story

Coral itself can tell us what happened in the past.

As corals grow, the chemistry of their skeleton reflects the ocean conditions at the time – including its temperature. In particular, large boulder-shaped corals , known as Porites , can live for centuries and are excellent recorders of the past.

Our study sought to understand how surface temperatures in the Coral Sea, which includes the reef, have varied over the past four centuries. We focused on the January–March period – the warmest three months on the reef.

First, we collated a network of high-quality, continuous coral records from the region. These records were analysed by coral climate scientists and consist of thousands of measurements of Porites corals from across the Western tropical Pacific.

From these records, we could reconstruct average surface temperatures for the Coral Sea from the year 1618 to 1995, and calibrate this to modern temperature records from 1900 to 2024. The overall result was alarming.

From 1960 to 2024, we observed annual average summer warming of 0.12°C per decade.

And average sea surface temperatures in 2016, 2017, 2020, 2022 and 2024 were five of the six warmest the region has experienced in four centuries.

Humans are undoubtedly to blame

The next step was to examine the extent to which increased temperatures in the Coral Sea can be attributed to human influence.

To do this, we used published computer model simulations of the Earth’s climate – both with and without human influence, including greenhouse gases from the burning of fossil fuels.

So what did we find? Without human influence, Coral Sea surface temperatures during January–March remain relatively constant since 1900. Add in the human impacts, and the region warms steadily in the early 1900s, then rapidly after the 1960s.

In short: without human-caused global warming, the very high sea temperatures of recent years would be virtually impossible, based on our analysis using the world’s top climate models.

There is worse news. Recent climate projections put us on a path to intensified warming, even when accounting for international commitments to reduce emissions. This places the reef at risk of coral bleaching on a near-annual basis .

Back-to-back bleaching is likely to be catastrophic for the Great Barrier Reef, because it thwarts the chances of corals recovering between bleaching events.

Even if global warming is kept under the Paris Agreement goal of 1.5°C above pre-industrial temperatures, 70% to 90% of corals across the world could be lost .

We must stay focused

The Australian government has a crucial role to play in managing threats to the Great Barrier Reef. The devastation is in their backyard, on their watch.

But what’s happening on the Great Barrier Reef should also be an international wake-up call. The fourth global mass coral bleaching event occurred this year; the Great Barrier Reef is not the only one at risk.

Every fraction of a degree of warming we avoid gives more hope for coral reefs. That’s why the world must stay focused on ambitious action to reduce greenhouse gas emissions.

Emissions reduction targets must be met, at the very least. The solutions are available and our leaders must implement them.

Our research equips society with the scientific evidence for what’s at stake if we don’t act.

The future of one of Earth’s most remarkable ecosystems depends on all of us.

The authors of this piece gratefully acknowledge the contributions of Andrew King, Ariella Arzey, David Karoly, Janice Lough, Tom DeCarlo and Brad Linsley and the producers of the coral data which made this study possible.

• Climate change
• Great Barrier Reef
• Global warming
• Coral bleaching
• Coral reefs

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THE JOURNAL OF OUR OCEAN PLANET

Is the Great Barrier Reef making a comeback?

The world’s largest reef saw record growth after years of bleaching, but it’s not out of the woods yet

Estimated reading time: 5 minutes

Ocean acidification is no big deal, right?

Is sea-level rise exaggerated?

In 2022, the Australian Institute of Marine Science (AIMS) reported the highest levels of coral cover across two-thirds of the Great Barrier Reef (GBR) in over 36 years. After recent massive bleaching events impacted nearly 90% of Australia’s corals, it seems that anyone could see this news as a victory. So, why aren’t scientists celebrating?  

“There’s no question this is positive news—these data show reefs can recover rapidly from damage,” says WHOI’s Konrad Hughen, a principal investigator on the institution’s Reef Solutions Initiative . But are they still under threat?  

“Yes, they are,” said Hughen.  

Since 2016, reef experts and marine park authorities have been in a near-constant state of damage control. Marine heatwaves, pollution, and a voracious outbreak of coral-eating crown-of-thorns starfish (COTs) have delivered sucker punch after heart-wrenching sucker punch to this popular world wonder. In 2020, a study funded through an ARC Center for Excellence found that roughly half of the Great Barrier Reef’s corals had disappeared in the last few decades, with the remainder projected to vanish in the next century if we don’t curb planetary warming. In early 2022, following four of the biggest marine heatwaves in the GBR’s history, the fever briefly broke, opening a small but significant window for some species to reclaim territory. One part of why scientists are still wary of the reef’s future has to do with which of these species are returning more than others.  

According to AIMS’s Long Term Monitoring Program , most are a weedy genus of fast-growing corals known as Acropora . These include species like staghorn, elkhorn, and tabletop corals, which, though prolific, are easily broken up by cyclones—weather events that are expected to become more frequent and intense. Worse, they’re a favorite food for COTs, a species that continues to grow more comfortable on the Great Barrier Reef as surrounding waters warm.  

Bleached staghorn corals take-up much of the seafloor on a patch of the Great Barrier Reef c.2006 (Photo courtesy of P. Marshall, © Commonwealth of Australia (GBRMPA))

“Instead of a diverse, old-growth forest, [the reef] may now be like a monoculture of planted pulp trees,’” says Hughen. With less diversity of corals on the Great Barrier, he adds, there will also be fewer structures that house and feed various species of fish and marine invertebrates. Some, like the parrotfish—a valuable grazer that keeps algae from smothering corals—have already suffered decline in the northern third of the reef following mass bleaching events that began in 2016.  

So how do we know whether to celebrate recovery on the Great Barrier Reef? This opens a long-held debate about the distinction between words like “recovery,” “recovered,” and “healthy.”   

“Health depends on your perspective,” says Hughen. “There’s a lot of variability on any given reef, so these things aren’t just perfect until they’re messed with. They’re in flux.”  

And not all scientists assess reef health in the same way. A coral biologist, for instance, may be excited at the prospect of higher coral cover, says Hughen, while a marine chemist on the same reef may find the presence of stress hormones a troubling sign. Hughen, along with colleagues on the Reef Solutions Initiative Team, are working to develop health diagnostic tools by factoring multiple indicators together—things like reef soundscapes, microbial communities, biochemical cues, and biodiversity levels.  

“We’re trying to create baselines for what ‘healthy’ reefs look like,” says Hughen.  

Currently, assessing coral cover alone can be a daunting task given the scale of the Great Barrier Reef. At more than 134,000 square miles, the reef is already bigger than the U.K., Switzerland, and Holland combined. In addition to aerial surveys, scientists with the Long Term Monitoring Program make observations by using manta tows, a technique where a snorkeler is towed in the water behind a boat to make visual assessments of coral cover, bleaching, and the presence of apex predators (among other things).  

Dr. Konrad Hughen collects seawater samples near coral colonies to study the chemical indicators of coral health. (Photo by Austin Greene, © Woods Hole Oceanographic Institution)

Like most coral reefs, the Great Barrier Reef has always experienced natural highs and lows in coral cover and biodiversity. How low those lows are, says Hughen, can tell us more about the overall impacts from human activity and climate change. During this latest period of regrowth, the Northern and Central Great Barrier reefs saw an average increase in coral cover back to 36%—up from a historic low of 27%. This may be short-lived, as the Intergovernmental Panel on Climate Change projects an additional die-off of 70-90% of global corals if the world reaches 1.5°C (2.7°F) of warming.    

There is still some encouraging news here. Despite multiple stressors like marine heatwaves, COTs, pollutants from agricultural runoff, and overfishing, this regrowth period demonstrates that the Great Barrier Reef is able to bounce back—even with one less pressure.  

“The point is that reefs are resilient and they’re always recovering , even if not fully recovered ,” Hughen emphasized. “The question is whether we’re going to keep impacting and damaging them faster than they can come back.”

A patchwork of the Great Barrier Reef frames the coastline around Queensland, Australia. (Photo courtesy of NASA)

Dietzel Andreas, Bode Michael, Connolly Sean R. and Hughes Terry P. 2020Long-term shifts in the colony size structure of coral populations along the Great Barrier ReefProc. R. Soc. B.2872020143220201432 http://doi.org/10.1098/rspb.2020.1432    

Emslie, Michael J., Annual Summary Report of Coral Reef Condition 2021/2022, Australian Institute Of Marine Science, 1 Aug. 2022. https://www.aims.gov.au/sites/default/files/2022-08/AIMS_LTMP_Report_on%20GBR_coral_status_2021_2022_040822F3.pdf . Accessed 10 Jan. 2023.  

Emslie, Michael J., et al. “Decades of Monitoring Have Informed the Stewardship and Ecological Understanding of Australia's Great Barrier Reef.” Biological Conservation, vol. 252, 2020, p. 108854., https://doi.org/10.1016/j.biocon.2020.108854 .   

Graham, N., Jennings, S., MacNeil, M. et al. Predicting climate-driven regime shifts versus rebound potential in coral reefs. Nature 518, 94–97 (2015). https://doi.org/10.1038/nature14140    

The Great Barrier Reef Marine Park Authority, and The Great Barrier Reef Marine Park Authority. Reef 2050 Plan Annual Report , Australian Government, July 2019. https://www.dcceew.gov.au/sites/default/files/documents/reef-2050-long-term-sustainability-plan-2021-2025.pdf . Accessed 8 Jan. 2023.  

Mellin, Camille, et al. “Spatial Resilience of the Great Barrier Reef under Cumulative Disturbance Impacts.” Global Change Biology, vol. 25, no. 7, 2019, pp. 2431–2445., https://doi.org/10.1111/gcb.14625 .   

Stuart-Smith, R.D., Brown, C.J., Ceccarelli, D.M. et al. Ecosystem restructuring along the Great Barrier Reef following mass coral bleaching. Nature 560, 92–96 (2018). https://doi.org/10.1038/s41586-018-0359-9    

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New 400-Year Record Shows Great Barrier Reef Faces Catastrophic Damage

Kevin Krajick

Australia’s Great Barrier Reef is under unprecedented pressure, with recent record-high sea-surface temperatures threatening to destroy its remarkable ecology, biodiversity and beauty, according to a new study. The study reconstructs 400 years of summer surface temperatures in the surrounding Coral Sea, providing new evidence that repeated recent coral-bleaching events are linked to increasingly warm summer temperatures―a result of human-caused climate change, the authors say. The study was just published in the journal Nature .

The Great Barrier Reef, encompassing some 133,000 square miles off Australia’s northwest coast, is the world’s largest reef system. It contains thousands of species of fish, molluscs, sponges, crustaceans and many other creatures. Hundreds of coral species comprise the base of the ecosystem, but the corals are stressed when water temperatures suddenly rise beyond normal levels in the austral summer. This causes them to expel the colorful symbiotic algae that inhabit their white skeletons, leading to so-called mass bleaching events. Bleaching does not kill corals outright, but it does make them more vulnerable to starvation and disease, especially if events happen frequently enough that algae populations have trouble recovering.

The research team combined sea-surface temperature reconstructions using geochemical data from coral cores previously collected from the region. They also analyzed climate-model simulations of sea-surface temperatures run with and without climate change. They found that six years over the past two decades were the warmest in the entire 400-year record. In order, starting with the warmest, these were 2024, 2017, 2020, 2016, 2004 and 2022. All the years except 2004 coincided with mass bleaching events. The study concluded that human-caused climate change is to blame.

The magnitude of the recent warming astounded the researchers. University of Melbourne lecturer Benjamin Henley , who led the study, said, “When I plotted the 2024 data point, I had to triple check my calculations. It was off the charts, far above the previous record high in 2017. Tragically, mass coral bleaching has occurred yet again this year.”

“At least over the past 400 years, the frequent bleaching going on now year to year seems unprecedented,” said study coauthor Braddock Linsley, a coral specialist at the Columbia Climate School’s Lamont-Doherty Earth Observatory. “It seems to be connected with what is going on with the global climate.”

Helen McGregor of the University of Wollongong, the second author of the study, said urgent action to stem climate change is needed to prevent devastation of the reef system. “There is no ‘if, but or maybe,’” she said. “The ocean temperatures during these bleaching events are unprecedented in the past four centuries.”

The authors say the research has implications for coral reefs throughout the world, highlighting the link between the long-term trajectory of extreme ocean temperatures and the health and biodiversity of marine ecosystems.

Adapted from a press release by the University of Wollongong.

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The biggest threats to the Great Barrier Reef

Climate change is the single biggest threat to the Great Barrier Reef, as it is to many ecosystems around the world.  The cumulative impact of climate change, land run-off and other threats is testing the ability of the Reef to recover from major disturbances.

Climate change

The most dramatic impact of climate change is on coral and other species. Increasing water temperature is one of the main causes of coral bleaching, which is becoming more common. If these events are severe and frequent enough to hinder recovery, coral can die. Scientists know that sea surface temperatures of the Great Barrier Reef have increased by 0.8°C (on average) since the late 19 th century and will continue to rise.

The indirect threats are just as great. Climate change is predicted to increase the intensity of extreme weather events such as cyclones and floods.

Linked with climate change is ocean ‘acidification’, which is caused by the oceans absorbing about a quarter of all carbon dioxide (CO 2 ) released into the atmosphere. The higher the levels of atmospheric CO 2 , the greater the impact on water quality.

Land run-off

Poor water quality, including nutrients, sediments and pesticides flowing from the land to the Great Barrier Reef from activities like agriculture, is a major threat.

Nutrients as they occur naturally in Reef ecosystems are vital. They are the natural chemical elements and compounds that plants and animals need to grow. However, if excessive amounts of nutrients, notably nitrogen and phosphorus, are brought in through land run-off, this can upset the natural balance of the Reef systems.

Impacts can include increased coral-eating crown-of-thorns starfish outbreaks, increased macroalgae abundance and algal blooms which can take over and reduce coral diversity, and reduced light available for corals and seagrasses. Excess nutrients can also increase coral bleaching susceptibility and coral disease.

Studies show that most of the excess dissolved inorganic nitrogen and phosphorus comes from fertiliser use on land. These nutrients are of greatest concern because they are immediately and completely available for uptake by marine plants. Annual discharge of nutrients from catchment land use has more than doubled since European settlement.

Sediments, like nutrients, are a natural part of Reef ecosystems, but they are also one of the biggest pressures on the health of inshore reefs and seagrass. Again, problems arise when excessive amounts of the wrong type of sediments find their way into the system. In this case, ’wrong’ refers to the very fine sediments that remain suspended in the water and can be transported long distances.

This leads to increased turbidity and decreased water clarity (the water looks muddy), which in turn reduces the amount of light that reaches seagrasses and coral, stunting their growth. When this sediment settles, it can also have detrimental effects on the early life stages of corals – even smothering coral and seagrasses in more extreme conditions. Sediment can also carry nutrients into the Reef environment.

Studies have shown that the vast majority of these unwanted fine sediments are washed into the sea from grazing activities or streambank erosion, and the impact is greater during floods.

Pesticides are a threat because what they are designed to do on land – kill pests such as  weeds and insects – means they also impact plants and animals in rivers and creeks, as well as some coastal and inshore areas. The pesticides commonly used for weed control act by inhibiting photosynthesis, which is why they are so good at controlling weeds, and can affect non-target species such as seagrasses.

Pesticides, including herbicides, insecticides and fungicides, are generally not found in the natural environment and can take months or even years to break down. They are carried in river run-off and have been detected in Great Barrier Reef ecosystems at concentrations high enough to affect organisms.

The effects of ongoing low-level pesticide exposures in inshore environments are unknown but likely to impact coral fertility and reproduction. Less is known of the effect on freshwater, wetland and estuarine ecosystems, although the proximity of these ecosystems to pesticide sources suggests some impacts are likely.

Except for a few locations, monitoring of pesticides in marine waters shows they are below the level expected to cause significant risk to ecosystems.

The effects of ongoing low-level pesticide exposures are continuing to be researched.

Other threats

The other greatest threats to the Reef are coastal development, some remaining impacts of fishing and illegal fishing and poaching.

Outbreaks of coral-eating crown-of-thorns starfish are also a big concern.

Crown-of-thorns starfish are native to the Great Barrier Reef but when found in large numbers, and when coral is under stress, they can quite simply destroy corals by eating their living tissue or ‘skin’. Research shows that coral cover on surveyed reefs fell by 50% between 1985 and 2012 and that crown-of-thorns starfish were responsible for almost half of this decline.

There have been four documented outbreaks on the Reef since the 1960s, occurring on roughly a 17-year cycle. The latest started in 2010 and a control program is in place.

However, the threat of future damage is increasing because the Reef is now under greater stress than ever before, reducing its ability to recover. Scientists believe one of the causes of that stress – increased nutrient levels – may also increase crown-of-thorns outbreaks.

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• 19 April 2024

Australia’s Great Barrier Reef is ‘transforming’ because of repeated coral bleaching

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The Great Barrier Reef in Australia is undergoing its worst coral-bleaching event on record. Credit: David Gray/AFP via Getty

Australia’s iconic Great Barrier Reef is fundamentally changing because of repeated bleaching caused by high ocean temperatures brought on by climate change, according to marine biologists.

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Can new science save dying coral reefs?

Researchers are grappling with how to preserve Australia's Great Barrier Reef—and coral reefs around the world—from warming seas.

Thirty miles off the coast of Queensland, Australia, a small piece of history was made last summer: Scientists transplanted hundreds of nursery-grown coral fragments onto the beleaguered Great Barrier Reef .

The process itself is not new—coral transplants have been used to help restore damaged reefs for decades. What’s new is that it’s happening on the world’s largest reef, an icon of marine life that has been dubbed one of the seven wonders of the natural world.

Marine biologist David Suggett is investigating the hardy corals of Low Isles mangroves, near the Great Barrier Reef, to see if these tough individuals can help other corals weather change.

The Australian authority that manages the Great Barrier Reef has traditionally resisted intervening in the reef’s ecology, preferring to let it recover naturally. But the bruising reality of climate change is forcing a more hands-on approach.

A report released on November 28 by the US National Academies of Sciences, Engineering, and Medicine (NAS) comes to the same conclusion: Human intervention is needed to ensure the persistence of the world’s coral reefs, which are of incalculable value to “human well-being, national economies, and future wonder.”

Once a popular diving spot, Opal Reef on the Great Barrier Reef has experienced severe bleaching. Scientists are looking to understand the few survivors.

These corals among the mangroves of the Low Isles can withstand high salinity and acidity, as well as extreme temperatures and tides.

“The coral report is a pragmatic list of tools for helping reefs survive climate,” says Stanford University biologist Stephen Palumbi , who chaired the NAS committee (and who is also a member of the National Geographic Society’s executive committee). “Kind of like what always happens when the panic of a crisis ebbs and you have to get down to solutions.”

On the Great Barrier Reef, that process has begun.

Almost a third dead

In 2016 and 2017, the Great Barrier Reef experienced back-to-back “marine heat waves ”—periods of elevated sea temperatures that resulted in the death of almost a third of all the reef’s corals.

