marine environment essay introduction

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• Introduction

Origins of marine life

Geography, oceanography, and topography.

• Physical and chemical properties of seawater
• Ocean currents
• Links between the pelagic environments and the benthos
• Organisms of the deep-sea vents
• Distribution and dispersal
• Migrations of marine organisms
• Dynamics of populations and assemblages
• The pelagic food chain
• Seasonal cycles of production

marine ecosystem

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• Defenders of Wildlife - Basic Facts About Marine Habitats
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marine ecosystem , complex of living organisms in the ocean environment .

Marine waters cover two-thirds of the surface of the Earth . In some places the ocean is deeper than Mount Everest is high; for example, the Mariana Trench and the Tonga Trench in the western part of the Pacific Ocean reach depths in excess of 10,000 metres (32,800 feet). Within this ocean habitat live a wide variety of organisms that have evolved in response to various features of their environs.

The Earth formed approximately 4.5 billion years ago. As it cooled, water in the atmosphere condensed and the Earth was pummeled with torrential rains , which filled its great basins , forming seas. The primeval atmosphere and waters harboured the inorganic components hydrogen , methane , ammonia , and water. These substances are thought to have combined to form the first organic compounds when sparked by electrical discharges of lightning . Some of the earliest known organisms are cyanobacteria (formerly referred to as blue-green algae ). Evidence of these early photosynthetic prokaryotes has been found in Australia in Precambrian marine sediments called stromatolites that are approximately 3 billion years old. Although the diversity of life-forms observed in modern oceans did not appear until much later, during the Precambrian (about 4.6 billion to 542 million years ago) many kinds of bacteria , algae , protozoa , and primitive metazoa evolved to exploit the early marine habitats of the world. During the Cambrian Period (about 542 million to 488 million years ago) a major radiation of life occurred in the oceans. Fossils of familiar organisms such as cnidaria (e.g., jellyfish ), echinoderms (e.g., feather stars), precursors of the fishes (e.g., the protochordate Pikaia from the Burgess Shale of Canada ), and other vertebrates are found in marine sediments of this age. The first fossil fishes are found in sediments from the Ordovician Period (about 488 million to 444 million years ago). Changes in the physical conditions of the ocean that are thought to have occurred in the Precambrian—an increase in the concentration of oxygen in seawater and a buildup of the ozone layer that reduced dangerous ultraviolet radiation—may have facilitated the increase and dispersal of living things.

The marine environment

The shape of the oceans and seas of the world has changed significantly throughout the past 600 million years. According to the theory of plate tectonics , the crust of the Earth is made up of many dynamic plates. There are two types of plates— oceanic and continental —which float on the surface of the Earth’s mantle , diverging, converging, or sliding against one another. When two plates diverge , magma from the mantle wells up and cools, forming new crust; when convergence occurs, one plate descends—i.e., is subducted—below the other and crust is resorbed into the mantle. Examples of both processes are observed in the marine environment . Oceanic crust is created along oceanic ridges or rift areas, which are vast undersea mountain ranges such as the Mid-Atlantic Ridge . Excess crust is reabsorbed along subduction zones , which usually are marked by deep-sea trenches such as the Kuril Trench off the coast of Japan .

The shape of the ocean also is altered as sea levels change. During ice ages a higher proportion of the waters of the Earth is bound in the polar ice caps , resulting in a relatively low sea level. When the polar ice caps melt during interglacial periods, the sea level rises. These changes in sea level cause great changes in the distribution of marine environments such as coral reefs . For example, during the last Pleistocene Ice Age the Great Barrier Reef did not exist as it does today; the continental shelf on which the reef now is found was above the high-tide mark.

Marine organisms are not distributed evenly throughout the oceans. Variations in characteristics of the marine environment create different habitats and influence what types of organisms will inhabit them. The availability of light , water depth, proximity to land, and topographic complexity all affect marine habitats.

The availability of light affects which organisms can inhabit a certain area of a marine ecosystem. The greater the depth of the water, the less light can penetrate until below a certain depth there is no light whatsoever. This area of inky darkness, which occupies the great bulk of the ocean, is called the aphotic zone . The illuminated region above it is called the photic zone , within which are distinguished the euphotic and disphotic zones . The euphotic zone is the layer closer to the surface that receives enough light for photosynthesis to occur. Beneath lies the disphotic zone, which is illuminated but so poorly that rates of respiration exceed those of photosynthesis. The actual depth of these zones depends on local conditions of cloud cover, water turbidity, and ocean surface. In general, the euphotic zone can extend to depths of 80 to 100 metres and the disphotic zone to depths of 80 to 700 metres. Marine organisms are particularly abundant in the photic zone, especially the euphotic portion; however, many organisms inhabit the aphotic zone and migrate vertically to the photic zone every night. Other organisms, such as the tripod fish and some species of sea cucumbers and brittle stars, remain in darkness all their lives.

Marine environments can be characterized broadly as a water, or pelagic, environment and a bottom, or benthic, environment . Within the pelagic environment the waters are divided into the neritic province, which includes the water above the continental shelf, and the oceanic province, which includes all the open waters beyond the continental shelf. The high nutrient levels of the neritic province—resulting from dissolved materials in riverine runoff—distinguish this province from the oceanic. The upper portion of both the neritic and oceanic waters—the epipelagic zone —is where photosynthesis occurs; it is roughly equivalent to the photic zone. Below this zone lie the mesopelagic , ranging between 200 and 1,000 metres, the bathypelagic , from 1,000 to 4,000 metres, and the abyssalpelagic , which encompasses the deepest parts of the oceans from 4,000 metres to the recesses of the deep-sea trenches.

The benthic environment also is divided into different zones. The supralittoral is above the high-tide mark and is usually not under water. The intertidal, or littoral, zone ranges from the high-tide mark (the maximum elevation of the tide) to the shallow, offshore waters. The sublittoral is the environment beyond the low-tide mark and is often used to refer to substrata of the continental shelf, which reaches depths of between 150 and 300 metres. Sediments of the continental shelf that influence marine organisms generally originate from the land, particularly in the form of riverine runoff , and include clay, silt, and sand. Beyond the continental shelf is the bathyal zone , which occurs at depths of 150 to 4,000 metres and includes the descending continental slope and rise. The abyssal zone (between 4,000 and 6,000 metres) represents a substantial portion of the oceans. The deepest region of the oceans (greater than 6,000 metres) is the hadal zone of the deep-sea trenches. Sediments of the deep sea primarily originate from a rain of dead marine organisms and their wastes.

Introductory essay

Written by the educators who created The Deep Ocean, a brief look at the key facts, tough questions and big ideas in their field. Begin this TED Study with a fascinating read that gives context and clarity to the material.

How inappropriate to call this planet Earth when it is quite clearly Ocean. Arthur C. Clarke

Planet Ocean

In the late 1960s, the Apollo Mission captured images of Earth from space for the very first time. These iconic photos gave people around the world a fresh perspective on our home planet — more specifically, its vast and dazzling expanses of blue. It's perhaps unsurprising that science has subsequently established the key roles that the ocean and its marine organisms play in maintaining a planetary environment suitable for life.

While the Apollo astronauts were sending back pictures of our blue planet, a scientist at the Jet Propulsion Laboratory in California was searching for ways to detect life on other planets such as Mars. James Lovelock's investigations led him to conclude that the only way to explain the atmospheric composition of Earth was that life was manipulating it on a daily basis. In various publications, including his seminal 1979 book Gaia: A New Look at Life on Earth , Lovelock launched the Gaia hypothesis, which describes how the physical and living components of the natural environment, including humankind, interact to maintain conditions on Earth. During the same period, marine scientists including Lawrence Pomeroy, Farooq Azam and Hugh Ducklow were establishing a firm link between the major biogeochemical cycles in the oceans and marine food webs, particularly their microbial components. In the late 1980s and 1990s, large-scale research programs like the Joint Global Ocean Flux Study (JGOFS) explored ocean biogeochemistry and established the oceans' pivotal role in the Earth's carbon cycle.

Research efforts like these underscored the oceans' critical importance in regulating all the major nutrient cycles on Earth. It's now widely recognized that the ocean regulates the temperature of Earth, controls its weather, provides us with oxygen, food and building materials, and even recycles our waste.

The advent of deep-sea science

It seems remarkable that until fairly recently many scientists believed that life was absent in the deep sea. Dredging in the Aegean Sea in the 1840s, marine biologist Edward Forbes found that the abundance of animals declined precipitously with depth. By extrapolation he concluded that the ocean would be azoic (devoid of animal life) below 300 fathoms (~550m depth). Despite evidence to the contrary, scientists supported the azoic hypothesis, reasoning that conditions were so hostile in the deep ocean that life simply could not survive. Extreme pressure, the absence of light and the lack of food were viewed as forming an impenetrable barrier to the survival of deep-sea marine species.

But others were already proving this hypothesis wrong. As Edward Forbes published his results from the Aegean, Captain James Clark Ross and the famous naturalist John Dalton Hooker were exploring the Antarctic in the Royal Navy vessels HMS Terror and HMS Erebus . During this expedition, Ross and Hooker retrieved organisms from sounding leads at depths of up to 1.8km, including urchin spines and other fragments of various marine invertebrates, a number of bryozoans and corals. Ross remarked, "I have no doubt that from however great a depth we may be enabled to bring up the mud and stones of the bed of the ocean we shall find them teeming with animal life." This contention was supported by work of Norwegian marine biologists Michael Sars and George Ossian Sars who dredged hundreds of species from depths of 200 to 300 fathoms off the Norwegian coast.

Further evidence came from natural scientists William Carpenter and Charles Wyville-Thomson, who mounted expeditions in 1868 and 1869 on the vessels HMS Lightening and HMS Porcupine to sample the deep ocean off the British Isles, Spain and the Mediterranean. The findings of these expeditions, which Wyville-Thomson published in his 1873 book The Depths of the Sea , confirmed the existence of animal life to depths of 650 fathoms — including all the marine invertebrate groups — and suggested that oceanic circulation exists in the deep sea.

This convinced the Royal Society of London and the Royal Navy to organize the circumnavigating voyage of HMS Challenger in the 1870s. In part, the expedition's purpose was to survey potential routes for submarine telegraph cables, and so the links between scientific exploration and human use of the deep sea were established in the very early days of oceanography. The Challenger expedition was a watershed for deep-ocean science, establishing the basic patterns of distribution of deep-sea animals, and that their main food source was the rain of organic material from surface waters.

In the 1950s, the Danish Expedition Foundation's Galathea voyage established that life occurred at depths of more than 10km in the Philippines Trench. In 1960 marine explorers Auguste Picard and Don Walsh reached the bottom of the Challenger Deep in the Marianas Trench, at a depth estimated to be 10,916 meters--the deepest part of the ocean — where they observed flatfish from the porthole of their pressure sphere. This feat was not repeated until 2012 when James Cameron visited the bottom of the Challenger Deep in the submersible Deepsea Challenger .

Hype or hyper-diversity in the deep sea?

While working at Woods Hole Oceanographic Institution in the late 1960s, scientists Howard Sanders and Robert Hessler developed new types of deep-sea trawls called epibenthic sleds that featured extra- fine mesh in the nets. When the new trawls were tested, they recovered an astonishing diversity of species from the deep sea. It became apparent that the species richness of deep-sea communities actually increased with greater depth to a peak somewhere on the continental slope between 2,000 and 4,000 meters depth. Beyond these depths, diversity appeared to decrease (but not everywhere), or the pattern was unclear.

How to explain this amazing diversity in the deep sea? Initially, scientists credited the species richness to the stability of environmental conditions in the deep ocean, which would support extreme specialization of the animals and thus allow many species to coexist. This is known as the stability-time hypothesis. Some scientists considered that small-scale variations of the sediments of the deep ocean, including reworking of seabed by animals, was important in maintaining microhabitats for many species. In the late 1970s other scientists suggested that conditions in shallow waters allow competitive exclusion, where relatively few species dominate the ecosystem, whereas in deeper waters environmental factors associated with depth and a reduced food supply promote biological communities with more diversity.

Fred Grassle and Nancy Maciolek added substantially to our knowledge of deep-sea biodiversity when they published a study of the continental slope of the eastern coast of the USA in the early 1990s. Grassle and Maciolek based their study on quantitative samples of deep-sea sediments taken with box cores. These contraptions retrieve a neat cube-shaped chunk of the seabed and bring it to the surface enclosed in a steel box. Scientists then sieve the mud and count and identify the tiny animals living in the sediment.

In a heroic effort, Grassle and Maciolek analyzed 233 box cores, an equivalent of 21 square meters of the seabed, identifying 90,677 specimens and 798 species. They estimated that they found approximately 100 species per 100 km along the seabed they sampled. Extrapolations of this figure suggested that there may be 1 - 10 million macrofaunal species in the deep sea.

What's more, some scientists argued that Grassle and Maciolek's estimates represented only a small part of the species diversity in the ocean depths. Dr John Lambshead of London's Natural History Museum pointed out that Grassle and Maciolek had not examined the smallest animals in sediments — the meiofauna — made up of tiny nematode worms, copepods and other animals. These are at least an order of magnitude more diverse than the macrofauna, suggesting that as many as 100 million species may inhabit the deep ocean.

However, given that the latest approximation of the Earth's biodiversity is 10 million species in total, Lambshead's number appears to be an overestimate. Scientists have since realized that there are major problems with estimating the species richness of large areas of the deep sea based on local samples. Today we understand that species diversity in the deep ocean is high, but we still don't know how many species live in the sediments of the continental slope and abyssal plains. We also don't understand the patterns of their horizontal distribution or the reasons for the parabolic pattern of species diversity as it relates to depth. Evidence suggests, however, that the functioning of deep-sea ecosystems depends on a high diversity of animals — although exactly why remains open to conjecture.

The creation of deep-sea environments: "Drifters" and "Fixists"

In 1912, German scientist Alfred Wegener put forward his theory of continental drift to address many questions that engaged the geologists and biologists of his time. For example, why do the continents appear to fit together as though they had once been joined? Why are many of the large mountain ranges coastal? And, perhaps most intriguing, why do the rocks and fossil biotas (combined plant and animal life) on disconnected land masses appear to be so similar?

Wegener's theory provoked a major scientific controversy that raged for more than 50 years between "drifters" and "fixists." Critics of Wegener's — the "fixists" — pointed out that Wegener's proposed mechanism for drift was flawed.

In the search for an alternate mechanism to explain continental drift, British geologist Arthur Holmes suggested that radioactive elements in the Earth were generating heat and causing convection currents that made the Earth's mantle fluid. Holmes argued that the mantle would then rise up under the continents and split them apart, generating ocean basins and carrying the landmasses along on the horizontally-moving currents.

Following World War II, scientific expeditions employing deep-sea cameras, continuously recording echo-sounders, deep-seismic profilers and magnetometers lent support to the arguments of Holmes and his fellow "drifters." Scientists realized that the deep sea hosted a vast network of mid-ocean ridges located roughly in the center of the ocean basins. These ridges were characterized by fresh pillow lavas, sparse sediment cover, intense seismic activity and anomalously high heat flow. Scientists found geologically-synchronous magnetic reversals in the rocks of the ocean crust moving away from either side of the mid-ocean ridges. Added to this was the fact that nowhere could scientists find sediments older than the Cretaceous in age. Together, these findings suggested that new oceanic crust was being formed along the mid-ocean ridges, while old oceanic plates are forced underneath continental plates and destroyed along the ocean trenches. By the late 1960s, the bitter scientific debate between the "fixists" and the "drifters" was finally settled.

Life without the sun

During the next decade, scientists investigating volcanic activity at mid-ocean ridges became interested in the associated phenomenon of hot springs in the deep sea. Anomalously high temperature readings over mid-ocean ridge axes led scientists to mount an expedition in 1977 to the 2.5 km-deep Galápagos Rift. From the submersible Alvin, the scientists observed plumes of warm water rising from within the pillow lavas on the seabed. Living amongst the pillows were dense communities of large vesicoyid clams, mussels, limpets and giant vestimentiferan tube worms (Siboglinidae). An abundance of bacteria around the Galápagos Rift site immediately suggested that these communities might be based on bacterial chemosynthesis, or chemolithotrophy, using chemical energy obtained by oxidizing hydrogen sulphide to drive carbon fixation. Subsequent investigation confirmed that the giant tube worms, clams and mussels actually hosted symbiotic sulphur-oxidizing bacteria in their tissues.

The discovery caused huge excitement in the scientific community. Here was life thriving in the deep sea, where primary production — the basis of the food web — was independent from the sun's energy. Furthermore, as scientists discovered additional vent communities and surveyed elsewhere in the mid-ocean ridge system, they found that environmental conditions were extreme, with high temperatures, acidic waters, hypoxia (lack of oxygen) and the presence of toxic chemicals the norm.

The implications of this were enormous and went well beyond the study of the ocean itself. First, it meant that life could exist elsewhere in our solar system in environments previously thought too extreme. Second, it widened the potential area for habitable planets around suns elsewhere in the universe. For example, the discovery in 2000 of the Lost City alkaline hydrothermal vents presented an environment that some scientists suggest is analogous to the conditions in which life evolved on Earth.

Subsequently, chemosynthesis has been discovered in many places in the ocean, including deep-sea hydrocarbon seeps, in large falls of organic matter such as whale carcasses, and from shallow-water sediments associated with, for example, seagrass beds.

Drawing down the oceans' natural capital

Over the past two decades, we've developed a much deeper understanding of the relationship between humankind and the natural world, including the Earth's oceans. In 1997 Robert Costanza and his colleagues published a paper in Nature that estimated the economic value of the goods and services provided by global ecosystems. Costanza and his colleagues argued that the living resources of Earth could be viewed as a form of natural capital with a value averaging $33 trillion per annum, upon which the entire human economy depended. These goods and services were later grouped into supporting (e.g. primary production), provisioning (e.g. food), regulating (climate regulation) and cultural (e.g. education) services.

While this knowledge may have been intuitive for many people, Costanza's recasting of the environment in economic terms forced policymakers, industry leaders and others to recognize the importance of long-term environmental sustainability. With the support of international agencies such as the World Bank, many countries are now implementing natural capital accounting procedures through legislation. The purpose of this is to help monitor and regulate the use and degradation of the environment and to ensure that the critical ecosystem goods and services underpinning economic activity and human well-being are not undermined.

Although it seems like a modern preoccupation, sustainability is actually a centuries-old challenge, particularly as it relates to marine environments. For example, there is evidence that aboriginal fisheries in ancient times may have overexploited marine species. Certainly by medieval times in Europe, a thriving market for fish, coupled with other developments like changing agricultural practices, forced species such as salmon and sturgeon into decline.

The Industrial Revolution led to an increase in hunting fish, seals and whales, thanks to the development of steam- and then oil-powered fishing vessels that employed increasingly sophisticated means of catching animals. Pelagic whaling began in the early 20th century; the development of explosive harpoons, the ability to process whales at sea, and the strong demand for margarine made from whale oil all contributed to dramatic rises in catches. Despite the initiation of the International Whaling Commission in 1946, a serial depletion of whale populations took place from the largest, most valuable species (e.g. blue whale) through to the smallest species (minke whale). The failure to regulate catches of whales led to the establishment of a near-moratorium on whaling in 1986.

Over the same post-war period, fishing fleets underwent a major expansion and deployed increasingly powerful fishing vessels. Improved technologies for navigating, finding fish and catching them led to increasing pressure on fish stocks and the marine ecosystems in which they lived. In 1998, after analyzing catch statistics from the United Nations Food and Agricultural Organisation (FAO), Daniel Pauly and his colleagues from the University of British Columbia identified a global shift in fish catches from long-lived, high trophic level predators to short-lived, low trophic level invertebrates and plankton-eating fish. This was the first evidence that fishing was having a global impact on marine ecosystems, causing major changes in the structure of ocean food webs. Aside from the economic impacts of "fishing down the food web," evidence was accumulating that it also affected the vulnerability and/or resilience of marine ecosystems to shocks such as invasions by alien species and climate-change effects such as mass coral bleaching.

Further evidence came in 2003 from a study by Ransom Myers and Boris Worm. Myers and Worm documented a significant decline over time in the stocks of certain large, predatory fish after analyzing information from research trawl surveys and the catches of the Japanese long-line fleet. Other studies over the same time period suggested that sharks, seabirds and turtles were suffering large-scale declines as they became by-catch in many industrial fisheries. Scientists also asserted that some fishing technologies, such as bottom trawling, were extremely damaging to seabed communities — deep-sea ecosystems in particular — by documenting the devastation of cold-water coral communities.

These studies sparked a bitter war of words between marine ecologists, fishing industry executives and fisheries biologists. While it has now been demonstrated that fish stocks can recover if levels of exploitation by fisheries are reduced through management measures, it's clear that in many parts of the world's oceans this is not happening. Overall, global yields from marine capture fisheries are in a downward trajectory. By-catch of some marine predators, such as albatrosses, still poses a threat of extinction. Habitat destruction resulting from fishing is continuing.

In addition to overfishing, other human activities are damaging marine ecosystems. During the 1960s and 1970s, several major accidents with oil tankers and oil installations resulted in serious oil spills. While oil pollution is still a significant problem, as illustrated by the Deepwater Horizon disaster in the Gulf of Mexico in 2010, other less-visible sources of pollution are causing large-scale degradation of the ocean.

Persistent organic pollutants and heavy metals such as mercury are being recognized as major health issues for marine animals (especially high trophic level predators, such as killer whales and tuna) and also for humans. The oceans are becoming the dumping ground for a wide range of chemicals from our personal care products and pharmaceuticals, as well as those that leach out of all manner of plastics that are floating in our seas. Agrochemicals are pouring into the oceans through rivers; in some cases these artificially fertilize coastal waters, generating blooms of algae which are broken down by bacteria, thus stripping the water of oxygen and creating dead zones.

