Product Code Database
A wild fishery is a natural body of water with a sizeable free-ranging fish or other aquatic animal ( and ) population that can be fishing for its commercial value. Wild fisheries can be marine (seawater) or lacustrine/riverine (freshwater), and rely heavily on the carrying capacity of the local aquatic ecosystem.
Wild fisheries are sometimes called capture fisheries. The aquatic life they support is not artificially controlled in any meaningful way and needs to be "captured" or fished. Wild fisheries exist primarily in the oceans, and particularly around and continental shelves, but also exist in and . Issues with wild fisheries are overfishing and Marine pollution. Significant wild fisheries have collapsed or are in danger of collapsing, due to overfishing and pollution. Overall, production from the world's wild fisheries has levelled out, and may be starting to decline.
As a contrast to wild fisheries, fish farm can operate in sheltered coastal waters, in rivers, lakes and , or in enclosed bodies of water such as pools or . Farmed fisheries are technological in nature, and revolve around developments in aquaculture. Farmed fisheries are expanding, and China aquaculture in particular is making many advances. Nevertheless, the majority of fish consumed by humans continues to be sourced from wild fisheries. As of the early 21st century, fish is humanity's only significant wild food source.
| The productivity of marine fisheries is largely determined by marine topography, including its interaction with and the diminishment of sunlight with depth.
Marine topography is defined by various coastal and oceanic landforms, ranging from coastal Estuary and ; to continental shelves and ; to underwater and deep sea features such as ocean rises and . |
| map.]] An ocean current is continuous, directed movement of ocean water. Ocean currents are rivers of relatively warm or cold water within the ocean. The currents are generated from the forces acting upon the water like the planet rotation, the wind, the temperature and salinity (hence isopycnal) differences and the tide. The , the and other currents influence the current's direction and strength. |
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can flow for thousands of kilometers. Surface ocean currents are generally wind driven and develop their typical clockwise spirals in the northern hemisphere and counter-clockwise rotation in the southern hemisphere because of the imposed wind stresses. In wind driven currents, the Ekman spiral effect results in the currents flowing at an angle to the driving winds. The areas of surface ocean currents move somewhat with the ; this is most notable in equatorial currents.
Deep ocean currents are driven by density and temperature gradients. Thermohaline circulation, also known as the ocean's conveyor belt, refers to the deep ocean density-driven ocean basin currents. These currents, which flow under the surface of the ocean and are thus hidden from immediate detection, are called . Upwelling and downwelling areas in the oceans are areas where significant vertical movement of ocean water is observed. Surface currents make up about 10% of all the water in the ocean. Surface currents are generally restricted to the upper 400 meters of the ocean. The movement of deep water in the ocean basins is by density driven forces and gravity. The density difference is a function of different temperatures and salinity. Deep waters sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase. The main causes of currents are: solar heating, winds and gravity. Ocean currents are also very important in the dispersal of many life forms. A dramatic example is the eel story. Currents also determine the disposition of marine debris. |
are large-scale ocean currents caused by the Coriolis effect. Wind-driven surface currents interact with these gyres and the underwater topography, such as seamounts and the edge of continental shelves, to produce downwellings and . Wind Driven Surface Currents: Upwelling and Downwelling These can transport nutrients and provide feeding grounds for plankton eating forage fish. This in turn draws larger fish that prey on the forage fish, and can result in productive fishing grounds. Most upwellings are coastal, and many of them support some of the most productive fisheries in the world, such as small pelagics (sardines, anchovies, etc.). Regions of upwelling include coastal Peru, Chile, Arabian Sea, western South Africa, eastern New Zealand and the California coast. |
* The Humboldt Current. This gyre produces a cold, low-salinity ocean current that flows north-westward along the west coast of South America from the southern tip of Chile to northern Peru. This results in the most prominent upwelling system in the world, supporting an extraordinary abundance of marine life. Upwelling occurs off Peru year-round and off Chile during the spring and summer. Approximately 18-20% of the world's fish catch comes from the Humboldt Current LME. The species are mostly pelagic: , anchovy and jack mackerel. The LME's high primary and secondary productivity supports other important fishery resources as well as marine mammals.
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produced by photosynthesis from September 1997 to August 2000. This is a rough indicator of the primary production potential in the oceans. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE.]]