For reasons that still aren’t entirely clear, coral polyps respond to elevated heat by expelling the symbiotic, photosynthesizing algae that nourish them; the loss of colorful algae “bleaches” corals and can ultimately lead to their death. Coral cover in the northern section of the Great Barrier Reef—which stretches 1,400 miles (2,300 km), roughly the length of Florida’s coastline—is now at its lowest point on record.

Members of the science team work with coral samples at the Low Isles.

Parts of Opal Reef, a popular dive tourism site and one of more than 2,900 individual reefs that make up the Great Barrier Reef system, suffered catastrophic mortality during the recent bleaching. It was here, in late August, that the coral transplantation took place.

David Suggett, a marine biologist who leads the Future Reefs Progam of the University of Technology Sydney, worked with a team of researchers and a local reef-tour company to take fragments of coral that had survived the bleaching and grow them on mesh platforms in a sandy lagoon adjacent to the reef. Twelve species were chosen, covering a range of coral forms from branching to plate-shaped to globular.

After a few months of growth and stabilization, these fragments were planted out using a novel type of clip that enables quick-and-easy attachment to the reef matrix.

PhD student Trent Haydon and Emma Camp collect samples on Low Isles.

The question the research is trying to answer, says Suggett, is whether propagation and outplanting of stress-surviving corals can speed up reef recovery, rather than having to rely on the slower natural process of coral reproduction to replace the individuals that died.

“The success of the project won’t be known until we have another marine heat wave,” says Suggett. That’s likely to be sooner rather than later.

The hammer and the vise

Large-scale coral bleaching events used to occur every 27 years, notes Australia’s independent climate-communication organization the Climate Council in a report on the reef published in July . The current rate is once every six years. If climate change is not curtailed, the report advises, by the 2030s the Great Barrier Reef could experience mass coral bleaching every two years.

By 2050, says the National Academies report, most of the world’s reefs will be exposed to bleaching conditions annually.

Corals can recover from bleaching, but not at that frequency. Hence the search for ways to boost coral abundance, such as the transplant technique Suggett is testing. Another Australian team is currently testing a different approach: They are seeding damaged patches of Great Barrier Reef with more than a million lab-raised coral larvae.

Transplanted corals are grown on platforms on sandy bottoms, before being transferred to reefs being restored.

“Recovery is the key to having reefs in the future,” says Suggett.

But so is resilience. Reefs these days are not only suffering the hammer-blows of catastrophic bleaching events. They’re also being subjected to a slow, vise-like squeezing, as our carbon emissions steadily increase the background temperature and acidity of the water around them to levels that most corals haven’t encountered before.

Worldwide, a search is on for corals that have seen such conditions—hotspots of resilience where corals have already adapted to the extremes of heat and acidity that are likely to prevail on most reefs in the coming century. The idea is that such corals—or some of their critical genes, or the symbiotic algae that nourish them—can be transplanted to more vulnerable reefs, bolstering their chances of survival.

At some volcanic vents and submarine springs, for example, where CO2 bubbles naturally from the seafloor, corals form viable calcium-carbonate skeletons in water that’s acidic enough to be lethal to corals elsewhere. In American Samoa and in Palau, Stanford’s Palumbi and his colleagues have identified shallow-water corals with exceptional tolerance for heat, and they’ve also identified some of the genes that are responsible.

Corals harvested from the mangroves at Low Isles are being transplanted to their new location on the reef at Low Isles by David Suggett and Emma Camp. First, they are "seeded" onto a metal platform.

For sustained heat extremes, few marine environments match the Persian Gulf, where summer sea-surface temperatures peak at more than 95 degrees F (35 C). Yet more than 55 species of coral live there, with bleaching threshholds several degrees higher than those for most corals. Some of them incorporate heat-tolerant symbiotic algae which, if they could be introduced to other corals, might increase their bleaching resistance.

There’s a tradeoff to be weighed, however. Research has shown that one thermally tolerant symbiotic alga, while reducing bleaching mortality by 30 percent, also reduces coral growth rates by more than 50 percent. Corals on a vulnerable reef that received such algae as a transplant might be more likely to survive a bleaching event—but they would contribute less to the reef’s recovery or to its diversity.

Solutions from the mangroves

Suggett’s team has been looking for resilient corals in a different extreme environment: near mangroves. Twenty miles closer to the mainland from Opal Reef, off Port Douglas, lie the Low Isles, a coral platform bearing a pair of small islands—one a sandy cay that’s popular with snorkellers, and the other a mangrove swamp.

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The shallow, sheltered waters in which mangroves grow are typically hotter than those flowing over an open reef, and the trees make them more acidic. Yet corals thrive here among the mangroves as well as offshore.

Suggett and his team have been studying the mangrove corals to find out what physiological and behavioral adaptations enable them to survive. They have transplanted corals from near mangroves to the reef further offshore—and vice versa.

Most coral polyps are nourished primarily by the photosynthesis of the symbiotic algae that reside in their tissues. The polyps typically remain retracted inside their skeletons during the day, emerging only at night to supplement their diet by using their tentacles to catch plankton and other organic particles in the water.

Coral reefs are sensitive and can be easily broken up by rough seas or storms.

“At night there is more plankton in the water and less risk from visual predators, so it’s a logical time for polyps to be feeding,” says Suggett. “And of course photosynthesis doesn’t happen after dark.”

By contrast, the scientists often see the polyps of the mangrove corals extended during the day. The metabolic demands of living in that harsh environment may be driving increased feeding activity. “Presumably the benefit of boosting energy intake outweighs the risk of visibility to predators,” says Suggett. As the environment on open reefs gets harsher, active feeding may become a more necessary option for corals there too.

The team heads back to the boat after samples were collected in the mangroves at Low Isles.

The coming climate onslaught

Climate pressures are intensifying and the time frames are short. Coral reefs are confronting not just rising heat and acidity but also declining oxygen levels, increasingly intense storms, and predators such as the infamous crown of thorns starfish, which remains a threat on the Great Barrier Reef.

An early morning journey out to Opal Reef is rewarded with a rainbow. The scientists' work remains unproven, but some think it offers hope for the future of surviving reefs.

Nevertheless, Suggett describes himself as a “pragmatic optimist” about the future. The great wild card, he points out, is the extent to which corals themselves are capable of adapting to the changes coming at them.

“Everywhere I go in the world, I see corals surviving where you would not expect them to,” Suggett says. “This gives me hope that there are coral communities that can cope with the stresses we’re throwing at reefs. Perhaps corals have been given less credit than they deserve in terms of their ability to tolerate and adapt to stress.”

One of the surprises at Low Isles, he says, was what happened when his team transplanted corals from the offshore reef into the mangrove lagoons—that is, from relatively benign conditions into hot, acidic ones. “We expected those corals to die,” Suggett says. “But after four months in the mangroves they have all done very well.”

That jibes with an observation by Palumbi’s team. The Stanford researchers found that the heat-tolerance genes they identified in corals in American Samoa are also present in corals in the cooler waters of the Cook Islands, 800 miles southeast. Researcher Rachael Bray, now at the University of California at Davis, found that these genes are rare in the Cook Islands today, but could spread as the waters warm.

At the rate humankind is emitting carbon, the researchers calculate, that spread probably won’t happen fast enough to ensure the survival of the reef. A slower emissions rate would help—but transplanting a few heat-tolerant corals from warmer climes could also speed the process along.

“What we’re trying to do with this work is understand what would happen in a situation where we had to rely on human intervention in order to keep reefs viable,” Suggett says. “That’s not what we want, of course. Plan A is to reduce emissions, solve climate change and take away the threat to reefs. But we have to prepare for the possibility of Plan F—dealing with global reef meltdown.

“Everyone’s wary about intervention, and rightly so, because the larger the scale of reef restoration the larger the ecological ripple effects. Let’s hope we don’t need to go there, but let’s understand the science in case we do.”

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Great Barrier Reef Waters Hottest in 400 Years, Study of Coral Reveals

The Great Barrier Reef is vast and spectacular. But repeated mass coral bleachings, driven by high ocean temperatures, are threatening the survival of coral colonies which are the backbone of the reef.

Our study, published today in Nature , provides a new long-term picture of the ocean surface temperatures driving coral bleaching. It shows recent sea surface heat is unprecedented compared to the past 400 years. It also confirms humans are to blame.

The results are sobering confirmation that global warming – caused by human activities – will continue to damage the Great Barrier Reef.

All hope is not lost. But we must face a confronting truth: if humanity does not divert from its current course, our generation will likely witness the demise of one of Earth's great natural wonders.

One-of-a-kind ecosystem

The Great Barrier Reef is the most extensive coral reef system on Earth. It is home to a phenomenal array of biodiversity , including more than 400 types of coral, 1,500 species of fish and 4,000 types of molluscs, as well as endangered turtles and dugongs.

However, mass coral bleaching over the past three decades has had serious impacts on the reef. Bleaching occurs when corals become so heat-stressed they eject the tiny organisms living inside their tissues. These organisms give coral some of its colour and help power its metabolism .

In mild bleaching events, corals can recover. But in the most recent events, many corals died .

The Great Barrier Reef has suffered five mass bleaching events in the past nine summers. Is this an anomaly, or within the natural variability the reef has experienced in previous centuries? Our research set out to answer this question.

A 400-year-old story

Coral itself can tell us what happened in the past.

As corals grow, the chemistry of their skeleton reflects the ocean conditions at the time – including its temperature. In particular, large boulder-shaped corals , known as Porites, can live for centuries and are excellent recorders of the past.

Our study sought to understand how surface temperatures in the Coral Sea, which includes the reef, have varied over the past four centuries. We focused on the January–March period – the warmest three months on the reef.

First, we collated a network of high-quality, continuous coral records from the region. These records were analysed by coral climate scientists and consist of thousands of measurements of Porites corals from across the Western tropical Pacific.

From these records, we could reconstruct average surface temperatures for the Coral Sea from the year 1618 to 1995, and calibrate this to modern temperature records from 1900 to 2024. The overall result was alarming.

From 1960 to 2024, we observed annual average summer warming of 0.12°C per decade.

And average sea surface temperatures in 2016, 2017, 2020, 2022 and 2024 were five of the six warmest the region has experienced in four centuries.

Humans are undoubtedly to blame

The next step was to examine the extent to which increased temperatures in the Coral Sea can be attributed to human influence.

To do this, we used published computer model simulations of the Earth's climate – both with and without human influence, including greenhouse gases from the burning of fossil fuels.

So what did we find? Without human influence, Coral Sea surface temperatures during January–March remain relatively constant since 1900. Add in the human impacts, and the region warms steadily in the early 1900s, then rapidly after the 1960s.

In short: without human-caused global warming, the very high sea temperatures of recent years would be virtually impossible, based on our analysis using the world's top climate models.

There is worse news. Recent climate projections put us on a path to intensified warming, even when accounting for international commitments to reduce emissions. This places the reef at risk of coral bleaching on a near-annual basis .

Back-to-back bleaching is likely to be catastrophic for the Great Barrier Reef, because it thwarts the chances of corals recovering between bleaching events.

Even if global warming is kept under the Paris Agreement goal of 1.5°C above pre-industrial temperatures, 70% to 90% of corals across the world could be lost .

We must stay focused

The Australian government has a crucial role to play in managing threats to the Great Barrier Reef. The devastation is in their backyard, on their watch.

But what's happening on the Great Barrier Reef should also be an international wake-up call. The fourth global mass coral bleaching event occurred this year; the Great Barrier Reef is not the only one at risk.

Every fraction of a degree of warming we avoid gives more hope for coral reefs. That's why the world must stay focused on ambitious action to reduce greenhouse gas emissions.

Emissions reduction targets must be met, at the very least. The solutions are available and our leaders must implement them.

Our research equips society with the scientific evidence for what's at stake if we don't act.

The future of one of Earth's most remarkable ecosystems depends on all of us.

Ben Henley , Lecturer, School of Agriculture, Food and Ecosystem Sciences, The University of Melbourne ; Helen McGregor , Professor, Environmental Futures & Securing Antarctica's Environmental Future, School of Earth, Atmospheric and Life Sciences, University of Wollongong , and Ove Hoegh-Guldberg , Professor, School of the Environment, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article .

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The Great Barrier Reef Through Time

August 9, 2020 JPEG

The Great Barrier Reef off the northeast coast of Queensland, Australia, is the world’s largest reef system and one of the richest and most biodiverse natural ecosystems on Earth. Spread across 346,000 square kilometers (134,000 square miles) of the Coral Sea, it comprises 2,500 individual reefs, more than 900 islands.

In recent years, this natural wonder has been facing multiple threats, including ocean acidification and warming sea surface temperatures that cause coral bleaching. There have been six widespread bleaching events on the reef since 1998, four of which occurred since 2016, including this year . Although still higher than normal, sea surface temperatures began to wane in early April 2022. The Great Barrier Reef Marine Park Authority is assessing the effects the bleaching event had on the reef's health and its potential for recovery.

Global sea level rise will also bring changes to the reef system, as research shows it has in the past. The Great Barrier Reef has declined, migrated, and rebounded many times before.

Part of the southern Great Barrier Reef off Mackay is shown in these images acquired on August 9, 2020, by the Operational Land Imager (OLI) on Landsat 8 .

August 9, 2020

Some fossil reef structures and the shelf upon which the modern reefs have been built are several hundred thousand years old. However, the living reef that we see today is less than 10,000 years old. It is just the latest of at least five reefs that have grown here over the past 30,000 years, according to research reported in 2018 .

The University of Sydney-led research team drilled cores in the reef at Hydrographer’s Passage off Mackay and at Noggin Pass off Cairns. They found multiple landward and seaward migrations caused by sea level change, which is the primary driver of reef growth and migration. During ice ages, massive amounts of water are locked up in glaciers and ice sheets; sea level drops and sea surface temperatures cool. During interglacial periods, sea levels rise and water temperatures warm. As sea level changes, coral polyps will build up their calcium carbonate skeletons to stay within the photic zone, the upper ocean layers where sunlight can penetrate.

At times, the reef tracked rising sea level, growing vertically up to 20 meters (65 feet) per thousand years and migrating laterally at 1.5 meters (5 feet) per year, the researchers found. At other times, however, sea level rose too quickly for the corals to keep up and the reefs were drowned. Rapid sea level drops also caused some die-offs by exposing the reef above the water surface.

The researchers also examined the reefs’ responses to changes in water depth, sea surface temperature, and the influx of sediment. “As an ecosystem, the Great Barrier Reef has been more resilient to past sea-level and temperature fluctuations than previously thought,” they wrote, “but it has been highly sensitive to increased sediment input over centennial–millennial timescales.”

NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey . Story by Sara E. Pratt .

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Geological evidence shows the reef system has a history of demise and resilience.

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References & Resources

• Great Barrier Reef Marine Park Authority (2022) Reef Facts . Accessed April 13, 2022.
• NASA Earth Observatory (2022, April 7) Great Barrier Reef Mass Bleaching Event .
• NASA Earth Observatory (2017, March 16) Stress on the Great Barrier Reef .
• Pandolfi, J. M. & Kelley, R., (2019) The Great Barrier Reef in Time and Space: Geology and Palaeobiology In Hutchings, P. A., et al. eds. The Great Barrier Reef: Biology, Environment and Management , 2e, CSIRO Publishing, pp. 25–46.
• Schmidt Ocean Institute (2020) Ice Age Geology of the Great Barrier Reef . Accessed April 13, 2022.
• Webster, J.M., et al. (2018) Response of the Great Barrier Reef to sea-level and environmental changes over the past 30,000 years . Nature Geoscience, 11, 426–432.

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Biodiversity of the Great Barrier Reef—how adequately is it protected?

Zoe t. richards.

1 Trace and Environmental DNA Laboratory, School of Molecular and Life Sciences, Curtin University of Technology, Perth, WA, Australia

2 Aquatic Zoology Department, Western Australian Museum, Welshpool, WA, Australia

3 ARC Centre of Excellence for Coral Reef Studies, James Cook University of North Queensland, Townsville, QLD, Australia

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The following information was supplied regarding data availability:

This research did not generate any data or code.

The Great Barrier Reef (GBR) is the world’s most iconic coral reef ecosystem, recognised internationally as a World Heritage Area of outstanding significance. Safeguarding the biodiversity of this universally important reef is a core legislative objective; however, ongoing cumulative impacts including widespread coral bleaching and other detrimental impacts have heightened conservation concerns for the future of the GBR.

Here we review the literature to report on processes threatening species on the GBR, the status of marine biodiversity, and evaluate the extent of species-level monitoring and reporting. We assess how many species are listed as threatened at a global scale and explore whether these same species are protected under national threatened species legislation. We conclude this review by providing future directions for protecting potentially endangered elements of biodiversity within the GBR.

Most of the threats identified to be harming the diversity of marine life on the GBR over the last two–three decades remain to be effectively addressed and many are worsening. The inherent resilience of this globally significant coral reef ecosystem has been seriously compromised and various elements of the biological diversity for which it is renowned may be at risk of silent extinction. We show at least 136 of the 12,000+ animal species known to occur on the GBR (approximately 20% of the 700 species assessed by the IUCN) occur in elevated categories of threat ( Critically Endangered, Endangered or Vulnerable ) at a global scale. Despite the wider background level of threat for these 136 species, only 23 of them are listed as threatened under regional or national legislation.

To adequately protect the biodiversity values of the GBR, it may be necessary to conduct further targeted species-level monitoring and reporting to complement ecosystem management approaches. Conducting a vigorous value of information analysis would provide the opportunity to evaluate what new and targeted information is necessary to support dynamic management and to safeguard both species and the ecosystem as a whole. Such an analysis would help decision-makers determine if further comprehensive biodiversity surveys are needed, especially for those species recognised to be facing elevated background levels of threat. If further monitoring is undertaken, it will be important to ensure it aligns with and informs the GBRMPA Outlook five-year reporting schedule. The potential also exists to incorporate new environmental DNA technologies into routine monitoring to deliver high-resolution species data and identify indicator species that are cursors of specific disturbances. Unless more targeted action is taken to safeguard biodiversity, we may fail to pass onto future generations many of the values that comprise what is universally regarded as the world’s most iconic coral reef ecosystem.

Introduction

The Great Barrier Reef (GBR) is a diverse ecosystem extending for more than 2,300 km along Australia’s northeast coast. It is recognised internationally as being of outstanding universal value ( United Nations Educational, Scientific and Cultural Organisation, 1981 ; Lucas et al., 1997 ; GBRMPA, 2014a ). Its diversity includes but is not restricted to over 410 species of hard coral, over 1,620 species of fish, 2,000 species of sponge, 14 species of sea snake, six of the world’s seven species of marine turtle, at least 300 mollusc species, 630 species of echinoderm, and 500 species of marine alga. No other World Heritage Area on the planet contains such diversity ( Day, 2016 ) and the GBR’s exceptional biodiversity values were specifically mentioned in two of the four criteria for natural heritage (ix and x) when it was World Heritage listed in 1981 ( United Nations Educational, Scientific and Cultural Organisation, 1981 ).