Our release of greenhouse gases into the atmosphere, particularly carbon dioxide (CO2), is leading to a profound disturbance in ocean temperatures and ocean chemistry. Since the late 1970s, mass coral bleaching from ocean warming has killed large areas of tropical coral reefs. Marine animals are changing their distribution and the timing of their lifecycles, sometimes with catastrophic effects across the wider ecosystem. Such effects are often propagated from lower levels of food webs up through to predators such as fish and seabirds: witness recent declines in spectacled sea duck populations in the Arctic and the decline of cod populations in the North Sea. The oceans are becoming more acidic, which affects the growth rates of animals with calcium carbonate shells or skeletons and has other negative impacts on animal physiology. Many of these different stresses on marine species interact in a form of "negative synergy", inducing more severe effects than if they had presented in isolation. At the ecosystem level these stresses reduce the resilience of marine ecosystems to "shocks" arising from large-scale effects, such as anomalous warming events associated with climate change.

Ocean future

The TEDTalks in The Deep Ocean illuminate many current topics in marine science and oceanic exploration. These include the call for better conservation management in the face of unprecedented threats to marine ecosystems, the discovery and application of as-yet-untapped natural resources from the ocean depths, and the quest for improved technologies to support both of these endeavors. As Sylvia Earle eloquently reminds us in her 2009 TEDTalk, the oceans are critically important to maintaining the planet in a condition that is habitable, and better cooperative, international management of marine ecosystems is essential. However, as other TED speakers like Robert Ballard and Craig Venter argue, the oceans should also interest us because they contain vast untapped resources: unexploited mineral resources as well as genes, proteins and other biomolecules of marine life, which may furnish the medicines and industrial materials of the future.

Smart management of these natural resources requires knowledge, as do our efforts to ensure the oceans' ongoing species richness and their critical function in maintaining the Earth system. In their TEDTalks, explorers and scientists Edith Widder, Mike deGruy and Craig Venter share some of the amazing physical and biological features of ocean habitats and describe how new technologies allow more careful study and exploitation of deep-sea environments.

Despite these advances, there are still enormous gaps in our knowledge. In a TEDTalk he gave in 2008, Robert Ballard noted that many parts of the ocean remain entirely unexplored and he advocated for increased resources for organizations like NOAA. As many of the TED speakers in The Deep Ocean argue, marine science is more important than ever because the oceans are under serious threat from a range of human impacts including global-scale climate change.

However, these speakers also offer a message of hope, underscoring that there is still time to alter the current trajectory of degradation. Scientists including TED speaker John Delaney present a vision for the future where ecosystem-based management, coupled with the advent of new technologies that allow us to monitor ocean health in real time, provide us with tools to heal marine ecosystems. This may allow us to restore their capacity to provide goods and services for humankind over the long term. Measures such as marine-protected areas can maintain the oceans' important biogeochemical functions, but will also conserve the remarkable and beautiful marine ecosystems that have culturally enriched the human experience for millennia.

We'll begin our journey into The Deep Ocean with legendary explorer and oceanographer Sylvia Earle, who shares disturbing data about the decline of marine ecosystems and proposes one method to protect what she calls "the blue heart of the planet."

Sylvia Earle

My wish: protect our oceans, relevant talks.

Craig Venter

On the verge of creating synthetic life.

David Gallo

Underwater astonishments.

Edith Widder

Glowing life in an underwater world.

John Delaney

Wiring an interactive ocean.

Mike deGruy

Hooked by an octopus.

Robert Ballard

The astonishing hidden world of the deep ocean.

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The marine environment is an essential component of the global life-support system

Oceans cover 71 per cent of the Earth’s surface and provide us with food, oxygen and jobs. But they are probably the least understood, most biologically diverse, and most undervalued of all ecosystems.

From deep oceans to coastal reefs, from mudflats to sea grass beds, ocean and marine systems provide us with essential services: carbon capture for climate mitigation, renewable energy and protection from storm surges, to name but a few. As the global population grows, we are probing deeper and further into the oceans - for fish, oil, gas, minerals and new genetic resources - in an attempt to keep pace with increasing consumption. This is damaging the oceans that sustain us.

Estimating the total value of marine ecosystems could provide policymakers with a strong rationale to improve ocean management and invest in marine conservation. This would reduce environmental risks and ecological scarcities while boosting human well-being.

This year’s tagline for World Oceans Day (8 June) “Healthy Oceans, Healthy Planet”, aptly encapsulates the importance of oceans and seas in our ecosystem, and represents an opportunity to raise awareness.  

Managing a complex ecosystem UNEP has been busy supporting an integrated management of oceans and seas. Within UNEP, the Ecosystems Management Subprogramme works to drive change over both the short and long term through innovative solutions, build partnerships, and support countries to better manage, monitor and account for biodiversity and the health and productivity of ecosystems.

Central to a transformational response to decades of overfishing, pollution and unplanned coastal development will be moving from sectoral management, to an approach that marries seemingly competing interests in relation to marine and coastal resources and space within a robust framework and a spatial planning perspective. This is central to ensuring equitable access among diverse interests and users.

Oceans face the threats of marine and nutrient pollution, resource depletion and climate change, all of which are caused primarily by human actions. These threats place further pressure on environmental systems, like biodiversity and natural infrastructure, while creating global socio-economic problems, including health, safety and financial risks.

In order to promote ocean sustainability, innovative solutions that prevent and mitigate detrimental impacts on marine environments are essential. The internationally agreed Sustainable Development Goals (SDGs) guide governments towards creating a world in which we better value the global ecosystem upon which we all depend for life.

We have 14 years to meet SDG 14: Conserve and sustainably use the oceans, seas and marine resources for sustainable development.

What’s UNEP’s Regional Seas Programme? Established in 1974, the UNEP Regional Seas Programme focuses on the protection of specific bodies of water from pollution, from land-based and sea-based sources; on promoting assessments of the status of the marine environment; and on the conservation and sustainable management of oceans through support to the establishment of regional conventions and action plans.

There are currently 18 Regional Seas Conventions and Action Plans across the world, of which 14 were established under the auspices of UNEP. They received initial support, and continue receiving technical assistance from UNEP upon request.

These programmes aim to restore the health and productivity of oceans and marine ecosystems by promoting responsible stewardship. Over the last 40 years, they have helped countries to reduce land-based pollution, improve the management of coastal zones, and brought nations together to conserve the marine environment.

Some examples of change The number of Marine Protected Areas (MPAs) is growing. With support from UNEP, Haiti last year designated its first nine MPAs and others are set to follow suit.

The EU Common Fisheries Policy, which came into force in 2014, is phasing out the practice of throwing unwanted fish overboard and requires the industry to stick to quotas designed to achieve healthy fish stocks. The government of the Seychelles has pledged to expand Marine Protected Areas  to cover 30 per cent of its exclusive economic zone (400, 000 square kilometres), with 15 per cent designated as no-take areas. The commitment has been incorporated in the Seychelles’ first Protected Areas Policy which was endorsed in 2013.

Traditional fishers in Madagascar have carried out more than 250 temporary closures over about 450 km of coastline, a practice that has dramatically increased the size of their catch.

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Bringing the Ocean Back: An Introduction to Ocean Conservation

In this overview of ocean science and the Pristine Seas initiative, students can learn how the ocean works, what we’ve done to it, and how to bring it back.

Biology, Conservation, Oceanography

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National geographic | pristine seas.

This resource is provided in both English and Spanish. Scroll down for the Spanish edition.

Introduction

When I was a kid growing up in the Mediterranean, I was fascinated by the life I saw in shallow waters: algae, anemone, little crabs and small fish. But I never saw anything large—until I obtained my scuba diving license and dived in a fully protected marine reserve. I remember that first dive vividly. The big fish missing from the sea of my childhood were there: groupers, sea bream, seabass ... It took many years of education for me to learn how the ocean works, what we’ve done to it, and how to bring it back. I hope this handbook will provide a good introduction I wish I had when I was a kid wanting to be part of the sea.

-Enric Sala National Geographic Explorer in Residence

Three lives have I. Wet enough to quench your thirst, Light enough to touch the sky, Hard enough to break down rock. What am I?

Water is the only substance on Earth that naturally occurs in three physical states: solid, liquid, and gas. It is our planet’s defining feature. Most of our water is found in the ocean. Water also exists as a solid in ice caps and as a vapor in the air. Earth is a closed system. Its water is finite. That means the amount of water in, on, and above our planet does not increase or decrease. Instead, it flows endlessly between the ocean, atmosphere, and land in a system we call the water cycle .

Most of our Earth is covered by water: 29 percent land, 71 percent water.

Most of our water is saltwater: 97 percent salt water, 3 percent freshwater.

Only a small portion of Earth's water is accessible to people: 0.3 percent accessible, 99.7 percent stored in the ocean, soil, ice caps, and in the atmosphere.

While there is only one global ocean, the vast body of water that covers our planet is geographically divided into distinct, named regions. The boundaries of these have evolved over time for historical, cultural, geographical, and scientific reasons. You may know these regions as the Atlantic, Pacific, Indian, and Arctic. Not long ago, the Southern Ocean, which encircles Antarctica, joined the list. All of these basins are connected and exchange water as part of a single world ocean.

Each ocean basin is made up of the seafloor and all of its geological features, such as trenches, islands, ridges, volcanoes, and seamounts. Each basin varies in size, shape, and features due to the movement of Earth’s crust. Some of Earth’s highest peaks, deepest valleys, and flattest plains are found underwater.

Ocean in Motion

The ocean is never still. Both quick-moving surface currents and slower-moving deep ocean currents circulate water around the globe. Surface currents are mostly driven by wind and Earth’s rotation. Deeper ocean currents are controlled by temperature and salinity . That’s because both heat and salt influence the density of seawater. Saltier water is more dense than freshwater. Cold water is denser than warm water. Denser water sinks.

Ocean water always moves toward equilibrium, or balance. For example, if surface water cools and becomes denser, it will sink. The warmer water below will rise to balance out the missing surface water.

Ocean currents move a lot like a conveyor belt that delivers luggage at an airport. The ocean doesn’t move as fast as luggage, though. Scientists estimate that it takes the ocean conveyor belt about 1,000 years to make one trip around the world.

This conveyor belt helps keep our planet warm. When sunlight reaches Earth’s surface, the ocean absorbs some of this energy and stores it as heat. Ocean currents help move heat around the world. For example, warmer, surface water from the Equator moves toward the poles, and colder, deep water from the poles moves back to the tropics. Without this exchange, it would be even hotter at the Equator and colder toward the poles, and much less of our planet would be habitable.

As we know, increasing greenhouse gas concentrations are trapping more energy from the sun in Earth’s atmosphere. Water has a much higher heat capacity than air, meaning the ocean can absorb larger amounts of heat energy with only a slight increase in temperature. As such, our ocean has absorbed more than 90 percent of Earth’s extra heat since 1955.

Ocean temperature plays an important role in Earth’s climate system, too, because heat from ocean surface waters provides energy for storms. As our climate warms, we’re experiencing stronger winds, higher storm surges, and record rainfalls—which is also why these storms are becoming more destructive and costly.

You may be familiar with the terms climate and weather. Climate is how the weather usually is over the whole year in a particular place. Weather is the short-term atmospheric conditions of a place. Here’s one way to think about it. What’s in your closet? Weather is how you decide what you’re going to wear today. Climate is how you decide what kind of clothes you have in your entire closet.

Earth’s Lungs

You may have heard Earth’s rainforests sometimes described as a lung because they draw in carbon dioxide and expel oxygen. But just like most of us, Earth has two lungs. The ocean is its second lung.

The ocean relies on tiny, single-celled organisms called phytoplankton . Though a phytoplankton cell is smaller than the width of a human hair, there are a billion billion billion phytoplankton in the ocean, and they are some of Earth’s most critical organisms. Phytoplankton generate about half of our planet’s oxygen—as much per year as all land plants.

Through photosynthesis, phytoplankton consume carbon dioxide and expel oxygen. Some of the carbon is carried to the deep ocean when phytoplankton die and sink. This removes greenhouse gases from the atmosphere in a process known as carbon sequestration . The ocean stores 50 times more carbon dioxide than our atmosphere, and the top floor of the sediment on the seafloor stores twice more carbon that the soils of the land.

Some carbon is transferred to different layers of the ocean as phytoplankton are eaten by other creatures. Phytoplankton are the foundation of virtually every aquatic food web. They are eaten by everything from microscopic, animal-like zooplankton to massive whales.

Biodiversity

You may have heard that the ocean has the greatest biodiversity on our planet. Marine biodiversity refers to the variety of what lives in our ocean—all the animals, plants, and microorganisms. While that might sound simple, biodiversity is a fairly complex concept and can be measured in several ways.

Species Diversity (also called Species Richness ) refers to the number of species in a place. A place might have many different species of fish, for example.

Genetic Diversity is the range of inherited traits within a species. If a population consists of individuals with a wide variety of different traits, it may have high genetic diversity.

Functional Diversity reflects the ecological complexity of an ecosystem. Many organisms with different roles in the food web would indicate a high level of functional diversity.

We know that each species is an integral part of its ecosystem, and it performs functions that are essential to that ecosystem. Here’s an example: Hard corals grow by forming skeletons made of limestone, which over the centuries, build coral reefs. Those reefs will act as a barrier that protects coral islands and atolls and provide habitat for many species of fish. Here are some other functions species might provide in an ecosystem:

• Produce oxygen
• Produce organic material
• Decompose organic material
• Cycle water and nutrients
• Control erosion or pests
• Help regulate climate and atmospheric gases

Removing species from ecosystems removes these important functions. Therefore, the greater the diversity of an ecosystem, the better it can maintain balance and productivity and withstand environmental stressors. Biodiversity means that our ocean can be productive, resilient, and adaptable to any environmental changes. We say an ecological system is resilient if it can bounce back after a disturbance hits it—for example, a coral reef coming back after an ocean warming event kills some of its corals.

Biodiversity has intrinsic value because all species:

• Provide value beyond their economic, scientific, and ecological contributions
• Are part of our cultural and spiritual heritage
• Are valuable for their beauty and individuality
• Have a right to life on this planet

Biodiversity is critically important to us in terms of:

• Food resources
• Biomedical research
• Tourism and recreation

Food Resources

Fish are crucial to a nutritious diet in many areas across the world, especially among coastal communities. Fish provide about 3.3 billion people with almost 20 percent of their intake of animal protein. Global fish consumption increased 122 percent between 1990 and 2018, and that figure is expected to rise in the future.

We use our ocean as a roadway. As of 2021, maritime transport carries more than 80 percent of global trade by volume. It plays a critical role in the supply of essential goods such as food, clothing, shelter, and pharmaceuticals to countries. Fish fuel a $362 billion global industry. Millions of people in coastal communities depend on the fishing industry for their livelihood. Some 4.6 million fishing vessels of all sizes now ply the ocean, many with increasing capacity and efficiencies to catch more fish.

We drill for oil. Offshore oil drilling accounted for about 16 percent of the 12.2 million barrels of oil produced each day in the U.S. in 2019, according to federal records. But oil drilling pollutes our waters, land, and air. And drilling increases the risk of oil contamination to wildlife as well as destroys habitats.

Biomedical Research

We also mine our ocean for medicines. Most drugs in use today come from nature—many from flowers and plants on land. Aspirin, for example, was first isolated from the willow tree. As demand grows for new medicines, specifically anti-cancer and anti-inflammatory substances, researchers are looking to the ocean. Two such drugs are already in use—an anti-tumor medication made from sea squirts and a painkiller from a cone snail. More than a dozen other drugs are being tested, including ones to treat Alzheimer’s disease and lung cancer.

One group of researchers is focusing on the layer of mucus that coats some species of fish. This coating protects fish from bacteria, fungi, and viruses. Could this fish slime protect people, too? Could it be copied in a lab and produced in large quantities? If so, we could avoid harvesting it from the ocean, leaving our marine ecosystems healthy and intact.

Tourism and Recreation

Travel and tourism form one of the world’s largest industries, supporting more than 100 million jobs. Many visitors come to the ocean for nature-based tourism, such as diving, snorkeling, or whale-watching. Others come to enjoy the less direct benefits of swimming in calm waters or lying on white sandy beaches. More than 350 million people annually travel to coral reefs. Some go to see specific animals. An estimated 600,000 people spend more than $300 million (in U.S. dollars) annually to watch sharks, for example. In Palau, a population of about 100 sharks support $18 million worth of shark diving each year.

A New Frontier

More than 80 percent of our ocean is unmapped and unexplored. Let that sink in for a minute. Despite its size and impact on the lives of every organism on Earth, we know more about the surfaces of the moon and the planet Mars than we know about our own ocean floor. How can that be? Well, as marvelous a place as the ocean is, it’s also really challenging to explore and study.

Sunlight penetrates only the top 200 meters (645 feet) of the ocean. So, the deeper we go, the darker and colder it becomes. There’s also more pressure. At any depth in the ocean, the weight of the water above pushes on an object below it.

On land, our bodies experience an internal pressure of one atmosphere (atm). Pressure in the ocean increases about one atmosphere for every 10 meters (32 feet) of water depth. So, for example, at a depth of 100 meters, the pressure is 10 times greater than the pressure at sea level.

If we wanted to join a sperm whale on its hunt for giant squid, we’d need to swim down to about 2,000 meters (7,000 feet). At that depth, the pressure would be 200 atmospheres. That’s too much pressure for people; we’d be crushed!

To explore and study the full water column and the seafloor, we need specialized technologies such as SCUBA (Self Contained Underwater Breathing Apparatus), submersibles, and remotely operated vehicles.

With every breath we take, every drop we drink, we’re connected to the ocean. But our ocean faces major threats: overfishing, warming and acidification, Pollution, habitat destruction, and invasive species. Nearly 66 percent of the ocean is under cumulative stress, at an accelerating pace, from human activities. Easing these pressures is crucial to human survival.

Overfishing

Overfishing happens when we take fish out of the ocean faster than they can reproduce. Fish are a “renewable” resource in that they reproduce and can replenish their own populations but not if we catch too many of them too fast.

Overfishing became a global problem in the last century, as large-scale, industrial fishing methods grew to meet the demand of a rapidly growing human population. This demand has contributed to the development of more intensive fishing methods.

When you think of “fishing,” you probably don’t think of dynamite. But “blast fishing” or “fish bombing” is a destructive fishing practice that uses explosives to stun or kill schools of fish for easy collection. This often illegal practice destroys the underlying habitat that supports fish.

Trawling is one of the most harmful fishing methods. Enormous nets as wide as a football field are dragged through the water or across the seafloor, capturing almost everything in their path. Vulnerable habitats are damaged in the process. Every year, trawlers around the world drag nets that impact an area equivalent to twice the size of the U.S. while producing carbon dioxide emissions similar to those of global aviation.

Gill nets are walls of netting that drift in the water. Gill nets can be up to 3.2 kilometers (two miles) long. They are designed to trap fish around the gills when they try to swim through.

Longline fishers use lines that can extend for up to 80 kilometers (50 miles), with thousands of baited hooks branching off from the main line. These baited hooks often attract an array of other species, including diving birds.

These destructive practices have severe consequences for marine life: The global fishing catch has been declining since 1996. And today—according to the UN—90 percent of our fish stocks are said to be overfished or fished to full capacity, meaning they are close to reaching the level at which they will collapse.

Removing too many fish too fast can have a cascade-like effect across the marine ecosystem. It can reduce the size of fish remaining, as well as how much they reproduce and the speed at which they mature. Marine food webs are highly complex. Removing an apex predator, like sharks, or the base of the food web, like krill, could cause an entire ecosystem to collapse.

Overfishing is closely tied to bycatch—the capture of unwanted sea life while fishing for a different species. This, too, is a serious marine threat that causes the needless loss of billions of organisms, including hundreds of thousands of sea turtles and cetaceans.

Overfishing is only made worse by illegal catches and trade. Experts estimate illegal, unreported, and unregulated (IUU) fishing brings in up to $36.4 billion each year.

Food and Economic Security

Demand for fish continues to increase around the world, and that means more businesses and jobs are dependent on dwindling stocks. Aquaculture is the practice of breeding and farming fish for food rather than taking them from wild populations. In 2018, about 60 million people were employed by the fisheries and aquaculture sector.

Marine Pollution

Our ocean is filled with items that do not belong there. Marine pollution is a combination of chemicals and trash, most of which comes from land sources and is washed or blown into the ocean. Huge amounts of plastic, metal, rubber, paper, textiles, and other lost or discarded items enter the ocean every day. Debris can range in size from small plastic pieces, called microplastics, to huge abandoned vessels and gear. Although some of these items may eventually break down, others are made to last a long time—sometimes hundreds of years. Most marine debris is preventable.

Impact of Marine Debris

The National Oceanic and Atmospheric Administration (NOAA) tells us that marine debris can cause harm in the following ways:

Ingestion: Animals mistakenly eat plastic and other debris. More than 40 percent of seabird species eat plastic. All sea turtle species eat debris.

Entanglement: Marine life gets caught and killed in abandoned gear, nets, plastic bags, or other debris. Worldwide, more than 350 species are impacted by entanglement.

Habitat damage: Heavy marine debris crushes sensitive habitats, such as coral reefs and seagrass.

The problem isn’t just trash, though. Nutrient pollution from the overuse of fertilizers on farms runs into waterways that ultimately flow into the ocean. This increased concentration of chemicals, such as nitrogen and phosphorus, can be toxic to wildlife and harmful to people.

Ocean Warming

We know that our ocean is getting warmer as a result of the burning of fossil fuels and other activities. Since 1971, the ocean has absorbed 90 percent of the excess heat generated by our actions. Water can hold more heat than land or air, but this rate is alarming. The ocean’s surface layer, home to most marine life, takes most of this heat. As a result, fish species migrate farther to find cooler temperatures and food sources. This impacts communities and economies that depend on fishing. A warmer ocean can also change ocean chemistry, raise sea levels, and fuel extreme weather.

Ocean Acidification

As the amount of CO2 in the air increases from industry and other activities, the excess CO2 enters the ocean. This changes the chemistry of seawater.