In the ocean, the food chain typically follows the course:
Phytoplankton is usually the primary producer (the first level in the food chain or the first trophic level). Phytoplankton converts inorganic carbon into protoplasm. Phytoplankton is consumed by microscopic animals called zooplankton. These are the second level in the food chain, including krill, the larva of fish, squid, lobsters and crabs –as well as the small called , and many other types. Zooplankton is consumed by other, larger predatory zooplankton, fish, and baleen whales. Top ocean predators such as sharks, large seals, and dolphins then eat the fish or other organisms that eat zooplankton. Trophic levels differ among food webs around the world, for example, whales may consume zooplankton directly - leading to an environment with one less trophic level compared to an environment where the predator does not eat the zooplankton directly. |
Global primary production can be estimated from satellite observations. Satellites scan the NDVI (NDVI) over terrestrial habitats, and scan sea-surface chlorophyll levels over oceans. This results in 56.4 billion Organic carbon/yr (53.8%), for terrestrial primary production, and 48.5 billion tonnes C/yr for oceanic primary production. Thus, the total photoautotrophic primary production for the Earth is about 104.9 billion tonnes C/yr. This translates to about 426 gC/m2/yr for land production (excluding areas with permanent ice cover), and 140 gC/m2/yr for the oceans. However, there is a much more significant difference in standing stocks - while accounting for almost half of total annual production, oceanic account for only about 0.2% of the total biomass. The most successful animal species, in terms of biomass, is probably the Antarctic krill, Euphausia superba, with a biomass of about 500 million .Ross, R. M. and Quetin, L. B. (1988). Euphausia superba: a critical review of annual production. Comp. Biochem. Physiol. 90B, 499-505. However, as a group, the small aquatic called form the largest animal biomass on earth. Biology of Copepods at Carl von Ossietzky University of Oldenburg | ||||||
| (million km2) | (gram dryC / m2 / year) | (billion tonnes / year) | (kg dryC / m2) | (billion tonnes) | (years) | |
| Open ocean | 332.00 | 125.00 | 41.50 | 0.003 | 1.00 | 0.02 |
| Upwelling zones | 0.40 | 500.00 | 0.20 | 0.02 | 0.01 | 0.04 |
| Continental shelf | 26.60 | 360.00 | 9.58 | 0.01 | 0.27 | 0.03 |
| Algae and | 0.60 | 2,500.00 | 1.50 | 2.00 | 1.20 | 0.80 |
| Estuary & mangroves | 1.40 | 1,500.00 | 2.10 | 1.00 | 1.40 | 0.67 |
| Total marine | 361.00 | 152.01 | 54.88 | 0.01 | 3.87 | 0.07 |
| and | 2.00 | 250.00 | 0.50 | 0.02 | 0.04 | 0.08 |
| Terrestrial | 147.00 | 554.51 | 114.90 | 12.55 | 1,873.38 | 16.15 |
| Grand total | 510.00 | 333.87 | 170.28 | 3.68 | 1,877.29 | 11.02 |
| Source: ; Ecological Studies Vol 14 (Berlin) Darci and Taylre are biomass specialists. | ||||||
| Aquatic habitats have been classified into marine and freshwater by the Worldwide Fund for Nature (WWF). An ecoregion is defined as a "relatively large unit of land or water containing a characteristic set of natural communities that share a large majority of their species, dynamics, and environmental conditions (Dinerstein et al. 1995, TNC 1997). List of the Global 200 |
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Continental shelves are the extended perimeters of each continent and associated coastal plain, which is covered during Ice age such as the current epoch by relatively shallow (known as shelf seas) and gulfs. The shelf usually ends at a point of decreasing slope (called the shelf break). The sea floor below the break is the continental slope. Below the slope is the continental rise, which finally merges into the deep ocean floor, the abyssal plain. The continental shelf and the slope are part of the continental margin. Continental shelves are shallow (averaging 140 metres or 460 feet), and the sunlight available means they can teem with life. The shallowest parts of the continental shelf are called fishing banks. Fishing bank (2008) In Encyclopædia Britannica. Retrieved July 26, 2008, from Encyclopædia Britannica Online There the sunlight penetrates to the seafloor and the plankton, on which fish feed, thrive. |
| The character of the shelf changes dramatically at the shelf break, where the continental slope begins. With a few exceptions, the shelf break is located at a remarkably uniform depth of roughly ; this is likely a hallmark of past ice ages, when sea level was lower than it is now.Gross 43.