The long-term protection and conservation of biodiversity values is at the core of the primary legislative objective for the GBR (s. 2A of the Act, Great Barrier Reef Marine Park Act, 1975 ) of all recent GBR planning and management documents such as the 2014 Outlook Report ( GBRMPA, 2014a ), the 2014 Strategic Assessment ( GBRMPA, 2014b ) and the Reef 2050 Sustainability Plan (Reef 2050 Plan) ( Commonwealth of Australia, 2015 ) reflect this. However, a recent report on the feasibility of the Reef 2050 Plan suggests that maintaining the GBR’s Outstanding Universal Value and biodiversity as we know it may no longer be realistic, and it is recommended that the key managerial focus should be preserving the ecological function of GBR ecosystems ( Roth et al., 2017 ).

This recommendation is based on the ongoing habitat deterioration of the GBR, even in sectors where there is minimal human influence ( Hughes et al., 2017 ). It is also based on the finding that windows of opportunity for recovery after disturbances are narrowing ( Hughes et al., 2018 )—a consequence of the lack of progress that has been made towards global emission and local water quality targets. While such a policy change may be inevitable, it should not preclude biodiversity conservation. In addition to the moral and aesthetic reasons for protecting biodiversity, the conservation of diversity is important for protecting the functioning and resilience of the ecosystem as a whole. This is because inherent variation in species responses to, and recovery after disturbances provides ecological insurance in the face of change ( Nyström et al., 2008 ). Furthermore, diversity buffers ecosystems against environmental change and increases the stability and functioning of ecosystem processes ( Griffin et al., 2009 ; Loreau & de Mazancourt, 2013 ). Conversely, species loss can accelerate change in ecosystem processes ( Stachowicz, Bruno & Duffy, 2007 ; Perrings et al., 2011 ; Hooper et al., 2012 ) and the extinction of a species may have unforeseen impacts ( Dulvy, Sadovy & Reynolds, 2003 ).

There is little doubt that quantitative scenarios for the future of biodiversity in the 21st century are bleak ( Pereira et al., 2010 ), however there is still a chance to intervene through better policies. Given biodiversity is so intimately related to ecosystem functioning, in this review, we focus on the biodiversity values of the GBR. We acknowledge that in complex and socio-economically valuable ecosystems where there are multiple stakeholders and users, conservation decisions should never be made with biodiversity data alone. However, the purpose of this review is to introduce the biodiversity values of the GBR, summarise the threats directly or indirectly impacting these values, evaluate the status of marine life and examine the influence of scale on threatened species management approaches. Our objective is not to provide an exhaustive commentary on the biodiversity conservation literature (see Yoccoz, Nichols & Boulinier, 2001 ; Stem et al., 2005 ; Ferraro & Pattanayak, 2006 for general reviews of monitoring and evaluation in conservation), or the challenges faced by environmental managers and policymakers (see Anthony, 2016 ), but rather to highlight opportunities for optimizing the evaluation and protection of biodiversity on the GBR.

Survey Methodology

The 2014 GBR Outlook Report ( GBRMPA, 2014a ) was chosen as the initial primary source of key references of the key threats/pressures impacting upon the GBR. The 2014 Outlook Report is a comprehensive compilation of information about the GBR underpinned by many references. Searches of the Outlook Report were undertaken against the following keywords: climate change, water quality, coastal development, shipping, unsustainable fishing, diseases, pests, and marine debris. Eighty-two articles that referred to the consequences, impacts or implications of the threats/pressures for species on the GBR were retained and included in Table S1 . Table S1 was further augmented by conducting the same keyword searches of the James Cook University library, with only those articles directly relevant to species on the GBR retained. Articles that did not refer to consequences, impacts or implications of the threats/pressures for species were excluded. Precedence was given to articles published within the last 15 years; however, five articles published in the 1990s were included in Table S1 as they provided critical information not available elsewhere. In total, 125 titles were included in our review of the key threats/pressures impacting species within the GBR and these are listed in Table S1 . We also conducted Google Scholar searches focusing on the ecological, environmental management, and conservation planning literature for articles relating to the challenges presented by monitoring and managing diversity in coral reef ecosystems, coral reef surrogates and proxy metrics. We examined the 2014 GBR Outlook Report ( GBRMPA, 2014a ) to quantify how many species were known from the GBR and the threatened status of these fauna based on national (EPBC Act: http://www.environment.gov.au/marine/marine-species/marine-species-list ) and international threatened species lists (IUCN red-list http://www.iucnredlist.org/ ). This comparison was undertaken for approximately 700 species (including hard corals, sea cucumbers, giant clams, grouper, wrasse, parrotfish, sharks, rays, sea snakes, turtles, whales, dolphins, and dugong) whose conservation status has been assessed at a global level. Lastly we used a Google Scholar search to locate titles that relate to optimal coral reef monitoring and alternative coral reef monitoring technologies.

Results and Discussion

Current status of the diversity of marine life on the gbr.

Despite significant management actions ( Fernandes et al., 2005 ; Commonwealth of Australia, 2015 ), the diversity of marine life on the GBR is threatened by seven key pressures (climate change, declining water quality, coastal development, shipping impacts, fishing impacts, diseases and pest species, and marine debris) ( Fig. 1 ). These direct or indirect pressures have led to at least 43 impacts which may adversely impact species on the GBR ( Fig. 1 , see also Table S1 ). The latest extensive impact, the back-to back thermal stress events in 2015–2016, led to 91% of surveyed GBR reefs experiencing coral bleaching ( Hughes et al., 2017 ). This large-scale coral bleaching event heightens concerns about whether the biodiversity values of the GBR are intact because it occurred at a time when parts of the GBR system were recovering from three category five cyclones (2010–2015, Perry et al., 2014 ), and a legacy of cumulative pressures (e.g. the commercial harvesting of dugongs, green turtles, pearl shell, trochus, and sea cucumbers; catchment management issues, including land clearing, changes to natural water flows and water pollution ( GBRMPA, 2013a ; Anthony, 2016 )).

Cumulative impacts on the Great Barrier Reef that are directly or indirectly affecting species. For more information on key threats/pressures and the implications for species see Table S1 . Water quality image—Photographer: C. Honchin, Copyright Commonwealth of Australia (GBRMPA); Marine debris image—Photographer: S. Whiting, Copyright Commonwealth of Australia (GBRMPA); Shipping image—Photographer: P. Howorth, Copyright Commonwealth of Australia (GBRMPA); Coastal Development image courtesy Queensland Government Department of Heritage and Protection under Creative Commons Attribution 3.0 Australia (CC BY) license ( http://www.ehp.qld.gov.au/legal/copyright.html ). All other images by Zoe Richards.

Prior to the 2016 bleaching event, both habitats and species in the southern two-thirds of the GBR, and particularly in the inshore areas, had reportedly declined ( Brodie & Waterhouse, 2012 ; GBRMPA, 2009 , 2014a ; Osborne et al., 2011 ). A temporal analysis of the level of coral cover indicated that from 1985 to 2012 reef-wide coral cover declined by an average of 0.53% per year from 28.0% to 13.8% ( De’ath et al., 2012 ). Between 1988 and 2003 coral calcification rates are also reported to have declined from 1.96 g cm −2 year −1 (±0.05) to 1.59 cm −2 year −1 (±0.04), equivalent to a decline of 14–21% over this period ( Cooper et al., 2008 ; De’ath, Lough & Fabricius, 2009 ). Degradation was not, however, restricted to the corals; sea grass health, particularly in central GBR was poor ( Fairweather, McKenna & Rasheed, 2011 ; McKenzie, Collier & Waycott, 2015 ), dugong numbers had declined abruptly ( Marsh et al., 2001 ; Sobtzick et al., 2012 ), hawksbill turtles were in decline ( Bell, Schwarzkopf & Manicom, 2012 ) and some sharks, rays, and large fish populations were in decline, especially in coastal and inshore areas ( Chin et al., 2010 ; Ceccarelli et al., 2014 ). Overall, even before the 2016 bleaching event, the inherent resilience of this globally significant reef ecosystem had been seriously compromised and there was a concern that numerous elements of the biological diversity for which it is renowned may have been at risk ( World Heritage Committee, 2014 , 2015 ; Day, 2015 ).

In complex and dynamic ecosystems like coral reefs, biodiversity in the true sense of the word—encompassing genetic, species, community, and ecosystem diversity is enigmatic ( Gaston, 1998 ). On the GBR at least 12,000 species of marine vertebrates and invertebrates have been reported ( Table 1 ; Pitcher et al., 2007 ; Hutchings, Kingsford & Hoegh-Guldberg, 2008 ). However, this estimate of species diversity is highly conservative. For many groups, only preliminary estimates are available and these are often based on survey data that were collected 20–40 years ago. Furthermore, condition and trend information is only available for only a limited number of species ( Fabricius & De’ath, 2001 ; GBRMPA, 2014a ); hence even for many large charismatic species of high conservation significance, the status of populations is uncertain ( Hamann & Chin, 2015 ). Cryptic lineages ( Schmidt-Roach et al., 2013 ); new species (e.g. Hooper & Van Soest, 2006 ; Miller & Downie, 2009 ; Sutcliffe, Hooper & Pitcher, 2010 ; Hunter & Cribb, 2012 ; Schmidt-Roach, Miller & Andreakis, 2013 ; Capa & Murray, 2015 ) and even entire habitats such as sponge gardens, mesophotic reefs, and deep water corals, are still being discovered and mapped (e.g. Bridge & Guinotte, 2012 ; Bridge et al., 2012 ; Beaman, 2012 ; Harris et al., 2013 ; López-Cabrera et al., 2016 ; McNeil et al., 2016 ).

The number of animal species known to occur on the GBR contrasted with the number listed on national and global threatened species lists. Adapted from the 2014 Outlook Report ( GBRMPA, 2014a ) and the 2016 IUCN Red List.

Current approaches to informing coral reef management for biodiversity conservation

The task of protecting marine biodiversity is immense and exacerbated by the logistic challenges of conducting species-level surveys and the high level of taxonomic expertise needed to identify species. Hence, including a large number of species in routine monitoring can be regarded as both impractical and in some cases ineffective ( Bottrill et al., 2008 ). Moreover, in contemporary conservation science there is a growing view that monitoring can be a waste of resources rather than a prerequisite for optimal management ( Legg & Nagy, 2006 ). This perspective has been fuelled by the decades of monitoring studies that have reported population declines with no apparent link to management objectives ( Nichols & Williams, 2006 ), or without any responsive action being taken. Furthermore, the amount of money and capacity required to protect all biodiversity is considered astronomical and far beyond the current investment in conservation action ( James, Gaston & Balmford, 2001 ). Hence, by necessity, ecosystem management approaches adopt a triage approach that involves prioritizing the investment of scarce resources in a reduced set of factors that are more manageable ( Bottrill et al., 2008 ; Wilson et al., 2011 ).

The principal way managers are informed about the status of biodiversity is through surrogate information (defined in Hunter et al., 2016 ). In some cases, surrogate information can relate to subsets of data about indicator species ( Gardner et al., 2008 ), cross-taxon surrogates ( Rodrigues & Brooks, 2007 ), broad habitat-based proxy metrics ( Dalleau et al., 2010 ) or abiotic surrogates ( Beier et al., 2015 ). Some have argued that proxies reduce the time and cost required for data collection ( Humphries, Williams & Vane-Wright, 1995 ; Favareau et al., 2006 ) suggesting that developing indicator, surrogate or proxy metrics that adequately represent diversity trends is an important and pragmatic conservation objective ( Baillie et al., 2008 ). Numerous other studies, however, have questioned the ability for proxy metrics to effectively represent diversity ( Araújo et al., 2001 ; Rodrigues & Brooks, 2007 ; Andleman & Fagan, 2000 ), highlighting that all proxy metrics have limitations ( Pressey, 2004 ) especially if their performance is not evaluated with empirical data ( Vellend, Lilley & Starzomski, 2008 ). One study examining the efficacy of biological surrogacy in seabed assemblages on the GBR indicated that no one taxonomic group was a particularly good surrogate for another and recommended that examining multiple taxonomic groups together was the preferred approach ( Sutcliffe et al., 2012 ).

On the GBR, the overwhelming majority of diversity surrogate information is collected (and reported) at a habitat level. Relatively little data is available at the species-level. For example, all but two of the references cited in the 2014 Strategic Assessment ( GBRMPA, 2014b ) and the 2014 Outlook Report ( GBRMPA, 2014a ) to substantiate the condition and trend of coral species diversity on the GBR relate to the percentage of live coral cover. Likewise, a recent paper documenting the impact of the 2016 coral bleaching event ( Hughes et al., 2017 ) reports species-level responses for only two of the 410 coral species known to occur on the GBR despite claiming to document the resistant corals and susceptible species. Moreover, 21 taxa were recorded at the level of genera, two genera were further broken down into growth forms, three taxa were reported at the family level and soft corals were reported at the level of order. Despite their important role as ecosystem engineers, for hard corals, there has not been a comprehensive species-level assessment of coral diversity on the GBR since 2001 ( DeVantier et al., 2006 ) and species-level information is not routinely collected or reported on, hence the only species-level data available to underpin management decisions about the status of coral biodiversity on the GBR is now over 15 years old.

The situation is worse for other neglected marine taxa—no current information on status or trends exists for the overwhelming majority of marine taxa including highly targeted and vulnerable taxa such as sea cucumbers and giant clams ( Purcell et al., 2014 ). Thus, given multiple disturbances (e.g. including bleaching and mortality events, cyclones, freshwater flood plumes, and a new outbreak of crown of thorn (COT) sea stars ( Acanthaster planci ) have impacted the GBR over the last decade, the questions remain—how can we be sure we are adequately protecting biodiversity if we have only a partial understanding of what is there? Do we have adequate data to evaluate how biodiversity has responded to both management efforts and disturbance events?

Coral cover is a poor surrogate for biodiversity

On coral reefs, habitat proxies are commonly used to quantify the condition of coral reefs, with percent live hard coral cover being the most widely used metric in monitoring studies ( Bruno & Selig, 2007 ; Eakin et al., 2010 ; De’ath et al., 2012 ). It is stated in the Reef 2050 Plan that the extent, condition and trend of habitat provide the best indicators of biodiversity ( Commonwealth of Australia, 2015 ). However, despite its broad use, hard coral cover is not a robust indicator of coral diversity. A study undertaken at Lizard Island on the GBR showed that coral cover was not an effective proxy for coral diversity because coral cover is not related to species richness as a positive linear function ( Richards, 2013 ). To further explore the generality of this finding, the study was repeated at four additional locations (Ashmore Reef, Kosrae-Micronesia, Majuro-Marshall Is., and Christmas Island; Richards & Hobbs, 2014 ; Ryan, Richards & Hobbs, 2014 ). In those studies, percent live coral cover consistently performed poorly as an indicator of coral species richness ( Fig. 2 ).

(A). The results of a survey conducted at Lizard Island based on 28 sites showed that there was a polynomial relationship between coral species richness and percent live coral cover (adj r 2 = 0.351, SE 10.789, df = 25, p = 0.001) and significance of the quadratic term in multiple regression suggested a non-linear relationship where species richness peaked at intermediate levels of coral cover (Adapted from Richards, 2013 ). (B). When repeated at Christmas Island, no significant ( p > 0.05) linear or polynomial relationships were found between percent live coral cover and species richness at any scale (site, depth or transect) (Adapted from Ryan, Richards & Hobbs, 2014 ). (C). When the relationship was analysed at three additional locations Pacific and Indian Ocean locations, the overall r 2 values were considered too low (i.e. below 0.7) to provide meaningful estimates of coral species richness regardless of the scale of analysis (black bars: site means; white bars: transect level) (Adapted from Richards & Hobbs, 2014 ).

Numerous studies have maintained that the level of coral cover can be used to make inferences about fish biomass ( Chabanet et al., 1997 ); the prevalence of coral diseases ( Bruno et al., 2007 ); reef accretion potential ( Perry et al., 2012 ) and arguably reef aesthetics ( Pocock, 2002 ) or the economic value of reefs relating to tourism ( Stoeckl et al., 2011 ). However, focusing solely on collecting data on habitat condition using general indicators such as coral cover is counter-productive to species conservation because when used in isolation, habitat proxies are not informative about ecological condition ( Hughes et al., 2010 ), functionality ( Alvarez-Filip et al., 2013 ) or diversity ( Richards, 2013 ). Moreover, the finding of high coral cover can be deceptive because cover can be driven by the dominance of a small number of species whilst a high level of diversity can be sustained even when coral cover is low or moderate. Thus, it is important to note that a habitat with high coral cover does not guarantee functional diversity (defined by Cadotte, 2011 as the trait variation in an assemblage), or community reassembly after disturbance ( Hughes et al., 2010 ). Communities with high coral cover may be dominated by one or a small number of species and a single disturbance event (i.e. selective bleaching, disease outbreak or COTs infestation) could wipe out these dominant habitat formers with cascading ecosystem effects. With greater diversity comes the increased likelihood that some species would survive disturbance events and that critical functions such as reef building will be maintained. Thus, monitoring coral cover alone can fail to alert decision-makers to declines in resilience and it may in-fact mask losses of resilience.

The risk of silent extinctions in the absence of an effective understanding of biodiversity

Without appropriate empirical baseline data (e.g. current population size and trend data), it is impossible to accurately detect or predict population growth, depletions, range shifts, to identify species with superior tolerance or to understand how species respond to management effort. Furthermore, without baseline data it is likely that extinctions may be occurring as unrecorded silent extinctions ( Myers & Ottensmeyer, 2005 ). Silent extinctions may initially take place as ecological extinctions (when a species is reduced to such low abundance that, although still present, it no longer plays its typical ecological role); but they may also occur as undetected local extinctions (the disappearance of a species from part of its range) ( Estes, Duggins & Rathbun, 1989 ). Both of these types of extinctions are precursors to wider extinction events.

Even though there have been few, if any, known extinctions on the GBR, there is reason to believe that the threat of extinction is growing in tandem with the increasing frequency and velocity of disturbance events. The GBR Strategic Assessment ( GBRMPA, 2014b ) states there are significant concerns about a small number of species, including the spear tooth shark which may now be extinct in the GBR Region. While some potentially at risk species on the GBR are protected by other legislative mechanisms (e.g. all species of sawfish which are protected under Queensland legislation, GBRMPA, 2013b )—others are not. For example, two species of sea cucumbers ( Holothuria whitmaei and H. fuscogilva ) that are listed as Endangered and Vulnerable on the IUCN red-list index (RLI) ( IUCN, 2015 ) have been heavily fished, and the annual catch of another Vulnerable species ( Stichopus herrmanni ) rose at an average annual pace of 200% from 2007 to 2011 ( Eriksson & Byrne, 2013 ) however none of these species are protected under Australian legislation.