When CO2 enters the ocean, it dissolves and reacts with water, making it more acidic. What can happen as a result?

• It can reduce fish size and populations. Some fish grow slower, others may have difficulty reproducing.
• Some types of marine life have more difficulty avoiding predators.
• Animals that rely on shells become vulnerable. One reason for this is less carbonate in the ocean water. Carbonate is a necessary building block in skeletons and shells. Animals like corals and mollusks are at risk.
• Phytoplankton and zooplankton, which are the base of the marine food chain, are destroyed.

Rising Sea Levels

Warmer ocean waters also contribute to rising sea levels. Since 1880, average sea levels have swelled about 23 centimeters (more than eight inches), including about 7.6 centimeters (three inches) in the last 25 years. Every year, the sea rises about 3.6 millimeters (0.14 inch). New research projects this rise to accelerate.

The change is driven by three factors. First, when water heats up, it expands. About half of the sea-level rise over the past quarter century is a result of the water just taking up more space. Second, persistent higher temperatures are causing our glaciers to melt. And third, increased heat is causing the massive ice sheets that cover Greenland and Antarctica to melt more quickly. Higher waters can mean big trouble. Even small increases can have devastating effects on coastal habitats—causing destructive erosion, wetland flooding, aquifer and agricultural soil contamination, and lost habitat for fish, birds, and plants.

Extreme Weather

Rising ocean temperatures are also connected to weather extremes. Warmer sea surface temperatures influence weather patterns and shift precipitation. Some regions may experience intense rainstorms and flooding. Others may undergo drought conditions or wildfires. These changes spawn dangerous hurricanes and typhoons that move more slowly and drop more rain, which can strip away everything in their path.

If we are to create a planet in balance, our current practices must change.

Marine Protected Areas

We know that our ocean and its rich diversity are threatened by human impacts at all levels, there are proven solutions. Marine protected areas, or MPAs, are a key strategy for sustaining and restoring ocean ecosystems. MPAs are like national parks in the sea. MPAs that ban overfishing or other damaging activities constitute the most effective solution to restore ocean life and all the benefits it provides to people. Marine protected areas directly address three of the major problems affecting humanity: 1) the biodiversity crisis, 2) food security for a growing population, and 3) climate change.

How MPAs Protect

If well designed, MPAs can safeguard essential habitats, such as nurseries and feeding and breeding grounds. They shield vulnerable ecosystems and endangered species. They help maintain functional food webs.

MPAs are an effective tool for restoring ocean biodiversity and ecosystems and building resilience for future warming events and other natural disasters. Protected areas are able to rebound at a faster rate than they would if they weren’t protected.

Marine reserves help boost the yield of fisheries, increasing fish and food security for those who depend on the ocean for sustenance. They help secure marine carbon stocks. MPAs also support coastal communities and economies. They create opportunities for recreation and tourism, research, and education. Areas of cultural and historic significance, such as those of importance to Indigenous peoples, archeological sites, and shipwrecks, are often included in MPAs. And they help local fishing by replenishing adjacent fishing grounds through spillover of larvae and adult fish.

Ocean Problems

• Overfishing and global warming are depleting ocean life and bringing the ocean to a tipping point
• Coral reefs and other critical habitats are being annihilated by ocean warming and acidification
• 90 percent of the large fish in the ocean are gone
• 82 percent of fish stocks that are overexploited
• Loss of ocean biodiversity threatens the well-being of humanity and poses huge economic risks

MPA Solutions

• Average increase of 600 percent in fish biomass in fully protected MPAs
• MPAs help capture carbon and provide climate resilience
• Global science-based target to protect 30 percent of ocean surface by 2030
• Marine protected areas (MPAs) restore ocean biodiversity and its benefits to people
• MPAs help replenish fish stocks and improve food security

The international union for conservation of nature (iucn) tells us that mpas are “clearly defined geographical spaces, recognized, dedicated and managed, through legal or other effective means, to achieve the long-term conservation of nature with associated ecosystem services and cultural values.”

Levels of Protection

Not all MPAs are created equal.

Fully Protected MPAs › No mining, prospecting, or exploitation. No active pipelines allowed with potential to leak. No dredging or dumping of any kind. Only small-scale, short-duration anchoring with low impact. Only minimal-impact, small-scale infrastructure for conservation, scientific, navigational, or sustainable tourism purposes. Aquaculture is allowed only for restoration, not extraction. No fishing of any kind. Non-extractive activities include only small-scale, closely regulated use with low impact (snorkeling, swimming, scuba diving, tide pooling), cultural/ ceremonial gatherings, cultural education, teachings/ knowledge transmission, and other uses.

Highly Protected MPAs › No mining, prospecting, or exploitation. No active pipelines allowed with potential to leak. No dredging or dumping of any kind. Only small-scale, short-duration anchoring with low impact. Low-impact, small-scale infrastructure allowed (facilities associated with sustainable tourism and aquaculture, renewable-energy structures, artificial reefs). Aquaculture is allowed but only unfed aquaculture that is small-scale and low density. Infrequent fishing with only a few (five or fewer) gear types that are highly selective and low impact. For non-extractive activities, only small-scale, closely regulated use with low impact (snorkeling, swimming, scuba diving, tide pooling), cultural/ ceremonial gatherings, cultural education, teachings/ knowledge transmission, and other uses.

Lightly Protected MPAs › No mining, prospecting, or exploitation. No active pipelines allowed with potential to leak. Limited dredging allowed for navigation, restoration, shoreline protection, and for coastal erosion and safety. Moderate unregulated anchoring, anchoring in sensitive habitats allowed only if anchored at the same location for a short time. Some infrastructure allowed—moderate-impact facilities associated with sustainable tourism and aquaculture, renewable-energy structures, artificial reefs (may allow fishing). Unfed aquaculture that is commercial scale and semi-intensive to intensive; or fed aquaculture that is small-scale and low density allowed. Also, low-density, small-scale/traditional use (fish, shrimp). Fishing is allowed but with moderate number (10 or fewer) gear types. Unregulated use or high-impact, high-density, and/or large-scale non-extractive activities allowed.

Minimally Protected MPAs › No mining, prospecting, or exploitation. No active pipelines allowed with potential to leak. Limited dredging allowed for navigation, restoration, shoreline protection, and for coastal erosion and safety. Large-impact anchoring allowed only if compatible with biodiversity conservation goals. Large-impact infrastructure allowed only if compatible with biodiversity conservation goals. Fed aquaculture that is commercial scale and semi-intensive is allowed; may be located in or close to sensitive habitats. Fishing is allowed with high number (more than 10) gear types that are large impact but not industrial. Unregulated use or high-impact, high-density, and/or large-scale nonextractive activities allowed.

The higher the level of protection, the stronger the conservation outcomes.

Scope and Scale

There are currently more than 16,000 MPAs around the world. That might sound like a lot, but they cover only about 8 percent of our ocean. And less than 3 percent of the ocean is in highly or fully protected MPAs.

Approximate size of the world’s ocean: 363 Million km2 

Total size of the world’s marine protected areas: 29 Million km2 (That’s a little more than the combined size of Russia and Canada.)

Total size of the world’s highly and fully protected MPAs: 8.8 Million km2 (That’s a little smaller than the size of the United States.)

MPAs lead to:

• Bigger fish
• Greater diversity of species
• Protection of carbon stocks
• Respect for cultural traditions and practices
• Opportunities to study and learn
• Healthier fisheries for jobs and food security
• Tourism that supports economies

Based on scientific guidance, more than 100 countries have agreed to a goal of protecting at least 30 percent of the ocean by 2030.

Marine protected areas mean:

1 › Marine life recovers fish abundance increases on average 600 percent in marine reserves after full protection within a decade.

2 › Better fishing fish spill over the reserve boundaries and help to replenish adjacent fishing grounds. In california, local fishers are catching 225 percent more lobsters after protecting 35 percent of their fishing grounds—only six years after the reserve was created.

3 › Diving tourism when the fish come back, divers come in. In the medes islands, diving tourism employs hundreds of people and brings in 12 million euros per year—24 times more than fishing.

4 › Mitigate global warming the protection of carbon-rich sediments has the potential to avoid carbon dioxide emissions similar to those of global aviation, helping to mitigate global warming.

5 › Global benefits protection also produces benefits like oxygen production. This phenomenon has a global impact, since all life is connected to the ocean.

National Geographic Pristine Seas

Feeling that as an academic scientist he was just writing the obituary of the ocean, marine biologist Enric Sala quit academia in 2008 to dedicate his life to ocean conservation as a National Geographic Explorer in Residence. Sala was a professor at the Scripps Institution of Oceanography in California when he decided to take a more active role in protecting our ocean and restoring richness and diversity to counteract the decline he was documenting.

Pristine Seas is the National Geographic Society’s flagship ocean conservation initiative. It protects vital places in the ocean by combining exploration, research, media, economics, communication, and policy, in collaboration with local communities, Indigenous peoples, and governments.

How the Work Gets Done

It takes months to plan and prepare for a Pristine Seas expedition. Experts and local partners from varying disciplines team up to document and assess a target area’s biodiversity. Data gathered during the expedition are shared with the scientific community, government authorities, local communities, and Pristine Seas partners to inform the need for and design of a marine protected area. Traditional conservation practices of local and Indigenous communities—some of which have been in place for centuries—provide important models for the Pristine Seas team.

To date, Pristine Seas has carried out 43 expeditions in more than 30 countries and has worked with local communities to inspire the creation of 27 marine reserves. These MPAs cover more than 6.6 million square kilometers of ocean—an area two-thirds the size of the United States—where marine life thrives and helps replenish surrounding areas.

Pristine Seas will work with local communities, governments, and partners to establish new marine protected areas and catalyze the global community to protect at least 30 percent of the ocean by 2030.

MPAs at Work: Recovering Cabo Pulmo

When Juan Castro Montaño was a boy in Cabo Pulmo, Mexico, fish were plentiful. “Fishing was very important for this community because that was our means of living,” he said. Over time, commercial fishing took hold and grew to unsustainable levels. When the local community saw that their fish population was declining, they did something extraordinary. In 1995, they asked the Mexican government to create a national park in the sea to give their reef a chance to recover. This was not an easy choice. It meant that the people who made their living as fishers had to find a new path for themselves and their families.

“We stopped fishing from one day to the next,” said fisher Mario Castro Lucero. “Now we work in ecotourism. It was very, very difficult, but we made it. It is a way of preserving the reef and dedicating ourselves to something else.”

The results were astonishing. Cabo Pulmo National Marine Park has experienced the greatest recovery ever observed in a marine protected area. During a 10-year period, fish biomass increased by more than 460 percent, bringing the reef to a level of biomass (the accumulation of living matter) similar to that of a reef that had never been fished. “I think that my dad, my grandfather, seeing how the reef has recovered, would think of how it was when they were young. And they would say: ‘It came back. The riches that we had as kids came back.’ I think they would have been very proud,” said Mario.

Juan agreed. “Other generations will see this when we’re gone. We’re the sentinels, watching over and taking care of it.”

Cabo Pulmo became a model for Pristine Seas.

The Role of Pristine Seas

During 200 hours of scientific surveys at 39 locations, the Pristine Seas team assessed the biodiversity of the outer islands of the Seychelles. They found the island waters teeming with life. Working with local officials and nonprofit organizations, the team collected data that informed a proposal to create large no-take areas around the outer islands. Informed by their findings, the government of Seychelles created a 74,400 square-kilometer highly protected MPA around the outer islands, covering 10 percent of their waters.

Voices of Conservation: Alvania Lawen, Seychelles

For Alvania Lawen, a young ocean advocate living in the Seychelles, protecting these islands is a personal mission:

“Life in Seychelles is deeply integrated with the ocean. Protecting the ocean feels normal to me, like I’m meant to do it. I got my start in marine conservation at age 11 when I began snorkeling and experienced firsthand our diverse underwater life. From there I joined a successful campaign to ban certain single-use plastics led by the nongovernmental organizations (NGOs) Sustainability for Seychelles and SYAH-Seychelles. I advocated for plastic alternatives. Our combined efforts led to bans on the importation and distribution of items such as plastic bags and cups in 2017.

In Seychelles, our economy depends on tourism, and the tourism sector depends largely on the marine environment. The term ‘blue economy’ refers to this sustainable economic use of the ocean. NGOs play a big role in environmental protection here, and I am part of several women- and youth-led NGOs with an environmental focus.

Young people like me can make a difference. We can use social media as a tool to protect the ocean. You don’t need to be Instagram-famous or have a ton of followers, as long as you stay focused on your goals and make connections with like-minded people and organizations. Try to treat any negative news, such as an alarming report about climate change, as a reason to persist in your work.”

MPAs at Work: Discovering Nature's Resilience

In the remote Pacific Ocean, a chain of coral islands and atolls straddling the Equator make up the ecologically diverse southern Line Islands. Part of the Republic of Kiribati, these specks of land are among the most isolated atolls on Earth. They are uninhabited and rarely visited.

Divers spent more than a thousand hours underwater around the five islands in 2009. What they found astonished them. On some reefs, the corals were so dense they covered 90 percent of the seabed—vastly more than the average coral cover found in the Caribbean, which is typically less than 10 percent.

In parts of the lagoon at Caroline Island (Millennium Atoll), the density of giant clams reach up to four per square foot—an almost-unheard-of abundance for creatures highly sought for their meat and shells. These giant filter feeders act as water purifiers, cleansing the water of bacteria that can cause diseases in corals, fish, shellfish, and crustaceans.

As a result of the Pristine Seas team’s findings, the government of Kiribati announced that a 12-nautical-mile area around the southern Line Islands would be closed to commercial fishing beginning in 2015. This area was to be protected so that it could remain pristine. But then disaster struck.

Across the Pacific, water-temperature spikes caused by El Niño weather events in 2016 killed off massive amounts of corals. The Pristine Seas team returned to the islands in 2021, expecting to see destruction. But the reefs of the southern Line Islands had bounced back spectacularly. How? Corals tend to be resilient in places where other elements of the marine ecosystem are flourishing, too. In the southern Line Islands, the large abundance of fish kept the dead coral skeletons free of seaweed and provided the conditions for corals to grow back. As a result of its protected status, this place was resilient in the face of disaster.

MPAs at Work: Supporting Indigenous Solutions

Kawésqar National Park is one of the largest parks in the world and the second largest terrestrial park in Chile. The kelp forests off the coast of southern Chile are some of the healthiest on Earth.

In early 2020, Pristine Seas went on an expedition to the Patagonian fjords in partnership with the local Kawésqar and Yagan Indigenous communities. The explored area is threatened by intensive salmon aquaculture, which has become a major industry in Chile. Unfortunately, this industry has severe environmental, sanitary, and social impacts. The team conducted comprehensive scientific surveys of coastal and deepwater ecosystems and learned from members of the Kawésqar and Yagan about the cultural and ecological significance of the region. Pristine Seas is now supporting these communities to keep their culture alive and obtain full protection of their territories as a source of their identity, worldview, subsistence, and ancestral rights. The team produced a full scientific and cultural report from the expedition and a documentary film about this journey.

Protecting our ocean and restoring it to full health is a big task. There is no one-size-fits-all solution, but there are many things that we can do—individually and collectively—to help.

• Remember that our land and sea are connected. Visit your local MPA, or local coast, river, or lake to explore, snorkel, dive, or connect with nature.
• Boycott unsustainable fishing. Don’t eat unsustainable seafood. Look for labels that say “diver-caught” or “line-caught."
• Reduce your carbon footprint. Use less fossil fuel energy in daily life. Drive your car less or take public transporation. Reduce energy use by choosing energy-efficient appliances, and learn about solar initiatives in your community.
• Reduce the amount of waste you produce.
• Reuse items when you can. Choose reusable items over disposable ones. Recycle as much as possible. Avoid plastic bags. Buy second hand clothing instead of new.
• Conserve water. Freshwater is a limited resource, and it’s scarce in many parts of the world. Using less water leads to less runoff and wastewater dumped into the ocean.
• Volunteer. Conservation groups need your help.
• Lead or participate in a community cleanup. By picking up the trash we find on our local streets, rivers, streams, or beaches, we can prevent that waste from becoming marine debris.
• Plant trees. Our trees and forests help reduce atmospheric carbon dioxide, taking pressure off our ocean.
• Eat a plant-rich diet. Buy local produce to reduce transportation and production emissions.
• Watch what you flush! Avoid flushing household cleaners, pesticides, drain cleaner, and cat litter, because those chemicals can seep into our ocean, rivers, and lakes.
• Follow Explorer Enric Sala and Pristine Seas social media and stay up-to-date on their efforts across the globe. twitter.com/Enric_Sala instagram.com/enricsala/
• Learn, then teach. When we understand how our ecosystems work, we can take steps to protect them. Learn as much as you can, then raise awareness by sharing what you know with others.
• Speak up. Advocate for the change you want to see in your community and in the world.

Call to Action

What can you do in your community? After reading this handbook and seeing some of the suggestions on page 31, create a personal action plan to help conserve the ocean. Ask yourself a few key questions:

1 › What do you think is the best way to promote ocean conservation in your community?

2 › What are the advantages of this action or solution?

3 › Can you think of any disadvantages?

4 › What more do you need to know or to research to make a full plan?

5 › Make a list of all the parts of your plan. What will you do first? What next?

6 › Is this a plan that you can accomplish on your own or will you need help?

7 › List some individuals or groups who might be willing to support your idea.

8 › How might you approach these people to get their help?

9 › Create a timeline for your plan. How long will it take to do each part?

10 › Share your plan with others and get feedback.

11 › Refine the plan according to the feedback.

12 › When the plan is ready, take action!

Need to Know More?

If you’d like to know more about our ocean, the threats against it, and how you can help, consider using some of these resources:

• Pristine Seas
• Online Courses For Educators
• One Ocean Educator Guide (for Professional Learning)
• Earth Day 2021 Guide focused on the ocean
• Geo-Inquiry

For Learners

Citizen Science

• iNaturalist and Seek
• Sea-to-Source Toolkit
• MapMaker Pristine Seas

Offline Resources

This section includes example resources that could be downloaded or transmitted to communities that may not have access to strong internet. Many of these resources can be printed or downloaded to PDFs or zip files. Look for the appropriate icons on each resource next to the social media icons, typically just below the resource photo.

• Sustainable Fishing : A leveled encyclopedic entry that introduces the topic and defines key terms. Can print or save to PDF.

Spanish edition:

Recuperar el Océano

Introducción a la Conservación del Océano

Introducción

Crecí a orillas del mediterráneo. De niño me fascinaba la vida que se dejaba ver en las aguas someras de la playa: algas, anémonas, cangrejos pequeños y pececillos. No vi ningún animal marino grande hasta que me saqué el título de buceo y me sumergí en una reserva marina de protección integral. Recuerdo esa primera inmersión como si fuera ayer. Todos los peces que no podía ver en mi niñez estaban allí: los meros, las doradas, las lubinas.

Tuve que estudiar muchos años hasta entender plenamente cómo funcionaba el océano, los daños que le causamos y qué hace falta hacer para recuperarlo. Espero que este manual sea la introducción que hubiera necesitado aquel niño que anhelaba formar parte del mar.

Enric Sala Explorador en Residencia de National Geographic

Tres rostros tengo. Uno mojado para colmar tu sed. Uno tan liviano que sube al cielo. Y otro tan duro que cortaría una piedra. ¿Quién soy?

El agua es la única sustancia de la Tierra que aparece en la naturaleza en estado sólido, líquido y gaseoso. Es lo que define nuestro planeta. La mayor parte está en los océanos. En los polos se encuentra en estado sólido y en el aire en forma de gas.

La Tierra es un sistema cerrado. Su agua es finita. O sea, el agua que hay dentro, sobre y por encima de la Tierra ni aumenta ni disminuye, sino que fluye eternamente por el océano, la atmósfera y la tierra en el llamado ciclo del agua .

Casi toda la tierra está cubierta de agua: 29 por ciento tierra, 71 por ciento agua

Casi toda el agua es salada: 3 por ciento agua dulce, 97 por ciento agua salada

La gente tiene acceso a una porción muy limitada de agua: 0.3 por ciento accessible, 99.7 por ciento almacenada en el océano, el suelo, los polos y la atmósfera

Nuestro Océano

Sobre el Mapa

Aunque hay un solo océano global, la enorme masa de agua que recubre nuestro planeta está geográficamente fragmentada en regiones diversas con nombres específicos. Las fronteras de estas regiones han ido cambiando con el paso del tiempo por razones culturales, geográficas y científicas. Seguramente conocerás estas regiones marinas como océano Atlántico, Pacífico, Índico y Ártico. Hace no mucho tiempo, el océano Austral, en torno a la Antártida, se incorporó a la lista. Todas estas cuencas oceánicas están conectadas y forman un solo océano global.

Cada cuenca oceánica está formada por el lecho marino y sus accidentes geológicos: cañones, islas, cordilleras, volcanes y montañas submarinas. Los movimientos de la corteza terrestre hacen que las cuencas cambien de tamaño y forma. Algunos de los picos más altos, valles más profundos y vastas planicies de la Tierra están bajo el mar.

Océano en Movimiento

El océano nunca para. Sus aguas circulan impulsadas por corrientes rápidas de superficie y otras más lentas de profundidad. Las de superfice están impulsadas por el viento y la rotación de la Tierra. Las más profundas están causadas por la temperatura y la salinidad . Esto se debe a que tanto el calor como la sal afectan a la densidad del agua marina. El agua salada es más densa que el agua dulce. El agua fría es más densa que el agua cálida. El agua más densa se hunde.

El movimiento de los océanos siempre busca un estado de equilibrio. Por ejemplo, cuando el agua superficial se enfría, se hace más densa y se hunde. El agua más cálida del fondo sube a la superficie para ocupar el espacio que dejó el agua superficial al hundirse.

Las corrientes oceánicas recuerdan mucho a las cintas transportadoras que llevan las maletas en los aeropuertos, aunque el océano no se mueve tan rápido como las maletas. Los científicos estiman que la cinta transportadora oceánica tarda unos mil años en dar la vuelta al mundo.