The width of the continental shelf varies considerably – it is not uncommon for an area to have virtually no shelf at all, particularly where the forward edge of an advancing oceanic crust dives beneath continental crust in an offshore subduction zone such as off the coast of Chile or the west coast of Sumatra. The largest shelf – the Siberian Shelf in the Arctic Ocean – stretches to 1500 (930 ) in width. The South China Sea lies over another extensive area of continental shelf, the Sunda Shelf, which joins Borneo, Sumatra, and Java to the Asian mainland. Other familiar bodies of water that overlie continental shelves are the North Sea and the Persian Gulf. The average width of continental shelves is about . The depth of the shelf also varies, but is generally limited to water shallower than 150 metre (490 ft).Pinet, 37. Combined with the sunlight available in shallow waters, the continental shelves teem with life compared to the biotic desert of the oceans' abyssal plain. The pelagic (water column) environment of the continental shelf constitutes the neritic zone, and the benthic (sea floor) province of the shelf is the sublittoral zone.Pinet 316-17, 418-19. |
| are aragonite structures produced by living organisms, found in shallow, tropical marine waters with little to no nutrients in the water. High nutrient levels such as those found in runoff from agricultural areas can harm the reef by encouraging the growth of algae. Although corals are found both in temperate and tropical waters, reefs are formed only in a zone extending at most from 30°N to 30°S of the equator. |
| Coral reefs are estimated to cover 284,300 square kilometres, with the Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) accounting for 91.9% of the total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including Australia accounts for 40.8%. Atlantic and Caribbean coral reefs only account for 7.6% of the world total.Spalding, Mark, Corinna Ravilious, and Edmund Green. 2001. World Atlas of Coral Reefs. Berkeley, CA: University of California Press and UNEP/WCMC.
Coral reefs are either restricted or absent from the west coast of the Americas, as well as the west coast of Africa. This is due primarily to upwelling and strong cold coastal currents that reduce water temperatures in these areas.Nybakken, James. 1997. Marine Biology: An Ecological Approach. 4th ed. Menlo Park, CA: Addison Wesley. Corals are also restricted from off the coastline of South Asia from Pakistan to Bangladesh. They are also restricted along the coast around northeastern South America and Bangladesh due to the release of vast quantities of freshwater from the Amazon River and Ganges Rivers respectively. Famous coral reefs and reef areas of the world include:
Coral reefs support an extraordinary biodiversity; although they are located in nutrient-poor tropical waters. The process of nutrient cycling between corals, zooxanthellae, and other reef organisms provides an explanation for why coral reefs flourish in these waters: recycling ensures that fewer nutrients are needed overall to support the community. Coral reefs are home to a variety of tropical or reef fish, such as the colorful parrotfish, Pomacanthidae, damselfish, and butterflyfish. Other fish groups found on coral reefs include , Lutjanidae, Haemulidae and . Over 4,000 species of fish inhabit coral reefs. It has been suggested that the high number of fish species that inhabit coral reefs are able to coexist in such high numbers because any free living space is rapidly inhabited by the first planktonic fish larvae that occupy it. These fish then inhabit the space for the rest of their life. The species that inhabit the free space is random and has therefore been termed 'a lottery for living space'.Coexistence of coral reef fishes—a lottery for living space PF Sale 1978 - Environmental Biology of Fishes, 1978 Reefs are also home to a large variety of other organisms, including sea sponge, (which includes some types of corals and jellyfish), , (including shrimp, and ), (including ), (including starfish, sea urchins and Holothuroidea), , and .Castro, Peter and Michael Huber. 2000. Marine Biology. 3rd ed. Boston: McGraw-Hill. Human activity may represent the greatest threat to coral reefs living in Earth's oceans. In particular, pollution and over-fishing are the most serious threats to these ecosystems. Physical destruction of reefs due to boat and shipping traffic is also a problem. The live food fish trade has been implicated as a driver of decline due to the use of cyanide and disaster for peoples living in the tropics. Hughes, et al., (2003), writes that "with increased World population and improved storage and transport systems, the scale of human impacts on reefs has grown exponentially. For example, markets for fishes and other have become global, supplying demand for reef resources far removed from their tropical sources."Hughes, et al. 2003. Climate Change, Human Impacts, and the Resilience of Coral Reefs. Science. Vol 301 15 August 