Other habitat-forming species such as hard corals are listed as no-take species under the GBRMPA Act 1975 which affords them protection from extractive threats. However, no stony coral species are specifically listed as threatened species under the EPBC Act , and their actual population status is not known nor is the effectiveness of current legislation as a regulatory control. Furthermore, with no post-impact data recorded at a species-level, it is impossible to report the impact that disturbance events (such as the recent widespread coral bleaching event) have had, nor is it possible to substantiate species recovery.

The significant and escalating situation on the GBR was placed in the international spotlight by UNESCO’s World Heritage Committee (WHC) in 2011, and the Committee has since continued to raise concerns about the status of the GBR World Heritage Area (e.g. World Heritage Committee, 2013 , 2014 , 2015 ). In 2014, the WHC requested that the Australian government provide concrete and consistent management measures to ensure the overall long-term conservation of the property, including addressing cumulative impacts and increase reef resilience. In response, the Reef 2050 Plan was drafted ( Commonwealth of Australia, 2015 ). As highlighted elsewhere ( Australian Academy of Science, 2015 ; Hughes, Day & Brodie, 2015 ; Roth et al., 2017 ), the Reef 2050 Plan falls short on responding to these requests especially in the context of addressing climate change, shipping impacts, setting realistic, and measurable targets, cumulative impacts and a commitment to the level of funding required. The Reef 2050 Plan does, however, provide some useful actions and targets to monitor population trends for some mega fauna such as dugongs and turtles. The provision of strategies to evaluate and report on the population trends of other non-charismatic taxa like benthic invertebrates is notably absent. For example, the condition and trend for the ‘other invertebrates’ section in the GBR Strategic Assessment is listed as ‘very good’ and ‘stable’ but there is no confidence in the data and very limited evidence ( GBRMPA, 2014b ). Also in the ‘sea snakes’ section of the same assessment, it states abundance estimates are only available for a few species or for small areas, and there is little information about population trends.

Scale-based mismatches in threatened species assessments

For most of the 12,000+ animal species that are documented from the GBR ( Table 1 ), regional status information is notably absent (exceptions are nesting seabirds and shorebirds). However, for approximately 700 species including hard corals, sea cucumbers, giant clams, grouper, wrasse, parrotfish, sharks, rays, sea snakes, turtles, whales, dolphins, and dugong ( Carpenter et al., 2008 ; Elfes et al., 2013 ; Sadovy de Mitcheson et al., 2013 ; Conand et al., 2014 ; Dulvy et al., 2014 ), conservation status has been assessed at a global level using the Red List of Threatened Species (RLI) ( IUCN, 2015 ). The global assessments indicate that at least 136 species on the GBR (approximately 20% of species assessed) occur in elevated categories of threat ( Critically Endangered, Endangered or Vulnerable ) ( Table 1 ) including at least 89 species of hard coral, 10 species of sea cucumbers, 21 species of sharks and rays, two species of giant clam, and five species of bony fish ( Table S2 ).

Despite the wider background level of threat for these 136 species, only 23 of them (17%) are listed as threatened under the Environment Protection and Biodiversity Conservation Act, 1999 ( Australian Government, 2015 ) or defined as protected species under the Great Barrier Reef Marine Park Regulations, 1983 . The regional status of the other 113 assessed species that have been recognised as highly threatened on a global scale by their respective taxonomic experts is not known (e.g. the Narrow Sawfish ( A. cuspidata ), Purple Eagle Ray ( Myliobatus hamlyni ), Humphead Wrasse ( Cheilinus undulatus , see Fig. 3 ) and five species of sea cucumbers (Holothridae)). Nor is the status of an additional 35 species that are listed on the RLI as Data Deficient ( Table S2 , only three of which are protected under EPBC), or the other 11,000+ animal species known or likely to occur on the GBR which have not been assessed at any scale (global, national or regional, see Table 1 ). These species are not protected under the Environment Protection and Biodiversity Conservation Act, 1999 because they are not endemic to Australia and the global IUCN assessments have little bearing on decisions made under the EPBC Act unless the species in question is endemic to Australia.

(A) Tridacna gigas , a vulnerable clam species (see http://www.iucnredlist.org/details/22137/0 ). (B) Acropora donei , a vulnerable staghorn coral species (see http://www.iucnredlist.org/details/133223/0 ). (C) Cheilinus undulatus , an endangered species of wrasse (see http://www.iucnredlist.org/details/4592/0 ). Photos by Zoe Richards.

Future directions

In order to effectively manage the GBR a multi-pronged approach is needed ( McCook et al., 2009 ). Pragmatism has led to a preference for system-wide ecosystem management with the result that species-level initiatives have been de-emphasised. However, obtaining a comprehensive and up-to-date understanding of the status of GBR marine life through targeted taxonomic and ecological research on key knowledge gaps and long-term species monitoring remains a fundamental way to make informed management decisions ( GBRMPA, 2009 , 2013a , 2014a ) and creates opportunities to engage with the public and bolster support for biodiversity conservation. The key argument against species-level surveys is that they are prohibitively expensive. But is this true? By way of example, a large multi-institutional, multi-taxon marine biodiversity project ( Marine Life of Kimberley project) was recently conducted in NW Australia. Just like the GBR, the Kimberley marine bioregion comprises diverse coastal and offshore habitats and a large number of islands with fringing reef habitats. However, it covers a larger and even more remote area (Kimberley project area is 476,000 km 2 ( Bryce, Bryce & Radford, 2018 ); the GBR is 347,800 km 2 ( GBRMPA, 2014a )). The Kimberley Marine Life project had two phases. The first phase (2008–2011) involved the compilation and analyses of historic data from several Australian museums and the WA Herbarium to give a state of current knowledge for the region’s marine life. Phase 2 (2011–2015) involved a series of surveys to increase the resolution of the marine diversity data and fill knowledge gaps identified during Phase 1. The project targeted the region’s molluscs, crustaceans, fish, hard corals, soft corals, sponges, echinoderms, worms, marine algae, and sea grasses ( Bryce & Sampey, 2014 ; Fromont & Sampey, 2014 ; Hosie et al., 2015 ; Huisman & Sampey, 2014 ; Hutchings et al., 2014 ; Moore et al., 2015 ; Richards, Sampey & Marsh, 2014 ; Sampey & Marsh, 2015 ; Willan, Bryce & Slack-Smith, 2015 ). This $2.7 AUD million dollar project (plus in-kind support) has provided a comprehensive reference dataset to guide in the design of the newly gazetted marine parks in the region; informed a range of research projects (WAMSI; http://www.wamsi.org.au ); led to award-winning educational outreach opportunities ( http://museum.wa.gov.au/btw/ ) and established a knowledge legacy for future generations. If an equivalent annual financial investment was made into updating our understanding of the status of marine life on the GBR, this would equate to less than 0.42% of the estimated annual worth of the reef to Australia’s economy (valued at $6.4 billion annually, Deloitte Access Economics, 2017 ).

If new biodiversity studies are undertaken on the GBR, it would be crucial for this new information to be made available to decision-makers in a timely manner to ensure enduring and constructive links are made between monitoring and subsequent management actions ( Day, 2008 ). More specifically, it must align with the five-year GBR outlook reporting schedule (the next report is due in 2019). In lieu of new surveys, a value of information analysis ( Runge, Converse & Lyons, 2011 ; Moore & Runge, 2012 ; Yokomizo, Coutts & Possingham, 2014 ) could be undertaken to provide scientifically credible advice on how, when, and what new information is needed to broaden and accelerate efforts to conserve the biodiversity values of the GBR. Such an analysis may, for example, find there is a need to expand the existing monitoring program for the GBR to include key diversity indices. For some taxa, biodiversity proxies have been established e.g. particular families have been identified as good indicators of wider reef fish diversity ( Allen & Werner, 2002 ), however for most, this information is not available and more research is needed in this area.

Any expansion of the existing GBR long-term monitoring program would need to be carefully considered and negotiated amongst a body of experts, managers, stakeholders, independent advisors, and preferably, informed by a value of information analysis. As a start, some possible options for adapting and expanding the monitoring program include:

• Targeted top and tail monitoring which involves collating species-level data on a selection of the most common (keystone) species in addition to some of the most endangered and vulnerable species and/or invasive species.

If long-term monitoring programs are adapted, all decisions relating to target species and yearly taxa subsets would require expert discussion following baseline surveys or a Value of Information Analysis. Such a program would require resourcing and co-ordination but the vision could be for it to be conducted by two to three scientists per year (rotating based on expertise) and undertaken alongside the existing long-term monitoring program. Credits: Aerial—Photographer: M. Cowlishaw, Copyright Commonwealth of Australia (GBRMPA); Humpback Whale—Photographer: M. Simmons, Copyright Commonwealth of Australia (GBRMPA); Sea grass—Photographer: J. Jones, Copyright Commonwealth of Australia (GBRMPA); Great White Shark—Photographer: K. Hoppen, Copyright Commonwealth of Australia (GBRMPA); Halimeda —Photographer: G. Goby, Copyright Commonwealth of Australia (GBRMPA); Dugong—Photographer: B. Cropp, Copyright Commonwealth of Australia (GBRMPA); Turtle—Photographer: E. Goodwin, Copyright Commonwealth of Australia (GBRMPA). All other images by Zoe Richards.

• Stratified monitoring that involves in-depth taxonomic and ecological assessments at a smaller number of sites that overlap with key long-term monitoring stations.

While these are just a few examples of possible ways the monitoring and reporting program could evolve, they illustrate that if preventing coral biodiversity loss is a priority to coral reef management authorities, it is essential to begin the process of collecting species-level data, using that information to choose appropriate indicators or surrogates ( Beier et al., 2015 ) and adapting monitoring programs to collect additional complementary data that more effectively informs managers and the public about the status of biodiversity.

In addition, there are other reporting opportunities. In some cases, existing photographs and video records could be retrospectively analysed to identify trends for key species of interest (e.g. giant clams). Moreover, citizen science projects (such as ReefLife Surveys) hold promise for providing data on charismatic or easily identified fauna. For some taxa, estimates of generic diversity ( Richards, 2013 , Richards & Hobbs, 2014 ) or functional diversity ( Cadotte, 2011 ; Cernansky, 2017 ) may be useful and pragmatic additions to monitoring programs. An additional promising approach is to audit species composition is through the application of environmental DNA (eDNA) meta-barcoding technologies. Advances in DNA sequencing technologies and the swift drop in the cost of sequencing has led to a rapid rise in the applications of eDNA, particularly in the marine environment (e.g. Foote et al., 2012 ; Lejzerowicz et al., 2015 ; Thomsen et al., 2012 ; Valentini et al., 2016 ; Miya et al., 2015 ). The power and limitations surrounding eDNA as a tool for marine surveys of diversity, diet, food webs and invasive species is currently being explored by numerous molecular laboratories. So far it appears that so long as careful attention is paid to meta-barcoding workflows, assay development and the development of taxonomically sound reference datasets, eDNA represents a powerful new tool. eDNA is increasingly being used to evaluate the composition and health of marine communities ( Foote et al., 2012 ; Murray, Coghlan & Bunce, 2015 ; Clarke et al., 2017 ) including coral reefs ( Stat et al., 2017 ; Shinzato et al., 2018 ) and may be a useful complement to traditional monitoring approaches.

Most of the threats identified to be harming the diversity of marine life on the GBR over the last two–three decades remains to be effectively addressed and many are worsening. The habitat degradation that has already occurred will take decades to reverse and far greater resources than are currently being expended are required to document and protect biodiversity on the GBR ( Day, 2015 ; Brodie, 2016 ). What is urgently required is decisive and effective conservation action by key leaders to ensure the legal obligations of protecting biodiversity are met. Establishing sound taxonomic datasets and ensuring biodiversity is adequately and representatively monitored are urgent prerequisites for achieving efficient conservation plans and mitigating biodiversity loss ( Wilson, 2016 ; Troudet et al., 2017 ; Thomson et al., 2018 ). The problem of having a limited understanding of the species that inhibit our oceans and the threats they face is not restricted to the GBR or Australia ( Webb & Mindel, 2015 ). However, for Australia, the problem could also be an opportunity for best-practice marine conservation. The changing nature of the GBR necessitates we consider what additional dynamic approaches to monitoring and reporting are needed to more fully understand the current status of biodiversity and mitigate the risk that silent extinction events will occur. Unless more action is taken to evaluate and manage biodiversity and to provide current and comprehensive assessments of extinction risk ( Costello, May & Stork, 2013 ; Bland et al., 2015 ; Costello, 2015 ), we may fail to pass onto future generations many of the values that comprise what is universally regarded as the world’s most iconic coral reef ecosystem.

Supplemental Information

Supplemental information 1, supplemental information 2, funding statement.

This work was supported by the WA Museum and Woodside Energy and a Curtin Research Fellowship awarded to Zoe T. Richards. The work was undertaken as part of Linkage Project LP160101508. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Additional Information and Declarations

The authors declare that they have no competing interests.

Zoe T. Richards conceived and designed the experiments, analysed the data, prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.

Jon C. Day prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.

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• Copy URL https://www.pbs.org/newshour/world/the-great-barrier-reef-waters-were-the-warmest-in-400-years-over-the-past-decade-australian-study-finds

The Great Barrier Reef waters were the warmest in 400 years over the past decade, Australian study finds

WASHINGTON (AP) — Ocean temperatures in the Great Barrier Reef hit their highest level in 400 years over the past decade, according to researchers who warned that the reef likely won’t survive if planetary warming isn’t stopped.

WATCH: Record-breaking ocean heat triggers massive coral reef bleaching

During that time, between 2016 and 2024, the Great Barrier Reef, the world’s largest coral reef ecosystem and one of the most biodiverse, suffered mass coral bleaching events. That’s when water temperatures get too hot and coral expel the algae that provide them with color and food, and sometimes die. Earlier this year, aerial surveys of over 300 reefs in the system off Australia’s northeast coast found bleaching in shallow water areas spanning two-thirds of the reef, according to Great Barrier Reef Marine Park Authority.

Researchers from Melbourne University and other universities in Australia, in a paper published Wednesday in the journal Nature, were able to compare recent ocean temperatures to historical ones by using coral skeleton samples from the Coral Sea to reconstruct sea surface temperature data from 1618 to 1995. They coupled that with sea surface temperature data from 1900 to 2024.

They observed largely stable temperatures before 1900, and steady warming from January to March from 1960 to 2024. And during five years of coral bleaching in the past decade — during 2016, 2017, 2020, 2022 and 2024 — temperatures in January and March were significantly higher than anything dating back to 1618, researchers found. They used climate models to attribute the warming rate after 1900 to human-caused climate change. The only other year nearly as warm as the mass bleaching years of the past decade was 2004.

“The reef is in danger and if we don’t divert from our current course, our generation will likely witness the demise of one of those great natural wonders,” said Benjamin Henley, the study’s lead author and a lecturer of sustainable urban management at the University of Melbourne. “If you put all of the evidence together … heat extremes are occurring too often for those corals to effectively adapt and evolve.”

Across the world, reefs are key to seafood production and tourism. Scientists have long said additional loss of coral is likely to be a casualty of future warming as the world approaches the 1.5 degrees Celsius (2.7 degrees Fahrenheit) threshold that countries agreed to try and keep warming under in the 2015 Paris climate agreement.

Even if global warming is kept under the Paris Agreement’s goal, which scientists say Earth is almost guaranteed to cross, 70 percent to 90 percent of corals across the globe could be threatened, the study’s authors said. As a result, future coral reefs would likely have less diversity in coral species — which has already been happening as the oceans have grown hotter.

Coral reefs have been evolving over the past quarter century in response to bleaching events like the ones the study’s authors highlighted, said Michael McPhaden, a senior climate scientist at the National Oceanic and Atmospheric Administration who was not involved with the study. But even the most robust coral may soon not be able to withstand the elevated temperatures expected under a warming climate with “the relentless rise in greenhouse gas concentrations in the atmosphere,” he said.

The Great Barrier Reef serves as an economic resource for the region and protects against severe tropical storms.

As more heat-tolerant coral replaces the less heat-tolerant species in the colorful underwater rainbow jungle, McPhaden said there’s “real concern” about the expected extreme loss in the number of species and reduction in area that the world’s largest reef covers.

“It’s the canary in the coal mine in terms of climate change,” McPhaden said.

The Associated Press’ climate and environmental coverage receives financial support from multiple private foundations. AP is solely responsible for all content. Find AP’s standards for working with philanthropies, a list of supporters and funded coverage areas at AP.org.

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Great Barrier Reef , complex of coral reefs , shoals, and islets in the Pacific Ocean off the northeastern coast of Australia that is the longest and largest reef complex in the world. The Great Barrier Reef extends in roughly a northwest-southeast direction for more than 1,250 miles (2,000 km), at an offshore distance ranging from 10 to 100 miles (16 to 160 km), and its width ranges from 37 to 155 miles (60 to 250 km). The Great Barrier Reef has an area of some 135,000 square miles (350,000 square km), and it has been characterized , somewhat inaccurately, as the largest structure ever built by living creatures.

The reef actually consists of some 2,100 individual reefs and some 800 fringing reefs (formed around islands or bordering coastlines). Many are dry or barely awash at low tide ; some have islands of coral sand , or cays; and others fringe high islands or the mainland coast. In spite of this variety, the reefs share a common origin: each has been formed, over millions of years, from the skeletons and skeletal waste of a mass of living marine organisms. The “bricks” in the reef framework are formed by the calcareous remains of the tiny creatures known as coral polyps and hydrocorals, while the “cement” that binds these remains together is formed in large part by coralline algae and bryozoans . The interstices of this framework have been filled in by vast quantities of skeletal waste produced by the pounding of the waves and the depredations of boring organisms.

European exploration of the reef began in 1770, when the British explorer Capt. James Cook ran his ship aground on it. The work of charting channels and passages through the maze of reefs, begun by Cook, continued during the 19th century. The Great Barrier Reef Expedition of 1928–29 contributed important knowledge about coral physiology and the ecology of coral reefs. A modern laboratory on Heron Island continues scientific investigations, and several studies have been undertaken in other areas.

The reef has risen on the shallow shelf fringing the Australian continent , in warm waters that have enabled the corals to flourish (they cannot exist where average temperatures fall below 70 °F [21 °C]). Borings have established that reefs were growing on the continental shelf as early as the Miocene Epoch (23.0 million to 5.3 million years ago). Subsidence of the continental shelf has proceeded, with some reversals, since the early Miocene.

The water environment of the Great Barrier Reef is formed by the surface water layer of the southwestern Pacific Ocean. The reef waters show little seasonal variation: surface-water temperature is high, ranging from 70 to 100 °F (21 to 38 °C). The waters are generally crystal-clear, with submarine features clearly visible at depths of 100 feet (30 metres).

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'Wake-up call to humanity': Research shows the Great Barrier Reef is the hottest it's been in 400 years

by Ben Henley, Helen McGregor and Ove Hoegh-Guldberg, The Conversation

The Great Barrier Reef is vast and spectacular. But repeated mass coral bleachings, driven by high ocean temperatures, are threatening the survival of coral colonies which are the backbone of the reef.

