Difference between revisions of "Species extinction"

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Every species however small may have an important role in maintaining a well-balanced [[Ecosystem|ecosystem]]. Recent surveys suggest that the number of species (species richness) in an area may enhance ecosystem productivity and stability <ref>M. Loreau, S. Naeem, P. Inchausti, J. Bengtsson, J. P. Grime, A. Hector, D. U. Hooper, M. A. Huston, D. Raffaelli, B. Schmid, D. Tilman, and D. A. Wardle. Biodiversity and Ecosystem Functioning: Current Knowledge and Future Challenges. Science 26 October 2001 294: 804-808.</ref><ref>Margaret Palmer, Emily Bernhardt, Elizabeth Chornesky, Scott Collins, Andrew Dobson, Clifford Duke, Barry Gold, Robert Jacobson, Sharon Kingsland, Rhonda Kranz, Michael Mappin, M. Luisa Martinez, Fiorenza Micheli, Jennifer Morse, Michael Pace, Mercedes Pascual, Stephen Palumbi, O. J. Reichman, Ashley Simons, Alan Townsend, and Monica Turner. Ecology for a Crowded Planet. Science 28 May 2004 304: 1251-1252</ref>, hence the loss of any species could be detrimental to the ecosystem. Direct effects (e.g. [[over exploitation|overexploitation]], [[pollution]] and [[Habitat destruction and fragmentation|habitat destruction]]) and indirect effects as a result of [[climate change]] and perturbations of ocean biogeochemistry have been the major reasons for species extinction. There is evidence that regional ecosystems such as [[estuaries]], [[coral reefs]], and coastal and oceanic fish communities are undergoing rapid losses whether in individuals, whole species or entire functional groups<ref>Boris Worm, Marcel Sandow, Andreas Oschlies, Heike K. Lotze, and Ransom A. Myers. Global Patterns of Predator Diversity in the Open Oceans. Science 26 August 2005 309: 1365-1369; published online 28 July 2005</ref>.
 
  
  
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== Problems in Species Extinction ==
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Global extinction refers to the loss of species or other taxonomic units (e.g., subspecies, genus, family, etc.; each is known as a taxon) occurring when there are no surviving individuals elsewhere. The extinction of any species is an irreversible loss of part of the biological richness of the Earth. Extinction can be a natural occurrence caused by an unpredictable catastrophe, chronic environmental stress, or ecological interactions such as competition, disease, or predation. However, there have been dramatic increases in extinction rates since humans have become Earth's dominant large animal and the cause of global environmental change.
  
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'''Extinction''' refers to the loss of species or other taxonomic unit (e.g., subspecies, genus, family, etc.; each is known as a taxon) occurring when there are no surviving individuals elsewhere. The extinction of any species is an irreversible loss of part of the biological richness of the Earth. Extinction can be a natural occurrence caused by an unpredictable catastrophe, chronic environmental stress, or ecological interactions such as competition, disease, or predation. However, there have been dramatic increases in extinction rates since humans have become Earth's dominant large animal and the cause of global environmental change<ref>Les Kauffman and Kenneth Mallory (eds). "Grew out of a public lecture series entitled 'Extinction: saving the sinking ark,' held in Boston, Massachusetts, at the New England Aquarium during the fall of 1984". 242p</ref>.
 
  
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==Past global species extinctions==
  
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During the '''Late Ordovician''' extinction event, approximately '''85%''' of marine species died. This mass extinction occurred in 2 phases; at the beginning and in the middle of '''Hirnantian Age'''. In the first phase of extinction, changes in nutrient cycling as a result of glacially-forced regression were thought to be responsible. Stagnation of oceanic circulation and post-glacial temperature and sea level rise were the main cause of the second phase of extinction. Meanwhile, both extinction events were thought to be stimulated by the rapid change in [[Effects of global climate change on European marine biodiversity|climate]]<ref>Liam G. Herringshaw Neil S. Davies. 2008. Bioturbation levels during the end-Ordovician extinction event: a case study of shallow marine strata from the Welsh Basin. Aquatic Biology. Vol. 2: 279–287</ref>.  
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At least five major mass extinctions have probably occurred in the geologic past. During the [https://en.wikipedia.org/wiki/Ordovician%E2%80%93Silurian_extinction_events Late Ordovician Mass Extinction] events, approximately 85% of marine species died. The mass extinction occurred in 2 phases; at the beginning and in the middle of [https://en.wikipedia.org/wiki/Hirnantian Hirnantian Age]. In the first phase of extinction, changes in nutrient cycling as a result of glacially-forced regression were thought to be responsible. Stagnation of oceanic circulation and post-glacial temperature and sea level rise were the main cause of the second phase of extinction. Meanwhile, both extinction events were thought to be stimulated by the rapid change in [[Effects of global climate change on European marine biodiversity|climate]]<ref>Herringshaw, L.G. and Davies, N.S. 2008. Bioturbation levels during the end-Ordovician extinction event: a case study of shallow marine strata from the Welsh Basin. Aquatic Biology 2: 279–287</ref>. The greatest mass extinction in Earth’s history took place about 250 million years ago. This event, commonly known as [https://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_event “the Great Dying”] removed up to 95% of life on Earth. It is believed that a gigantic volcanic eruption triggered global warming through the release of carbon dioxide and methane. This mass extinction first started in the deep ocean area, and then moved up to the upper layers of ocean, killing almost all living creatures.  
  