2003 Currently researchers are working to determine the degree various factors impact the reef systems. The list of factors is long but includes the oceans acting as a carbon dioxide sink, changes in Earth's atmosphere, ultraviolet light, ocean acidification, biological virus, impacts of dust storms carrying agents to far flung reef systems, various pollutants, impacts of and others. Reefs are threatened well beyond coastal areas and so the problem is broader than factors from land development and pollution though those are too causing considerable damage. Southeast Asian coral reefs are at risk from damaging fishing practices (such as Cyanide fishing and blast fishing), overfishing, sedimentation, pollution and bleaching. A variety of activities, including education, regulation, and the establishment of marine protected areas are under way to protect these reefs. Indonesia, for example has nearly of coral reefs. Its waters are home to a third of the world's total corals and a quarter of its fish species. Indonesia's coral reefs are located in the heart of the Coral Triangle and have been victim to destructive fishing, unregulated tourism, and bleaching due to climatic changes. Data from 414 reef monitoring stations throughout Indonesia in 2000 found that only 6% of Indonesia's coral reefs are in excellent condition, while 24% are in good condition, and approximately 70% are in poor to fair condition (2003 The Johns Hopkins University). General estimates show approximately 10% of the coral reefs around the world are already dead.Save Our Seas, 1997 Summer Newsletter, Dr. Cindy Hunter and Dr. Alan FriedlanderTun, K., L.M. Chou, A. Cabanban, V.S. Tuan, Philreefs, T. Yeemin, Suharsono, K.Sour, and D. Lane, 2004, p:235-276 in C. Wilkinson (ed.), Status of Coral Reefs of the world: 2004. Problems range from environmental effects of fishing techniques, described above, to ocean acidification.Kleypas, J.A., R.A. Feely, V.J. Fabry, C. Langdon, C.L. Sabine, and L.L. Robbins, 2006, Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers: A guide for Future Research, NSF, NOAA, & USGS, 88 pp. Coral bleaching is another manifestation of the problem and is showing up in reefs across the planet. Inhabitants of Ahus Island, Manus Province, Papua New Guinea, have followed a generations-old practice of restricting fishing in six areas of their reef lagoon. While line fishing is permitted, net and spear fishing are restricted based on cultural traditions. The result is that both the biomass and individual fish sizes are significantly larger in these areas than in places where fishing is completely unrestricted.Cinner, J. et al. (2005). Conservation and community benefits from traditional coral reef management at Ahus Island, Papua New Guinea. Conservation Biology 19 (6), 1714–1723 It is estimated that about 60% of the world's reefs are at risk due to destructive, human-related activities. The threat to the health of reefs is particularly strong in Southeast Asia, where an enormous 80% of reefs are considered endangered. Organisations as Coral Cay, Counterpart 'The Coral Gardener'-documentary on coral gardening by Counterpart and the Foundation of the peoples of the South Pacific are currently undertaking coral reef/atoll restoration projects. They are doing so using simple methods of plant propagation. Other organisations as Practical Action have released informational documents on how to set up coral reef restoration to the public. |
| In the deep ocean, much of the ocean floor is a flat, featureless underwater desert called the abyssal plain. Many pelagic fish Fish migration across these plains in search of spawning or different feeding grounds. Smaller migratory fish are followed by larger predator fish and can provide rich, if temporary, fishing grounds.
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| A seamount is an underwater mountain, rising from the seafloor that does not reach to the water's surface (sea level), and thus is not an island. They are defined by Oceanography as independent features that rise to at least 1,000 meters above the seafloor. Seamounts are common in the Pacific Ocean. Recent studies suggest there may be 30,000 seamounts in the Pacific, about 1,000 in the Atlantic Ocean and an unknown number in the Indian Ocean.Morato, Telmo. Seamounts – hotspots of marine life. ICES. Retrieved 19 June 2008. |
| Seamounts often project upwards into shallower zones more hospitable to sea life, providing habitats for marine species that are not found on or around the surrounding deeper ocean bottom. In addition to simply providing physical presence in this zone, the seamount itself may deflect deep currents and create upwelling. This process can bring nutrients into the photosynthetic zone, producing an area of in an otherwise desert-like open ocean. Seamounts may thus be vital stopping points for some migratory animals such as . Some recent research indicates whales may use such features as navigational aids throughout their migration.