La cinta transportadora mantiene nuestro planeta templado. Cuando la luz del sol llega a la superficie de la Tierra, el océano absorbe parte de esa energía y la almacena en forma de calor. Las corrientes oceánicas distribuyen el calor por todo el mundo. Las aguas superficiales más cálidas del ecuador se desplazan hacia los polos, y las aguas frías y profundas de los polos viajan hacia los trópicos. Sin este intercambio global, las regiones ecuatoriales serían mucho más calurosas, las regiones polares serían mucho más frías y las zonas habitables de la Tierra serían muy reducidas.

Como ya sabemos, la creciente concentración de gases de efecto invernadero está atrapando más energía del sol en nuestra atmósfera. El agua almacena más calor que el aire y, por tanto, un leve aumento de la temperatura del aire hace que el océano absorba más energía térmica. De hecho, nuestro océano ha absorbido más del 90 por ciento del calor adicional generado en la Tierra desde 1955.

La temperatura del océano es clave en el sistema climático, ya que las tempestades se alimentan del calor de las aguas superficiales del océano. El creciente calentamiento del planeta hace que cada vez experimentemos vientos más fuertes, marejadas ciclónicas más intensas y precipitaciones sin precedentes, todo lo cual hace que las tempestades sean más y más destructivas y costosas.

Seguramente habrás oído hablar del clima y del tiempo. El clima hace referencia al tiempo atmosférico durante todo el año en una región específica. El tiempo alude a las condiciones atmosféricas de un lugar específico. Esta sería una forma de entenderlo: ¿qué hay en tu armario? El tiempo te dicta lo que tienes que llevar puesto hoy. El clima determina el tipo de prendas que tienes en todo el armario.

Los Pulmones de la Tierra

Quizá hayas oído decir que las selvas tropicales de la Tierra son como un pulmón, porque toman dióxido de carbono y expulsan oxígeno. Pero al igual que la mayoría de nosotros, la Tierra tiene dos pulmones. El océano es su segundo pulmón.

El océano depende de unos pequeños organismos unicelulares conocidos colectivamente como fitoplancton . La célula de fitoplancton mide menos de la mitad del grosor de un pelo humano; en el océano hay mil millones de billones de estos organismos, que son críticos para la vida en la Tierra. El fitoplancton genera aproximadamente la mitad del oxígeno del planeta: anualmente representa tanto como todas las plantas terrestres juntas.

A través de la fotosíntesis, el fitoplancton consume dióxido de carbono y libera oxígeno. Cuando el fitoplancton muere, se hunde y arrastra al fondo marino parte de ese carbono. Este proceso, llamado secuestro de carbono , elimina de la atmósfera gases de efecto invernadero. El océano almacena 50 veces más dióxido de carbono que la atmósfera, y la capa más externa de sedimentos del fondo marino almacena el doble de carbono que la tierra.

Parte del carbono es transferido por el fitoplancton a diversas capas de profundidad, donde es consumido por otros animales. El fitoplancton es la base de prácticamente todas las redes alimentarias acuáticas. Es consumido por todo tipo de criaturas, desde unos animalillos microscópicos conocidos como zooplancton a las descomunales ballenas.

Biodiversidad

Sabrás que el océano encierra la mayor biodiversidad del planeta. La biodiversidad marina se refiere a las diversas formas de vida que moran en nuestro océano: desde animales y plantas a microorganismos. Aunque pueda parecernos una idea sencilla, es un concepto complejo que puede medirse de diversas maneras.

Diversidad de Especies: (también conocida como Riqueza de Especies ) es el número de especies de un lugar determinado. El número de especies de pez de un lago, por ejemplo.

Diversidad Genética: gama de rasgos heredados propios de una especie. Una población con gran variedad de rasgos diferentes, es probable que tenga una gran diversidad genética.

Diversidad Funcional: complejidad ecológica de un ecosistema. La presencia de múltiples organismos con funciones diversas en una red alimentaria indica un nivel elevado de diversidad funcional.

Sabemos que cada especie forma parte integral de su respectivo ecosistema y cumple funciones esenciales en dicho ecosistema. Por ejemplo: los corales forman esqueletos de caliza que a lo largo de los siglos acaban creando arrecifes de coral y actúan a modo de barreras protectoras de islas y atolones coralinos, conformando el hábitat de muchas especies.

Las especies también cumplen estas funciones en sus respectivos ecosistemas:

• Producir oxígeno
• Producir materiales orgánicos
• Descomponer materiales orgánicos
• Filtrar el agua y reciclar nutrientes
• Controlar la erosión y las plagas
• Regular el clima y los gases atmosféricos

Al eliminar especies de los ecosistemas, eliminamos también estas importantes funciones. Cuanta mayor sea la diversidad de un ecosistema, mayor será su capacidad para mantener su equilibrio y productividad, y para resistir los factores ambientales de estrés. La biodiversidad hace que nuestro océano sea productivo y resiliente, y adaptable a los cambios ambientales. Decimos que un sistema ecológico es resiliente cuando puede recuperarse tras sufrir un episodio destructivo: por ejemplo, cuando un arrecife de coral revive tras un periodo de calentamiento.

La biodiversidad tiene un valor intrínseco porque cada especie:

• Genera un valor que trasciende su contribución económica, científica y ecológica
• Forma parte de nuestra herencia cultural y espiritual
• Es bella y singular
• Tiene derecho a vivir en este planeta

La biodiversidad es clave:

• Como recurso alimentario
• En la industria
• En la investigación biomédica
• En el turismo y el ocio

Recursos Alimentarios

El pescado es un elemento clave y nutritivo en la dieta de muchas áreas del mundo, especialmente entre las comunidades costeras. El pescado suministra casi el 20 por ciento de proteínas de origen animal a unos 3,300 millones de personas. El consumo mundial de pescado aumentó un 122 por ciento entre 1990 y 2018, y se espera que esta cifra siga aumentando.

Usamos el océano como medio de transporte. En 2021, el transporte marítimo representaba más del 80 por ciento del volumen del comercio mundial. Desempeña un papel fundamental en el suministro de bienes esenciales como alimentos, ropa, vivienda y productos farmacéuticos. La pesca representa una industria global por valor de $362,000 millones. Son innumerables las comunidades costeras que dependen de la pesca para su sustento. Unos 4.6 millones de buques pesqueros de todos los tamaños peinan el océano con una creciente capacidad y eficiencia.

Petróleo en el mar. En 2019, las perforaciones petroleras en alta mar representaron cerca del 16 por ciento de los 12.2 millones de barriles de petróleo producidos cada día en EE. UU., según fuentes federales de EE. UU. Las perforaciones petrolíferas contaminan el mar, la tierra y el aire, amenazan la flora y la fauna, y destruyen los hábitats.

Investigación Biomédica

También escrutamos el océano en busca de medicinas. La mayoría de los fármacos actuales proceden de flores y plantas terrestres, y de otros recursos de la Naturaleza. La aspirina, por ejemplo, se aisló por primera vez del sauce. Ante la creciente demanda de nuevos medicamentos (específicamente de anticancerígenos y antiinflamatorios) la ciencia está empezando a buscarlos en el océano. Ya se han aprobado dos de estos medicamentos: un fármaco antitumoral y otro para el dolor extraídos de la jeringa de mar y del caracol cono, respectivamente. Se están probando más de una docena de otros medicamentos, incluidos algunos para tratar el alzhéimer y el cáncer de pulmón.

Un grupo de científicos está investigando una mucosa que recubre la piel de algunas especies de pez. Este recubrimiento los protege de bacterias, hongos y virus. ¿Podría esta mucosa de pescado proteger también a las personas? ¿Podría ser replicada en un laboratorio para ser producida en grandes cantidades? Si se pudiera, evitaríamos tener que sacarla del océano para no afectar a los ecosistemas marinos.

Turismo y Ocio

El ocio y el turismo generan más de 100 millones de empleos en todo el mundo. Muchas personas van al océano en busca de experiencias naturales, ya sea buceo, esnórquel o avistamiento de ballenas; otros, simplemente van a nadar en aguas abiertas o a tomar el sol en playas de arena blanca. Cada año más de 350 millones de personas acuden a los arrecifes de coral. Algunos van a ver animales específicos. Se estima, por ejemplo, que cada año 600,000 personas gastan más de $300 millones en observar tiburones. En Palaos, un centenar de tiburones genera cada año $18 millones en ingresos por actividades de buceo.

Una Nueva Frontera

Más del 80 por ciento de nuestro océano no está ni cartografiado ni explorado. Piénsalo. A pesar de su tamaño y de su importancia en la vida de todos los seres vivos, sabemos más sobre las superficies de la luna y del planeta Marte que de la de nuestro propio fondo marino. ¿Cómo es esto posible? El océano es fascinante, pero explorarlo y estudiarlo es realmente difícil.

La luz del sol penetra tan solo hasta 200 metros (645 pies): a más profundidad, menos luz y más frío ... y presión. El peso del agua que hay por encima de un objeto sumergido a cualquier profundidad ejerce una fuerza sobre él.

En tierra firme, nuestros cuerpos tienen una presión interna de una atmósfera (atm). La presión en el océano aumenta alrededor de una atmósfera por cada 10 metros (32 pies) de profundidad adicional. Es decir, a una profundidad de, por ejemplo, 100 metros, la presión es diez veces mayor que la que experimentamos a nivel del mar.

Si quisiéramos acompañar a un cachalote en su búsqueda de calamares gigantes, tendríamos que sumergirnos hasta unos 2,000 metros (7,000 pies). A esa profundidad, la presión sería de 200 atmósferas. ¡Cualquier persona quedaría aplastada bajo esa presión!

Para explorar toda la columna de agua y el lecho marino, hacen falta aparatos de respiración subacuáticos autónomos (SCUBA, por sus siglas en inglés), sumergibles y vehículos a control remoto.

Cada hálito de aire y cada gota de agua nos conectan al océano. Pero el océano se enfrenta a grandes amenazas: la sobrepesca; el calentamiento y la acidificación; la contaminación; la destrucción de hábitats y la introducción de especies invasoras. Casi el 66 por ciento del océano está sometido al estrés constante y creciente de las actividades humanas. Aliviar estas presiones es crucial para nuestra supervivencia.

La sobrepesca se produce cuando capturamos los peces más rápido de lo que pueden reproducirse. Los peces son recursos “renovables”, o sea, reponen sus propias poblaciones, siempre que no capturemos demasiados o cada poco tiempo.

La sobrepesca fue un problema global en el siglo pasado, ya que los métodos de pesca industrial a gran escala se extendieron para satisfacer la demanda de una población humana en constante aumento. Esta demanda ha dado lugar a métodos de pesca más intensivos.

Generalmente no asociamos la pesca con la dinamita, pero la pesca con explosivos , o “bombardeo de peces”, es una práctica pesquera destructiva para aturdir o matar bancos de peces y facilitar así su captura. Estos métodos son tan ilegales como destructivos.

La pesca de arrastre es uno de los métodos de pesca más dañinos. Enormes redes del tamaño de un campo de fútbol son arrastradas por el agua o por el fondo marino, capturando todo lo que encuentran a su paso y destruyendo hábitats vulnerables. Cada año, barcos de arrastre de todo el mundo utilizan redes que afectan a un área equivalente a dos veces la extensión de EE. UU., y emiten unos niveles de dióxido de carbono similares a los de toda la aviación mundial.

El trasmallo es un arte de pesca que forma una barrera de redes de hasta 3.2 kilómetros (dos millas). Los peces quedan atrapados por las agallas cuando intentan atravesarlas.

En la pesca con palangre se usan sedales que pueden extenderse hasta 80 kilómetros (50 millas), con miles de anzuelos provistos de cebo que cuelgan del sedal principal. Estos anzuelos con cebo suelen atrapar accidentalmente aves buceadoras y otras especies.

Estas prácticas destructivas tienen graves consecuencias para la vida oceánica. Las capturas pesqueras mundiales llevan disminuyendo desde 1996, y hoy en día, según la ONU, el 90 por ciento de las poblaciones de peces están sobreexplotadas o se pescan a su máxima capacidad; es decir, están a punto de colapsar.

Atrapar demasiados peces con demasiada rapidez puede tener un efecto en cascada en todo el ecosistema marino. Puede reducir el tamaño de los peces supervivientes, así como su capacidad de reproducción y el tiempo que tardan en madurar. Las redes alimentarias marinas son muy complejas. La pérdida de un depredador principal, como el tiburón, o de la base de la red alimentaria, como el kril, podría provocar el colapso de todo el ecosistema.

La sobrepesca está muy ligada a las capturas accidentales de especies no comerciales. Es también una seria amenaza que provoca la pérdida innecesaria de miles de millones de organismos, incluidos cientos de miles de tortugas marinas y cetáceos.

La sobrepesca no hace sino empeorar con las capturas y el comercio ilegales. Se calcula que la pesca ilegal, no declarada y sin regular (IUU, en sus siglas en inglés) representa unos $36,400 millones anuales.

Seguridad Económica y Alimentaria

La demanda de pescado sigue aumentando en todo el mundo, lo que significa que cada vez más empresas y puestos de trabajo dependen de un recurso a la baja. La acuicultura consiste en la práctica de criar y cultivar peces para la alimentación en lugar de atraparlos en sus hábitats naturales. En 2018, el sector de la pesca y la acuicultura daba trabajo a 60 millones de personas.

Contaminación Marina

Nuestro océano está lleno de cosas que no deberían estar allí. La contaminación marina es causada por productos químicos y basura que se origina en tierra y es arrastrada por el agua o el viento hasta el océano. Cantidades ingentes de plástico, metal, caucho, papel, tejidos y otros residuos llegan al océano cada día. Varían de tamaño, desde trocitos de plástico (microplásticos) a enormes embarcaciones y aparejos abandonados. Aunque algunos de estos objetos se descomponen, otros están hechos para perdurar cientos de años. Casi todas estas basuras marinas son evitables.

Consecuencias de los Residuos Marinos

Según la Oficina Nacional de Administración Oceánica y Atmosférica (NOAA, en sus siglas en inglés), los desechos marinos pueden causar daños de las siguientes maneras:

Ingestión: más del 40 por ciento de especies de aves marinas y todas las especies de tortuga marina comen basura.

Enredo: los animales marinos quedan atrapados y mueren en artes de pesca abandonadas, redes, bolsas de plástico y otros desechos. En todo el mundo, ejemplares de más de 350 especies se enredan en artes de pesca.

Daños al hábitat: los residuos marinos pesados aplastan hábitats sensibles, como los arrecifes de coral y las praderas marinas.

El problema no es sólo la basura. La contaminación por el uso excesivo de fertilizantes en las explotaciones agrícolas llega a los ríos que los arrastran al océano. La concentración de nitrógeno y fósforo, y otras sustancias es tóxica para la Naturaleza y los seres humanos.

Calentamiento Oceánico

Sabemos que nuestro océano se está calentando por el uso de combustibles fósiles y de otras actividades. Desde 1971, el océano ha absorbido el 90 por ciento del exceso de calor generado por el ser humano. El agua retiene más calor que la tierra o el aire, pero el ritmo actual es alarmante. La capa superficial del océano, que alberga casi toda la vida marina, absorbe casi todo ese calor. Como resultado, los peces migran más lejos en busca de aguas más frías y ricas en alimento. Esto afecta a las comunidades y economías pesqueras. Un océano más cálido cambia su química interna, aumenta el nivel del mar y genera climatologías extremas.

Acidificación del Oceano

A medida que aumenta la cantidad de CO2 en el aire a causa de la industria y de otras actividades, ese CO2 adicional llega al océano y cambia la composición del agua marina.

Cuando el CO2 entra en contacto con el océano, se disuelve y reacciona con el agua, volviéndola más ácida. ¿Qué ocurre entonces?

› Se reduce el tamaño de los peces y de sus poblaciones. Algunos peces crecen más lentamente, otros tienen dificultades para reproducirse.

› Algunas especies marinas tienen más dificultades para evitar a sus depredadores.

› Los animales con concha se hacen más vulnerables por la reducción del carbonato en el agua oceánica. El carbonato es un componente necesario para la formación de conchas y exoesqueletos. Esto afecta a organismos como los corales y los moluscos.

› Se destruye el fitoplancton y el zooplancton, base de la cadena alimentaria marina.

Aumento del Nivel del Mar

El calentamiento de las aguas oceánicas también contribuye a la subida del nivel del mar. Desde 1880, el nivel medio del mar ha subido unos 23 centímetros (más de ocho pulgadas), incluidos unos 7.6 centímetros (tres pulgadas) en los últimos 25 años. Cada año, el mar sube unos 3.6 milímetros (0.14 pulgadas). Recientes estudios prevén que esta subida se intensificará.

Esto se debe a tres factores: en primer lugar, cuando el agua se calienta, se expande. El 50 por ciento de la subida del nivel del mar del último cuarto de siglo se debe al mayor volumen del agua. En segundo lugar, el aumento de las temperaturas está derritiendo los glaciares. Y por último, las enormes capas de hielo que cubren Groenlandia y la Antártida se están derritiendo más rápidamente. Hasta el más leve aumento del nivel del mar tendría efectos devastadores en los hábitats costeros, provocando erosiones destructivas, inundaciones de humedales, contaminación de acuíferos y suelos agrícolas, y pérdida de hábitats para peces, aves y plantas.

Climatología Extrema

El aumento de la temperatura oceánica también está relacionado con las climatologías extremas. El incremento de la temperatura de la superficie marina influye en los patrones meteorológicos y desplaza las precipitaciones. Algunas regiones pueden experimentar fuertes tempestades e inundaciones, mientras que otras sufren sequías e incendios forestales. Estos cambios dan lugar a huracanes y tifones que avanzan con lentitud descargando más y más agua de lluvia, y arrasando todo a su paso.

Si queremos equilibrar el planeta, nuestra forma de actuar debe cambiar.

Áreas Marinas Protegidas

Nuestro océano y su riqueza están amenazados por la acción humana a todos los niveles, pero tenemos soluciones de eficacia demostrada. Las áreas marinas protegidas (AMP) son una estrategia clave para sostener y restaurar los ecosistemas oceánicos. Las AMP son como parques nacionales del mar. Son una solución eficaz para restaurar la vida del océano y proporcionan grandes beneficios a los seres humanos, gracias a la prohibición de la sobrepesca y de otras actividades perjudiciales. Las AMP abordan tres grandes crisis de la humanidad: 1) la crisis de la biodiversidad, 2) la seguridad alimentaria y 3) el cambio climático.

Cómo nos Protegen las AMP

Bien concebidas, las AMP pueden salvaguardar hábitats esenciales, como son los criaderos y las zonas de alimentación y reproducción. Protegen los ecosistemas vulnerables y las especies en peligro y ayudan a mantener redes alimentarias funcionales.

Las AMP son herramientas eficaces para restaurar la biodiversidad del océano y sus ecosistemas, y generan resiliencia ante desastres naturales asociados al calentamiento global. Al protegerlas, estas zonas se recuperan mucho más rápido que si no lo estuvieran.

Las reservas marinas mejoran el rendimiento de las pesquerías, y la seguridad económica de quienes dependen del océano para su subsistencia. Además, custodian las reservas marinas de carbono y mantienen las economías y comunidades costeras. También generan oportunidades para el ocio y el turismo, la investigación y la educación. Las áreas de importancia cultural e histórica, como las de los pueblos indígenas, los yacimientos arqueológicos o los pecios de naufragios, suelen incluirse en las áreas marinas protegidas. Las AMP ayudan a reponer los caladeros adyacentes con el sobrante de larvas y ejemplares adultos.

Problemas Oceánicos

• La sobrepesca y el calentamiento están esquilmando el océano y llevándolo a un punto crítico
• Destrucción de arrecifes coralinos y otros hábitats por el calentamiento y acidificación del océano
• El 90 por ciento de los grandes peces han desaparecido del océano
• 82 por ciento: Porcentaje de pesquerías sobreexplotadas
• La crisis de biodiversidad del océano es una amenaza para la humanidad y para la economía

Las AMP Como Solución

• Las AMP restauran la biodiversidad del océano y benefician a la gente
• 600 por ciento: Las AMP reponen bancos de peces y generan seguridad alimentaria
• Incremento medio de biomasa piscícola en AMPs de protección integral
• Las AMP capturan carbono y mejoran la resiliencia ante el cambio climático
• 30 por ciento: Superficie de océano que se pretende proteger para 2030

La unión internacional para la conservación de la naturaleza (uicn) afirma que las amp son “espacios geográficos bien definidos, reconocidos, dedicados y manejados por medios legales y mecanismos eficaces de conservación de la naturaleza, y de sus valores ecosistémicos y culturales, a largo plazo.”

Niveles de Protección

No todas las AMP han sido concebidas de la misma manera.

AMP de protección integral › No se permite la prospección o explotación minera; ni canalizaciones activas con riesgo de fuga; ni dragados o vertidos. Sólo se permiten fondeaderos a pequeña escala, de corta duración y bajo impacto; infraestructuras menores y de impacto mínimo con fines de conservación, científicos, de navegación o de turismo sostenible. Acuicultura, solo a efectos de restauración, no de extracción. No se permite la pesca de ningún tipo. Las actividades no extractivas se limitarán a un uso a pequeña escala, rigurosamente regulado y de bajo impacto (esnórquel, natación, submarinismo, charcas mareales), reuniones culturales o ceremoniales, educación cultural, enseñanza y trasmisión de conocimientos, y otros usos.

AMP de protección elevada › No se permite la prospección o explotación minera; ni canalizaciones con riesgo de fugas; ni dragados o vertidos. Sólo se permiten fondeaderos a pequeña escala, de corta duración y bajo impacto, infraestructuras menores y de bajo impacto (instalaciones de turismo sostenible, acuicultura, energía renovable y arrecifes artificiales). Acuicultura sólo a pequeña escala, de baja densidad y sin aporte de piensos. Se permite, de forma ocasional, la pesca con sólo cinco o menos tipos de aparejos, muy selectivos y de bajo impacto. Para las actividades no extractivas, sólo se permite un uso a pequeña escala, rigurosamente regulado y de bajo impacto (esnórquel, natación, submarinismo, charcas mareales), reuniones culturales o ceremoniales, educación cultural, enseñanza y trasmisión de conocimientos y otros usos.