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Invertebrates are perhaps the most diverse group of marine organisms, and yet are being lost in the highest numbers. At the beginning of the Cambrian era (about 570 million years ago), numerous animals from this phyla propagated during an evolutionary radiation, but most of them are now extinct. The 15-20 extinct phyla from that period are known from the [https://en.wikipedia.org/wiki/Burgess_Shale Burgess Shale] of British Columbia. Other than invertebrates, species such as Steller’s sea cow (''Hydrodamalis gigas''), which was driven to extinction by visiting sea-otter hunters, and the great auk (''Pinguinus impennis'') are examples of recently extinct species in marine environments<ref name="kaufman">Kaufman, L. and Mallory, K.  (eds.) 1986. The Last Extinction. 2nd Edition. The MIT Press. 242 p</ref>.
  
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Current evidence suggests that few marine organisms have become globally extinct in the past '''300''' years, where 829 species have disappeared<ref name="baille">Baille, J.E.M., Hilton-Taylor, C. & Stuart, S. (2004) 2004 IUCN Red List of Threatened Species: a global species assessment</ref>. However, there is little precise information regarding how many species are being extinguished in the marine environment since nobody even knows the numbers of species actually present, and there is uncertainty about taxonomic status and also in defining when the last individual has gone<ref name="carlton">Carlton, J.T., Geller, J.B., Reaka-Kudla, M.L. & Norse, E.A. (1999) Historical extinctions in the sea. Annual Review of Ecology & Systematics 30: 525-538</ref>. This information is also lacking in other major habitats. However, there can be no doubt that currently, extinction is happening at an alarming rate and faster than it did prior to 1800<ref>Wilson, E.O. and Frances, M.P. 1988. Biodiversity. National Academy Press. 521p</ref>. Previous mass extinctions evident in the geological record are thought to have been brought about mainly by massive climatic or environmental shifts. Mass extinctions as a direct consequence of the activities of a single species are unprecedented in geological history. '''Invertebrates''' are perhaps the most diverse group of marine organisms, and yet are being lost in the highest numbers. At the beginning of the '''Cambrian era''' (about 570 million years ago), numerous animals from this phyla propagated during an evolutionary radiation, but most of them are now extinct. The 15-20 extinct phyla from that period are known from the '''Burgess Shale of British Columbia'''. Other than invertebrates, species such as Steller’s sea cow (''Hydrodamalis gigas''), which was driven to extinction by visiting sea-otter hunters, and the great auk (''Pinguinus impennis'') are examples of recently extinct species in marine environments<ref name="kaufman">Les Kaufman and Kenneth Mallory (eds.). The Last Extinction. 2nd Edition. The MIT Press. 242 p</ref>.
 
  
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==Present regional and global species extinctions==
  
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There is unequivocal evidence for the extinction of '''12''' marine species, comprising three mammals, five seabirds and four gastropods<ref name="carlton" />. An additional three bird and mammal species are listed as extinct by the World Conservation Union (IUCN) Red List<ref name="baille" />, and a recent survey by Dulvy et al. (2003)<ref>Dulvy, N.K., Sadovy, Y. & Reynolds, J.D. (2003) Extinction vulnerability in marine populations. Fish & Fisheries 4: 25-64</ref> has uncovered evidence to suggest the global extinction in the wild of a further six species comprising two fishes, two corals and two algae.
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Current evidence suggests that at least 829 species have become globally extinct in the past 300 years<ref name="baille">Baille, J.E.M., Hilton-Taylor, C. & Stuart, S. 2004. IUCN Red List of Threatened Species: a global species assessment</ref>. It is estimated that since the beginning of life on Earth, an average of 0.01-2 out of every million species have gone extinct every year<ref name=L20>Luypaert T., Hagan J.G., McCarthy M.L., Poti M. 2020. Status of Marine Biodiversity in the Anthropocene. In: Jungblut S., Liebich V., Bode-Dalby M. (eds) YOUMARES 9 - The Oceans: Our Research, Our Future. Springer, Cham. https://doi.org/10.1007/978-3-030-20389-4_4</ref>. Extinction ratios in recent centuries are 10-1000 times higher, which is attributed to human activity<ref>Rounsevell, M.D.A., Harfoot, M., Harrison, P.A., Newbold, T., Gregory, R.D. and Mace, G.M. 2020. A biodiversity target based on species extinctions. Science 368: 1193–1195</ref>. The extinction rate in the marine environment is probably more than 10 times lower than in the terrestrial environment<ref>McCauley, D.J., Pinsky, M.L., Palumbi, S.R., Estes, J.A., Joyce, F.H. and Warner, R.R. 2015. Marine defaunation: Animal loss in the global ocean. Science 347: 1255641</ref>. However, the marine figures are not very reliable. We don't really know how many marine species exist. About 240,000 marine species are known, while estimates of the total number of marine species range between 300,000 and 2 million<ref name=L20/>, see also [[Number of marine species]]. There is uncertainty about taxonomic status and also in defining when the last individual has gone<ref name="carlton">Carlton, J.T., Geller, J.B., Reaka-Kudla, M.L. and Norse, E.A. 1999. Historical extinctions in the sea. Annual Review of Ecology and Systematics 30: 525-538</ref>.
  