Due to the larger populations of fish in these areas overexpoitation by the fishing industry has caused some seamount fauna populations to decrease considerably.
The primary productivity of the epipelagic waters above the submerged peak can often be enhanced by the hydrography conditions of the seamount.Boehlert, G. W. and Genin, A. 1987. A review of the effects of seamounts on biological processes. 319-334. Seamount, islands and atolls. Geophysical Monograph 43, edited by B. H. Keating, P. Fryer, R. Batiza, and G. W. Boehlert. This increases the densities of the zooplankton and leads to the high concentrations of fish in these areas. Another theory for this is that the fish are sustained on the diurnal migration of zooplankton being interrupted by the presence of the seamount, and causing the zooplankton to stay in the area. It is also possible that the high densities of fishes has more to do with the fish life histories and interaction with the benthic fauna of the seamount. The benthic fauna of the seamounts is dominated by suspension feeders, including sea sponge and true . For some seamounts that peaks at 200–300 metres below the surface benthic macroalgae is common. The sedimentary infauna is dominated by polychaete worms. For a long time it has been surmised that many pelagic animals visit seamounts to gather food, but proof this of this aggregating effect has been lacking. The first demonstration of this conjecture has recently been published Morato, T., Varkey, D.A., Damaso, C., Machete, M., Santos, M., Prieto, R., Santos, R.S. and Pitcher, T.J. (2008) Evidence of a seamount effect on aggregating visitors. Marine Ecology Progress Series 357: 23-32. During the 1960s, Russia, Australia and New Zealand started to look for new stocks of fish and began to trawl the seamounts. The majority of the invertebrates brought up are corals, and are mainly used for the jewelry trade. The two major fish species were the orange roughy ( Hoplostethus atlanticus) and pelagic armourhead ( Pseudopentaceros wheeleri), which were quickly overexploited due to lack of knowledge of the longevity of the fish, late maturity, low fecundity, small geographic range and recruitment to the fishery. As well as the fishes being overexploited the benthic communities were destroyed by the trawling gear.Black, Richard (2004) Deep-sea trawling's great harm BBC.
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Freshwater fisheries are essential to supporting human life around the globe whether they are used for recreation or commercial use. Climate change presents several challenges in sustaining these fisheries as waters become warmer resulting in decreased dissolved oxygen, as the toxicity of pollutants increases, and as the physiological changes in fishes and changes in their habitat systems alter what we are used to. Deoxygenation and eutrophication are two major effects that are detrimental to fish and ecosystem health and the problem is more prevalent as the size of the body of water decreases. Details on the changes occurring in fish physiology and their habitats can be found at the respective citation.
Increased management and surveillance on freshwater fisheries will be vital to the longevity, sustainability, and productivity of the fisheries and essential to maintaining our food production from that source.
Discarded , six-pack rings and other forms of plastic waste which finish up in the ocean present dangers to wildlife and fisheries. Algalita.org Aquatic life can be threatened through entanglement, suffocation, and ingestion. UNEP.org Louisiana Fisheries - Fact Sheets
Nurdles, also known as mermaids' tears, are plastic pellets typically under five millimetres in diameter, and are a major contributor to marine debris. They are used as a raw material in plastics manufacturing, and are thought to enter the natural environment after accidental spillages. Nurdles are also created through the physical weathering of larger plastic debris. They strongly resemble fish eggs, only instead of finding a nutritious meal, any marine wildlife that ingests them will likely starve, be poisoned and die.
Many animals that live on or in the sea feeding flotsam by mistake, as it often looks similar to their natural prey. Plastic debris, when bulky or tangled, is difficult to pass, and may become permanently lodged in the digestive tracts of these animals, blocking the passage of food and causing death through starvation or infection. Tiny floating particles also resemble zooplankton, which can lead filter feeders to consume them and cause them to enter the ocean food chain. In samples taken from the North Pacific Gyre in 1999 by the Algalita Marine Research Foundation, the mass of plastic exceeded that of zooplankton by a factor of six. More recently, reports have surfaced that there may now be 30 times more plastic than plankton, the most abundant form of life in the ocean.