AMP de protección limitada › No se permite la prospección o explotación minera; ni canalizaciones con riesgo de fugas; ni dragados o vertidos. Se permiten dragados para navegación, restauración, protección del litoral y la erosión y seguridad costeras; el anclaje moderado no regulado; el anclaje en hábitats vulnerables, poco tiempo. Algunas de las estructuras permitidas son: instalaciones de impacto moderado de turismo sostenible y la acuicultura; estructuras de energía renovable y arrecifes artificiales (puede permitirse la pesca). Se permite la acuicultura sin piensos a escala comercial, de semiintensiva a intensiva; la acuicultura con piensos a pequeña escala y de baja densidad y la acuicultura de baja densidad, a pequeña escala y tradicional (peces, camarones). Se permite la pesca pero con una cantidad moderada de aparejos (diez o menos). Están permitidas las actividades no extractivas sin regulación o de alto impacto, de alta densidad y a gran escala.

AMP de protección mínima › No se permite la minería, la prospección o la explotación. Tampoco las canalizaciones activas con riesgo de fuga. Se permiten dragados para navegación, restauración, protección del litoral y la erosión y seguridad costeras. Se permite el anclaje de gran impacto cuando es compatible con los objetivos de conservación de la biodiversidad, así como infraestructuras de gran impacto en las mismas condiciones. Se permite la acuicultura con piensos a escala comercial y semiintensiva, y en hábitats vulnerables o cerca de ellos. Se permite la pesca con un número elevado (más de diez) de tipos de aparejos de gran impacto, pero no industriales, y las actividades no extractivas de alto impacto, alta densidad y a gran escala.

A mayor nivel de protección, mejores resultados de conservación.

Alcance y escala

Actualmente hay más de 16,000 amp en todo el mundo. Aunque parezca una cifra elevada, sólo cubren alrededor de un 8 por ciento de nuestro océano. Y menos del 3 por ciento está en una amp de protección integral o elevada.

363 Millones de km2: Área aproximada del océano

29 Millones de km2: Área total protegida del océano (algo más que las superficies de rusia y canadá juntas)

8.8 Millones de km2: Área total de las amp de protección elevada o integral (algo menos que la superficie de estados unidos)

Las amp generan:

• Mayores cantidades de peces
• Peces de mayor tamaño
• Mayor diversidad de especies
• Protección de reservas de carbono
• Respeto por las tradiciones y prácticas culturales
• Oportunidades de aprendizaje
• Mayor seguridad laboral y alimentaria
• Economías basadas en el turismo
• Ocio y diversión

Más de 100 países han acordado alcanzar el objetivo de proteger al menos el 30 por ciento del océano en 2030 siguiendo criterios científicos.

Las áreas marinas protegidas:

1 › Recuperan la vida marina tras una década de protección integral las poblaciones de peces aumentaron un 600 por ciento.

2 › Mejoran la pesca los peces desbordan los límites de la reserva y ayudan a reponer los caladeros adyacentes. En california, los pescadores locales capturan un 225 % más de langostas tras proteger el 35 % de sus caladeros, sólo seis años después de la creación del amp.

3 › Generan turismo de buceo cuando los peces regresan, los submarinistas también. En las islas medes, el buceo emplea a cientos de personas y aporta 12 millones de euros al año, 24 veces más que la pesca.

4 › Mitigan el calentamiento global la protección de los sedimentos de carbono evita emisiones de dióxido de carbono similares a las de la aviación mundial, con lo que se contribuye a frenar el calentamiento global.

5 › Aumentan los beneficios globales estimulan la producción de oxígeno. Este fenómeno tiene impacto a escala global, ya que toda la vida está relacionada con el océano.

Pristine Seas de National Geographic

El biólogo Enric Sala pensó que, como científico académico, lo único que hacía era escribir el obituario del océano. Así que en 2008 abandonó la enseñanza para dedicar su vida a la conservación como Explorador en residencia de National Geographic. Sala era profesor en el Instituto Scripps de océanografía de California cuando decidió trabajar más activamente en la protección del océano, y en la recuperación de su riqueza y diversidad, para contrarrestar el declive que él mismo estaba documentando.

Pristine Seas es la gran iniciativa de conservación de National Geographic Society. Protege zonas vitales del océano mediante la exploración, la investigación, los medios, la economía, la comunicación y la política, junto a comunidades locales, pueblos indígenas y gobiernos.

Cómo se Trabaja

Se tarda meses en planificar una expedición de Pristine Seas. Expertos y participantes locales de diversas disciplinas se unen para documentar y evaluar la biodiversidad de una zona determinada. Los datos recogidos durante la expedición se comparten con la comunidad científica, gobiernos, comunidades locales y miembros de Pristine Seas para informar de la necesidad de crear un AMP y de su diseño. Las prácticas tradicionales de conservación locales e indígenas –vigentes a veces durante siglos–ofrecen modelos clave para el equipo de Pristine Seas.

Hasta ahora, pristine seas ha realizado 43 expediciones en más de 30 países y ha trabajado con las comunidades locales en la creación de 27 de las mayores reservas marinas de la tierra. Estas amp cubren más de 6.6 Millones de kilómetros cuadrados —una extensión equivalente a dos tercios de los estados unidos—, donde la vida marina florece y repone las aguas adyancentes.

Pristine seas trabajará con comunidades, gobiernos y otros colaboradores en la creación de nuevas amp para proteger al menos un 30 porciento del océano para el año 2030.

AMP en Marcha: La Viva Vuelve a Cabo Pulmo

Juan Castro Montaño recuerda cuántos peces había en el mexicano Cabo Pulmo durante su niñez. “La pesca era muy importante, era el medio de vida de esta comunidad”, dice. La pesca comercial alcanzó tal desarrollo que se hizo insostenible. Al ver que las capturas de peces estaban cayendo, los pobladores locales hicieron algo extraordinario. En 1995, pidieron al gobierno mexicano que creará un parque nacional marino en su arrecife para recuperarlo. No fue una decisión fácil. Implicaba que las personas que vivían de la pesca tendrían que buscar otra forma de ganarse la vida.

“Dejamos de pescar de un día para otro”, dice el pescador Mario Castro Lucero. “Ahora nos dedicamos al ecoturismo. Fue difícilísimo, pero lo hemos logrado. Era la manera de preservar el arrecife y de ganarse la vida de otra forma”.

Los resultados fueron asombrosos. El Parque Nacional Marino Cabo Pulmo ha experimentado la mayor recuperación jamás observada en un área marina protegida. En 10 años, la población de peces aumentó en más del 460 por ciento, lo que llevó al arrecife a un nivel de biomasa (conjunto de materia viva) similar al de un arrecife en el que jamás se ha pescado. “Creo que si mi papá y mi abuelo vieran el arrecife así, dirían: ‘Resucitó. Toda esa riqueza que teníamos de niños ha regresado; ellos se sentirían muy orgullosos”, comenta Mario.

Juan está de acuerdo. “Otras generaciones podrán verlo cuando nosotros faltemos. Ahora nos toca ser los centinelas que vigilan el arrecife y cuidan de él”.

Cabo Pulmo pasó a ser un modelo para Pristine Seas.

AMP en Marcha: Proteger la Biodiversidad

Al norte de Madagascar, en el Océano Índico occidental, está el archipiélago de las Seychelles formado por 115 islas. Aldabra, uno de los mayores atolones coralinos del mundo, es Patrimonio de la Humanidad desde 1982.

El Papel de Pristine Seas

Durante 200 horas de sondeos en 39 puntos diferentes, el equipo de Pristine Seas evaluó la biodiversidad de las Islas Exteriores de las Seychelles. Vieron que las aguas de las islas estaban rebosantes de vida. Con el apoyo de funcionarios locales y de organizaciones sin fines de lucro, el equipo recopiló datos para proponer la creación de grandes zonas vedadas a la pesca en torno a las Islas Exteriores. Esta información fue reportada al gobierno de Seychelles, que creó un AMP de protección elevada de 74,400 kilómetros cuadrados. Esta AMP cubre el 10 por ciento de las aguas territoriales de las Seychelles.

Voces de la Conservación: Alvania Lawen, Islas Seychelles

Para Alvania Lawen, una joven defensora de los océanos, la protección de las islas Seychelles es algo personal:

“La vida en las Seychelles está ligada al océano. Proteger los océanos es algo que me sale del alma. Mi trabajo de conservación empezó a los 11 años cuando empecé a hacer esnórquel y descubrí nuestra biodiversidad. Luego me apunté a una campaña para prohibir ciertos plásticos de un solo uso orquestada por las organizaciones no gubernamentales (ONG) Sustainability for Seychelles y SYAH-Seychelles. Abogué activamente por alternativas al plástico. Gracias a nuestra labor, en 2017 conseguimos que se prohibiera la importación y distribución de bolsas y vasos de plástico.

Nuestra economía se basa en el turismo, un sector que depende en gran medida de los ecosistemas marinos. El término economía azul alude al uso económico sostenible del océano. Las ONG juegan un papel importante en la protección medioambiental; yo pertenezco a varias ONG medioambientales dirigidas por mujeres y jóvenes.

Los jóvenes como yo podemos marcar la diferencia y usar las redes sociales para proteger el océano. No hace falta ser una estrella de Instagram o tener millones de seguidores; solo debes tener claros tus objetivos y conectar con personas y organizaciones que compartan tu misión. Trata de convertir la información negativa, como las noticias alarmantes sobre el cambio climático, en una motivación para persistir en tu labor”.

AMP en Marcha: La Resiliencia de la Naturaleza

En lo más remoto del Pacífico, hay una cadena de islas y atolones coralinos a ambos lados del ecuador: las Islas de la Línea. Estas motas de tierra, pertenecientes a la república de Kiribati, son uno de los atolones más aislados de la Tierra. Están desiertos y apenas son visitados.

En 2009 los buzos pasaron más de mil horas bajo el agua entre las cinco islas. Su hallazgo les dejó boquiabiertos. En algunos arrecifes, los corales eran tan densos que cubrían el 90 por ciento del lecho marino, muchísimo más que el promedio de la cubierta coralina del Caribe, que es de menos del 10 por ciento.

En algunas partes de la laguna de la isla Caroline (atolón del Milenio), la densidad de almejas gigantes es de hasta cuatro por pie cuadrado, una abundancia casi inaudita para una especie tan buscada por su carne y sus conchas. Estos enormes filtradores actúan como depuradoras de agua, limpiándola de bacterias nocivas para corales, peces, moluscos y crustáceos.

En 2015, las averiguaciones de Pristine Seas llevaron al gobierno de Kiribati a delimitar una zona de 12 millas náuticas en torno a las islas de la Línea, que quedaron cerradas a la pesca comercial. La zona quedó protegida con el fin de mantenerla en su estado prístino.

Y entonces llegó el desastre. Los picos de calor causados en 2016 por la corriente de El Niño en todo el Pacífico, arrasaron grandes extensiones de coral. Pristine Seas volvió en 2021 esperando encontrar un paisaje desolado. Pero las islas de la Línea tuvieron una recuperación espectacular. ¿Cómo lo lograron? Los corales son resilientes allí donde hay otros elementos pujantes del ecosistema marino. Los abundantísimos peces de las islas de la Línea limpiaron los esqueletos de coral de algas y crearon las condiciones necesarias para que crecieran de nuevo. Gracias a su estatus de protección, este lugar demostró tener una gran resiliencia ante un desastre.

AMP en Marcha: Soluciones Indígenas

El Parque Nacional Kawésqar es de los más extensos del mundo y el segundo parque terrestre más grande de Chile. Los bosques de algas del sur de Chile están entre los más sanos de la Tierra.

A principios de 2020, Pristine Seas organizó una expedición a los fiordos patagónicos con las comunidades indígenas locales kawésqar y yagan. El área explorada está amenazada por la acuicultura intensiva de salmón, que se ha convertido en una importante industria en Chile. Lamentablemente, esta actividad tiene graves impactos ambientales, higiénicos y sociales. El equipo estudió a fondo los ecosistemas costeros y de aguas profundas, y aprendió de las comunidades kawésqar y yagan acerca del significado cultural y ecológico de la región. Pristine Seas está apoyando a estas comunidades para mantener su cultura viva y obtener la plena protección de sus territorios y, con ellos, de su identidad, cosmovisión, subsistencia y derechos ancestrales. El equipo elaboró un completo informe científico y cultural de la expedición y rodó un documental sobre este viaje.

Qué Puedes Hacer

Proteger nuestro océano y devolverle su plenitud e integridad es una gran tarea. No hay una única solución, pero son muchas las cosas que podemos hacer, individual y colectivamente, para ayudar.

• Recuerda que la tierra y el mar están conectados. Visita áreas marinas protegidas, costas, ríos o lagos locales donde hacer esnórquel o conectar con la Naturaleza.
• Boicotea la pesca insostenible. Si no es sostenible, no te lo comas. Que la etiqueta diga pescado a caña o por buceo.
• Reduce tu huella de carbono. Usa menos combustibles fósiles. No uses tanto el auto y viaja en transporte público. Compra electrodomésticos de bajo consumo y aprovecha los programas de energía solar.
• Reduce la basura que generas.
• Reutiliza todo lo que puedas. Elige productos reutilizables en lugar de desechables y recicla. No uses bolsas de plástico. Compra ropa de segunda mano. Ahorra agua. El agua dulce es un recurso limitado y escaso en muchas partes del mundo. Al utilizar menos agua, se reducen las escorrentías y las aguas residuales que se vierten al océano.
• Hazte voluntario. Los grupos conservacionistas necesitan tu ayuda.
• Organiza o participa en recogidas de basuras. Si ayudamos a recoger la basura de nuestras calles, ríos, arroyos o playas, podemos evitar que acabe en el mar.
• Planta árboles. Nuestros bosques ayudan a reducir el dióxido de carbono en la atmósfera, aliviando la presión sobre nuestro océano.
• Lleva una dieta rica en verduras. Compra alimentos locales para reducir las emisiones del transporte y la producción.
• ¡Ojo con qué tiras al inodoro! No botes al inodoro detergentes, pesticidas, desatascadores y arena para gatos, ya que estos productos químicos pueden filtrarse a nuestros ríos y lagos, y llegar al océano.
• Sigue al Explorador Enric Sala y a Pristine Seas en redes sociales para estar informado de sus trabajos por todo el mundo. twitter.com/Enric_Sala instagram.com/enricsala/
• Aprende primero y luego enseña. Cuando entendemos cómo funcionan los ecosistemas, podemos tomar medidas para protegerlos. Aprende lo que puedas y compártelo para crear una conciencia colectiva.
• Habla sin miedo. Defiende el cambio que quieres ver en tu comunidad y en el mundo.

Mueve a la Acción

¿Qué puedes hacer en tu comunidad? Después de leer este manual y de ver algunas de las sugerencias de la página 30, crea un plan de acción personal para ayudar a conservar el océano.

Hazte algunas importantes preguntas:

1 › ¿Cuál sería la mejor manera de promover la conservación del océano desde tu comunidad?

2 › ¿Cuáles son las ventajas de esta acción o solución?

3 › ¿Se te ocurre algún inconveniente?

4 › ¿Qué más necesitas saber o investigar para crear un plan integral?

5 › Haz una lista de todas las partes de tu plan. ¿Qué harás primero? ¿Cuál es el paso siguiente?

6 › ¿Es un plan que puedes llevar a cabo tú solo o necesitarás ayuda?

7 › Enumera algunas personas o grupos que pudieran apoyar tu idea.

8 › ¿Cómo te dirigirías a estas personas o grupos para que colaboren en tu plan?

9 › Elabora un calendario para tu plan. ¿Cuánto tiempo te llevará hacer cada parte?

10 › Comparte tu plan con otras personas y pide su opinión.

11 › Adapta tu plan en función de los comentarios recibidos.

12 › ¡Cuando el plan esté listo, actúa!

¿Qué Maás Quieres Saber?

Si quieres saber más sobre nuestro océano, las amenazas que se ciernen sobre él y cómo ayudar, puedes consultar estos recursos:

Para Educadores

• Cursos de aprendizaje profesional
• One Ocean Educator Guide (para aprendizaje profesional)
• Earth Day 2021 Guide (centrada en el océano)

Para Estudiantes

Ciencia ciudadana

• iNaturalist: inaturalist.org y Seek: inaturalist.org/pages/seek_app

Creación de mapas:

Recursos Fuera de Línea

Esta sección incluye ejemplos de recursos que podrían descargarse o transmitirse a comunidades sin acceso a Internet o con una conexión débil. Muchos de estos recursos pueden imprimirse o descargarse en PDF o archivos comprimidos (zip). Busca los iconos de cada recurso junto a los iconos de las redes sociales, normalmente justo debajo de la foto del recurso.

› Cadenas alimentarias marinas Los estudiantes utilizan tarjetas de organismos marinos y tipos de niveles tróficos para identificar y describir las cadenas alimentarias de varios ecosistemas marinos. Descarga el archivo comprimido que contiene múltiples PDF en bit.ly/3CsNQbj

› Pesca sostenible : Una entrada enciclopédica clasificada que plantea el tema y define los términos clave. Se puede imprimir o guardar en PDF en

› Proteger el océano Los estudiantes hablan sobre “quién es el dueño del océano” y trabajan en pequeños grupos para explorar cuestiones sobre la utilización del medio marino. Luego, miran videos y comentan conceptos relacionados con la creación y designación de las Áreas Marinas Protegidas (AMP). Descarga el archivo comprimido con dos PDF en bit.ly/3yFiIEa

› Nuestro océano interconectado Los estudiantes analizan la geografía del océano y exploran cómo se ha estudiado en el pasado y en la actualidad. Descarga los PDF en bit.ly/3CVU4Sm

› Gestión de áreas marinas protegidas Los estudiantes leen un estudio de caso y debaten sobre los pros y los contras de un área marina protegida (AMP) de la región. A continuación, seleccionan un AMP y elaboran y presentan un plan de gestión. Descarga los archivos comprimidos que contienen múltiples PDF en bit.ly/3RVdxH3

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Food webs describe who eats whom in an ecological community. Made of interconnected food chains, food webs help us understand how changes to ecosystems — say, removing a top predator or adding nutrients — affect many different species, both directly and indirectly.

Phytoplankton and algae form the bases of aquatic food webs. They are eaten by primary consumers like zooplankton, small fish, and crustaceans. Primary consumers are in turn eaten by fish, small sharks, corals, and baleen whales. Top ocean predators include large sharks, billfish, dolphins, toothed whales, and large seals. Humans consume aquatic life from every section of this food web.

Coral reefs are some of the most diverse ecosystems in the world. Coral polyps , the animals primarily responsible for building reefs, can take many forms: large reef building colonies, graceful flowing fans, and even small, solitary organisms. Thousands of species of corals have been discovered; some live in warm, shallow, tropical seas and others in the cold, dark depths of the ocean.

Seafood plays an essential role in feeding the world’s growing population. Healthy fish populations lead to healthy oceans and it's our responsibility to be a part of the solution. The resilience of our marine ecosystems and coastal communities depend on sustainable fisheries.

Estuaries are areas of water and shoreline where rivers meet the ocean or another large body of water, such as one of the Great Lakes. Organisms that live in estuaries must be adapted to these dynamic environments, where there are variations in water chemistry including salinity, as well as physical changes like the rise and fall of tides. Despite these challenges, estuaries are also very productive ecosystems. They receive nutrients from both bodies of water and can support a variety of life. Because of their access to food, water, and shipping routes, people often live near estuaries and can impact the health of the ecosystem.

Marine mammals are found in marine ecosystems around the globe. They are a diverse group of mammals with unique physical adaptations that allow them to thrive in the marine environment with extreme temperatures, depths, pressure, and darkness. Marine mammals are classified into four different taxonomic groups: cetaceans (whales, dolphins, and porpoises), pinnipeds (seals, sea lions, and walruses), sirenians (manatees and dugongs), and marine fissipeds (polar bears and sea otters).

Sea turtles breathe air, like all reptiles, and have streamlined bodies with large flippers. They are well adapted to life in the ocean and inhabit tropical and subtropical ocean waters around the world. Of the seven species of sea turtles, six are found in U.S. waters; these include the green, hawksbill, Kemp's ridley, leatherback, loggerhead, and olive ridley.

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Marine Biodiversity and Ecosystems Underpin a Healthy Planet and Social Well-Being

About the author, cristiana paşca palmer.

May 2017, Nos. 1 & 2 Volume LIV,  Our Ocean, Our World

I n no other realm is the importance of biodiversity for sustainable development more essential than in the ocean. Marine biodiversity, the variety of life in the ocean and seas, is a critical aspect of all three pillars of sustainable development—economic, social and environmental—supporting the healthy functioning of the planet and providing services that underpin the health, well­-being and prosperity of humanity.

The ocean is one of the main repositories of the world's biodiversity. It constitutes over 90 per cent of the habitable space on the planet and contains some 250,000 known species, with many more remaining to be discovered—at least two thirds of the world's marine species are still unidentified. 1

The ocean, and the life therein, are critical to the healthy functioning of the planet, supplying half of the oxygen we breathe 2 and absorbing annually about 26 per cent of the anthropogenic carbon dioxide emitted into the atmosphere. 3

Evidence continues to emerge demonstrating the essential role of marine biodiversity in underpinning a healthy planet and social well-being. The fishery and aquaculture sectors are a source of income for hundreds of millions of people, especially in low-income families, and contribute directly and indirectly to their food security. Marine ecosystems provide innumerable services for coastal communities around the world. For example, mangrove ecosystems are an important source of food for more than 210 million people 4  but they also deliver a range of other services, such as livelihoods, clean water, forest products, and protection against erosion and extreme weather events.