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A review of the scientific literature over the period 1990-2022 (Nikolaou and Katsanevakis, 2023<ref name=NK>Nikolaou, A. and Katsanevakis, S. 2023.  Marine extinctions and their drivers. Regional Environmental Change 23: 88</ref>) provides  evidence for the extinction of 717 marine species, of which 18 were global extinctions. Of the 18 global extinctions, ten were Aves, four Mammalia, two Osteichthyes, one Macroalga, and one Mollusc. A higher number of 21 global extinctions was reported in an older review by Dulvy et al. (2003<ref>Dulvy, N.K., Sadovy, Y. and Reynolds, J.D. 2003. Extinction vulnerability in marine populations. Fish and Fisheries 4: 25-64</ref>). However, for most of the reported extinctions there is a lack of solid evidence because ecological monitoring data are generally poor. Not all reports of extinctions are reliable, as the methods used or the detectability of the species can vary; thus, some populations may be wrongfully stated as extinct. For example, the mollusc ''Littoraria flammea'' was listed as globally extinct on the World Conservation Union (IUCN) Red List<ref name="baille" /> but was later found alive in its native habitat. Another example is the salt marsh snail ''Omphalotropis plicosa''<ref name=NK/>. Nevertheless, there can be no doubt that currently extinction is happening at an alarming rate and faster than it did prior to 1800<ref>Wilson, E.O. and Frances, M.P. 1988. Biodiversity. National Academy Press. 521p</ref>. Previous mass extinctions evident in the geological record are thought to have been brought about mainly by massive climatic or environmental shifts. Mass extinctions as a direct consequence of the activities of a single species are unprecedented in geological history.
  
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Although every species has their own importance to the functionality of an ecosystem, some species are more vulnerable to extinction than others<ref name="countryinfo">http://www.countrysideinfo.co.uk/biodvy.htm</ref> These include:
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[[File:PsephurusGladius.jpg|thumb|400px|right|Fig. 1. The Chinese paddlefish (''Psephurus gladius'') was formerly native to the Yangtze and Yellow River basins in China. It was officially declared extinct in 2022, with an estimated time of extinction around 2005<ref>[https://en.wikipedia.org/wiki/Chinese_paddlefish The Chinese paddlefish]</ref>. Image public domain.]]
  
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Most of the extinctions from the literature inventory<ref name=NK/> are on very localized and sub-ecoregion scales. The taxonomic group with the most reported local extinctions is molluscs (31%), followed by cnidarians (22%), fish (17%) and macroalgae (15%). Chondrichthyes (cartilaginous fishes with skeletons made of cartilage instead of bone, e.g. sharks, skates, rays and chimeras) is the taxonomic group with the most ecoregional and extensive extinctions. An example is the Chinese paddlefish, see Fig. 1.
  
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1. ''Species at the top of food chains, such as large carnivores.''
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While there are no doubts about the global decline of [[Marine Biodiversity|marine biodiversity]], this is less apparent on a local scale. Studies of local marine habitats do not provide clear evidence of a reduction in species richness<ref>Elahi, R., O’Connor, M.I., Byrnes, J.E., Jarrett, E. K., Dunic, J., Eriksson, B.,K., Hensel, M.J. S. and Kearns, P.J. 2015. Recent trends in local-scale marine biodiversity reflect community structure and human impacts. Curr. Biol. 25: 1938–1943. https://doi.org/10.1016/j.cub.2015.05.030</ref><ref>Hillebrand, H., Blasius, B., Borer, E.T., Chase, J.M., Downing, J.A., Eriksson, B.K., Filstrup, C.T., Harpole, W.S., Hodapp, D., Larsen, S., Lewandowska, A.M., Seabloom, E.W., Van de Waal, D.B and Ryabov, A.B. 2018. Biodiversity change is uncoupled from species richness trends: consequences for conservation and monitoring. J Appl Ecol 55:169–184. https://doi.org/10.1111/1365-2664.12959</ref><ref>Pilotto, F. et al. 2020. Meta-analysis of multidecadal biodiversity trends in Europe. Nature Communications 11: 3486  https://doi.org/10.1038/s41467-020-17171-y </ref>. Although these studies may not provide a complete representative picture, they provide a strong indication that changes in biodiversity on a global scale are not automatically reflected on a local scale.
  
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A fairly wide territory is needed by large carnivores to provide them with sufficient prey. Nevertheless, they are to some extent reducing in numbers due to the habitat shrinking as a result of increasing human populations.
 
  
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==Causes of species extinction==
  
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2. ''Endemic local species with a very limited distribution.''
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The dominant drivers of extinction mentioned in the literature differ by taxonomic group. High mobility taxa are driven extinct mainly by overexploitation, whereas low mobility taxa from pollution, climate change and habitat destruction. Most of these extinctions are recorded in the Temperate Northern Atlantic (41%) and the Central Indo-Pacific (30%). The main driver of global marine extinctions is overexploitation (in 13 cases reported as a possible driver), followed by invasive species (seven times reported), habitat destruction (five times reported), trophic cascades (three times reported), and pollution (one time reported) <ref name=NK/>. Overexploitation was historically the primary driver of marine local extinctions. However, in the last three decades, other drivers, such as climate change, climate variability, and pollution, prevail in the published literature<ref name=NK/>.
  