Toxic plastic additive used in the manufacture of plastic materials can out into their surroundings when exposed to water. Waterborne hydrophobic pollutants adsorption of plastic debris, thus making plastic far more deadly in the ocean than it would be on land. Hydrophobic contaminants are also known to bioaccumulate in fatty tissues, biomagnification up the food chain and putting great pressure on . Some plastic additives are known to disrupt the endocrine system when consumed, others can suppress the immune system or decrease reproductive rates.
Such toxins can accumulate in the tissues of many species of aquatic life in a process called bioaccumulation. They are also known to accumulate in benthic environments, such as estuary and : a geological record of human activities of the last century.
Some specific examples are
The biggest culprit are rivers that empty into the ocean, and with it the many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. An excess of oxygen depleting chemicals in the water can lead to hypoxia and the creation of a dead zone.Gerlach: Marine Pollution, Springer, Berlin (1975)
Surveys have shown that 54% of lakes in Asia are eutrophic; in Europe, 53%; in North America, 48%; in South America, 41%; and in Africa, 28%.ILEC/Lake Biwa Research Institute Eds. 1988–1993 Survey of the State of the World's Lakes. Volumes I-IV. International Lake Environment Committee, Otsu and United Nations Environment Programme, Nairobi. estuary also tend to be naturally eutrophic because land-derived nutrients are concentrated where run-off enters the marine environment in a confined channel. The World Resources Institute has identified 375 hypoxic coastal zones around the world, concentrated in coastal areas in Western Europe, the Eastern and Southern coasts of the US, and East Asia, particularly in Japan.
Selman, Mindy (2007) Eutrophication: An Overview of Status, Trends, Policies, and Strategies. World Resources Institute. In the ocean, there are frequent red tide algae blooms that kill fish and marine mammals and cause respiratory problems in humans and some domestic animals when the blooms reach close to shore.
In addition to land runoff, atmospheric anthropogenic fixed nitrogen can enter the open ocean. A study in 2008 found that this could account for around one third of the ocean's external (non-recycled) nitrogen supply and up to three per cent of the annual new marine biological production.Duce, R A and 29 others (2008) Impacts of Atmospheric Anthropogenic Nitrogen on the Open Ocean Science. Vol 320, pp 893–89 It has been suggested that accumulating reactive nitrogen in the environment may have consequences as serious as putting carbon dioxide in the atmosphere. Addressing the nitrogen cascade Eureka Alert, 2008.
A report from NOAA scientists published in the journal Science in May 2008 found that large amounts of relatively acidified water are upwelling to within four miles of the Pacific continental shelf area of North America. This area is a critical zone where most local marine life lives or is born. While the paper dealt only with areas from Vancouver to northern California, other continental shelf areas may be experiencing similar effects.
Fishing operations often use trawl netting dragging and dredging them across the ocean bottom. Numerous habitats and ecosystems are disturbed and destroyed by trawling including coral reefs, sediments, and grasses that provide feeding and breeding grounds for a plethora of marine organisms. Coastal habitats such as mangroves are often sites of aquaculture farming practices in which the mangroves are either destroyed for easier use of the land or experience harmful conditions due to the farm being abandoned once the area becomes too polluted with excess nutrients.
Overfishing presents many threats to fish population densities, obviously. However, as these populations plummet below the maximum sustainable yield (MSY) value for the specific population, you are now risking the loss of biodiversity and possibility for extinction due to less diversity. This loss in diversity is especially concerning as we deal with environmental changes from climate change since less diversity decreases a populations ability to adapt and survive the alterations of the habitat.
Species biodiversity is a major contributor to the stability of ecosystems. When an organism exploits a wide range of resources, a decrease in biodiversity is less likely to have an impact. However, for an organism which exploit only limited resources, a decrease in biodiversity is more likely to have a strong effect.
Reduction of habitat, hunting and fishing of some species to extinction or near extinction, and pollution tend to tip the balance of biodiversity. For a systematic treatment of biodiversity within a trophic level, see unified neutral theory of biodiversity.