Not surprisingly, given the resources that the ocean provides, human settlements have developed near the coast: 38 per cent of the world's population lives within 100 km of the coast, 44 per cent within 150 km, 50 per cent within 200 km, and 67 per cent within 400 km. 5 Roughly 61 per cent of the world's total gross domestic product comes from the ocean and the coastal areas within 100 km of the coastline. 6 Coastal population densities are 2.6 times larger than in inland areas and benefit directly and indirectly from the goods and services of coastal and marine ecosystems, which contribute to poverty eradication, sustained economic growth, food security and sustainable livelihoods and inclusive work, while hosting large biodiversity richness and mitigating the impacts of climate change. 7

Thus, pressures that adversely impact marine biodiversity also undermine and compromise the healthy functioning of the planet and its ability to provide the services that we need to survive and thrive. Moreover, as demands on the ocean continue to rise, the continued provisioning of these services will be critical. The consequences of biodiversity loss are often most severe for the poor, who are extremely dependent on local ecosystem services for their livelihoods and are highly vulnerable to impacts on such services.

Concerns over the drastic declines in biodiversity are what initially motivated the development of the Convention on Biological Diversity. The Convention encompasses three complementary objectives: the conservation of biodiversity, the sustainable use of its components, and the fair and equitable sharing of benefits arising from the utilization of genetic resources. With 196 Parties, participation in the Convention is nearly universal, a sign that our global society is well aware of the need to work together to ensure the survival of life on Earth.

The Convention also serves as a new biodiversity focal point for the entire United Nations system and a basis for other international instruments and processes to integrate biodiversity considerations into their work; as such, it is a central element of the global framework for sustainable development. The Convention's Strategic Plan for Biodiversity 2011-2020 and its 20 Biodiversity Targets, adopted by the Parties to the Convention in Nagoya, Aichi Prefecture, Japan, in 2010, provide an effective framework for cooperation to achieve a future in which the global community can sustainably and equitably benefit from biodiversity without affecting the ability of future generations to do so.

The centrality of marine biodiversity to sustainable development was recognized in the 2030 Agenda for Sustainable Development and the Sustainable Development Goals (SDGs), in which global leaders highlighted the urgency of taking action to improve the conservation and sustainable use of marine biodiversity. In particular, SDG 14 is aimed at con­serving and sustainably using the oceans, seas and marine resources for sustainable development and emphasizes the strong linkages between marine biodiversity and broader sustainable development objectives. In fact, many elements of Goal 14 and a number of other SDGs reflect the same objectives and principles agreed upon under the Aichi Biodiversity Targets. Thus, efforts at different scales to achieve the Aichi Targets will directly contribute to implementing the 2030 Agenda for Sustainable Development and achieving the SDGs.

Marine biodiversity and ecosystems are intrinsically connected to a wide range of services that are essential to sustainable development. These relationships are often complex and dynamic, and are influenced by feedback loops and synergistic effects. These outline the need to take an integrated and holistic approach to conservation and the sustainable use of marine biodiversity, based on the ecosystem and precautionary approaches, principles of inclusiveness and equity, and the need to deliver multiple benefits for ecosystems and communities.

Work under the Convention has evolved to reflect such an approach and to support Parties and relevant organizations in implementing the Convention, notably through national biodiversity strategies and action plans, and through policies, programmes and measures across different sectors that both affect and rely on biodiversity.

This work takes a thematic approach focused on (a) understanding the ecological and biological value of the ocean; (b) addressing the impacts of pressures and threats on marine and coastal biodiversity; (c) facilitating the application of tools for applying the ecosystem approach for conservation and sustainable use; (d) building capacity to put in place the enabling conditions for implementation; and (e) mainstreaming biodiversity into sectors.

Under the Convention on Biological Diversity, a global process for the description of ecologically or biologically significant marine areas (EBSAs) has served to enhance understanding of the ecological and biological value of marine areas in nearly all of the world's ocean regions. This work serves as an important foundation for conservation and management, and creates the enabling conditions to further enhance and utilize this knowledge by catalysing scientific networking and partnerships at the regional level. It also helps to identify gaps in knowledge and to prioritize monitoring and research activities in support of the application of the ecosystem approach. 8

Parties have also prioritized the need to address key pressures on marine biodiversity, including unsustainable fishing practices, marine debris and anthropogenic underwater noise, as well as climate change and ocean acidification. The secretariat, Parties to the Convention, other Governments and relevant organizations work with scientists and experts to synthesize best available knowledge on the effects of major pressures/stressors, and produce consolidated guidance on means to prevent and mitigate adverse impacts of these pressures.

Through expert workshops, publications and engagement with other relevant processes, the Convention on Biological Diversity has generated guidelines for the development and application of the ecosystem approach, including through area­based measures, such as marine spatial planning and marine and coastal protected areas, as well as biodiversity-inclusive environmental impact and strategic environmental assessments, integrating different sectoral policy measures to address various pressures on the biological and ecological values of the ocean.

Capacity-building to support implementation is also a central focus of the Convention on Biological Diversity. One of the tools for this is the Sustainable Ocean Initiative, a global partnership framework coordinated by the Convention secretariat, together with various United Nations entities and international partner organizations. The Initiative builds on existing efforts, resources and experiences by enhancing partnerships, disseminating lessons learned and knowledge gained, and facilitating improved coordination among sectors and stakeholder groups. It does this across multiple scales in order to create the enabling conditions needed for improved on-the-ground implementation. The Sustainable Ocean Initiative Global Dialogue with Regional Seas Organizations and Regional Fisheries Bodies on Accelerating Progress Towards the Aichi Biodiversity Targets works to facilitate cross-sectoral regional-scale dialogue and coordination. 9

Parties have also prioritized the mainstreaming of bio­diversity considerations into economic sectors that both affect and rely on healthy marine ecosystems for sustainable economic growth. Mainstreaming was at the forefront of the Convention on Biological Diversity at the recent United Nations Biodiversity Conference, held in Cancun, Mexico, in December 2016. Ministers of environment, fisheries and tourism, among others, at the high-level segment of the Conference expressed their commitment, through the adoption of the Cancun Declaration, to work at all levels within Governments and across sectors to mainstream biodiversity in sectoral development. In this vein, the Convention secretariat has worked closely over the years with the Food and Agriculture Organization of the United Nations, regional fishery bodies and other stakeholders to support enhanced implementation by the Parties to the Convention to better mainstream biodiversity into the fisheries and aquaculture sectors.

If we are to achieve the SDGs and the Aichi Biodiversity Targets, we will have to abandon business-as-usual approaches and mainstream biodiversity into our development planning, governance and decision-making. We will have to mobilize resources to make the on-the-ground changes that are so desperately needed. Furthermore, stakeholders at all levels will need to be conscious of how their actions and behaviours affect the marine ecosystems on which we all depend, and make conscious decisions to improve our relationships with the ocean, which has given us so much throughout human history.

The forthcoming Ocean Conference, to be held at the United Nations in New York from 5 to 9 June 2017, represents a momentous opportunity to build the necessary political will and put in place the enabling conditions to foment enhanced implementation at all levels with the inclusion of all stakeholders in order to realize a future of healthy and productive marine biodiversity that supports societal well-being. In line with the principles of intergenerational equity, we must also recognize the right of future generations to inherit a planet thriving with life, and to reap the economic, cultural and spiritual benefits of a healthy ocean.

1   For further information, see the Census of Marine life website:  http://coml.org.

2   The First Global Integrated Marine Assessment (World Ocean Assessment I) (United Nations, 2016). Available from http://www.un.org/depts/los/global_reporting/WOA_RegProcess.htm .

3   Corinne Le Quere and others, "Global carbon budget 2015", Earth Sys tem Science Data , Vol. 7, No. 2 (December 2015), 349-396 (371).

4   Mark Spalding, Robert D. Brumbaugh and Emily Landis, Atlas of Ocean Wealth (Arlington, VA, The Nature Conservancy, 2016), p. 14.

5   Christopher Small and Joel E. Cohen, Continental physiography, climate, and the global distribution of Human Population", Current Anthropology Vol. 45, No. 2 (April 2004), 269-277 (272).

6   Paulo A.L.D. Nunes and Andrea Ghermandi, The economics of marine ecosystems: reconciling use and conservation of coastal and marine systems and the underlying natural capital, Environmental and Resource Economics , Vol. 56, No. 4 (October 2013), 459-465 (460).

7   Ibid.

8   For further information on ecologically or biologically significant marine areas, see  https://www.cbd.int/ebsa/ .

9   For further information on the Sustainable Ocean Initiative, see https://www.cbd.int/soi/ .

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Human impacts on marine environments.

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Throughout human existence we have relied on the oceans – for food, as a waste dump, for recreation, for economic opportunities and so on. However, it’s not only our activities in the marine environment that affect life in the sea – it’s also the things we do on land.

With more than half the world’s population now living within 100 kilometres of the coast, it’s not surprising that our activities are taking their toll. Human impacts have increased along with our rapid population growth, substantial developments in technology and significant changes in land use. Over-fishing, pollution and introduced species are affecting life in the sea – and New Zealand is no exception!

Threats to marine habitats

Human actions at sea and on land are putting increasing pressure on the ocean and the species that live there.

Humans living near the coast have probably always used the ocean as a source of food. However, with advances in fishing equipment, larger ships and new tracking technologies, many fish stocks around the world have reduced significantly. Fish stocks on continental shelf areas are now widely considered to be fully or over exploited. Aside from reducing fish stocks, unsustainable fishing practices can have other negative impacts on the marine environment. For example, some fishing techniques such as dredging and trawling can cause widespread damage to marine habitats and organisms living on the sea floor. These techniques also often capture non-target species (known as bycatch) that are then discarded.

Commercial fishing boat

Fishing was probably the first use of the oceans by humans. In the last century, significant increases in commercial fishing have resulted in the over-exploitation of many fish stocks.

In New Zealand, fisheries are managed by a quota system that sets catch limits for commercially important species and aims at sustainable management of our fish stocks. The Royal Forest and Bird Protection Society (NZ) used to publish the Best Fish Guide to try and encourage us to make more sustainable choices when purchasing seafood. The list evaluated fish stocks and bycatch levels and the fishing methods used.

Our oceans have long been used as an intentional dumping ground for all sorts of waste including sewage, industrial run-off and chemicals. In more recent times, policy changes in many countries have reflected the view that the ocean does not have an infinite capacity to absorb our waste. However, marine pollution remains a major problem and threatens life in the sea at all levels.

Phytoplankton bloom

This image shows a large phytoplankton bloom that occurred around New Zealand in October 2009. The image was acquired by the Moderate-resolution Imaging Spectroradiometer (MODIS), flying aboard NASA’s Terra satellite.

Some marine pollution may be accidental, for example, oil spills caused by tanker accidents. Some may be indirect, when pollutants from our communities flow out to sea via stormwater drains and rivers. Some effects may not be immediately obvious, for example, bioaccumulation – the process where levels of toxic chemicals in organisms increase as they eat each other at each successive trophic level in the food web.

All marine pollution has the potential to seriously damage marine habitats and life in the sea. Scientists are concerned that marine pollution places extra stress on organisms that are already threatened or endangered.

Eutrophication

Eutrophication is the result of a particular type of marine pollution. It is caused by the release of excess nutrients into coastal areas via streams and rivers. These nutrients come from fertilisers used in intensive farming practices on land. Additional nutrients in the sea can lead to excessive phytoplankton growth that results in ‘blooms’. When these large numbers of organisms die, the sharp increase in decomposition of the dead organisms by oxygen-using bacteria depletes oxygen levels. In some cases, this can result in the death by oxygen starvation of large numbers of other organisms such as fish.

Introduced species

Since the arrival of humans in New Zealand, introduced species in our terrestrial ecosystems have contributed to a significant loss of biodiversity. Introduced species also present a threat to our marine environment. It is not always easy to monitor or prevent the introduction of unwanted marine organisms, and visiting ships may introduce them accidentally on their hulls, in ballast water or on equipment.

Not all introduced species will spread or even survive, but once established, they may be difficult or impossible to remove. For example, the Japanese seaweed, wakame Undaria pinnatifida , which probably arrived in 1987, is now widespread. Scientists are still monitoring its impact on our native marine organisms.

In New Zealand, the Ministry of Primary Industries is responsible for providing border inspectors who manage risks from people, planes, vessels (like ships) and goods coming into the country. They also coordinate responses when new, harmful pests and diseases are detected in our country.

Nature of science

Scientific research sometimes uncovers environmental problems that are linked to human lifestyles. This research shows that the way we live needs to be balanced with environmental needs, which sometimes puts scientists in a difficult position in defending their work.

Ocean acidification

There is evidence to suggest that human activities have caused the amount of carbon dioxide in our atmosphere to rise dramatically. This impacts on the marine environment as the world’s oceans currently absorb as much as one-third of all CO 2 emissions in our atmosphere. This absorption of CO 2 causes the pH to decrease, resulting in the seawater becoming more acidic.

Our role in ocean acidification

In this video, Associate Professor Abby Smith, from the University of Otago, talks about what we can do to help reduce ocean acidification.

Scientists have long understood that an increase in carbon dioxide in the atmosphere will result in higher levels of dissolved CO 2 in seawater. However, a relatively recent discovery is that even small changes in water pH can have big impacts on marine biology. Ocean acidification is a worldwide issue, but as CO 2 is more soluble in colder water, it is of particular concern in New Zealand’s temperate oceans.

It is difficult to predict the overall impact on the marine ecosystem but many scientists fear that ocean acidification has the potential to decrease marine biodiversity on a very large scale.

New Zealanders are aware that old ways of managing our seas are in need of a rethink. The Sustainable Seas National Science Challenge is tasked with helping New Zealand enhance the value of our marine resources while ensuring they are safeguarded for future generations.

Related content

Explore the timeline to look at some of the historical aspects of fisheries in New Zealand.

Overfishing is an ongoing environmental issue in our oceans. This article answers the question: how do you locate ships that have gone ‘dark’ and are fishing illegally?

The Rena disaster impacted the habitat of many species, read how marine life adapts to habitats and how it deals with stress caused by human impacts .

Waitā is a whetū in the Matariki cluster connected to the oceans and marine environments. He reminds us that the mauri of the people is closely connected to the mauri of the moana.

Raʻui: Giving it back to the gods is a Connected article that takes a Pacific worldview and describes how the people of the Cook Islands have attempted to manage and protect their marine resources with the re-introduction of the tradition of ra‘ui.

• Identifying marine stressors
• Investigating marine and costal tipping points
• Modelling marine stressors and tipping points

Activity ideas

In Introducing biodiversity , students make models of a marine ecosystem and then explore ways humans might impact on that ecosystem.

After watching the video Our role in ocean acidification , explore why egg shells are dissolving and can you get a fisherman and a conservationist to agree ?

Changes on the beach is a cross-curricular activity that explores natural and human-induced changes to beach environments.

Citizen science

Using online citizen science opportunities as a way to deepen student learning and engagement is easier than you think. Have a look at this example, Adrift , looking at marine microbes drifting continually in our ocean systems. Read about these schools’ citizen science projects in the Connected articles Down the drain and Sea science .

Useful links

Visit the Department of Conservation’s website to find out more about marine reserves and other efforts being made to protect life in the sea.

In this recording, Marine reserves, part of Te Papa’s Science Express programme, hear biologist Jonathan Gardner discuss marine reserves around the world – their importance as ecosystems, and the competing interests that threaten or help protect them.

The OECD commissioned the report 2023 Agency in the Anthropocene . This easy to read report, co-authored by Dr Chris Eames at the University of Waikato, explains the competencies youth need to address local and global challenges in this Anthropocene epoch of human influences on the planet.

This classroom module for marine biosecurity is designed for years 5-8 to help them understand the role they play in protecting our coastlines. It is provided in both Google Docs and as printable PDFs so that it's easy for teachers to use. Part 3 uses the Marine Metre Squared project.

The Marine Stewardship Council is an international non-profit organisation that aims to protect oceans and safeguard fish stocks. It has a system for labelling sustainable seafood for consumers. Some critics argue the system is ‘greenwashing’, take a look at the Greenpeace article Understanding the true price of fish . Do either of the articles align with the 2017 Best Fish guide by the New Zealand Forest and Bird? If you were buying seafood, how would you decide on what species are sustainable?

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Home — Essay Samples — Environment — Ocean — Marine Pollution: A Growing Threat to Oceanic Ecosystems

Marine Pollution: a Growing Threat to Oceanic Ecosystems

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ENCYCLOPEDIC ENTRY

Marine pollution.

Marine pollution is a combination of chemicals and trash, most of which comes from land sources and is washed or blown into the ocean. This pollution results in damage to the environment, to the health of all organisms, and to economic structures worldwide.

Biology, Ecology, Earth Science, Oceanography

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Marine pollution is a growing problem in today’s world. Our ocean is being flooded with two main types of pollution: chemicals and trash.

Chemical contamination, or nutrient pollution, is concerning for health, environmental, and economic reasons. This type of pollution occurs when human activities, notably the use of fertilizer on farms, lead to the runoff of chemicals into waterways that ultimately flow into the ocean. The increased concentration of chemicals, such as nitrogen and phosphorus, in the coastal ocean promotes the growth of algal blooms , which can be toxic to wildlife and harmful to humans. The negative effects on health and the environment caused by algal blooms hurt local fishing and tourism industries.

Marine trash encompasses all manufactured products—most of them plastic —that end up in the ocean. Littering, storm winds, and poor waste management all contribute to the accumulation of this debris , 80 percent of which comes from sources on land. Common types of marine debris include various plastic items like shopping bags and beverage bottles, along with cigarette butts, bottle caps, food wrappers, and fishing gear. Plastic waste is particularly problematic as a pollutant because it is so long-lasting. Plastic items can take hundreds of years to decompose.

This trash poses dangers to both humans and animals. Fish become tangled and injured in the debris , and some animals mistake items like plastic bags for food and eat them. Small organisms feed on tiny bits of broken-down plastic , called micro plastic , and absorb the chemicals from the plastic into their tissues. Micro plastics are less than five millimeters (0.2 inches) in diameter and have been detected in a range of marine species, including plankton and whales. When small organisms that consume micro plastics are eaten by larger animals, the toxic chemicals then become part of their tissues. In this way, the micro plastic pollution migrates up the food chain , eventually becoming part of the food that humans eat.

Solutions for marine pollution include prevention and cleanup. Disposable and single-use plastic is abundantly used in today’s society, from shopping bags to shipping packaging to plastic bottles. Changing society’s approach to plastic use will be a long and economically challenging process. Cleanup, in contrast, may be impossible for some items. Many types of debris (including some plastics ) do not float, so they are lost deep in the ocean. Plastics that do float tend to collect in large “patches” in ocean gyres. The Pacific Garbage Patch is one example of such a collection, with plastics and micro plastics floating on and below the surface of swirling ocean currents between California and Hawaii in an area of about 1.6 million square kilometers (617,763 square miles), although its size is not fixed. These patches are less like islands of trash and, as the National Oceanic and Atmospheric Administration says, more like flecks of micro plastic pepper swirling around an ocean soup. Even some promising solutions are inadequate for combating marine pollution. So-called “ biodegradable ” plastics often break down only at temperatures higher than will ever be reached in the ocean.

Nonetheless, many countries are taking action. According to a 2018 report from the United Nations, more than sixty countries have enacted regulations to limit or ban the use of disposable plastic items. The National Geographic Society is making this content available under a Creative Commons CC-BY-NC-SA license . The License excludes the National Geographic Logo (meaning the words National Geographic + the Yellow Border Logo) and any images that are included as part of each content piece. For clarity the Logo and images may not be removed, altered, or changed in any way.

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Article Contents

Introduction, certifications as sustainable, sustainability of target species, impact of trawling on benthic ecosystems, indirect impact of trawling on productivity of target species, bycatch and discards, carbon footprint of fuel use, impact of trawling on carbon sequestration, interaction of bottom trawling and hypoxia, is the trawl footprint expanding, conflicts with other fishing gears and ocean uses, management actions to reduce impacts, can other fishing methods replace bottom trawling, environmental impacts compared to alternative foods, conclusions, acknowledgement, data availability, author contributions, conflict of interest.

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Evaluating the sustainability and environmental impacts of trawling compared to other food production systems

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R Hilborn, R Amoroso, J Collie, J G Hiddink, M J Kaiser, T Mazor, R A McConnaughey, A M Parma, C R Pitcher, M Sciberras, P Suuronen, Evaluating the sustainability and environmental impacts of trawling compared to other food production systems, ICES Journal of Marine Science , Volume 80, Issue 6, August 2023, Pages 1567–1579, https://doi.org/10.1093/icesjms/fsad115

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Mobile bottom contact gear such as trawls is widely considered to have the highest environmental impact of commonly used fishing gears, with concern about impact on benthic communities, bycatch, and carbon footprint frequently highlighted as much higher than other forms of fishing. As a result, the use of such gears has been banned or severely restricted in some countries, and there are many proposals to implement such restrictions elsewhere. In this paper, we review the sustainability of bottom trawling with respect to target-species sustainability, impact on benthic communities, bycatch and discards, carbon footprint from fuel use, and impact on carbon sequestration. We compare the impact to other forms of fishing and other food production systems. We show that bottom-trawl and dredge fisheries have been sustained, and where well managed, stocks are increasing. Benthic sedimentary habitats remain in good condition where fishing pressure is well managed and where VME and species of concern can be protected by spatial management. Bycatch is intrinsically high because of the mixed-species nature of benthic communities. The carbon footprint is on average higher than chicken or pork, but much less than beef, and can be much lower than chicken or pork. The impact on carbon sequestration remains highly uncertain. Overall, the concerns about trawling impacts can be significantly mitigated when existing technical gear and management measures (e.g. gear design changes and spatial controls) are adopted by industry and regulatory bodies and the race-to-fish eliminated. When these management measures are implemented, it appears that bottom trawling would have a lower environmental impact than livestock or fed aquaculture, which would likely replace trawl-caught fish if trawling was banned. A total of 83 bottom-trawl fisheries are currently certified by the Marine Stewardship Council, which is the most widely accepted measure of overall sustainability.