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'''Endemic''' species has limited geographical distribution, and this makes them very vulnerable to local habitat disturbance or human development. Several species such as damselfish (''Azurina eupalama''), the Mauritius green wrasse (''Anampses viridis'') and two corals (''Millepora boschmai'' & ''Siderastrea glynni''), the Turkish towel algae (''Gigartina australis'') and Bennett’s seaweed (''Vanvoortsia bennettiana'') are also thought to be extinct throughout their small geographic ranges.  
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====Overexploitation====
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The intensive exploitation of marine organisms has a short history in comparison with the terrestrial organisms, only commencing in the last few hundred years. Initially, marine animals were not obviously threatened by the wave of extinction that land species were subjected to. However, marine species have been put under great pressure since humans became able to travel over the sea. In this short period, human exploitation of marine resources has been a major factor of extinction, both through direct mortality of target species and multiple collateral effects on non-target species (bycatch). For example, exploitation is responsible for 55% of the main extinction threat to North American marine fishes<ref>Musick, J.A., Harbin, M.M., Berkeley, S.A., Burgess, G.H., Eklund, A.M., Findley, L., Gilmore, R.G., Golden, J.T., Ha, D.S., Huntsman, G.R., McGovern, J.C., Parker, S.J., Poss, S.G., Sala, E., Schmidt, T.W., Sedberry, G.R., Weeks, H. and Wright, S.G. 2000. Marine, estuarine, and diadromous fish stocks at risk of extinction in North America (exclusive of Pacific salmonids). Fisheries 25: 6-30</ref>. Fisheries are also indirectly responsible for biodiversity loss and ecosystem disturbance by abandoning huge amounts of derelict fishing gear in the ocean, which is deadly to many marine top predator species. See also the articles [[Overexploitation]] and [[Effects of fisheries on marine biodiversity]].
  
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====Habitat Disturbance====
  
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3. ''Species with chronically small populations.''
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[[Image:BeamTrawler.jpg|thumb|right|250px|Figure 2: Beam trawling is one of the fishing activities that greatly destruct marine habitats. Photo credit Government of Flanders.]]
  
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These species (e.g. Leafscale Gulper Shark, ''Centrophorus squamosus''; and Portuguese dogfish, ''Centrophorus coelolepis'' are exposed to extinction given the fact that their reproduction rate is comparatively slow when comparing with other abundance species.
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Biological, physical and chemical factors in most ecosystems are tightly intertwined. Hence changes in one of these factors can result in changes of others. Exploitation of habitat can therefore profoundly influence many components of a system. Examples of habitat destruction are:
  
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''Physical alterations:''
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* Marine aggregate dredging
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* [[Effects of fisheries on marine biodiversity|Trawl fishing]]  (Fig. 2)
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* Reclamation of coastal wetlands (mangroves, salt marshes) for economic uses
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* [[Hard coastal protection structures|Coastal protection structures]]
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''Chemical alterations:''
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* [[:Category:Coastal and marine pollution|Chemical (industrial, agricultural) pollution, oil pollution]]
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* [[Eutrophication]]
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* Plastics and non-degradable litter
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* [[Ocean acidification]]
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''Biological alterations:''
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* Introduction of [[Non-native species invasions|non-native species]]
  
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4. ''Migratory species.''
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====Climate Change====
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Recent [[Effects of global climate change on European marine biodiversity|climate change]] such as global warming has increased local water temperatures beyond the suitable range of many species. Such changes have made highly productive areas, such as up-welling regions, become less productive due to changes in the [[Food web|food web]]. Lower primary production supports a lower biomass of primary consumers. In the oceans, krill are major primary consumers that support many important ecosystems. Therefore climate change will inevitably impact food webs based on krill and this will be reflected in the reduction of top level consumer such as large plankton-grazing fish and sea mammals<ref>Myers, N. 1993. Sharing the earth with whales. In: Les Kaufman and Kenneth Mallory (eds.). The Last Extinction. 2nd Edition. The MIT Press. 242 p</ref>. See also [[Ecological thresholds and regime shifts#Climate-induced regime shifts|Climate-induced regime shifts]].
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Migratory species need suitable habitats to feed and rest in widely spaced locations. Such species, for example, dugong (''Dugong dugon''), Loggerhead turtle (''Caretta caretta''), Hawksbill turtle (''Eretmochelys imbricata'') and Mediterranean Monk Seal (''Monachus monachus'') are very vulnerable if one of their habitats’are lost.
 
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5. ''Species with exceptionally complex life cycles.''
 
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Species such as a Tunicate (''Ciona intestinalis'') and a Brown bryozoan (''Bugula neritina'') normally need several different elements to be in place at very specific times to complete their life cycles, making them vulnerable if there is disruption of any single element in the cycle.
 
  
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== Mechanisms Causing Species Extinction ==
 
  
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[[Habitat destruction and fragmentation|Habitat destruction]] is the primary cause for the decline of biodiversity in the East Indian and Central Pacific marine regions. The annual global loss of coastal habitat has been estimated to be between 1–9% for coral reefs, around 1.8% for mangroves and  about 7% for seagrass beds<ref name=L20/>.
  
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'''1 Direct Take or Killing'''
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[[Overexploitation]] appears to be the primary cause in the Atlantic and Mediterranean regions. Important, but relatively lesser causes of biodiversity loss are [[pollution]], [[eutrophication]], [[climate change]] and [[Non-native species invasions|invasive species]], see Fig. 3.
  
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For many years, killing by human was a major factor of extinction. Humans kill other species for many reasons including food, recreation, and to protect themselves and their properties. For example, exploitation is responsible for 55% of the main extinction threat to North American marine fishes<ref>Musick J.A., Harbin M.M., Berkeley S.A., Burgess G.H., Eklund A.M., Findley L., Gilmore R.G., Golden J.T., Ha D.S., Huntsman G.R., McGovern J.C., Parker S.J., Poss S.G., Sala E., Schmidt T.W., Sedberry G.R., Weeks H. & Wright S.G. (2000) Marine, estuarine, and diadromous fish stocks at risk of extinction in North America (exclusive of Pacific salmonids). Fisheries, 25, 6-30</ref>. Initially, marine animals were not obviously threatened by the wave of extinction that land species were subjected to. However, marine species have been put under great pressure since humans became able to travel over the sea. One species, respectively from three major orders of marine mammals (Cetacea, Pinnipedia and Sirenia) were believed to become extinct in North America mainly due to human activities<ref>James D. Williams and Ronald M. Nowak. 1993. Vanishing species in our own backyard: Extinct fish and wildlife of the United States and Canada. In: Les Kaufman and Kenneth Mallory (eds.). The Last Extinction. 2nd Edition. The MIT Press. 242 p</ref>.
 