By 2008, the IUCN had assessed about 3,000 marine species. This includes assessments of known species of shark, ray, chimaera, reef-building coral, grouper, marine turtle, seabird, and marine mammal. Almost one-quarter (22%) of these groups have been listed as threatened.IUCN: Status of the world's marine species
An ambitious project, called the Global Marine Species Assessment, is under way to make IUCN Red List assessments for another 17,000 marine species by 2012. Groups targeted include the approximately 15,000 known marine fishes, and important habitat-forming such , , certain and the remaining ; and important invertebrate groups including and
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In the 2008 IUCN Red List, about 6,000 or 22% of the known freshwater species have been assessed at a global scale, leaving about 21,000 species still to be assessed. This makes clear that, worldwide, freshwater species are highly threatened, possibly more so than species in marine fisheries.IUCN: Freshwater biodiversity a hidden resource under threat However, a significant proportion of freshwater species are listed as data deficient, and more field surveys are needed.
Toxins
Apart from plastics, there are particular problems with other toxins which do not disintegrate rapidly in the marine environment. Heavy metals are metallic chemical elements that have a relatively high density and are toxic or poisonous at low concentrations. Examples are mercury, lead, nickel, arsenic and cadmium. Other persistent toxins are PCBs, DDT, , , dioxins and phenols.
Eutrophication
Eutrophication is an increase in chemical , typically compounds containing nitrogen or phosphorus, in an ecosystem. It can result in an increase in the ecosystem's primary productivity (excessive plant growth and decay), and further effects including lack of oxygen and severe reductions in water quality, fish, and other animal populations.
Acidification
The oceans are normally a natural carbon sink, absorbing carbon dioxide from the atmosphere. Because the levels of atmospheric carbon dioxide are increasing, the oceans are becoming more acidic.
The potential consequences of ocean acidification are not fully understood, but there are concerns that structures made of calcium carbonate may become vulnerable to dissolution, affecting corals and the ability of shellfish to form shells.
Effects of fishing
Habitat destruction
that have been left or lost in the ocean by fishermen are called , and can entangle fish, , , , , , , , and other creatures. Acting as designed, these nets restrict movement, causing starvation, laceration and infection, and—in those that need to return to the surface to breathe—suffocation.
Overfishing
Some specific examples of overfishing.
Our World in Data provides a figure showing the trend in global fishing exploitation over a few decades to reveal the intensifying circumstances at hand:
Loss of biodiversity
Each species in an ecosystem is affected by the other species in that ecosystem. There are very few single prey-single predator relationships. Most prey are consumed by more than one predator, and most predators have more than one prey. Their relationships are also influenced by other environmental factors. In most cases, if one species is removed from an ecosystem, other species will most likely be affected, up to the point of extinction.
Threatened species
The global standard for recording threatened marine species is the IUCN Red List of Threatened Species. The 2008 IUCN Red List of Threatened Species This list is the foundation for marine conservation priorities worldwide. A species is listed in the threatened category if it is considered to be critically endangered, endangered, or vulnerable. Other categories are near threatened and data deficient.
Marine
Many marine species are under increasing risk of extinction and marine biodiversity is undergoing potentially irreversible loss due to threats such as overfishing, bycatch, climate change, invasive species and coastal development.
, Batoidea, and 17% 13% 47% 12% 14% 30% Coral 845 27% 20% 17% 25% 27% 7 86%
Freshwater
Freshwater fisheries have a disproportionately high diversity of species compared to other ecosystems. Although freshwater habitats cover less than 1% of the world's surface, they provide a home for over 25% of known vertebrates, more than 126,000 known animal species, about 24,800 species of freshwater fish, molluscs, and dragonfly, and about 2,600 .
Continuing industrial and agricultural developments place huge strain on these freshwater systems. Waters are polluted or extracted at high levels, wetlands are drained, rivers channelled, forests deforestated leading to sedimentation, invasive species are introduced, and over-harvesting occurs.
Fisheries management
A recent paper published by the National Academy of Sciences of the USA warns that: "Synergistic effects of habitat destruction, overfishing, introduced species, warming, acidification, toxins, and massive runoff of nutrients are transforming once complex ecosystems like coral reefs and kelp forests into monotonous level bottoms, transforming clear and productive coastal seas into anoxic dead zones, and transforming complex food webs topped by big animals into simplified, microbially dominated ecosystems with boom and bust cycles of toxic dinoflagellate blooms, jellyfish, and disease".Jackson, Jeremy B C (2008) Ecological extinction and evolution in the brave new ocean Proceedings of the National Academy of Sciences of the USA.
See also
External links
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