Our study, published today in Nature , provides a new long-term picture of the ocean surface temperatures driving coral bleaching . It shows recent sea surface heat is unprecedented compared to the past 400 years. It also confirms humans are to blame.

The results are sobering confirmation that global warming—caused by human activities—will continue to damage the Great Barrier Reef.

All hope is not lost. But we must face a confronting truth: if humanity does not divert from its current course, our generation will likely witness the demise of one of Earth's great natural wonders.

One-of-a-kind ecosystem

The Great Barrier Reef is the most extensive coral reef system on Earth. It is home to a phenomenal array of biodiversity , including more than 400 types of coral, 1,500 species of fish and 4,000 types of mollusks, as well as endangered turtles and dugongs.

However, mass coral bleaching over the past three decades has had serious impacts on the reef. Bleaching occurs when corals become so heat-stressed they eject the tiny organisms living inside their tissues. These organisms give coral some of its color and help power its metabolism .

In mild bleaching events, corals can recover. But in the most recent events, many corals died.

The Great Barrier Reef has suffered five mass bleaching events in the past nine summers. Is this an anomaly, or within the natural variability the reef has experienced in previous centuries? Our research set out to answer this question.

A 400-year-old story

Coral itself can tell us what happened in the past.

As corals grow, the chemistry of their skeleton reflects the ocean conditions at the time—including its temperature. In particular, large boulder-shaped corals, known as Porites , can live for centuries and are excellent recorders of the past.

Our study sought to understand how surface temperatures in the Coral Sea, which includes the reef, have varied over the past four centuries. We focused on the January–March period—the warmest three months on the reef.

First, we collated a network of high-quality, continuous coral records from the region. These records were analyzed by coral climate scientists and consist of thousands of measurements of Porites corals from across the Western tropical Pacific.

From these records, we could reconstruct average surface temperatures for the Coral Sea from the year 1618 to 1995, and calibrate this to modern temperature records from 1900 to 2024. The overall result was alarming.

From 1960 to 2024, we observed annual average summer warming of 0.12°C per decade.

And average sea surface temperatures in 2016, 2017, 2020, 2022 and 2024 were five of the six warmest the region has experienced in four centuries.

Humans are undoubtedly to blame

The next step was to examine the extent to which increased temperatures in the Coral Sea can be attributed to human influence .

To do this, we used published computer model simulations of the Earth's climate—both with and without human influence, including greenhouse gases from the burning of fossil fuels.

So what did we find? Without human influence, Coral Sea surface temperatures during January–March remain relatively constant since 1900. Add in the human impacts, and the region warms steadily in the early 1900s, then rapidly after the 1960s.

In short: without human-caused global warming, the very high sea temperatures of recent years would be virtually impossible, based on our analysis using the world's top climate models.

There is worse news. Recent climate projections put us on a path to intensified warming, even when accounting for international commitments to reduce emissions. This places the reef at risk of coral bleaching on a near-annual basis .

Back-to-back bleaching is likely to be catastrophic for the Great Barrier Reef, because it thwarts the chances of corals recovering between bleaching events.

Even if global warming is kept under the Paris Agreement goal of 1.5°C above pre-industrial temperatures, 70% to 90% of corals across the world could be lost .

We must stay focused

The Australian government has a crucial role to play in managing threats to the Great Barrier Reef. The devastation is in their backyard, on their watch.

But what's happening on the Great Barrier Reef should also be an international wake-up call. The fourth global mass coral bleaching event occurred this year; the Great Barrier Reef is not the only one at risk.

Every fraction of a degree of warming we avoid gives more hope for coral reefs. That's why the world must stay focused on ambitious action to reduce greenhouse gas emissions.

Emissions reduction targets must be met, at the very least. The solutions are available and our leaders must implement them.

Our research equips society with the scientific evidence for what's at stake if we don't act.

The future of one of Earth's most remarkable ecosystems depends on all of us.

Journal information: Nature

Provided by The Conversation

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Research Article

Finding common ground: Understanding and engaging with science mistrust in the Great barrier reef region

Roles Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

Affiliation CSIRO Environment, Australian Tropical Science and Innovation Precinct, James Cook University, Townsville, Queensland, Australia

Roles Conceptualization, Formal analysis, Validation, Visualization, Writing – original draft, Writing – review & editing

Affiliations CSIRO Environment, Australian Tropical Science and Innovation Precinct, James Cook University, Townsville, Queensland, Australia, The Cairns Institute, James Cook University, Smithfield, Cairns, Queensland, Australia

Roles Conceptualization, Writing – original draft, Writing – review & editing

Affiliation Queensland Department of Environment and Science, Brisbane, Queensland, Australia

Affiliation C2O Consulting, James Cook University, Townsville, Queensland, Australia

Roles Conceptualization, Methodology, Writing – original draft, Writing – review & editing

Affiliation CSIRO Environment, Dutton Park, Brisbane, Queensland, Australia

Roles Conceptualization, Funding acquisition, Methodology, Project administration, Writing – original draft, Writing – review & editing

Roles Conceptualization, Data curation, Investigation, Methodology, Writing – review & editing

Roles Data curation, Visualization, Writing – review & editing

Affiliations CSIRO Environment, Australian Tropical Science and Innovation Precinct, James Cook University, Townsville, Queensland, Australia, James Cook University, Townsville, Queensland, Australia

• Matthew I. Curnock, 
• Danielle Nembhard, 
• Rachael Smith, 
• Katie Sambrook, 
• Elizabeth V. Hobman, 
• Aditi Mankad, 
• Petina L. Pert, 
• Emilee Chamberland

• Published: August 16, 2024
• https://doi.org/10.1371/journal.pone.0308252
• Peer Review
• Reader Comments

At a time when ambitious environmental management initiatives are required to protect and restore aquatic ecosystems, public trust in the science that underpins environmental policy and decision-making is waning. This decline in public trust coincides with a rise in misinformation, and threatens to undermine public support for, and participation in, environmental protection. Our study investigates the prevalence and predictors of mistrust in science associated with the protection and management of the Great Barrier Reef (GBR) and its catchments. Using survey data from 1,877 residents of the GBR region, we identify environmental values, perceptions, and attitudes that are associated with science mistrust. Our results include a typology of GBR science trust and scepticism. Science-sceptical respondents, representing 31% of our sample, were likely to perceive waterway management decisions as being unfair, felt less responsible, and were less motivated to contribute to improving waterway health than those with greater trust in science. Science-sceptical respondents also had differing perceptions of some threats to waterways, in particular climate change. However, similarities and ‘common ground’ between respondents with varying levels of trust in science included a shared recognition of the importance of waterways’ ecosystem services, and a shared perception of the relative health and problems within their regions’ waterways. Our findings can help to break down assumptions about science-sceptical groups in the GBR region and elsewhere. We offer recommendations to guide more constructive engagement that seeks to restore trust and build consensus on mutual goals and pathways to protect vital ecosystem functions and services.

Citation: Curnock MI, Nembhard D, Smith R, Sambrook K, Hobman EV, Mankad A, et al. (2024) Finding common ground: Understanding and engaging with science mistrust in the Great barrier reef region. PLoS ONE 19(8): e0308252. https://doi.org/10.1371/journal.pone.0308252

Editor: Umberto Baresi, Queensland University of Technology, AUSTRALIA

Received: March 5, 2024; Accepted: July 21, 2024; Published: August 16, 2024

Copyright: © 2024 Curnock et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All data files are available from the CSIRO Data Access Portal database (DOI: https://doi.org/10.25919/6wp0-7m86 ).

Funding: Funding for this study was provided by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation, delivered in partnership with CSIRO, the Great Barrier Reef Marine Park Authority, and the Queensland Government’s Reef Water Quality Program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

The role of public trust in environmental science and policy.

Public trust in government, public institutions, and science is a fundamental tenet of modern democratic societies. Science underpins technological advancement and humanity’s ability to understand and overcome complex problems, and trust is placed in scientists to curate complex information and knowledge [ 1 ]. Effective environmental policy depends simultaneously on sound science–to incorporate an understanding of system processes and risks, and public participation–to weigh the plurality of human values and trade-offs associated with rules and decisions [ 2 ]. Tension at this interface is perpetual; however, in recent decades the politicisation of science in many countries has been accompanied by the polarisation of public views on certain issues and a rise in science mistrust [ 3 – 5 ]. Among environmental management issues, the most prominent example of this phenomenon is anthropogenic climate change, for which the scientific evidence is now irrefutable, yet political and public discourse remains intractably divided [ 6 – 8 ].

Just as scepticism plays a critical role in science, an informed, questioning public is a vital feature of a deliberative and democratic governance system [ 9 ]. Where science interacts with government policy, trust in the institutions, actors, and processes is a prerequisite for stakeholder and public engagement and acceptance [ 10 ]. However, excessive trust can lead to complacency and overlooked risks, undermining progress towards well-meaning objectives [ 11 , 12 ]. Trust between parties (e.g., policy makers, scientists, stakeholders, and the public) fluctuates over time in response to emerging information and relationship dynamics [ 13 ]. Fostering and maintaining ‘optimal’ levels of trust between institutions and citizens by monitoring and remediating deviations towards too little or too much trust is a desirable strategic objective, as effective resource governance requires parties’ adherence to long-term commitments and expectations [ 11 , 12 ].

Optimal trust dynamics between resource managers, stakeholders, rightsholders, scientists and communities do not exist independently of the institutional structures, policy settings, power dynamics, and other contextual factors in a natural resource governance system [ 12 , 14 , 15 ]. While trust is vital for resilient partnerships and cooperation, there are numerous antecedent and mutually dependent factors that influence governance outcomes. Among these, the integrity of scientific and government institutions and the way they and their agents interact in policy development is crucial [ 12 , 15 , 16 ], as is public engagement in resource governance via deliberative, transparent, and equitable processes [ 14 , 17 , 18 ]. In the current period of rapid social and environmental change, effective governance of natural resources requires leaders, resource managers and scientists to invest increasing effort into inclusive and participatory processes for assessing risks and guiding decisions [ 14 , 19 – 21 ]. Desirable outcomes and objectives of such processes, beyond prudent decision-making and building trust, include social learning and the empowerment of participants, enhanced adaptive capacity and community resilience. Indeed, such processes are worthwhile even if they do not result in measurable improvements in public trust, which is often misplaced as an end-goal, rather than an enabling condition to improved resource and risk governance [ 14 ].

Conceptualising trust for natural resource management

While varying definitions exist in the literature, there is broad agreement that trust is a psychological state of willingness to accept risk or vulnerability, based on one’s appraisal and expectations of another party’s intentions and behaviour [ 22 – 24 ]. Trust can be placed in people, as well as in non-person entities. One can trust an institution, an object, or a process, though these entities are still implicitly tied to people by virtue of being produced, practiced, or proven by people [ 24 ]. Trust can be based on different attributes, including the perception of integrity, competence, benevolence, and charisma. Beyond the perceived characteristics of the trustee, it is also important to acknowledge that the trustor brings with them their own predisposition to be trusting in any given situation (ibid.). People can form a range of trusted relationships at different scales, representing the diversity of individuals, organisations, and institutions they encounter and/or interact with, each with potentially different qualities, needs and interdependencies [ 25 ].

Where trusted relationships coalesce, such as in multi-party resource management or policymaking settings, complex networks of trust can form, creating challenges and opportunities for effective decision-making [ 12 , 25 ]. In this context, four broad types of trust described by Stern and Coleman [ 24 ] provide a useful conceptual framework to understand how diverse trust manifests and underpins relationships critical to collaborative natural resource management: (i) dispositional trust , which refers to an individual’s dispositional and normative tendency to trust (or distrust) institutions, objects or formal roles that have authority or legitimacy, (ii) rational trust , which arises from an individual’s calculated assessment of an expected benefit or outcome from an exchange or interaction with the trustee, and which requires knowledge of the trustee’s ability and/or integrity, (iii) affinitive trust , which arises from a perception of the trustee’s benevolence, shared values, integrity and/or other personal qualities and character traits, and (iv) procedural (or systems-based) trust , which is based on an individual’s assessment of control systems, procedures, or rules (rather than an individual or organisation) and which requires knowledge of the legitimacy, fairness, and transparency of the procedure(s) or system. It is proposed that these four types of trust operate across different scales and interact to contribute to a trustor’s overall psychological state of trust in real-world situations [ 24 , 25 ].

Different manifestations of the above trust types can affect an individual’s motivations and behaviour in myriad ways [ 24 ]. For example, a person may have strong dispositional trust for an organisation but lack affinitive trust for its employee(s) and consequently may be motivated to participate in a particular process with those employee(s) to ensure their interests are not misrepresented. Alternately, an individual who has complete trust in an organisation, its processes, and employees might be less motivated to participate in a collaborative process, due to confidence that their interests will be duly considered (ibid.). There are conceptual distinctions too between a lack of trust , mistrust , and distrust . A lack of trust can exist in situations where the trustor is unable to make a judgement about the trustworthiness of an individual or other entity, and this may be expressed through apathy or a hesitancy to engage in participatory opportunities. Mistrust can be distinguished as a cautious, doubtful, or sceptical attitude towards others. And distrust arises from an explicit negative appraisal, and may be expressed through disengagement, the rejection of information, or active opposition [ 24 – 27 ].

Declining trust in science and the rise of misinformation

A decline in public trust in governments, public institutions, and in science has been documented in many countries over the last few decades [ 3 , 28 , 29 ]. Due to its inherent complexity and specialised nature, scientific information typically requires synthesis and translation by intermediaries, such as science communicators and journalists, to make it accessible for target audiences and the wider public. The involvement of such intermediaries, however, increases the risk that the scientific information is misinterpreted or framed to serve a particular narrative [ 29 , 30 ]. Once in the public domain, scientific information can be reinterpreted, reframed, and retransmitted by further intermediaries across any number of channels and platforms [ 30 ]. Growth in the use of social media as a news source and the increasing fragmentation of news media outlets means that news stories with a scientific component are likely to be viewed by an increasingly smaller audience [ 31 , 32 ]. Despite such risks and challenges, the public communication of science remains essential for its credibility, impact, and the accountability of taxpayer-funded research [ 30 , 33 ].

Misinformation is a growing global problem with often severe consequences. Despite burgeoning research into the phenomenon and its effects, an academic consensus on a precise definition remains elusive due to its many forms and manifestations, including fake news, disinformation, conspiracy theories, and propaganda [ 34 – 37 ]. In the context of science communication, Southwell et al. [ 36 ] define scientific misinformation as “publicly available information that is misleading or deceptive relative to the best available scientific evidence and that runs contrary to statements by actors or institutions who adhere to scientific principles” (p.98). Misinformation undermines public support for evidence-based policy and has stymied collective action to address problems in multiple domains including the environment, public health, politics, and social inequity [ 38 – 40 ]. The rise of misinformation, accompanying the emergence and growth of social media, is widely attributed as one of the major drivers of declining public trust in science [ 34 , 41 , 42 ]. However, the causal pathways to becoming mistrustful of science are complex and the relationship between science mistrust and receptivity to misinformation may be one of mutual reinforcement, in which many people turn to misinformation on social media because they are distrustful of the science [ 34 , 43 ].

Scientists and science communicators are also susceptible to pitfalls of misinformation. In a fragmented media landscape scientific news competes for public attention, and science communicators are incentivised to adopt the same tactics that make misinformation appealing, including the use of hyped headlines and overstated results and implications [ 38 ]. Other pitfalls faced by scientists include biases favouring the citation and publication of significant results over non-significant results, the misuse of statistics and over-emphasis of p -values, and biases in the visualisation and interpretation of results [ 38 , 44 ]. In modern academic culture, the high pressure on scientists to publish frequently and attain notability can erode standards of rigour and ethics in their pursuit of publication metrics and media attention. Meanwhile, a boom in open-access predatory publishers, whose business model relies on collecting authors’ fees rather than upholding scientific standards, tempts authors with a shortcut to publication [ 38 , 45 ]. The combined effect of these factors is that scientists can unwittingly contribute to the proliferation of scientific misinformation that undermines public trust in science [ 38 ].

Measuring trust and its associated factors

While in-depth empirical research into the trust process can be performed in the context of interactions between science and everyday citizens, the more commonly reported research is that derived from large-scale population surveys that measure public opinion [ 29 , 46 ]. This type of research often provides headline statistics on comparative levels of public trust in broad sectors and institutions (e.g., scientists, business leaders, politicians, health authorities), and enables comparisons of different cohorts (e.g., by demography, political orientation) and countries, and the assessment of temporal changes, including in relation to significant events (e.g., the COVID-19 pandemic) [ 46 – 48 ]. While trust is ideally measured across multiple dimensions, limitations inherent to survey design result in many studies employing only a single item to measure trust within a specific context, and the variation across such studies limits their comparability [ 29 ]. Single-item, generic measures of public trust in science are nonetheless useful for understanding associated factors and for monitoring trends in an applied context [ 24 , 29 , 46 ].

In the context of environmental management, public and stakeholder trust is a focal topic for many case studies that explore the relationships between trust and pro-environmental behaviours, risk perceptions, and support for management initiatives and policy [ 24 , 49 ]. Empirical studies across a variety of contexts have shown that trust in science and management institutions has a strong influence on perceptions of environmental threats and risks, which in turn affects support for protective measures and the adoption of conservation-related behaviours [e.g., 50 – 54 ]. The relationship between trust and personal environmental values, however, is more complex. While an affinity for nature has been shown to correlate positively with support for environmental protection and pro-environmental behaviour [ 55 , 56 ], personal environmental values appear to have an indirect relationship with trust, serving as an antecedent factor in the trust-forming process [ 57 ].

Research to inform trust-building engagement

Increased recognition of the importance of trust in environmental management and of declining public trust in science has prompted growth in research to understand underlying factors and provide advice to scientists, communicators and resource managers who seek to build and maintain trust for improved management outcomes. Much of this research focuses on public and stakeholder engagement [e.g., 58 – 63 ], and while engagement on its own is insufficient to build and maintain trust due to its multi-dimensional nature and emergence in a societal context, it nonetheless plays a critical role in fostering trust within a wider governance system [ 12 , 14 , 18 ]. Some communication and engagement approaches that can contribute to building trust in a wide range of contexts and domains include:

• Engagement by relatable and credible leaders and spokespeople who are regarded as ‘trusted messengers’ [ 60 , 64 – 68 , among others].
• Demonstration of empathy, commonality of values and social identity, and a shared vision for the future [ 50 , 59 , 60 , 62 , 66 , 69 , among others].
• Clear and relatable message framing (using appropriate language, metaphors, and images) of relevant issues, risks, and opportunities, to build a shared understanding of problems and consensus on objectives or solutions, and pathways to achieving mutual goals [ 65 , 68 , 70 , 71 , among others].
• Demonstration of scientific consensus, scientific expertise, and competency, as well as robustness of scientific methods and data [ 50 , 63 , 72 – 74 , among others].
• Honesty and transparency about knowledge gaps, uncertainties, risks, and expected outcomes [ 50 , 59 , 62 , 63 , 65 , 75 , among others].
• Consistent demonstration of scientific integrity, and impartiality regarding its contribution to policy development and decision-making processes [ 12 , 14 , 15 , 62 , 76 , 77 , among others].
• Demonstration of a long-term commitment to participatory engagement, two-way information sharing, fairness, and deliberative governance [ 14 , 63 , 78 – 80 , among others].