  
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[[File:CausesSpeciesLossMap.jpg|thumb|center|700px|Fig. 3. Major threats of species loss for different marine regions. From Luypaert et al. (2020<ref name=L20/>) Creative Commons licence.]]
  
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'''2 Habitat Disturbance'''
 
  
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Biological, physical and chemical factors in most ecosystems are tightly intertwined. Hence changes in one of these factors can result in changes of others. Exploitation of habitat can therefore profoundly influence many components of a system. Examples of habitat destruction are given below<ref name="kaufman" />:
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==Vulnerability of species==
  
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Although every species contributes to the ecosystem function, some species are more vulnerable to extinction and have a greater impact than others. These include:
  
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''Physical alterations:''
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''Species at the top of food chains, such as large carnivores.''  
  
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* Marine aggregate dredging
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Top predators (also called 'apex predators') play a critical role in ecosystems, by regulating directly and indirectly all underlying trophic levels. They need a large territory to get sufficient prey and their abundance is relatively low. Reproduction and growth is slower than for smaller species and so is their recovery after partial depletion. They are a favorite target of the fishery and therefore prone to overfishing<ref>Roberts, C.M. and Hawkins, J.P. 1999. Extinction risk at sea. Trends Ecol. Evol. 14: 241–246</ref><ref>Olden, J.D., Hogan Z.S. and Van der Zanden, M.J. 2007. Small fish, big fish, red fish, blue fish: size-biased extinction risk of the world’s freshwater and marine fishes. Glob. Ecol. Biogeogr. 16: 694–701</ref>. Top predators are therefore a vulnerable group of which most species have declined sharply, in some cases more than 90%<ref name=W5>Worm, B., Sandow, M., Oschlies, A., Lotze, H.K. and Myers, R.A. 2005. Global Patterns of Predator Diversity in the Open Oceans. Science 309: 1365-1369</ref>. For example, even light fishing pressure is sufficient to cause strong population declines in many large shark species<ref>Ferretti, F., Worm, B., Britten, G.L., Heithaus, M.R. and Lotze, H.K. 2010. Patterns and ecosystem consequences of shark declines in the ocean. Ecology Letters 13: 1055–1071</ref>. This 'trophic downgrading' has generated widespread concern because of the fundamental role that apex predators can play in ecosystem functioning, disease regulation, and biodiversity maintenance<ref>Stier, A. C., Samhouri, J. F., Novak, M., Marshall, K. N., Ward, E. J., Holt, R. D. and Levin, P. S. 2016. Ecosystem context and historical contingency in apex predator recoveries. Science advances, 2(5), e1501769. https://doi.org/10.1126/sciadv.1501769</ref>. See also the article [[Trophic cascade]].
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* Commercial development and construction
 
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* Structures for water diversion
 
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* Coastal engineering
 
  
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''Specialized endemic species.''
  
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''Chemical alterations:''
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Specialized species with a small geographic range are especially vulnerable to disturbance by [[Non-native species invasions|invasive species]] and human intervention. These species can fulfill important functions for the local ecosystem, which are lost when they are replaced by non-native generalist species that compete more efficiently on a larger scale<ref>Clavel, J., Julliard, R. and Devictor, V. 2011. Worldwide decline of specialist species: toward a global functional homogenization? Front. Ecol. Environ 9: 222–228</ref>.
  
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* Ocean acidification
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Several species such as damselfish (''Azurina eupalama''), the Mauritius green wrasse (''Anampses viridis'') and two corals (''Millepora boschmai'' and ''Siderastrea glynni''), the Turkish towel algae (''Gigartina australis'') and Bennett’s seaweed (''Vanvoortsia bennettiana'') are highly endangered or extinct throughout their small distribution areas.
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* Organic waste
 
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* High concentration of heavy metals
 
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* Industrial and agricultural chemicals
 
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* Plastics and particles
 
  
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''Migratory species.''
  
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''Biological alterations:''
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Migratory species need suitable habitats to feed and rest in widely spaced locations. Such species, for example, Dugong (''Dugong dugon''), Loggerhead turtle (''Caretta caretta''), Hawksbill turtle (''Eretmochelys imbricata'') and Mediterranean Monk Seal (''Monachus monachus'') are very vulnerable if one of their habitats is lost.
  
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* Introduction of non-native species
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''Species with exceptionally complex life cycles.''
  
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Species such as a Tunicate (''Ciona intestinalis'') and a Brown bryozoan (''Bugula neritina'') normally need several different elements to be in place at very specific times to complete their life cycles, making them vulnerable if there is disruption of any single element in the cycle.
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'''3 Climate Change'''
 
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The largest mass extinction took place in Earth’s history about 250 million years ago. This incident, commonly known as “the Great Dying” removed up to 95% of life on Earth. It is believed that a gigantic volcanic eruption triggered global warming through the release of carbon dioxide and methane. This mass extinction was first started in the deep ocean area, and then moved up to the upper layers of ocean, killing almost all living creatures<ref name="sciencedaily">http://www.sciencedaily.com/releases/2007/10/071025091047.htm</ref>.
 