Bottom trawls (such as beam trawls, otter trawls, and shellfish dredges, which we will refer to as bottom trawls) are designed to catch target species that live close to, in, and on the seabed. The use of bottom trawls as a means of catching fish has met with increasing opposition due to its impact on seafloor habitats and biological communities (Watling and Norse, 1998 ; Watling, 2013 ), its high bycatch rates (Pérez Roda et al ., 2019 ; Gilman et al ., 2020 ), CO 2 release from fuel use (Tyedmers, 2004 ; Sala et al ., 2022 ), and, lately, its potential contribution to greenhouse emissions through the release of stored carbon from disturbed seabed sediments (Sala et al ., 2021 ). Although the magnitude of those impacts remains the subject of intense scientific debate (Pitcher et al ., 2022 ), concerns about the environmental impacts of trawling have fueled strong public campaigns, resulting in bottom trawling being demonized (Willer et al ., 2022 ), severely restricted, or effectively banned in some countries and regions (McConnaughey et al ., 2020 ).

However, bottom trawling accounts for 26% of global marine fisheries catches (Steadman et al ., 2022 ), providing food and employment for millions of people at a time when the contributions of marine fisheries towards the United Nations Sustainable Development Goals (United Nations, 2002 ) and, specifically, to meet the food and nutrient needs of a growing population, are increasingly recognized. While alternative fishing gears and methods may be available and economically viable in some cases, many benthic and demersal target species would be difficult to catch without some form of bottom trawling (Ziegler and Valentinsson, 2008 ; Suuronen et al ., 2012 ).

From this perspective, bottom trawling needs to be considered as one form of food production, and its sustainability and environmental footprint should be compared to footprints of other ways of producing food, including other capture fisheries, aquaculture, livestock, and crop production.

The purpose of this paper is to summarize the current knowledge about the sustainability and environmental impacts of bottom trawling, to compare trawling impacts to other forms of food production, to identify important information gaps, and to suggest the best ways to minimize the environmental impacts of trawling.

At present, 83 bottom-trawl fisheries representing 252 bottom-trawl-caught species/fisheries combinations have been certified by the Marine Stewardship Council (personal communication, Mike Melnychuk, MSC staff) as sustainable. These include 122 units of certification from Europe, 63 from the United States, 19 from Canada, 15 from Australia, 12 each from Chile and New Zealand, 5 from Africa, and 2 from Argentina. Many are recommended by the Seafood Watch programme of the Monterey Bay Aquarium ( www.seafoodwatch.org ). These are the two best-known international standards for fisheries sustainability, and the fact that bottom-trawl fisheries meet their standards is evidence that bottom-trawl fishing can be sustainable. These sustainability evaluations consider not only the status of the target stock but also the marine environmental impacts of the fishing method and have specific criteria regarding the management of bottom-trawl impacts on benthic communities (Monterey Bay Aquarium, 2023 ) (Marine Stewardship Council, 2023 ).

Bottom trawling is the primary method used to harvest many demersal species known as groundfish, which include cod, haddock, pollock, hake, and multiple species of flatfish and rockfish. Globally, almost all the catch of groundfish comes from fish stocks whose trends in abundance are scientifically assessed (Hilborn et al ., 2021 ). Groundfish populations are increasing overall and above the target levels for sustainable exploitation ( Figure 1 ) (Hilborn et al ., 2021 ). Arguments that bottom trawling is incompatible with sustaining a fishery for the target species are contradicted by the trends in the abundance of groundfish stocks. The mixed-stock nature of all bottom fishing methods (trawl, longline, Danish seine, gillnet) poses challenges to sustainable exploitation of mixed species of differential productivity, but the increasing trend of groundfish in many regions of the world shows that even in mixed-species fisheries, good management can lead to sustainability (Fernandes and Cook, 2013 ; Zimmermann and Werner, 2019 ).

The abundance trend in global groundfish stocks relative to management targets (solid black line). In most cases, management targets are based on achieving maximum sustainable yield. Vertical bars show the range of 50% of the stocks, with 25% being below and 25% above. The thin grey horizontal line shows where the stock abundance is equal to the management target. Redrawn from Hilborn et al . (2021 ).

There are of course many stocks that are overexploited with bottom trawls, but this is a failure of fisheries management to control fishing pressure rather than a direct consequence of the fishing gear used, as it has been clearly demonstrated that well-regulated bottom-trawl fisheries can avoid overfishing (Hilborn et al ., 2021 ). Bottom trawling and related mobile bottom-contact gear like dredges are also commonly used for many invertebrates, but there has been no global summary of the trends in abundance of these species.

The magnitude of the effect of the trawl disturbance on benthic communities depends on the frequency of trawling, the impact (or depletion rate) per trawl pass, and the individual recovery rates of biota exposed to trawling (Hiddink et al ., 2017 ). The effects of trawling on the commonly fished sedimentary habitats, such as muddy and sandy seabeds, are much less severe than on the more sensitive habitats, such as oyster reefs in shallow waters and vulnerable marine ecosystems (VMEs) (Parker et al ., 2009 ), such as sponge gardens or cold-water coral reefs (Clark and Rowden, 2009 ; Clark et al ., 2015 ; Kaiser et al ., 2018 ), in deeper waters. For sedimentary habitats, average depletion rates (the percentage of benthic invertebrates killed per passage of the gear) range from 4.7 to 26.1% depending on trawl type, gear penetration depth, and habitat type, with otter trawls causing the lowest depletion, followed by beam trawls and towed dredges causing the most impact (Sciberras et al ., 2018 ). Depletion rates are lower in sand than in gravel and mud (Collie et al ., 2017 ; Pitcher et al ., 2022 ). Recovery rates are related to the longevity of the affected species (Hiddink et al ., 2019 ). Meta-analysis of studies reporting how the biomass of the benthic community declines with increasing trawling intensity produced estimates of recovery rates that ranged from 29 to 68% per year along a gravel-to-mud continuum (Pitcher et al ., 2022 ). Slower recovery with increasing gravel reflects the greater proportions of longer-lived species found in more stable gravel habitats. Epibenthic megafauna and biogenic habitats are the most sensitive to all forms of trawling, and recovery rates are often measured in decades (Kaiser et al ., 2018 ). However, complex habitats like coral reefs and rocky bottoms are generally avoided by trawlers because of the threats to their nets. When these habitats are trawled, they are heavily impacted (Parker et al ., 2009 ; Williams et al ., 2020 ), and a consensus is growing that the best practise is to close such areas to mobile bottom contact gear (McConnaughey et al ., 2020 ).

A global modelling assessment of trawl impacts on macro epifauna and infauna in sedimentary habitats showed that the status of benthic populations relative to an untrawled state differs greatly among regions and was related to the total amount of trawling (Pitcher et al ., 2022 ). The model included 24 regions worldwide and used fine-scale data on the frequency of trawling and recovery rates of biota estimated from meta-analysis ( Figure 2 ). The measure used, relative benthic status (RBS), reflects the extent to which the macrofauna have been numerically reduced and is an aggregated measure across many species (Pitcher et al ., 2017 ). A status of 0.9, for instance, would mean that the abundance of benthic macrofauna averaged across taxa would be 90% of the abundance in the absence of trawling. Even with a RBS of 0.9, some more sensitive species would be reduced more than that and more resilient species less. The RBS for a region will reflect the average across untrawled, lightly trawled, and heavily trawled areas in the region, weighted by the area of each level of trawl intensity. Mazor et al . (2021 ) were able to look at the impacts on specific species where data were available. There are no established targets for this index, and as in discussions of changes in biodiversity, multiple measures are potentially usable. RBS allows us to compare widely across benthic habitats in many different regions.

Depletion level (RBS) of benthic flora and fauna in different regions of the world where data on trawl effort and sediment type are available. Data from Pitcher et al . ( 2022 ).

Overall impacts are low in most regions examined, and much of the seabed is untrawled in many regions. Regional average status relative to an untrawled state (status = 1.0) was high (>0.9) in 15 regions (mostly outside Europe) but <0.7 in three European regions and only 0.25 in the Adriatic Sea. Across all regions, 66% of the seabed area was not trawled, 1.5% was depleted (status = 0), and 93% had status >0.8 ( Figure 2 ) (Pitcher et al ., 2022 ).

The RBS is calculated for each region in the most recent range of years where trawl effort data were available (mostly 2010–2014), and reflects the expected status of benthos at that intensity of trawling. RBS depends on habitat type (reflecting both the taxa found and the sensitivity to trawling) and the intensity of trawling. In most areas where we have trawl-effort data, there is declining fishing pressure (see a later section on trends in trawl footprint), so we would expect that in general RBS would be improving.

Mazor et al . (2021 ) provide more detail on impacts within different taxonomic groups. The status of populations of benthic-invertebrate groups was examined for 13 of the 24 regions for which suitable invertebrate distribution data were available and ranged between 0.86 and 1 (mean = 0.99), with 78% of benthos-groups having a status >0.95 (Mazor et al ., 2021 ). Again, mean benthos status was lower in European regions than regions elsewhere, which accords with the intensity and history of fishing in Europe.

Assessing the status of sedimentary habitats (the habitat types where most trawling occurs) is critical to ensuring the integrity of the seabed ecosystems because sedimentary habitats constitute most of the continental shelves. Nevertheless, much concern surrounds rarer, more sensitive habitat types that can characterize VMEs and biogenic habitats (FAO, 2009 ). These habitats are not well mapped over large scales in most regions, and while impact rates are known to be high in many cases, there are few quantitative estimates of the impact that bottom trawling has on them because few studies have been carried out because it is hard to justify trawling over such sensitive habitats for a scientific experiment (Hall-Spencer and Moore, 2000 ). Even the most resilient of these VMEs cannot withstand trawling more than once every three years (Thompson et al ., 2016 ). A preliminary assessment conducted by Pitcher et al . (2022 ) calculated the percentage of each of the 24 regions in their study where trawl intensity exceeded that frequency, which was used as a local extinction threshold for highly sensitive biota. The percentage of seabed trawled at least once every three years ranged from 0.2% in southern Chile to 82% in the Adriatic Sea and was >20% for 10 regions (all European regions and northern Benguela) (Pitcher et al ., 2022 ). In those regions, we would expect the sensitive species in VMEs to be eliminated in proportion to the amount of area trawled three times or more. Because of the high sensitivity of the habitat-forming biota types that characterize VMEs, fisheries management should seek to prevent significant adverse impacts on them, according to the Deep-Sea Fisheries Guidelines (FAO, 2009 ).

The data on trawl intensity in Pitcher et al . ( 2022 ) covers almost all European waters, Australia, New Zealand, South Africa, Namibia, Argentina, Chile, the western US, and Alaska. There is no coverage of Asia, where trawling is thought to be quite intense (Suuronen et al ., 2020 ), and Africa with the exception of Namibia and South Africa.

Intense bottom trawling causes a high level of local mortality to benthic fauna, and for fish species that depend on benthic fauna for food, shelter, productivity, and hence sustainable harvest may decline with increasing levels of bottom fishing disturbance. Indirect effects of bottom fishing have been demonstrated experimentally and with dynamic models in which trawling affects the target species, their benthic prey, and the habitat-forming epifauna (Collie et al ., 2017 ; Pitcher et al ., 2022 ). Ultimately, the response of fish productivity to bottom fishing depends on the interplay between reduced benthic prey abundance and reduced competition for benthic food as fish density declines (Hiddink et al ., 2011 ; 2016 ). Historically, trawling may have modified habitat and reduced the carrying capacity of fish stocks, but these effects are difficult to distinguish empirically because fishing and other factors may impact the abundance of target species. Over large areas of the continental shelf with sandy sediments, these indirect effects are estimated to be small compared with the direct mortality caused by fishing target species (Collie et al ., 2017 ; Pitcher et al ., 2022 ). A possible explanation for this small effect is that the distribution of fishing effort is very patchy—small fractions of fishing grounds are heavily fished, while large fractions are lightly fished or unfished (Amoroso et al ., 2018 ). Therefore, the indirect effects of bottom fishing are also likely to be localized, for example, where target species live on vulnerable habitats.

Bycatch is generally defined as the “unintended, non-targeted organisms caught while fishing for particular species (or sizes of species),” including “landed bycatch,” which is retained to be eaten or sold (Pérez Roda et al ., 2019 ). Discards are the portion of the catch that are returned to the sea whole, alive or dead. Fishers are discarding in response to numerous and continuously changing factors, including market conditions, regulations, and the size and quality of the catch.

Using Food and Agriculture Organization (FAO) databases on country-specific landings, Pérez Roda et al . (2019 ) estimated the discard rate and magnitude for the period 2010–2014 for global marine capture fisheries using fishery-specific discard rates derived from direct observations and global gear-specific discard rates. Discard rates for trawl fisheries and selected other gear types are shown in  Table 1 .

Mean discard rates and 95% confidence bound (CI) for different fishing gears from Pérez Roda et al ., 2019 (Table B1).

Table 1 shows that the dominant determinant of discard rate is whether the fishing occurs on the bottom or surface or midwater. Bottom trawls generally have the highest discard rate and account for an estimated 46% of all discards, with shrimp trawls having particularly high discards (Pérez Roda et al ., 2019 ). In many trawl fisheries (and most other fisheries), most of the discarded catch will not survive, but this depends largely on species, size of organisms, handling practises (e.g. sorting time), environmental conditions (e.g. air temperature), and haul duration and depth (Broadhurst et al ., 2006 ). For instance, many crustaceans typically incur <50% discard mortalities, whereas small pelagic fish may suffer very high mortality (reviewed by Broadhurst et al ., 2006 ).

When comparing the FAO discard estimates covering four decades (Alverson et al ., 1994 ; Kelleher, 2005 ; Pérez Roda et al ., 2019 ), it is obvious that there has been a declining trend from the late 1980s, as the latest discard estimate is less than half of the initial estimate. The estimates from the current assessment are consistent with the findings of Zeller et al . (2018 ), who found that annual discards peaked at around 19 million tonnes in 1989 and gradually declined to under 10 million tonnes by 2014.

Improved gear selectivity and reduction of fishing effort have contributed to the reduction of discards in many trawl fisheries in Europe, North America, and Australia (Kennelly and Broadhurst, 2021 ). A major change has also been the increased utilization of all species in trawl fisheries of SE Asia, where trawling has been largely non-selective and thus has resulted in large volumes of juvenile fish, small-sized fish species, and other organisms in the landings (Funge-Smith et al ., 2012 ; Suuronen et al ., 2020 ). Most of these fish are now used in SE Asia both for local markets and for aquaculture feed, and discarding is uncommon. Increased use of trawl “bycatch” is also growing in Africa and Latin America, leading to reduced discards.

The capture of endangered, threatened, or protected species, such as rays, sharks, and sea turtles, as well as juveniles of target species, remains a cause of concern in some trawl fisheries (Gray and Kennelly, 2018 ). They estimated that 19% of sea turtles discarded globally at sea were taken by trawls (both pelagic and bottom), that the extensive Alaska bottom-trawl fishery annually discarded 534 seabirds, the Argentine factory trawl fleet discarded 8500 seabirds and suggest that the global trawl impact on seabirds may be on the same order as the longline fleets.

The majority of the carbon footprint of capture fisheries comes from the fuel used, and Parker and Tyedmers (2015 ) assembled an impressive collection of 878 studies of fuel use in fisheries since 1990, measured as litres of fuel used per metric tonne (MT) landed. The data are predominantly from Europe, North America, and Oceania, with few studies from Africa or Asia. For bottom trawl gear, Europe had a fuel consumption per MT landed that was 1.8 times as high as North America and Oceania.  Table 2 shows the fuel use and carbon released by fuel use for different fishing gears.

The average, minimum, and maximum amount of fuel used to capture one MT (litres per MT) of fish for different gear types and the amount of carbon released per kilogramme (Kg) of fish wet weight landed (Kg CO 2 per kg landed).

Data source is Parker and Tyedmers (2015 ).

The most important feature of these data is the high variability within and among different fisheries, indicating that almost any fishing gear type can catch fish with a much lower carbon footprint than the average, and no method is consistently best. Nevertheless, bottom trawls are among the least fuel-efficient gear types. Two-thirds of the bottom trawl data set is from Europe, and many of the data are from the 1990s, a time of low stock status and highly competitive fisheries (i.e. greater fishing effort was required to catch the same amount of fish relative to when stock status was more abundant). In contrast, trawl fisheries for stocks at high abundance and where the race-to-fish has been eliminated by the allocation of quota to cooperatives have much lower fuel use and carbon footprint (Fissel et al ., 2016 ). Two Alaskan trawl fisheries have quite low carbon footprint per unit of edible product (0.83 and 1.17 kg CO 2 /kg; see  Table 3 ) and exemplify how the carbon footprint of trawling can be reduced by maintaining high stock size and eliminating the race-to-fish and sets a standard for other trawl fisheries to aspire to. The New Zealand deepwater trawl fleet has a carbon footprint of 2.24 kg CO 2 /kg (Mazzetto and Ledgard, 2023 ). Similarly, a well-managed territorial use rights-based scallop dredge fishery in the Isle of Man (Irish Sea) resulted in emissions of 1.73 kg CO 2 /kg of scallop meat, compared with up to 4.07–13.61 kg CO 2 /kg scallop meat in the adjacent open access scallop fishery (Bloor et al ., 2021 ). At present, both the Alaskan and Isle of Man fisheries are dominated by older vessels, and it would be expected that newer, more fuel-efficient vessels could reduce the carbon footprint further.

Kg CO 2 per kg of processed product from life cycle analysis.

Data sources: crops and livestock from Poore and Nemecek (2018 ); Pollock from Zhang et al . (2022 ); Alaska bottom trawl converted by ratio of fuel used in pollock fishery (Fissel et al ., 2016 ); scallop fishery (Bloor et al ., 2021 ); Impossible Burger (Khan et al ., 2019 ); New Zealand (Mazzetto and Ledgard 2023, ); Norwegian farmed salmon (Ziegler and Hilborn, 2023 ).

Carbon stocks in seabed sediments are a large natural asset (e.g. 0.52 Pg of organic and 2 Pg of inorganic carbon in UK waters) (Parker et al ., 2020 ; Smeaton and Austin, 2022 ), and bottom-trawl fishing is the most extensive anthropogenic physical disturbance to these sediments (Legge et al ., 2020 ). The impacts of fishing on carbon stocks are currently unquantified and unregulated. The available evidence suggests that the seabed disturbance could result in greenhouse gas release (CO 2 , CH 4 , and others) from the seabed into the water column (Epstein et al ., 2022 ). A global extrapolation by Sala et al . (2021 ) suggested that seabed disturbance with mobile fishing gears releases 0.16–0.4 Pg carbon per year to the ocean, but this estimate has been widely criticized and is likely to be two orders of magnitude too high (Epstein et al ., 2022 ) (Hiddink et al ., 2023 ), meaning that mineralization of benthic carbon stores comes primarily from natural processes.

This controversy has highlighted major uncertainties in the magnitude and even the direction of the response of sediment carbon stores due to sediment mixing, resuspension, and a reduction in the bioturbation activity as a result of the loss of benthic fauna following trawling disturbance (Smeaton et al ., 2021 ; Epstein et al ., 2022 ). Knowledge about how these effects translate into changes in carbon storage and fluxes into or out of seabed sediments and across the air-sea interface showed that of 49 investigations reporting the effect of bottom trawling on seabed carbon, 61% of studies showed no significant effect, 29% reported lower organic carbon after fishing, and 10% reported higher seabed organic carbon after fishing (Epstein et al ., 2022 ). Only five studies have estimated changes in carbon mineralization and O 2 uptake, and the majority of these recorded a decrease rather than an increase in CO 2 production with trawling (e.g. Polymenakou et al ., 2005 ). With respect to potential impacts on climate change, even if trawling does significantly increase the mineralization of seabed carbon, only a fraction of it would make it into the atmosphere (Collins et al ., 2022 ). We conclude that there is little evidence that trawling increases sediment carbon mineralization significantly, even less that it impacts atmospheric CO 2 levels, but uncertainty certainly remains.

Marine benthic habitats in continental shelf regions are increasingly impacted by hypoxia [dissolved oxygen (DO) ≤2 mg L −1 ] caused by the combination of eutrophication and climate warming. Environmental hypoxia has been documented in over 400 marine systems globally and affects >240000 km 2 of coastal habitat (Diaz and Rosenberg, 2008 ; Breitburg et al ., 2018 ). The combined effects of trawling and hypoxia on benthic community biomass and seabed processes may be synergistic and disproportionally impact benthic fauna, or trawl impacts may be smaller in hypoxic areas. Despite the high annual trawling intensities in the southern Baltic Sea (each square metre of bottom is trawled seven times per year on average), van Denderen et al . (2022 ) found that the benthic community was predominantly impacted by low oxygen concentrations (DO at sites studied ranged between 0.8 and 5.8 ml O 2 L −1 ) and found neither an effect of trawling nor a synergistic effect of trawling and hypoxia. In such cases, benthic communities may be expected to benefit most from management actions targeting reductions of nutrient loads and reversing eutrophication and hypoxia. Conversely, management efforts for regulating trawling are better targeted to regions that are not in a prolonged state of hypoxia.

Hypoxia has also been demonstrated to alter catch and effort patterns. Purcell et al . (2017 ) showed that hypoxia-induced changes in the distribution of shrimp also alter the spatial dynamics of the Gulf of Mexico shrimp fleet, with potential consequences for harvest interactions and the economic condition of the fishery. Bio-economic simulations of the Gulf shrimp trawl fishery suggest that hypoxia can lead to both short-term increases or decreases in catch, depending on the effects of hypoxia on components of shrimp production (e.g. growth, mortality) and the behaviour of the fishery (e.g. catchability) (Smith et al ., 2014 ).