Effectively addressing points two and three above requires an in-depth understanding of the target audience, which can emerge from a history of direct engagement, shared experiences, and/or peer networks. For cases in which there is an incomplete understanding of a cohort’s values, perceptions, and normative beliefs relevant to a specific context or issue, social research utilising surveys can be useful for eliciting insights about ‘common ground’ on which constructive engagement may be built.

Case study context–the great barrier reef

The Great Barrier Reef (GBR; the Reef) is an iconic, complex, and dynamic socio-ecological system. Its diverse marine ecosystems are connected to adjacent coastal habitats and river catchments, which provide passageways for mobile and migratory species, and drain terrestrial runoff into the GBR lagoon, linking the Reef with human activities in its catchment areas [ 81 , 82 ]. However, the GBR is threatened by a range of human-caused pressures that are affecting its ecology, values, and resilience. These pressures include anthropogenic climate change, which contributes to marine heatwaves and the intensification of extreme weather events [ 83 ], large-scale outbreaks of coral-eating crown-of-thorns starfish, poor coastal and inshore water quality from sediments, pesticides and nutrients in land-based runoff, and direct human uses such as illegal fishing [ 81 , 82 , 84 ]. Coastal and catchment habitats in the GBR region too, are under pressure from increasingly frequent and severe climatic events (e.g., flooding, heatwaves, bushfires), as well as degradation from land developments and uses that exacerbate vegetation loss and soil erosion [ 81 , 85 , 86 ].

The high value that humans place on the GBR is evident in the efforts that have been made to protect and conserve its ecological integrity and heritage, nationally through the Great Barrier Reef Marine Park Act 1975 , globally through its 1981 World Heritage listing, and in response to more recent events and pressures through the Reef 2050 Long-Term Sustainability Plan [ 87 ]. Recognising that climate change is a global issue that cannot be managed at a local or regional scale, the State and Federal government authorities responsible for protection and management of the GBR have largely focused on mitigating local and regional pressures, including improving catchment water quality through policies aimed to improve agricultural practices, direct interventions to limit impacts from crown-of-thorns starfish outbreaks, and regulation and enforcement of commercial and recreational fishing [ 82 , 87 , 88 ]. Scientific evidence has played a critical role in guiding the governments’ policy development, decision-making and investments, through demonstrating the condition and trend of ecosystems, the extent of current and projected impacts, the source of stressors, and importantly, the actions that are required to mitigate pressures and protect ecological values and processes [e.g., 81 , 89 – 91 ].

Like other major policy initiatives, water quality improvement from the GBR’s catchments requires community support and stakeholder participation to be effective. Management efforts to date under the Reef 2050 Water Quality Improvement Plan [ 88 ] and other policy instruments have had a major focus on landholder and industry initiatives to reduce sediment, nutrients, and pesticide runoff, with incentives to promote voluntary changes in agricultural land use practices and to restore degraded ecosystems. However, the uptake of land use practice change has been slow, and policy initiatives have faced strong and sustained opposition from some groups [ 92 – 95 ].

Within the last decade, the science underpinning Reef and water quality management has been the subject of increased scrutiny and criticism, as well as misinformation on social media and partisan news media platforms [ 94 , 96 – 98 ]. A series of high-profile events within the GBR have attracted extensive media coverage, generating international interest and arousing public sentiment about the Reef’s health and protection. Such events have included government approvals for major port developments in 2014 [ 99 ], mass coral bleaching events of unprecedented scale and severity in 2016 and 2017 [ 100 – 102 ], and reactive monitoring missions by the UNESCO World Heritage Centre in 2012 and 2022 to assess the state of conservation of the GBR World Heritage property and consider its inclusion on the list of World Heritage properties “in Danger” [ 96 , 97 ]. These events, particularly the mass coral bleaching, have been accompanied by both sensationalised media representations of the GBR’s demise [e.g., 103 ], and misinformation that claims the GBR is in good health and is unthreatened by climate change and poor water quality [ 97 , 98 , 104 ].

Among the narratives promulgated by some media platforms, challenges to the veracity of GBR science and the integrity of its scientific institutions have become a frequent feature, garnering sufficient public and political interest to prompt an Australian Senate Committee Inquiry in 2020 into the evidence base underpinning regulation of farm practices that impact GBR water quality. While the adverse claims about this evidence base and the quality of GBR science were ultimately dismissed by the Committee [ 105 ], misinformation that sows doubt about the quality and integrity of Reef and water quality science continues to proliferate in the region and nationally, particularly as the health of the GBR epitomises characteristics of the broader climate change debate [ 98 ].

While the direct effects of misinformation on public trust in GBR science and management are not well understood, there are concerns that declining public trust in science could undermine political support for efforts to protect and restore its waterways at a critical time. Indications from long-term social surveys in the region suggest that while Reef management and scientific institutions are the most trusted sources of information about the GBR, residents’ trust in these institutions has decreased since 2017 [ 106 , 107 ].

Research aims and questions

The rationale for our case study was to better understand and articulate the characteristics of science mistrust in the GBR region. Using statistical analyses of data from a survey of residents in the catchments of the GBR region, and by adopting a typological approach, we categorised respondents into groups based on their levels of stated trust in the science about waterway health and management ( trust in science ) and compared their responses to a broad set of rating-scale questions about waterway values, behaviours, perceptions, and attitudes. From the analysis we sought to identify commonalities, or ‘common ground’ that can be leveraged for more effective engagement with those stakeholders and communities who are mistrustful (or distrustful) of the science underpinning GBR and water quality management. Specific research questions included:

• What is the prevalence of mistrust in science associated with waterway health and management among residents of the GBR catchment area?
• What environmental values, activities, perceptions, and attitudes are associated with (or are potential predictors) of trust and mistrust in such science?
• What values, perceptions and attitudes do ‘science trusting’ and ‘science sceptical’ groups of residents have in common?
• How might such commonalities serve as a basis for trust-building communication and engagement?

Findings from this case study are intended to be applied in the GBR region and potentially elsewhere by scientists, science communicators, leaders, and resource managers who seek to improve their engagement with science-sceptical groups to advance environmental protection goals. While insights about distinctive characteristics of science-sceptical and science-trusting groups can be informative, an improved understanding of the ‘common ground’ between parties is more likely to serve as a basis for productive dialogues.

Materials and methods

Survey dataset and data collection.

We used a social survey dataset of 1,877 residents of the GBR catchment region. The survey was conducted in November 2021 by four Regional Report Card (RRC) partnerships, each representing a major catchment of the GBR, in collaboration with the research team and management agency staff from the Queensland Government. Four different survey instruments were deployed simultaneously by the RRC partnerships, tailored to each region’s characteristics; however, many of the questions were identical across the four surveys, enabling cross-regional comparisons. The purpose of the survey was to provide a baseline for long-term monitoring of ‘human dimension’ indicators that would help to evaluate government management agencies’ progress towards achieving a set of objectives in the Reef 2050 Long Term Sustainability Plan [ 87 ], and to inform adaptive management of waterways, including strategic communication with communities and stakeholder engagement in the regional catchments. The surveys were co-designed via a participatory process involving officers from each of the Regional Report Card partnerships, relevant management agency staff, and social scientists. Details of the co-design process, the objectives and constructs underpinning the survey metrics, data collection, and the curation of the survey dataset are documented in a technical report [ 108 ]. The dataset itself is publicly accessible via the CSIRO Data Access Portal (‘ Great Barrier Reef Catchment Regional Waterway Partnerships Baseline Social Surveys ’; CC-BY-NC 4.0 Licence; DOI: 10.25919/52yr-rg31 [ 109 ]).

Respondents participated in the survey online and were recruited via one of two possible pathways: either (a) as part of an online panel administered by a market research provider, or (b) via regionally targeted advertising through local print media (with QR codes) and social media (via Facebook TM ). The panel consisted of volunteers who periodically undertake market research surveys to earn credits (e.g., redeemable loyalty card points), and are selected to participate in surveys based on their demography and location. The panel provider used for this survey was an accredited member of the Australian Data and Insights Association, holding ISO 20252 certification for ‘Market, opinion, and social research’. Such panel providers typically draw on suitable respondents from a large pool of members in metropolitan areas; however, in regional areas the pool can be smaller. In the four GBR catchment regions, the number of eligible respondents was estimated (by the provider) to range between 100 and 400 people per region. To achieve a desired sample from each region that would enable robust statistical comparisons, the survey recruitment was supplemented using paid social media advertisements (targeted within regional postcodes), as well as via local newspapers and other regional channels. Each RRC partnership was responsible for the supplementary recruitment in their region. Two of the regions used a prize draw (local tour voucher) to attract a larger pool of respondents. An underlying principle of the supplementary recruitment was to avoid sampling bias, thus paid social media advertisements were used instead of ‘organic’ sharing of the survey link, to avoid over-representation of sympathetic respondents or ‘friends’ of the RRC partnerships, and to capture a representative and diverse field of community views on the survey topics. The abovementioned technical report [ 108 ] provides further details of the survey methods, data returns, geographic boundaries, and respondent demography in each region.

Survey ethics

Participation in the online survey was voluntary and respondents remained anonymous. An introductory information page outlined the purpose of the survey, the lead organisations and funding source, the intended uses of the survey data, potential risks and benefits associated with participation, confidentiality and privacy provisions, as well as details of the ethical clearance and contacts. Informed consent by respondents was indicated via a tick box (“Do you consent to take part in the survey?”; “Yes” or “No”) at the end of the introductory information, prior to commencement of the survey questions. The study, its procedures, the survey questions, the introductory information, and the means of obtaining prior consent were reviewed and approved by CSIRO’s Social Science and Human Research Ethics Committee (CSSHREC; Approval number 140/21), in accordance with Australia’s National Statement on Ethical Conduct in Human Research (2007), prior to survey commencement.

Survey questions

The survey’s main focal topic was regional waterways , which were defined in the preamble as encompassing freshwater systems (‘all creeks, streams, rivers, lakes, dams, and wetlands’), estuaries (‘the lower reaches of creeks and rivers that are tidal where salt and freshwater mix’), and marine habitats (‘coastal waters including beaches and islands extending to the Great Barrier Reef’) within the RRC boundary. A figure depicting these different zones within each region’s boundaries was also provided as a visual reference [ 108 ].

The surveys focussed on residents’ (i) uses , benefits and values associated with waterways, (ii) their perceptions of the waterways’ health, problems, and threats, (iii) participation in waterway stewardship and enabling factors such as their motivation and capacity, and (iv) their perceptions of waterway governance , including support and trust for management institutions, and their trust in the science underpinning waterway management (i.e., “ I trust the science about waterway health and management ”; hereafter referred to as ‘ trust in science’ ). Most of the survey questions, including that for trust in science above, utilised ten-point Likert-type scales, representing their relative agreement with a statement (1 = ‘very strongly disagree’; 10 = ‘very strongly agree’), or the extent to which they value a characteristic of their region’s waterways (1 = ‘I don’t value this at all’; 10 = ‘I value this extremely highly’). Some questions used shorter response scale options with defined response categories. For example, perceptions of the health of different ecological habitats were elicited via a three-point scale (1 = ‘in poor health’, 2 = ‘in fair health’, 3 = ‘in good health), and a five-point scale was used for eliciting perceptions of the problems and threats affecting different waterway habitats (1 = ‘does not represent a problem/threat at all’, 2 = ‘a small problem/minor threat’, 3 = ‘a moderate problem/threat’, 4 = ‘a big problem/serious threat’, 5 = ‘represents a very big problem/extremely serious threat’). An ‘I don’t know’ option was provided for questions of this type where relevant. Other questions in the survey utilised ‘tick box’ categories (e.g. age, gender, employment sector, participation in specific waterway recreation and stewardship activities).

Basis of typology

Our typology in the following results was based on respondents’ numeric ratings indicating their level of agreement or disagreement with the above trust in science statement. We assigned respondents a category based on their numeric responses. Respondents who gave ratings of one or two (indicating strong disagreement with the statement) were assigned to the ‘Strongly Sceptical’ group; respondents who gave ratings of three to five were classified as ‘Mildly Sceptical’; those who gave ratings of six to eight were classified as ‘Mildly Trusting’; and those who gave ratings of nine or ten (indicating strong agreement) were assigned to the ‘Strongly Trusting’ group.

Typological comparisons of the four groups were made using a two-step process. First, we used regression tests to determine any statistically significant relationships for a range of potential predictors with trust in science . We then examined any statistically significant results by comparing the mean ratings (±SE), to make a qualitative assessment of the differences for descriptive purposes. In some cases, a meaningful difference between the typology groups’ mean scores was not apparent even when a statistically significant regression was found.

Statistical tests

Statistical tests were performed using R Statistical Software (v4.3.1) [ 110 ]. To identify variables associated with science mistrust we performed a series of ordinal logistic regression analyses with respondents’ rated level of agreement (1–10, as per above) with the trust in science statement as the response variable. Ordinal logistic regression analyses are useful for determining the likelihood that an ordered, categorical response variable can be explained by variation in the predictor variables [ 111 – 113 ]. The Cumulative Logit Model (CLM), also known as Proportional Odds Model (POM), assumes that the effect of the predictor variables on the response variable is the same for all categories of the response variable [ 114 , 115 ]. The CLM is the most widely used model and enables the evaluation of the correlation between the response and predictor variables without having to fit separate models for each category of the response variable [ 112 ]. Separate regression models were run for each survey question that was treated as a potential predictor.

We tested for the assumptions of ordinal logistic regressions: (i) multicollinearity, (ii) proportional odds, and (iii) goodness of fit. The validity of ordinal regression models relies on the absence of high multicollinearity. To check for multicollinearity, we calculated variance inflation factors (VIFs), where higher VIF values indicate higher multicollinearity. In general, VIF values above five are of concern while a VIF greater than 10 indicates severe multicollinearity. Therefore, only variables with VIF values less than five were included in the final ordinal regression analyses for each survey question. The proportional odds assumption, also known as the assumption of parallel lines, states that the odds of one unit change in the predictor variable influencing the response variable are constant across all levels of the dependent variable [ 116 ]. The Brant Test was applied to test the assumption of parallel lines [ 117 ]. It should be noted that there are instances when these statistical tests falsely reject the null hypothesis that the assumption is satisfied, leading to incorrect conclusions that the analyses are invalid [ 118 ]. As such, we used exploratory graphical analyses of residuals (residual plots) along with statistical hypothesis tests to evaluate the goodness-of-fit of the assumptions’ models [ 119 ]. We also used Pearson tests to evaluate goodness-of-fit, comparing the observed and predicted frequencies of the outcome variable to determine the overall fit of the regression models [ 120 ].

Sample description and prevalence of science mistrust

From the total sample of 1,877 respondents, 31% (n = 579) gave a rating of five or lower on the ten-point scale, indicating disagreement with the statement ‘I trust the science about waterway health and management’ (‘ trust in science’ ). Among these, from the total sample, 8% (n = 141) were assigned to the ‘Strongly Sceptical’ (SS) group, and 23% (n = 438) were classified as ‘Mildly Sceptical’ (MS). Among those who gave ratings of six or above on the response scale, indicating degrees of trust in science , 45% of the total sample (n = 839) were classified as ‘Mildly Trusting’ (MT) and 24% (n = 459) were assigned to the ‘Strongly Trusting’ (ST) group.

A comparison of demographic characteristics across the four trust groups ( Table 1 ) revealed a higher proportion of males comprising the SS group (69%), while the MS, MT and ST groups had comparable representation of genders, albeit with a higher proportion of female respondents that was inherent in the overall survey sample (54% were female). While the median age (in categories) was the same across the four groups, the SS group had a higher proportion of respondents in age categories over 55 years (49%), when compared with the MS (42%), MT (41%), and ST (35%) groups. Similarly, SS and MS respondents had lived in their region longer on average (31 years and 26 years respectively) than MT (24 years) and ST respondents (20 years). The SS group was also represented by a higher proportion of respondents who were employed in primary industries (28%), including the agriculture sector (16%), than the other three trust groups ( Table 1 ; see also S1 Table ).

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https://doi.org/10.1371/journal.pone.0308252.t001

Waterway values

Ordinal regression results showing the relationship between respondent ratings for trust in science and a series of value statements relating to aspects of regional waterways (1 = ‘I don’t value this at all’; 10 = ‘I value this extremely highly’) are presented in Fig 1 (panel a), with additional details for each of the test results reported in S2 Table . Significant positive relationships were found for First Nations heritage (‘the waterways have rich heritage to First Nations people/Traditional Owners’), local recreation (‘the waterways offer a place for local residents to enjoy recreation activities’), existence value (‘the fact that the waterways exist, even if I don’t use or directly benefit from them’), tourism attraction (‘the waterways are an important attraction for tourists visiting the region’), and iconic status (‘our waterways are recognised nationally and internationally for their iconic status, e.g., World Heritage, RAMSAR sites’). These results indicate that respondents who placed a higher trust in science were more likely to value these aspects of their region’s waterways to a higher degree than respondents who had a lower trust in science . A significant negative relationship was found between trust in science and local agriculture (‘the waterways support local agriculture’) indicating that respondents who had a lower trust in science were more likely to value local agriculture uses of waterways higher than those with greater trust in science .

Upper panels show ordinal regression test results plotting survey respondents’ trust in science with (a) their values attributed to regional waterways, and (c) their perceptions of waterway governance (n = 1,877). Regression coefficients [dots] and standard error [SE] bars show statistical significance of the relationship where intersection of the SE bar with zero indicates lack of significance. Blue colouring indicates a significant positive relationship and red colouring indicates a significant negative relationship. Lower panels (b, d) show the mean rating scores (±SE) from four groups with differing stated trust in science (SS = strongly sceptical, MS = mildly sceptical, MT = mildly trusting, ST = strongly trusting) for selected survey items with a significant regression result.

https://doi.org/10.1371/journal.pone.0308252.g001

To inform our descriptive typology, it was important to carefully examine the response patterns for the four trust groups. While the abovementioned regressions were statistically significant, such results do not always reflect a linear relationship between response and predictor variables, nor do they indicate low or high mean ratings for any group per se . When comparing the mean ratings between the four groups for First Nations heritage values of regional waterways, we see that the relationship to trust in science does appear to be linear. The SS group’s mean rating was near the middle of the response scale (5.56 ± 0.28 SE), while the ST group’s mean rating was relatively high (8.14 ± 0.11 SE), and the MS and MT groups’ mean scores fell in between ( Fig 1B ). Comparing other waterway values that were correlated significantly with trust in science , we observe that while the ST group gave a very high mean rating for their regional waterways’ existence value (9.46 ± 0.05 SE), the mean ratings for all groups were relatively high (i.e., all above 8.0), indicating a shared strong value. Similarly, we observe that the mean ratings for all four trust groups’ values for waterways supporting local agriculture are very similar (all between 6.89 and 7.28 on the ten-point scale; Fig 1B ). The mean scores corresponding to regression results for other waterway values ( S2 Table ) show small and/or non-significant differences, indicating similarity in the importance attributed to these waterway values between the four trust groups.