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Meanwhile, more recent climate change such as global warming has increased local water temperatures beyond the suitable range of many species. Such changes have made exceptionally productive areas, such as up welling regions, become less productive due to changes in the food web. Lower primary production supports a lower biomass of primary consumers. In the oceans, krill are major primary consumers that support many important ecosystems.  Therefore climate change will inevitably impact food webs based on krill and this will be reflected in the reduction of top level consumer such as large plankton-grazing fish and sea mammals<ref>Myers, N. 1993. Sharing the earth with whales. In: Les Kaufman and Kenneth Mallory (eds.). The Last Extinction. 2nd Edition. The MIT Press. 242 p</ref>.
 
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== Impact of Species Extinction on Biodiversity ==
 
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An international group of researchers has recently provided the first comprehensive and large-scale assessment of the services provided. They suggest that species extinction has impaired at least three critical ecosystem services: number of viable fisheries (-33%); provision of nursery habitats such as oyster reefs, seagrass beds and wetlands (-69%); and filtering and detoxification services provided by suspension feeders, submerged vegetation and wetlands (-63%). Additionally, the loss of filtering services has the potential to increase the risks of harmful algal blooms (e.g. ‘red tide’), oxygen depletion and declining water quality. Meanwhile, coastal flooding was also increased as a result of species extinction. Although this event is linked to sea level rise, historical losses of floodplain and erosion control provided by coastal wetlands, reefs and submerged vegetation is also responsible<ref>Stachowicz, J.J., Whitlatch, R.B., Osman, R.W., 1999. Species diversity and invasion resistance in a marine ecosystem. Science, 286:1577–79</ref><ref name="worm">Worm B, Barbier EB, Beaumont N, Duffy JE, Folke C, et al. (2006) Impacts of biodiversity loss on ocean ecosystem services. Science 314: 787–790</ref>.
 
  
  
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This effect (through extinction) will be more notable with combining effect from species gain (e.g. through invasion). The reason for this phenomenon is because most extinction (approximately 70%) occurs at high trophic level (predators and primary consumers), whilst the lower trophic (70%; plankton feeders, deposit feeders and detritivores) levels are where most invasions occurs. Marine food webs will re-organise following these simultaneous changes; from a normal pyramid capped by a large range of predators and consumers to a shorter structure dominated by filter feeders and scavengers<ref name="byrnes">Byrnes JE, Reynolds PL, Stachowicz JJ (2007) Invasions and Extinctions Reshape Coastal Marine Food Webs. PLoS ONE 2(3): e295. doi:10.1371/journal.pone.0000295</ref>.
+
==Consequences of species extinctions at local or regional scales==
  
 +
Species extinction at local or regional scales implies in general a decline in [[Measurements of biodiversity|species richness]] (number of species) and a decline in [[Marine Biodiversity|biodiversity]]. There is strong evidence that species richness in an area enhances ecosystem productivity and stability <ref>Loreau, M., Naeem, S., Inchausti, P., Bengtsson, J., Grime, J. P., Hector, A., Hooper, D. U., Huston, M. A. ,Raffaelli, D., Schmid, B., Tilman, D. and Wardle D. A. 2001. Biodiversity and Ecosystem Functioning: Current Knowledge and Future Challenges. Science 294: 804-808</ref><ref>Palmer, M., Bernhardt, E., Chornesky, E., Collins, S., Dobson, A., Duke, C., Gold, B., Jacobson, R., Kingsland, S., Kranz, R., Mappin, M., Martinez, M.L., Micheli, F., Morse, J., Pace, M., Pascual, M., Palumbi, S., Reichman, O.J., Simons, A., Townsend, A. and Turner, M. 2004. Ecology for a Crowded Planet. Science 304: 1251-1252</ref><ref name=W6>Worm, B., Barbier, E.B., Beaumont, J., Duffy, E., Folke, C., Halpern, B.S., Jackson , J.B.C., Lotze, H.K., Micheli, F., Palumbi, S.R., Sala, E., Selkoe, K.A., Stachowicz, J.J. and Watson, R. 2006. Impacts of biodiversity loss on ocean ecosystem services. Science 314:787–790. https://doi.org/10.1126/science.1132294</ref><ref>Gamfeldt, L., Lefcheck, J.S., Byrnes, J.E., Cardinale, B.J., Duffy, J.E. and Griffin, J.N. 2015. Marine biodiversity and ecosystem functioning: what’s known and what’s next? Oikos 124: 252–265. https://doi.org/10.1111/oik.01549</ref>. The loss of any species can be detrimental to the ecosystem. This is especially true of the loss of species from the higher trophic levels that suffer the greatest risk of (local) extinction as a result of hunting by humans, loss of habitat or bioaccumulation of toxins. Loss of top predators can result in a so-called [[trophic cascade]] - a complete restructuring of the ecosystem and the food web relationships. Reintroduction of lost species is not always possible, as return is prevented by species that have taken their niche in the food web (see the article [[Trophic cascade]] for an example).
  
−
There are several studies that suggest that marine species biodiversity will be altered solely due to species extinction, without any additional effect by species invasion. Although these studies have been completed in laboratories and may only include relatively strongly interacting species, they are to some extent robust and produce data similar to that from field surveys and fisheries that incorporate the diversity of the whole community. Furthermore, a strong impact on ecosystem function has been recorded even when the invasive and extinct species are not strong interactors<ref name="byrnes" />.
+
Invasion of alien species can in some cases compensate for a decline in species diversity (see the article [[Non-native species invasions]]). However, most alien invasions are by species from lower trophic levels. The structure of marine food webs then changes from a trophic pyramid covered by a diverse array of predators and consumers to a shorter, squatter configuration dominated by filter feeders and scavengers<ref name="byrnes">Byrnes, J.E., Reynolds, P.L. and Stachowicz, J.J. 2007. Invasions and Extinctions Reshape Coastal Marine Food Webs. PLoS ONE 2(3): e295. doi:10.1371/journal.pone.0000295</ref>.
  