A common perception of trawling is that it is expanding worldwide and new areas are being impacted each year. Some have compared trawling to forest clear cutting and stated that the area trawled each year, estimated from trawl effort, speed, and width of trawl nets, is 150 times the area of forest clearcut (Watling and Norse, 1998 ). The obvious flaw in this analogy is that, for the most part, the same areas are trawled each year, and indeed, in some cases, many times each year, but you cannot clearcut the same area twice.

Amoroso et al . (2018, SM) calculated the increase in the cumulative area impacted by trawling as a function of the number of years considered using data from 32 regions of the continental shelf. They found that the trawling footprint tended to be rather stable, especially in mid-to-highly impacted regions. For example, in regions where >30% of grid cells were annually impacted by trawling, the cumulative number of cells impacted over a three-year period was at most 40% larger than the annual impact, indicating a substantial overlap in fishing areas from year to year. Using detailed tow-by-tow data by individual vessel in the British Columbia bottom trawl fleet, Branch et al . (2005 ) showed that each vessel fished over a limited number of standard locations (an average of 26 per vessel), where the vessel had previously fished, and exploration of new fishing grounds was uncommon.

Certainly some new areas have been explored, particularly in deeper waters as gear technology has permitted deeper tows, and as species distributions shift fishing effort may also shift. For the major bottom-trawl fisheries on groundfish (cod, pollock, haddock, hake, and flatfish), the annual harvest rates and catches have been declining, the total effort declining, and hence the area trawled is presumably also declining (Hilborn et al ., 2021 ). However, without a longer time series of spatial data on trawl effort, it is difficult to determine if the extent of bottom trawl footprints is expanding.

Bottom-trawl fisheries have a long history of conflict with static fishing gears that lie on the bottom, such as longlines, gillnets, and pots, and when fishing grounds overlap, interference may result in fixed gear losses and hazards for the trawls. This has led, in some circumstances, to formal or informal zoning or rotational arrangements. In many cases, inter-gear conflicts reflect competition for the same target resources between small and large-scale fleets, which has led to the establishment of exclusive coastal zones for artisanal or small-scale fisheries where trawling is banned (McConnaughey et al ., 2020 ). An example of this is the Inshore Potting Agreement (IPA), a voluntary fishery management system designed and operated by fishers of south Devon, England to reduce conflict between static-gear (pot and net) and towed-gear (trawl and dredge) fishers. The IPA is regarded as a successful fisheries management regime by fishers and managers because it has effectively allowed fishers from both sectors to operate profitably on traditional fishing grounds (Hart et al ., 2002 ). Oil and gas pipelines and communication cables laid on the seafloor are also typically in conflict with fisheries, and new demands on the seafloor, such as wind farms (Rodmell and Johnson, 2002 ; Stokesbury et al ., 2022 ), tidal power, and seabed mining, have added to the competition for space. On the West Coast of the United States, communication companies negotiated financial arrangements with trawl fleets, providing research funds administered by the trawl-fishing organizations ( https://bandoncable.org/history.asp ).

A variety of management measures reduce the impacts of bottom trawling on benthic biota and habitats, minimize bycatch, and reduce fuel usage to address sustainability goals. These measures, voluntary industry actions, and their interactions with existing management systems address conflicting societal, environmental, and economic objectives, often requiring trade-offs. They broadly consist of technical measures related to gear and operations, spatial controls, impact quotas, and fishing-effort controls. Their efficacy and practicality, alone or in combination, depend on the characteristics of the fishery, the management capacity, and the local tradeoffs between environmental effects, food security, income, and employment. Guidance has been proposed to evaluate potential best practises for a region (McConnaughey et al ., 2020 ). In most cases, compliance and performance are predicated on stakeholder engagement (Suuronen et al ., 2020 ; Suuronen, 2022 ).

Direct impacts on the benthos can be significantly reduced by gear modifications that reduce contact with the seafloor and/or penetration depth while maintaining or increasing the catchability of the target species. Impacts have been reduced with otter trawl doors that do not touch the bottom, elevated footropes, and the use of electricity to cause the fish to swim into a net that is not making bottom contact (Delaney et al ., 2022 ). An absolute prohibition of bottom trawling is the most comprehensive measure of protection and typically provides additional fishing opportunity to alternative gears and thus has been advocated for reasons other than conservation (Blyth-Skyrme et al ., 2006 ). At the same time, absolute prohibition directly affects those employed in the trawl industry and may cause redistribution of effort if the prohibition is localized. Alternative trawl restrictions include freezing the trawling footprint to prevent expansion into previously untrawled areas, but this limits a fleet's adaptability to changing fish distributions.

Particularly sensitive habitats, such as coral, sponge, and nearshore nurseries, can be effectively protected when their locations are known and closures are implemented prior to significant disturbance. Substantial invertebrate bycatch can be mitigated by voluntary or regulated movement to other areas with real-time reporting and closures; however, such “move-on” rules displace effort to similar areas, thereby expanding the overall footprint and its effects. When move-on rules were combined with tradable quotas, detailed maps of sensitive areas, and onboard observers, a substantial reduction in invertebrate bycatch was achieved in British Columbia, Canada without affecting overall fleet performance (Groenbaek et al ., 2023 ). Perhaps the simplest change is to reduce fishing effort when overfishing occurs. This reduces impacts on benthic biota and increases fishery yield (Amoroso et al ., 2018 ; McConnaughey et al ., 2020 ), which may confer economic benefits due to trip reductions and lower fuel usage but would normally have short-term negative economic impacts.

Fuel consumption is the primary source of the carbon footprint for all fishing vessels. Gear modifications that reduce contact with the seafloor reduce fuel consumption and extend gear life, which improves overall profitability if target-species catchability is maintained or nearly so. However, in some fisheries, there is a trade-off between the catchability of the target species and bycatch reduction. Gear that reduces bycatch may require more effort (and fuel) to achieve the same landings. Management measures that increase target-species abundance will normally be expected to increase catch rates and thus lower fuel use per tonne captured. Newly constructed vessels tend to have reduced fuel use as a major design criterion.

Many of the same measures that reduce benthic impacts and reduce fuel use are also used to manage bycatch and reduce discards. Technical, administrative, and economic measures include modifications to fishing gear or fishing practises, time and area restrictions, bycatch limits, effort restrictions, and discard bans (i.e. landing obligations), and may also lead to active avoidance of high bycatch areas and involve cooperative fleet communications, awareness raising, and training (Pascoe, 1997 ; Suuronen and Gilman, 2020 ; Suuronen et al ., 2020 ). Technical measures to manage trawling bycatch are based on a large body of empirical experiments intended to improve species- and size-selectivity by modifying gear and operations (Kennelly and Broadhurst, 2021 ), with attention paid to unobserved mortality rates (Rose et al ., 2013 ). Real-time closures involving move-on protocols may be effective in dynamic situations where the bycatch level is unpredictable. Bycatch quotas or limits on “choke species” are incentives to avoid premature closures of target fisheries before quota uptake is achieved. Measures to limit effort are based on the simple rationale that less effort equates to less bycatch (Alverson et al ., 1994 ). An outright discard ban, where all catches of species or stocks with an established TAC or covered by minimum landing size regulations must be kept on board, landed, and deducted from established quotas, was implemented by the EU Common Fisheries Policy and represents a fundamental regulatory shift from landings to catches (Karp et al ., 2019 ), but has proven ineffective because of numerous exceptions and the difficulty in implementation and enforcement (Uhlmann et al ., 2019 ; Borges, 2021 ).

Management measures that minimize the footprint of fishing have been shown in one study to lead to higher yields than measures that spread fishing activity more widely and evenly across the seabed (Bloor et al ., 2021 ). This was demonstrated in a case study in the Isle of Man, where a territorial use rights-based fishery ring-fenced vulnerable habitat from fishing while demarcating a fishing zone within the management system. Pre-open season fishery surveys directed fishing activity specifically to high-density aggregations of target species (scallops), thereby increasing the efficiency with which the total allowable catch was taken and reduced the amount of seabed impacted to a negligible level (3% of the available area for fishing; Bloor et al ., 2021 ). Using such approaches or regulating the overall fishing mortality rate proportionally mitigates the indirect effects of bottom trawling.

Bottom trawling, like other forms of fishing, may cause bycatch of species of conservation concern; the best known is the bycatch of turtles. Technical solutions, in the form of turtle excluder devices, have been shown to be very effective at reducing turtle bycatch (Magnuson et al ., 1990 ) (Jenkins, 2012 ). Similarly, excluder devices for marine mammal bycatch have been implemented and shown to be effective (Hamilton and Baker, 2015 ).

A significant obstacle in bycatch reduction has been the limited uptake by fishers of remedial changes proposed that they consider inconvenient and costly (Suuronen, 2022 ). Some demersal trawl fleets have made great strides in reducing bycatch, and the bottom-trawl fishery for flatfish in the Bering Sea now has only 6–8% bycatch of all species (personal communication Phil Ganz, NMFS). This reduction has been achieved primarily by bycatch limits and fleet coordination providing strong incentives for vessels to avoid areas with high bycatch. This example serves as an aspirational target for other trawl fisheries.

It is possible to capture some of the same species caught with bottom trawls with other gears. However, transitioning from one gear type to another is seldom easy or practical and has many uncertainties and economic risks (Suuronen et al ., 2012 ). The size and design of existing fishing vessels and their machinery often limit the possibilities of changing the fishing method. Furthermore, fishing practises have evolved over time and are often “tailor-made” to particular species and conditions.

Pots and longlines have been demonstrated to be an economically viable fishing method for Pacific cod and sablefish in the Gulf of Alaska and the Bering Sea (Thomsen et al ., 2010 ), and such gears can be more species- and size-selective in addition to having a lower benthic impact. In some circumstances, bottom seining can be used. The seine net is lighter in construction, but the area swept can be 1.25–10 times larger than other bottom trawling. Because there are no trawl doors or warps, there is less pressure on the seabed. Nonetheless, there are several operational limitations in bottom seine fisheries, and it can be an alternative for bottom trawling only in specific cases (Suuronen et al ., 2012 ). As with all fishing methods, increasing the use of pots and longlines will increase the risk of entanglement and bycatch of species of concern, for example, right whales in the Gulf of St. Lawrence, which interact with lobster fisheries.

There does not appear to be an economically viable alternative to bottom trawling to catch high volumes of flatfish, and bottom trawling or dredges appear to be the only effective method for capturing offshore scallops, clams, and certain species of shrimp.

The use of electric stimulation (e.g. in pulse trawling) (Soetaert et al ., 2015 ) and lights (Lomeli et al ., 2021 ) to lift fish off the bottom and reduce the need for bottom contact has been highly developed. Scientific trials have shown that pulse trawls reduce the mortality of non-target invertebrate benthic megafauna, discards, and fuel emissions compared to the conventional tickler chain beam trawl (ICES, 2018 ; Bergman and Meesters, 2020 ). Nevertheless, in early 2019, the European Union parliament decided to forbid any pulse trawling after July 2021 due to concerns over possible damage to fauna from electrical stimulation.

All food production has multidimensional environmental impacts, including fuel use, carbon footprint, water use, nutrient release into water, soil, and atmosphere, acidifying compound release, antibiotics use, toxic chemical use, including pesticides and herbicides, soil erosion, and introduction of exotic species and diseases in aquaculture, livestock, and for pest control. There is an extensive literature of some of these impacts using life cycle assessment (LCA) that covers some of these metrics (for instance, see the meta-analysis in Hilborn et al ., 2018 ; Tlusty et al ., 2019 ).

In the following sections, we present data comparing the environmental impacts of different forms of food production. But in comparing bottom trawling to other food production systems, two issues arise. There are relatively few LCAs of trawling, but more of capture fisheries and individual LCAs differ in whether the impacts are limited to harvesting, or also include consideration of processing, transport, and retail. As a generalization, all capture fisheries use no antibiotics, no fertilizer or pesticides, do not introduce exotic species, do not cause soil erosion, and use very little freshwater. The use of fuel in capture fisheries releases some acidifying compounds, and toxic antifouling paint is used. However, processing and packaging require considerable amounts of water, and a range of toxic substances may be used in the manufacture of the packaging. The environmental impacts may be dramatically different depending on the product form. For instance, Vázquez-Rowe et al . (2014 ) found 50-fold differences in water demand between canned and fresh sardines. The sample size of bottom trawl LCAs is too small to do a realistic comparison to livestock or crops for anything except energy use and carbon footprint.

Carbon footprint

Table 3 compares the carbon footprint of processed products from LCA of crops, livestock, and capture fisheries. The average carbon footprint for bottom-trawl fisheries from published LCAs is higher than all other foods listed except beef and much higher than plant-based foods. But we include the three bottom-trawl fisheries that represent the most well-managed in terms of stock condition and capacity management, and these show carbon footprints below chicken and pork but above crops. The Alaska pollock fishery uses midwater gear but is estimated to be in bottom contact roughly half the time, so it is included here. These cases illustrate that bottom trawling does not necessarily have a high carbon footprint, and the high carbon footprint of bottom-trawl fisheries on average reflects the fact that most of the LCA studies of trawl fisheries have a competitive race-to-fish feature and stock abundance is relatively poor.

The Impossible Burger is included because it is the only example we know of for which a plant-based meat or fish imitation has had an LCA performed, and this product is frequently billed as more environmentally friendly because it is plant-based.

Biodiversity

Under an ecosystem-based approach to fisheries management, the sustainability of fisheries is assessed considering both the impact on the target species and on the marine ecosystem. Both the MSC standard and the Seafood Watch scoring criteria consider bycatch of species of concern and impacts on habitat. But when we consider calls to greatly reduce or ban trawling, we must consider the consequences not only to the marine ecosystem, but the ecosystem consequences in both the ocean and on land if that food production is replaced by other fisheries, aquaculture, agriculture, and livestock. The most likely aquaculture replacement for trawl-caught fish is through fed aquaculture, which largely relies on crops as feed, as does almost all livestock production. Crop production, whether directly for human consumption or feed for livestock and aquaculture, replaces the natural, although potentially degraded, ecosystem with a totally artificial monoculture, intentionally removing the native vegetation and any biota dependent upon that. The most prominent cause of extinction risk is agriculture (IUCN, 2020 ), and the impact of agriculture on biodiversity has been shown to be the most significant form of land use after urbanization (Newbold et al ., 2015 ). LCAs have not provided useful data on the biodiversity impacts of food production systems.

One of the few studies to directly compare a wide range of biodiversity between farming and undisturbed habitat was done in Tanzania. The study compared small-scale farmland to the adjacent Serengeti National Park and to biodiversity in a nearby national park. Hilborn and Sinclair (2021 ) found that the primary producers, grasses, shrubs, and trees on farmland had been reduced by 80–90%, and the ungulates, birds, and predators that depend on the primary producers were all reduced by over 80%. Only rodents were more abundant in the farmland. In contrast, even the places most heavily impacted by trawling are transformed less than by agriculture. As we saw earlier, well-managed trawl fisheries uniformly reduce benthic ecosystem biota in sand, mud, and gravel systems by <10% (Mazor et al ., 2021 ). Hilborn and Sinclair (2021 ) also summarize data from 26 marine ecosystem models used to compare current fished conditions to unfished conditions. They found no significant change in trophic levels 1, 2, and 3 due to fishing, and only a 10% reduction in the abundance of trophic level 4 and a 30% reduction of trophic level 5. While the total abundance of a trophic level may not be the most relevant measure of fishing impact, it does illustrate the fact that lower trophic levels in marine ecosystems are largely unaffected by fishing—although individual species may be. In contrast, agriculture intentionally removes the lowest trophic levels.

Perhaps the clearest difference between the ecosystem impacts of marine capture fisheries and agriculture’s impact on terrestrial systems is encapsulated in the MSC’s Principle 2, which states, “Fishing operations should allow for the maintenance of the structure, productivity, function, and diversity of the ecosystem on which the fishery depends. The ecosystem includes habitat and associated dependent and ecologically related species.” Many trawl fisheries have met this standard, yet no form of large-scale crop production could do so, whether for direct human consumption or as feed for livestock or aquaculture.

Other impacts

Catching fish in the ocean uses no pesticides or fertilizer, almost no freshwater, and no antibiotics (Sharpless and Evans, 2013 ). The global impacts from these would be increased if bottom trawling was banned and/or agriculture or aquaculture increased to compensate, although there are significant differences in these impacts among cropping systems. Crops grown on unirrigated land do not require water other than rainfall to grow, and organic agriculture does not use antibiotics, synthetic fertilizers, or pesticides, although organic fertilizer contributes to significant nutrient release and hypoxia. Livestock raised in natural habitats has far less impact on native flora and fauna than the land transformation required for crop production.

A major issue for many forms of agriculture is exotic pests, and one method used to control these has been the introduction of exotic predators. This has often had a serious impact on native species (Hoddle, 2004 ), with the cane toad introduction in Australia perhaps the best known.

Aquaculture deserves special consideration because it is the most obvious immediate substitute for food produced by trawling. There are two basic types of aquaculture: those species cultured with feed supplied by the grower and those that feed themselves. Unfed production systems typically have a very low impact (Hilborn, 2018 ), with farmed seaweed, and mollusks having a particularly low impact. But the species of fish grown in aquaculture most similar, or identical to those from bottom-trawl fisheries are almost all fed, primarily from crops as well as fish meal from capture fisheries. While aquaculture species often are more efficient converters of feed to flesh than livestock, fed aquaculture has a higher environmental impact relative to capture fisheries across most measures (Hilborn, 2018 ).

Another concern about aquaculture is how diseases, both endemic and exotic, which have been a recurring problem in aquaculture (Diana, 2009 ), negatively impact native species.

Summary of the comparison of environmental impacts of bottom trawling to alternative foods

Bottom trawling appears to have a lower impact on most environmental indicators than most other food production systems and, on average, has a higher carbon footprint. There are efforts to reduce the impact of every food production system by technical innovation and changing practise among producers. In bottom-trawl fisheries, fuel consumption and carbon footprint can be reduced by new designs of doors and nets, more efficient vessel engines, better management of fish stocks, and restructuring access to fishing quotas to eliminate competitive fishing. We saw three examples in  Table 3 of how successful these efforts can be. Similar efforts are underway to reduce the amount of water needed to grow crops and to lower pesticide, fertilizer, and antibiotic use. Thus, the comparisons made here are not static, and we would expect the various impacts to decline over time in all the food production systems.

Our synthesis of information on the relative sustainability of food production systems has brought to attention improvements needed to better assess fishing with bottom trawls and guide management measures or industry actions for meeting sustainability goals. In particular, a global assessment requires studies of the unknown carbon footprint of fuel consumption by the Asian and African fleets, as well as new data from Europe to reflect contemporary fishery conditions. Subsequently, comprehensive LCAs of bottom trawling, including loads and impacts for the harvesting, processing, transport, and retail components, are needed for a more informed sustainability evaluation and for comparisons with other food production systems.

Bottom trawling is a food production method that has environmental impacts. However, trawling impacts are well below most animal-source foods from livestock or fed aquaculture for many categories of impacts such as water use, antibiotic use, and nutrient release. We suggest that while banning bottom trawling would decrease marine impacts, it would actually increase negative global environmental impacts as trawl caught foods would be replaced with those of terrestrial origin or aquaculture species fed largely with higher-impact crops. The negative environmental impacts of bottom trawling have been reduced by maintaining stocks at high abundance with low fishing mortality rates, eliminating the race to fish through cooperative fisheries, bycatch limits that incentivize bycatch avoidance (Calderwood et al ., 2023 ), technical modification of fishing gear to reduce or eliminate bottom contact and bycatch (Bloor et al ., 2021 ), fuller utilization of lower-value species that would otherwise be discarded, and reduction of subsidies—especially fuel subsidies that encourage inefficient fisheries and increase CO 2 emissions. These proven management measures and voluntary actions are adaptable to a range of local conditions (McConnaughey et al ., 2020 ) and, if applied on a global basis, would dramatically reduce the negative environmental impacts of bottom trawling.

The overall sustainability of bottom-trawl fisheries is perhaps best demonstrated by the 83 bottom-trawl fisheries that are currently certified by the MSC, which represent 252 individual fishery species units of certification. Collectively, MSC-certified fisheries constitute 50% of the global harvest of groundfish stocks summarized in Hilborn et al ., ( 2021 ). Taking this as a measure of progress, it is largely confined to large industrial fisheries in temperate latitudes. However, MSC certification of bottom trawls is not totally confined to groundfish; 48 of the bottom trawl units of certification are for shrimp, prawns, nephrops, or scallops. The evidence is that bottom-trawl fisheries can be well managed and be considered sustainable, but many fisheries using bottom trawl gear need to improve their performance to meet current standards.

Alaska groundfish fleet age data came from J. Lee. Alaska Fisheries Science Center reviewers who provided suggestions on this manuscript were G. Harrington, M. Martin, and R. Reuter. Dr Michael Melnychuk retrieved data on MSC certification of bottom-trawl fisheries from MSC data bases.

No new data were assembled for this project.

All authors contributed to the writing and editing of the paper.

No specific funding was received for this paper, but all of the authors were part of a study group entitled “Trawling best practices” that has produced over a dozen papers on trawl footprints and the impacts of trawling on benthic biota. The project was initially funded by the Walton Family Foundation and the David and Luciele Packard Foundation, with later funding from FAO, the Australian Government through CSIRO, and several fishing companies. The authors have received funds from a range of sources including governments, foundations, nongovernmental organizations, and industries that have interests in conservation, sustainable use, and effective fisheries management—which may be perceived as a conflict of interest. However, the authors declare that neither these nor any other interests have directly or indirectly influenced the objectivity of this paper, and the findings and conclusions in the paper are those of the authors alone, independent of their organizations or funding sources. Several authors have current or past relationships with the Marine Stewardship Council. MJK was formerly the Science & Standards Director of the MSC from 2018–2019. JGH has funding from MSC for two projects. AMP is part of a project funded by MSC. No other authors have funding or relationships with MSC.

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