Governance perceptions

Fig 1 (panel c) shows ordinal regression results between respondents’ trust in science and their ratings for a series of statements reflecting their perceptions and attitudes towards waterway governance (1 = ‘very strongly disagree’; 10 = ‘very strongly agree’). We found significant positive relationships between respondents’ trust in science and their perceptions that management decisions are fair (‘I think that decisions about managing local waterways are made in a fair way’), that they are able to provide input into management of waterways (‘I feel able to have input into the management of waterways in my region if I choose to’), and that uses of regional waterways by the tourism and fisheries sectors are well managed (‘I think that tourism uses of waterways in our region are well managed’; ‘I think that the fisheries in our region are well managed’). Significant negative relationships were found between trust in science and respondents’ perceptions that they don’t have fair access to waterways (‘I do not have fair access to all the waterways in my region that I would like to use’) and that agriculture uses (of regional waterways) are well managed (‘I think that agriculture uses of waterways in our region are well managed’).

A comparison of the mean ratings from our four trust groups for the above governance perceptions ( Fig 1D and S3 Table ) shows a relatively linear, positive relationship between trust in science and perceptions that management decisions are fair and that respondents can provide input into management of waterways . The mean ratings for SS respondents for these variables were particularly low (3.65 and 2.91 out of 10, respectively), indicating that GBR residents with low trust in science do not perceive sufficient opportunities to contribute to management decisions affecting their regional waterways, and have a dim view of those management institutions’ procedural fairness.

Despite a significant negative correlation between trust in science and the perception that agricultural uses of waterways are well managed , a comparison of the trust groups’ mean ratings shows only minor differences in such perceptions between science sceptical and trusting respondents ( Fig 1D ). Similarly, while significant positive relationships were found for perceptions of tourism uses and fisheries ( Fig 1C ), the spread of mean ratings between the trust groups were smaller than those for other predictor variables, and there was no discernible difference between the SS and MS groups ( tourism uses SS = 5.50 ± 0.227; MS = 5.47 ± 0.097; MT = 6.33 ± 0.057; ST = 7.00 ± 0.101, and fisheries SS = 4.74 ± 0.249; MS = 4.93 ± 0.090; MT = 5.90 ± 0.063; ST = 6.42 ± 0.110; S3 Table ).

A significant relationship was not found between trust in science and respondents’ satisfaction with waterway management (‘overall, I feel satisfied with how local waterways are managed’) despite an incremental rise in the mean satisfaction ratings across the four groups coinciding with increasing trust in science (SS = 3.65 ± 0.235; MS = 4.88 ± 0.098; MT = 5.77 ± 0.063; ST = 6.23 ± 0.116). Similarly, the mean ratings for respondents’ personal influence on waterway management (‘I feel I personally have some influence over how local waterways are managed’) rose incrementally across the trust groups (SS = 2.60 ± 0.193; MS = 3.73 ± 0.095; MT = 4.29 ± 0.073; ST = 4.81 ± 0.130; S3 Table ), noting that the mean ratings for all groups were relatively low.

Waterway uses and benefits

Participation in a range of waterway recreation activities was elicited (‘when visiting all the different waterways in the region in the past 12 months, what recreational activities have you participated in?’), with respondents selecting applicable activities from a list. Logistic regression tests found significant positive relationships between trust in science and appreciating nature (‘wildlife watching and appreciating nature’) and participating in in-water activities such as snorkelling and diving and swimming ( Fig 2A ). Significant negative relationships were found between trust in science and participation in fishing and motorised watersports (e.g. water skiing and jet skiing). A comparison of the mean ratings for the four trust groups revealed appreciably higher participation in wildlife watching and appreciating nature among ST respondents, and in fishing among SS respondents when compared to the other three groups, but little apparent difference in participation in motorised watersports between the four groups, despite the significant regression result ( Fig 2B ; see also S4 Table ).

Upper panels show ordinal regression test results plotting survey respondents’ trust in science with (a) their recreation uses of waterways of regional waterways, and (c) their perceptions of personal benefits derived from waterways (n = 1,877). Regression coefficients [dots] and standard error [SE] bars show statistical significance of the relationship where intersection of the SE bar with zero indicates lack of significance. Blue colouring indicates a significant positive relationship and red colouring indicates a significant negative relationship. Lower panels (b, d) show the mean rating scores (±SE) from four groups with differing stated trust in science (SS = strongly sceptical, MS = mildly sceptical, MT = mildly trusting, ST = strongly trusting) for selected survey items with a significant regression result.

https://doi.org/10.1371/journal.pone.0308252.g002

The importance of specific personal benefits from regional waterways (i.e., individual benefits derived from ecosystem services) were rated by respondents on a ten-point agreement scale. Experiencing nature (‘the waterways are important for allowing me to experience, appreciate and interact with the natural environment’) and providing a domestic water supply (‘the waterways are an important source of my water supply for drinking and household use’) were found to have a significant positive relationship with trust in science , while providing fish and seafood (‘waterways in the region are important for providing fresh fish and seafood for me to eat’) was negatively correlated ( Fig 2C ). The plotted mean ratings for the four trust groups show perceptible but minor differences for experiencing nature and domestic water supply , and little discernability for providing fish and seafood ( Fig 2D ; see also S5 Table ). The minor differences for these few variables, and the absence of significant relationships for other items indicates a broadly shared appreciation for ecosystem-derived benefits between science sceptical and trusting groups.

Participation in waterway stewardship

Respondents indicated their participation in a set of activities associated with environmental stewardship in or around their region’s waterways (‘For the following questions, we would like to ask you about several personal actions that are intended to improve waterway health. Which of the following do you personally do?’). Regression tests of a binary response option (yes or no) found small but statistically significant relationships between trust in science and contributing to environmental monitoring (‘contribute to environmental monitoring programs, e.g., by participating in data collection, or reporting wildlife sightings’; positively correlated) and reporting suspicious activities (‘report suspicious activity to relevant authorities, e.g., illegal dumping, illegal fishing practices, chemical or oil spills’; negatively correlated; Fig 3A ). Small distinctions were apparent between the trust groups’ mean scores for these two variables ( Fig 3B ; see also S6 Table ); however, for the purposes of a typological comparison these distinctions did not indicate a substantive difference between science sceptical and science trusting respondents in their participation in environmental stewardship.

Upper panels show ordinal regression test results plotting survey respondents’ trust in science with (a) their self-reported participation in stewardship actions, and (c) personal capacity and motivational ‘stewardship enabling’ factors (n = 1,877). Regression coefficients [dots] and standard error [SE] bars show statistical significance of the relationship where intersection of the SE bar with zero indicates lack of significance. Blue colouring indicates a significant positive relationship and red colouring indicates a significant negative relationship. Lower panels (b, d) show the mean rating scores (±SE) from four groups with differing stated trust in science (SS = strongly sceptical, MS = mildly sceptical, MT = mildly trusting, ST = strongly trusting) for selected survey items with a significant regression result.

https://doi.org/10.1371/journal.pone.0308252.g003

Stewardship enablers and barriers

Personal capacity and motivational factors associated with environmental stewardship were elicited from respondents via their agreement/disagreement ratings (1–10 scale, as above) for a series of statements. Regression tests found significant positive relationships between trust in science and feeling responsible (‘I feel a sense of responsibility to help improve waterway health’), wanting to do more to help (‘I want to do more to help improve waterway health in my region’) and personal efficacy (‘I can make a personal difference to improving waterway health in my region’; Fig 3C ). For these three motivational factors, the distinctions between the four trust groups’ mean ratings indicate that science sceptical (both SS and MS) respondents feel less responsible, less motivated, and less empowered to make an effective personal contribution to the health of waterways in their region than science trusting respondents, and ST respondents in particular ( Fig 3D ).

Ratings for statements reflecting normative beliefs about community participation and support for waterway stewardship, such as local residents taking action (‘many local residents in my region are taking action to improve waterway health’) and local residents support action (‘local residents in my region are supportive of taking action to improve waterway health’) revealed no significant relationship with trust in science . Likewise, significant relationships were not found for statements reflecting respondents’ capacity in terms of time (‘I don’t have enough time to contribute to improving waterway health in my region’) and knowledge (‘I don’t know how I could contribute to improving waterway health in my region’) to contribute to waterway stewardship, nor for a statement reflecting their hope for the future of their region’s waterways (‘I feel hopeful about the future health of waterways in my region’; Fig 3C ; S7 Table ).

Perceptions of waterway health, problems, and threats

Respondents’ perceptions of the relative health of different waterway habitats from the catchment to offshore coral reefs (indicated via a three-point scale as described in methods) were largely unrelated to their trust in science ( Fig 4A ). Two exceptions were a significant (but slight) positive correlation with perceptions of the health of beaches and the coast , and a significant negative correlation with that of inshore coral reefs . For the latter result a distinct difference in mean ratings was evident, indicating that SS respondents perceived inshore coral reefs to be in much better health than the other trust groups ( Fig 4D ; S8 Table ).

Panels a–c show ordinal regression test results plotting survey respondents’ trust in science with (a) perceptions of waterway health (n = 767), (b) perceptions of waterway problems (n = 1,251) and (c) perceptions of waterway threats (n = 1,877). Regression coefficients [dots] and standard error [SE] bars show statistical significance of the relationship where intersection of the SE bar with zero indicates lack of significance. Blue colouring indicates a significant positive relationship and red colouring indicates a significant negative relationship. Panel (d) shows the mean rating scores (±SE) from four groups with differing stated trust in science (SS = strongly sceptical, MS = mildly sceptical, MT = mildly trusting, ST = strongly trusting) for selected survey items with a significant regression result.

https://doi.org/10.1371/journal.pone.0308252.g004

Perceptions of potential problems manifested in regional waterways (elicited via a five-point scaled response as per methods) were also mostly unrelated to trust in science ( Fig 4B ); however, significant positive correlations were found for perceptions that chemical pollutants (‘chemical pollutants, e.g., pesticides, PFAS’) and riverbank erosion were problematic issues in regional waterways. When examining the mean ratings ( Fig 4D ; S9 Table ), discernible differences between the trust groups were evident, in which the problem perception for both items was lowest among SS respondents.

A strong and significant positive relationship was found between trust in science and the perception of climate change as a threat to waterways, with an apparent polarity between the trust groups’ mean rating scores ( Fig 4C and 4D ). For nearly all other listed potential threats to waterways there was no significant relationship between perceptions of their severity and trust in science . Despite a significant regression result for tourism activities , a comparison of the mean ratings showed no distinguishable difference between the four trust groups ( S10 Table ).

Descriptive typology

Distinguishing characteristics of the four trust groups, drawn from our results above, are summarised below ( Table 2 ). In this descriptive summary we have included only those predictors that were found to be statistically significant and that could be described as qualitatively distinct. I.e., some statistically significant predictors are excluded due to insufficiently distinct differences in the mean ratings of the four trust groups. For example, while there was a significant regression result for ratings of the threat posed by tourism activities and trust in science , the mean ratings for the four trust groups differed by only 0.03 on the five-point scale, indicating little dissimilarity in this perception ( S10 Table ). Similarly, the mean ratings for waterways’ existence value (all above 8.2 on the 10-point scale), indicate that all four groups value this very highly, despite the significant regression test result ( Fig 1B ).

https://doi.org/10.1371/journal.pone.0308252.t002

Prevalence and characteristics of science mistrust in the GBR region

Our study found that 31% of survey respondents, representing residents of four major catchments in the GBR region, were mistrusting of the science underpinning waterway health and management to some degree. Considering the time since our survey data were collected (November 2021) and indications from a more recent study of the same population [ 107 ], it is possible that this proportion has grown, mirroring a trend in Australia, the USA, and numerous other countries [ 121 ]. In recent years, cross-national studies have sought to identify drivers of public mistrust in science, in the context of resurging populist politics, the COVID-19 pandemic, and growth in misinformation presented in news media and across social media [ 42 , 121 , 122 ]. While it was beyond the scope of our study to identify specific drivers of science mistrust in the GBR region, it is likely that multiple factors have contributed, and that science sceptical attitudes and beliefs are not homogeneous. Relevant to our case study population, and considering the relatively high proportion of SS respondents employed in the agriculture sector ( Table 1 ), factors contributing to the erosion of trust in the GBR region could include resentment among landowners to regulatory land use changes (intended to improve GBR water quality and underpinned by the GBR Scientific Consensus Statement on land use impacts on GBR health [ 81 ]), as well as climate change misinformation and denial narratives in social media [ 98 ]. An empirical assessment of social media posts by Lubicz-Zaorski et al. [ 98 ] found that a small group of politically aligned actors were responsible for a campaign of misinformation specifically about the GBR, with an apparent motive to erode public support for Australian climate change policy. While further research into the drivers of science mistrust is needed, knowing the factors associated with this mistrust can be useful for understanding how it is manifested in the regional context, and for understanding viewpoints that are shared or divergent when seeking constructive engagement.

Characteristics of mistrust—disempowerment

Some of the distinguishing characteristics of the SS and MS groups (in Table 2 ) warrant further consideration by both scientists and natural resource managers. Respondents in these groups were likely to perceive that waterway management decisions are unfair, that they are unable to provide input into management, and perhaps consequently–they felt less responsible, less motivated and had a lower sense of personal efficacy in contributing to the improvement of waterway health. A sense of moral responsibility and of personal efficacy have been established as key motivating factors in people’s adoption of stewardship behaviours [ 123 ]. However, the extent to which the empowerment of individuals mediates their trust in science and institutions in governance systems is a topic of ongoing research and debate. While some studies have found that higher levels of citizen participation and information transparency can yield greater trust among citizens [ 80 ], others have argued that trust-eroding suspicion and blame can arise as a perverse consequence of increased information sharing [ 124 ], and that contextual factors such as citizens’ knowledge of relevant issues and predisposition to trust play an important mediating role [ 125 ]. Nonetheless, the apparent disempowerment of science-sceptical residents in the GBR region may be worthy of efforts to better understand and address real or perceived barriers to their participation in waterway governance and stewardship.

Characteristics of mistrust—climate change scepticism

While perceptions of ecosystem health, problems and threats were mostly unrelated to respondents’ trust in science ( Fig 4 ), the divergent perceptions of climate change as a threat are characteristic of a broader societal phenomenon. While individual belief systems and forms of climate change scepticism and denialism vary, an underlying characteristic is the rejection of scientific findings that conflict with the individual’s interests, beliefs and/or worldview [ 126 – 128 ]. At the extremes, such views can become entrenched in an individual’s identity, political allegiance, and/or religion [ 128 – 130 ]. However, cognitive biases and the tendency to reject or superficially manipulate conflicting evidence in favour of a preferred interpretation are universal flaws that can be expressed by individuals of any persuasion [ 128 , 131 ]. Proponents of climate change misinformation often exploit these psychological biases by appealing to people’s identity, values, and belief systems, and often promote pseudoscience to create fake controversies and/or frame conspiracies (e.g. ‘scientists falsifying results to obtain more funding’) to elicit emotional reactions and to sow doubt and mistrust [ 127 , 131 , 132 ].

In the GBR context and region, climate change misinformation is pervasive and has been shown to be deployed opportunistically in response to emergent scientific reports and news about the Reef and its health [ 98 ]. A predominant misinformation narrative is that the Reef is ‘in great health’ and is unaffected by climatic and other anthropogenic pressures, such as poor water quality (ibid.). Conversely, media narratives arising from major disturbance events, such as the mass coral bleaching in 2016 and 2017, have tended to portray the Reef as ‘dead’ or ‘dying’ in a sensationalist manner [ 96 , 97 , 104 ]. Public risk perceptions can be influenced by ‘risk events’ and accompanying media representations, and in 2017 an increase was observed in the proportion of GBR residents and stakeholders who identified climate change as ‘an immediate threat requiring action’ [ 101 , 102 ]. While a potential counteractive effect of climate change misinformation in the GBR region has not yet been determined, repeat studies in 2021 and 2023 have shown that the proportion of residents who perceive climate change as an ‘immediate threat’ has decreased considerably [ 106 , 107 ]. Of additional concern is the potential effect of the opposing narratives ‘in great health,’ and ‘dead’ or ‘dying’, on individuals’ personal efficacy and motivation to adopt pro-environmental behaviours. Both narratives serve to rationalise inaction, whether it be efforts to reduce carbon emissions or to improve coastal water quality, because acting is either unnecessary, or it’s too late.

Engaging with science mistrust

At a global scale, countering climate change and anti-science misinformation in the public sphere is seen increasingly as an imperative for deliberative democracies that seek to mitigate a worsening climatic outlook [ 133 – 135 ]. While communication techniques that debunk misinformation and ‘inoculate’ the public can reduce the influence of misinformation [ 136 , 137 ], public communication on its own is not sufficient to rebuild or maintain trust in science among citizens and stakeholders [ 12 , 14 , 18 ]. A healthy relationship between science, policy, and publics with optimal levels of trust requires integrity and credibility of both scientific and government institutions [ 12 , 15 , 16 ], and requires communities and stakeholders to be engaged in equitable processes and partnerships that recognise shared and diverse values, address shared goals, and build shared understandings of risks, opportunities, costs, and benefits [ 14 , 17 , 18 , 25 ].

The group characteristics summarised in our typology ( Table 2 ) are useful to consider when engaging with communities and stakeholders in environmental management initiatives in the GBR region, and some of these characteristics may be relatable to other regions and contexts. But despite the differences between the four trust groups, more importantly, our results also reveal many similarities between science sceptical and science trusting residents. Encompassing their environmental values, uses and benefits, motivations, attitudes and perceptions, these similarities can be considered ‘common ground’ and can provide a useful basis for consensus-building discussions and message framing. Noting that individual viewpoints can and do vary, some key ‘common ground’ factors in our results (i.e. factors not associated with trust or mistrust in science) included:

• Shared appreciation of ecosystem values , including biodiversity, existence, and icon values of regional waterways, such as the GBR ( Fig 1A ).
• Shared recognition of the importance of ecosystem services . For example, waterways supplying fish and seafood, supporting regional industry and economies, enabling social opportunities, recreation, lifestyle, aesthetic appreciation and contributing to personal wellbeing ( Fig 2C and 2D ).
• Shared perceptions of community norms around environmental stewardship , including levels of support and participation in some stewardship actions within the local community ( Fig 3A and 3C ).
• Shared perceptions of the relative health of most aquatic ecosystems , including freshwater habitats, estuaries and offshore waters ( Fig 4A ).
• Shared perceptions of many problems present in their region’s waterways , including erosion, the presence of weeds and invasive species, litter and debris, and reduced fish stocks ( Fig 4B ).
• Shared perceptions of many threats to their region’s waterways , including over-fishing and illegal fishing, extreme weather, land clearing and land-based runoff ( Fig 4C ).