 +
A review of global databases related to the impact of biodiversity loss on marine ecosystem services shows that the number of viable fisheries has declined by -33%, the provision of nursery habitats such as oyster reefs, seagrass beds and wetlands has declined by -69% and filtering and detoxification services provided by suspension feeders, submerged vegetation and wetlands has declined by -63% <ref name="worm">Worm B, Barbier EB, Beaumont N, Duffy JE, Folke C, et al. (2006) Impacts of biodiversity loss on ocean ecosystem services. Science 314: 787–790</ref>. The loss of filtering services has the potential to increase the risks of [[Harmful algal bloom|harmful algal blooms]] (e.g. ‘red tide’), oxygen depletion and declining water quality. Moreover, the loss of coastal habitats has also resulted in historical losses of floodplain buffer area and loss of erosion control from coastal wetlands, thus increasing flooding risks to coastal inhabitants<ref>Stachowicz, J.J., Whitlatch, R.B., Osman, R.W., 1999. Species diversity and invasion resistance in a marine ecosystem. Science, 286:1577–79</ref>. Analysis of the FAO Global Catch Database shows that the rate of fishery collapses, defined here as catches falling below 10% of the recorded maximum, has accelerated over time, with 29% of currently fished species considered to have collapsed in 2003<ref name="worm"/>.
  
  
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== How to Avoid Species Extinction ==
+
==Mitigation of species extinction==
  
 +
The importance of biodiversity in maintaining a stable ecosystem implies that species extinction should be avoided. Several measures can contribute to this objective.
  
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The importance of biodiversity in maintaining a stable ecosystem implies that we need to avoid species extinction, and there are a number of practices that can be employed to help conserve our marine species.  
+
The most practiced measure to protect marine ecosystems is the instauration of [[Marine Protected Areas (MPAs)]]. These designated areas help to protect depleted, threatened, rare or endangered species and populations, as well as to preserve habitats of critical species. Currently (2020) MPAs cover about 4% of the oceans; the target of 10% formulated in the [https://www.cbd.int/convention/ Convention on Biological Diversity] is still a long way off. In addition, only part of the MPAs offer full protection. These fully protected MPAs, where any kind of resource removal is prohibited, are often referred to as Marine Reserves. A study of 44 Marine Reserves shows an average increase of 23% in species richness. This increase in biodiversity coincides with a sharp increase in fishery productivity<ref name="worm"/>. MPAs cover different habitats (e.g sandbank, mudflat, lagoon, mangrove and reef) and therefore provide protection to different assemblages of species (e.g. Lamprey, Bottlenose Dolphin and Loggerhead Turtle), according to the needs and natural states in different countries.  
  
 +
Also crucial to the conservation of species is the elimination, as far as possible, of the various causes of species extinction, by measures such as:
 +
* Maintenance and ecologically sound management of essential habitats, especially coastal wetlands.
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* Prevention of [[Coastal pollution and impacts|marine pollution]], or at least, the reduction by integrated coastal and river basin planning to limit the passage of nutrients or other pollutants to the marine environment.
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* Sustainable fisheries and mariculture by implementing the [http://www.fao.org/fishery/code/en FAO code of conduct for responsible fisheries].
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*Prevention of [[non-native species invasions]]<ref>[https://www.cbd.int/invasive/doc/marine-menace-iucn-en.pdf IUCN booklet Marine Menace; Alien invasive species in the marine environment]</ref>.
  
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One of the important approaches to protect marine ecosystems that has been widely applied is Marine Protected Areas (MPAs). MPAs are established in order to protect the richness of marine life and the environment. Moreover, these designated areas help to protect depleted, threatened, rare or endangered species and populations, as well as to preserve habitats of critical species. MPAs differ (e.g sandbank, mudflat, lagoon and reef) and so the protected different assemblages of species (e.g. Lamprey, Bottlenose Dolphin and Loggerhead Turtle), based on the needs and natural states in different countries. Currently there are several areas in the UK have been chosen as potential MPAs area, such as Dogger Bank, West Water of Amrum / Sylt, and Western Irish Sea. An example of MPAs application is through fishery closures where a sea area is closed to a certain fishing gear or vessel size, or for a certain target species. The closure to fishing activities help to avoid species extinction since it can increase the species richness. Additionally, it can also be a powerful economic tool helping fisheries remain productive and profitable<ref>http://www.ngo.grida.no/wwfneap/Projects/MPAmap.htm</ref><ref>http://www.naturalengland.org.uk/ourwork/marine/protectandmanage/mpa/default.aspx</ref>.
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Above all, great efforts should be made to increase public awareness of the urgent need for action. People around the world should understand the causes and consequences of extinctions and the fact that loss of diversity is happening everywhere.  
  
 +
Knowledge of life on Earth is far from complete. In the past 250 years of research, taxonomists have named about 1.78 million species of animals, plants and micro-organisms, yet the total number of species is unknown and probably between 5 and 30 million. Taxonomy provides a major foundation of conservation practice and sustainable management of the world living resources. Worldwide research on taxonomy is fostered by the [https://www.cbd.int/gti/ Global Taxonomy Initiative].
  