Insights about shared values and viewpoints, like those above, are often applied in communications and engagement efforts to demonstrate an understanding of others’ perspectives, and common goals [ 66 ]. Numerous authors have studied and offer advice on communication techniques for public relations and organisational leadership that can help to establish a shared understanding of situation and risks, and to engender a commitment to shared goals and pathways to achieving them [e.g., 64 , 67 ]. Communications from relatable leaders and ‘trusted messengers’ (i.e. recognisable spokespeople with credibility among the target audience) can be influential in framing issues and building consensus [ 65 , 66 , 68 ]. However, as media and social media platforms have become increasingly fragmented, and as science-sceptical audiences have turned away from sources that report factual and scientific information, connecting such audiences with scientific or technical content has become increasingly difficult [ 31 , 32 ]. Communicating with science-sceptical audiences thus requires the use of a wider range of platforms, and interpersonal forms of communication stand a greater chance of resonating with audiences on polarised and technical subjects [ 32 , 65 ]. Fundamentally, trust arises from social relationships, when individuals and institutions demonstrate their competence, reliability, and trustworthiness [ 12 , 138 ].

Some anti-science views can be entrenched and are unlikely to change, especially when they are reinforced frequently by misinformation and peer networks [ 128 , 139 ]. Directly challenging or dismissing extreme viewpoints as flawed or invalid often results in alienation and estrangement [ 130 , 139 ]. Pursuing opportunities for respectful discourse on less contentious topics and shared viewpoints instead may yield more constructive and sustained engagement. For example, landowners who are sceptical of climate change and the effects of terrestrial runoff on inshore reefs may be more receptive to waterway management initiatives that seek to mitigate topsoil erosion and other impacts from extreme weather events such as floods or drought.

Limitations, knowledge gaps and further research

The scope of our study was limited by using quantitative data derived from a survey that was designed for long-term monitoring of a broad selection of indicators relevant to ‘human dimensions’ of GBR regional waterways (i.e. social, economic, cultural and governance aspects). The primary metric for ‘trust in science’ was framed as a general concept, which did not allow for deeper investigation of the different types and component attributes of such trust (e.g., perceptions of the competence of scientists, of their motivations, and of systems underpinning scientific integrity; as described by Stern & Baird [ 25 ]). Future research that explores such attributes may help to identify specific drivers of mistrust and their proportionate influence. Our study’s description of trust characteristics at the macro scale can guide in-depth, qualitative research that is necessary for understanding individual and smaller group characteristics [ 140 , 141 ].

Among the underlying drivers of mistrust in the science underpinning waterway health and management in our case study region, the extent to which such views are influenced by misinformation, and/or personal experience is of particular interest. Considering the misinformation campaign that specifically targets Reef and water quality science [ 98 ] and an observed trend of declining trust in the region’s science and management institutions [ 107 ], further research that deconstructs this misinformation could be explored in controlled laboratory experiments, manipulating trust factors that are known to be important. Such research should be useful in counter-communications to inoculate the public against its corrosive effects (e.g. as reported by Cook and others [ 136 , 137 ]).

Long-term monitoring of community values and perceptions of environmental health, problems and threats remains important. As public risk perceptions can change in response to disturbance events and associated media representations [ 101 , 102 ], they may be similarly responsive to misinformation. Lastly, further research is needed into the effectiveness of communications that seek to rebuild public trust in science. While appeals to common values and other communication techniques have been studied extensively in the context of public relations and organisational leadership, there is still a paucity of empirical research on their influence on public trust in science.

Our empirical case study in the GBR region achieves two things: (1) it contributes to an improved understanding of how science mistrust manifests in relation to aquatic ecosystem management at a regional scale, and (2) it provides insights on characteristics of science sceptical groups and on ‘common ground’ that can be applied by scientists, communicators, and resource managers when engaging with stakeholders and communities to build consensus on mutual goals and pathways, trust, and support to protect and restore habitats and vital ecosystem functions.

The management of waterways encompassing the Great Barrier Reef World Heritage Area and its adjacent catchments is at a pivotal stage, with significant government investments and scientific research focussed on reducing human pressures and enhancing ecosystem resilience to withstand impacts of increasing severity as the oceans and climate become warmer. The modern trend of increasing climate change denialism, anti-science sentiment, and misinformation represents a significant challenge to environmental policy in the GBR region and worldwide. Leaders, resource managers and scientists must contend with this challenge, and they face an increased impetus to uphold the integrity of science and its relationship with government policy, to counter misinformation, and to engage and empower communities in natural resource governance processes.

Our findings may challenge some assumptions and stereotypes about science scepticism but may confirm others. It should be somewhat reassuring to scientists and resource managers in the region that most residents are trusting of the science about waterway health and management. However, such levels of public trust are not guaranteed to be self-sustaining, and other results indicate widespread perceptions that aspects of community involvement in waterway management can be improved ( S3 Table ). It may also be reassuring then that there are many similarities (and abundant ‘common ground’) in environmental values and perceptions shared among people who trust the science and those who do not. While a lack of trust in science may affect how one perceives threats to the environment, it does not necessarily affect how one sees the environment itself.

Supporting information

S1 table. results of ordinal regression models testing the relationship between survey respondents’ ‘trust [in] the science about waterway health and management’ and predictor variables from five survey questions about respondent demography..

https://doi.org/10.1371/journal.pone.0308252.s001

S2 Table. Results of ordinal regression models testing the relationship between survey respondents’ ‘trust [in] the science about waterway health and management’ and predictor variables from survey questions about values attributed to regional waterways, and mean rating scores (±SE) from four groups with differing stated trust in science (strongly sceptical, mildly sceptical, mildly trusting, strongly trusting) for each predictor variable.

https://doi.org/10.1371/journal.pone.0308252.s002

S3 Table. Results of ordinal regression models testing the relationship between survey respondents ‘trust [in] the science about waterway health and management’ and predictor variables from survey questions about perceptions of waterway governance, and mean rating scores (±SE) from four groups with differing stated trust in science (strongly sceptical, mildly sceptical, mildly trusting, strongly trusting) for each predictor variable.

https://doi.org/10.1371/journal.pone.0308252.s003

S4 Table. Results of ordinal regression models testing the relationship between survey respondents ‘trust [in] the science about waterway health and management’ and predictor variables from survey questions about recreational uses of regional waterways, and mean rating scores (±SE) from four groups with differing stated trust in science (strongly sceptical, mildly sceptical, mildly trusting, strongly trusting) for each predictor variable.

https://doi.org/10.1371/journal.pone.0308252.s004

S5 Table. Results of ordinal regression models testing the relationship between survey respondents ‘trust [in] the science about waterway health and management’ and predictor variables from survey questions about personal benefits derived from regional waterways, and mean rating scores (±SE) from four groups with differing stated trust in science (strongly sceptical, mildly sceptical, mildly trusting, strongly trusting) for each predictor variable.

https://doi.org/10.1371/journal.pone.0308252.s005

S6 Table. Results of ordinal regression models testing the relationship between survey respondents ‘trust [in] the science about waterway health and management’ and predictor variables from survey questions about respondents’ participation in waterway stewardship actions, and mean rating scores (±SE) from four groups with differing stated trust in science (strongly sceptical, mildly sceptical, mildly trusting, strongly trusting) for each predictor variable.

https://doi.org/10.1371/journal.pone.0308252.s006

S7 Table. Results of ordinal regression models testing the relationship between survey respondents ‘trust [in] the science about waterway health and management’ and predictor variables from survey questions about respondents’ motivation and capacity to participate in stewardship actions to improve the health of their region’s waterways (i.e. stewardship enablers), and mean rating scores (±SE) from four groups with differing stated trust in science (strongly sceptical, mildly sceptical, mildly trusting, strongly trusting) for each predictor variable.

https://doi.org/10.1371/journal.pone.0308252.s007

S8 Table. Results of ordinal regression models testing the relationship between survey respondents ‘trust [in] the science about waterway health and management’ and predictor variables from survey questions about perceptions of waterway health, and mean rating scores (±SE) from four groups with differing stated trust in science (strongly sceptical, mildly sceptical, mildly trusting, strongly trusting) for each predictor variable.

https://doi.org/10.1371/journal.pone.0308252.s008

S9 Table. Results of ordinal regression models testing the relationship between survey respondents ‘trust [in] the science about waterway health and management’ and predictor variables from survey questions about perceptions of waterway problems, and mean rating scores (±SE) from four groups with differing stated trust in science (strongly sceptical, mildly sceptical, mildly trusting, strongly trusting) for each predictor variable.

https://doi.org/10.1371/journal.pone.0308252.s009

S10 Table. Results of ordinal regression models testing the relationship between survey respondents ‘trust [in] the science about waterway health and management’ and predictor variables from survey questions about perceptions of threats to regional waterways, and mean rating scores (±SE) from four groups with differing stated trust in science (strongly sceptical, mildly sceptical, mildly trusting, strongly trusting) for each predictor variable.

https://doi.org/10.1371/journal.pone.0308252.s010

Acknowledgments

This research was conducted using data from the Social and Economic Long-Term Monitoring Program for the Great Barrier Reef (SELTMP; https://research.csiro.au/seltmp ), collected in partnership with the Queensland Office of the Great Barrier Reef and World Heritage, and the five Regional Report Card Partnerships in the Great Barrier Reef catchment region: Wet Tropics Waterways, Dry Tropics Partnership for Healthy Waters, Mackay-Whitsunday-Isaac Healthy Rivers to Reef Partnership, Fitzroy Partnership for River Health, and Gladstone Healthy Harbour Partnership. The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the authors and do not necessarily reflect the views of the Australian Government or the Queensland Government and their respective Ministers for the Environment.

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Image source: Greens MPs / Flickr .

• Earth & environment

Biodiversity of the Great Barrier Reef

There are a lot of animals living on the Great Barrier Reef—and they’ve all got their own job to do.

Expert reviewers

Professor David Bellwood

Distinguished Professor, College of Marine & Environmental Sciences

James Cook University

Dr Jennie Mallela

Environmental and Coral Reef Specialist

Australian National University

• The Great Barrier Reef is the largest living structure on Earth.
• It provides habitat for nearly 9,000 species of marine life—and that’s just the (relatively) easy to count ones!
• The reef’s rich biodiversity helps it to maintain a stable and healthy coral reef system.
• Another way to look at biodiversity is from the perspective of the ‘jobs’ that organisms do within the system.
• High biodiversity in terms of numbers of species does not necessarily ensure high resilience or robustness.

The enormous coral reef that graces the waters of eastern Queensland extends for 2,300 kilometres, is the planet’s largest living structure, and can be seen from space. Its 2,500 individual reefs and 900 islands extend from the northern tip of Queensland down to south of Gladstone, and its ecosystems range from shallow near shore environments to deep waters 250 kilometres offshore. It is the largest coral reef ecosystem on our planet and home to not just corals, but countless other marine life. It’s our Great Barrier Reef.

How the reef formed

Coral reefs form under a rather specific set of circumstances—the temperature, water chemistry and water depth have to be just right. Although deep water corals do exist, the majority of reef builders like to be in shallow waters, where sufficient sunlight can penetrate to fuel the photosynthesis of the algae that lives alongside the coral animals and provides them with essential food. As sea level rises and slowly floods coastal plains, coral reefs will follow.

A reef’s beginnings occur when coral larvae floating around in the ocean attach themselves to a solid substrate, such as a rock, or older coral skeleton. The coral animals build their skeleton, which is made from calcium carbonate (CaCO 3 ), pulling the calcium (Ca) and carbonate (CO 3 ) from the seawater. Over time, the skeletons of dead corals and shells become cemented together to form massive deposits of the rock limestone. 

There are three types of coral reef structure: fringing reefs, which form close to shore, barrier reefs, which are more substantial, stronger reef structures, located further offshore, and atolls, which are essentially fringing reefs that formed around an island and remained as a ring of coral after the island became submerged.

As its name implies, the Great Barrier Reef is a barrier reef. Its strong limestone structures, formed by the cemented skeletons of corals and other reef carbonates, protect much of the Queensland coastline .

In geological terms, the Great Barrier Reef is pretty young. At the end of the most recent ice age, sea level on the coast of Queensland was around 120 metres lower than today. As it rose, reef systems started to develop, most likely forming fringing reefs along the coastline. These became submerged as the sea continued to rise, and the modern reef as we know it started growing somewhere between 6,000 and 9,000 years ago, when sea level stabilised close to today’s level. Over these few thousand years, it’s grown and developed into one of the world’s most diverse ecosystems.

Biodiversity of the reef

A simple way to look at an ecosystem’s biodiversity is to look at the number and variety of different species that it supports —k nown as species diversity. Other measures of biodiversity include genetic diversity (the variety of a specific organism’s genes), and ecosystem diversity (the number of different ecosystems found within a particular area).

Using species diversity, it is certainly justified to describe the Great Barrier Reef as one of the most diverse habitats on the planet. Close to 9,000 species of marine life call it home, and this doesn’t include any of the huge number of microbes, plankton and fungi that also live there. And although the modern reef system is only around 6,000 to 9,000 years old, many of the creatures that call it home have existed for millions of years.

The Great Barrier Reef is home to more than fish and coral. Below is a snapshot of just some of the animals it supports. This information is also available as an infographic .

Source: Great Barrier Reef Marine Park Authority and Brodie and Waterhouse (2012)

A different perspective on biodiversity

Another way to look at the diversity of the Great Barrier Reef is to examine all the organisms and animals that live there as if they were machines all working together in an integrated system. So, instead of looking at a fish and seeing a pretty bright orange guy, called Nemo, we would look at him as a machine that performs a job. Figuring out exactly how that machine works helps us understand what job he does, and how important both the job and machine are to the reef ecosystem as a whole. This is known as functional diversity.

Using this approach to look at fish fossils provides insights into the sorts of roles fish played in the reef systems in the past, and how those jobs might have changed (or not!) over time. This is known as functional evolution and it’s a very useful tool for understanding reef evolution, adaptation and potential vulnerability. 

For example, fish jawbones have changed a lot over the past 100 million years. Once upon a time, fish were limited to catching their prey by simply grabbing at prey as it swam past them. Over time, some fish’s bones have evolved into structures that let the fish jaw protrude out from its head by up to 8 centimetres. This means the fish are now able to snap up their prey, turning them into more efficient feeders that can catch smaller prey. And, at the same time as fish have evolved these longer jawbones, the prey animals have also evolved: they have become smaller. On the reef today, the average size of a crustacean is less than 1 millimetre. They’re harder to catch and they can hide more easily. 

Another change has been seen in the sort of teeth fish have. Prior to 25 million years ago, fish teeth ranged from long and pointy, designed to puncture and tear, to short and round, designed to scrape and grind. Fish that lived on the reef ate crustaceans, and the crustaceans fed on the detritus found on the surface of the reef—fine dust-like particles high in nutrients. The development of long teeth shaped a bit like toothbrushes meant that fish can feed directly on the nutrient-rich detritus on the reef, and leave the crustaceans alone. This change in feeding dynamics would have had an impact upon the entire reef system and played a role in the development of modern reefs.

A job for everyone, and everyone doing their job

Looking at things from this functional approach also enables us to ask some important questions about biodiversity—sure we’ve got lots of species here on the Great Barrier Reef, but is that really important? Does having so many different species actually offer a meaningful benefit to the reef system as a whole? Maybe it’s okay if we lose one or two species, surely another species can just take over their job?

Research done on the Great Barrier Reef says … a little bit of yes and quite a lot of no. There is a very small subset of jobs that are extremely popular—there are lots of species all doing the same job, so yes, if one of those species disappears, the job will still get done. Eating plankton is one of these jobs of choice. 

Probably the most important job is providing the actual ‘bricks and mortar’ of the reef structure. The ‘bricks’ are formed by the reef-building scleractinian corals and there are various encrusting organisms (e.g. bryozoans, coralline algae, bivalves) that make up the ‘mortar’. There are several different species of scleractinian corals, and lots of different encrusting organisms, but the role they collectively perform is crucial.

More alarmingly, of the numerous roles performed by reef fish, nearly 40 per cent are performed by a single species. If these specialists disappear, there’s no one waiting in the wings to step in and do their job. High biodiversity clearly does not necessarily ensure high resilience or robustness. 

This graph shows the functional diversity of fish communities in the Indo-Pacific region, which includes the Great Barrier Reef. While there are some jobs that are performed by lots of fish, the steep downward slope of the curve indicates that most jobs are done by only a few species, and nearly 40 per cent of jobs are done by only one species. Adapted from Mouillot et al. (2014) PNAS 111:38, 13757–13762.

Giant hump-headed parrotfish ( Bolbometopon muricatum ), for example, are integral to a healthy reef system . Parrotfish eat more than 5 tonnes of coral reef material a year, around half of which is live corals. In a healthy system, parrotfish help keep the coral growth in check, with coral growth rates roughly balancing the amount of coral eaten by the parrotfish. 

Parrotfish also eat a lot of macroalgae GLOSSARY macroalgae Seaweeds and other plants that grow in marine environments that are visible to the naked eye, as opposed to microalgae, such as diatoms, phytoplankton and zooxanthellae, that can’t be seen without a microscope. , which is also important within the reef system. In over-fished or nutrient-enriched reefs, macroalgae can out-compete the corals. So, without parrotfish, coral growth and reef structure could change dramatically. 

Another example is the role played by the giant moray eel ( Gymnothorax javanicus ). The eel only eats at night. This means it preys on fish and other animals that are also active at night. These species escape being eaten by predators that operate in the daytime, and so the eel is potentially important in keeping these species in check.

Another specialised predator is the giant triton ( Charonia tritonis ). This snail is one of the very few animals that can eat the extremely voracious, coral-eating crown-of-thorns starfish ( Acanthaster planci ). Although they generally would only eat one starfish a week, their very presence helps to disperse groups of crown-of-thorns starfish , weakening their ability to breed and multiply on the reef.

The surgeonfish is another important reef-dweller. Like the parrotfish, it is essential in the process of sediment removal. A study looking at surgeonfish ( Ctenochaetus striatus ) on the Lizard Island reef, in the northern end of the Great Barrier Reef, found these fish ate somewhere between 8 and 66 grams of sediment per fish per day. They generally get rid of their stomach contents in a different location to their eating grounds, and around one third of the sediment they eat is deposited off the reef, in deep water. This process helps maintain the reef, and possibly specific algal habitats in particular, which are a valuable food source for herbivore fish.

Whether looking at the sheer numbers of species of marine life, or the range of tasks and jobs they carry out on the Great Barrier Reef, it’s clear that it’s an amazingly intricate and dynamic system. It’s also fragile. The specialised nature of many of the jobs carried out by the different species on the reef mean that we can not take the reef’s resilience for granted.

Climate change and coral bleaching

Keeping our great barrier reef great, more than just temperature—climate change and ocean acidification.