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Other ways to avoid species extinction are through integrated pollution control, and maintenance of essential habitats. Marine pollution could be prevented, or at least, reduced, by integrated coastal and river basin planning limiting the passage of nutrients or other pollutants to the marine environment. On the other hand, crucial habitats could be maintained by limiting physical activities such as fishing and coastal construction, or through mooring systems in sensitive yet important (e.g. coral reef) environments<ref name="worm" />.
 
  
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==Related articles==
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:[[Overexploitation]]
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:[[Effects of fisheries on marine biodiversity]]
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:[[Measurements of biodiversity]]
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:[[Ecological thresholds and regime shifts]]
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:[[Resilience and resistance]]
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:[[Trophic cascade]]
  
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Above all, formidable efforts should be made to increase public awareness of the urgent need for action. People around the world should understand the causes and consequences of extinctions and the fact that the loss in diversity could be happening everywhere. Furthermore, intensive study of the living biota is very important, as this knowledge will provide evidence of what we might expect to happen in the future. The need of more research is very obvious since at present, data on the rates and direction of biodiversity loss remains scarce and often uncertain. This data is urgently needed in predicting the eventual impacts that will result from extinction<ref>Paul R. Ehrlich. The loss of diversity: Causes and consequences. In: E.O. Wilson and Frances M. Peter. (eds). Biodiversity. 1994. National Academy Press. 521p</ref>.
 
  
  
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[[Category:Coastal and marine ecosystems]]

Latest revision as of 17:44, 23 February 2024


Global extinction refers to the loss of species or other taxonomic units (e.g., subspecies, genus, family, etc.; each is known as a taxon) occurring when there are no surviving individuals elsewhere. The extinction of any species is an irreversible loss of part of the biological richness of the Earth. Extinction can be a natural occurrence caused by an unpredictable catastrophe, chronic environmental stress, or ecological interactions such as competition, disease, or predation. However, there have been dramatic increases in extinction rates since humans have become Earth's dominant large animal and the cause of global environmental change.


Past global species extinctions

At least five major mass extinctions have probably occurred in the geologic past. During the Late Ordovician Mass Extinction events, approximately 85% of marine species died. The mass extinction occurred in 2 phases; at the beginning and in the middle of Hirnantian Age. In the first phase of extinction, changes in nutrient cycling as a result of glacially-forced regression were thought to be responsible. Stagnation of oceanic circulation and post-glacial temperature and sea level rise were the main cause of the second phase of extinction. Meanwhile, both extinction events were thought to be stimulated by the rapid change in climate[1]. The greatest mass extinction in Earth’s history took place about 250 million years ago. This event, commonly known as “the Great Dying” removed up to 95% of life on Earth. It is believed that a gigantic volcanic eruption triggered global warming through the release of carbon dioxide and methane. This mass extinction first started in the deep ocean area, and then moved up to the upper layers of ocean, killing almost all living creatures.

Invertebrates are perhaps the most diverse group of marine organisms, and yet are being lost in the highest numbers. At the beginning of the Cambrian era (about 570 million years ago), numerous animals from this phyla propagated during an evolutionary radiation, but most of them are now extinct. The 15-20 extinct phyla from that period are known from the Burgess Shale of British Columbia. Other than invertebrates, species such as Steller’s sea cow (Hydrodamalis gigas), which was driven to extinction by visiting sea-otter hunters, and the great auk (Pinguinus impennis) are examples of recently extinct species in marine environments[2].


Present regional and global species extinctions

Current evidence suggests that at least 829 species have become globally extinct in the past 300 years[3]. It is estimated that since the beginning of life on Earth, an average of 0.01-2 out of every million species have gone extinct every year[4]. Extinction ratios in recent centuries are 10-1000 times higher, which is attributed to human activity[5]. The extinction rate in the marine environment is probably more than 10 times lower than in the terrestrial environment[6]. However, the marine figures are not very reliable. We don't really know how many marine species exist. About 240,000 marine species are known, while estimates of the total number of marine species range between 300,000 and 2 million[4], see also Number of marine species. There is uncertainty about taxonomic status and also in defining when the last individual has gone[7].

A review of the scientific literature over the period 1990-2022 (Nikolaou and Katsanevakis, 2023[8]) provides evidence for the extinction of 717 marine species, of which 18 were global extinctions. Of the 18 global extinctions, ten were Aves, four Mammalia, two Osteichthyes, one Macroalga, and one Mollusc. A higher number of 21 global extinctions was reported in an older review by Dulvy et al. (2003[9]). However, for most of the reported extinctions there is a lack of solid evidence because ecological monitoring data are generally poor. Not all reports of extinctions are reliable, as the methods used or the detectability of the species can vary; thus, some populations may be wrongfully stated as extinct. For example, the mollusc Littoraria flammea was listed as globally extinct on the World Conservation Union (IUCN) Red List[3] but was later found alive in its native habitat. Another example is the salt marsh snail Omphalotropis plicosa[8]. Nevertheless, there can be no doubt that currently extinction is happening at an alarming rate and faster than it did prior to 1800[10]. Previous mass extinctions evident in the geological record are thought to have been brought about mainly by massive climatic or environmental shifts. Mass extinctions as a direct consequence of the activities of a single species are unprecedented in geological history.

Fig. 1. The Chinese paddlefish (Psephurus gladius) was formerly native to the Yangtze and Yellow River basins in China. It was officially declared extinct in 2022, with an estimated time of extinction around 2005[11]. Image public domain.

Most of the extinctions from the literature inventory[8] are on very localized and sub-ecoregion scales. The taxonomic group with the most reported local extinctions is molluscs (31%), followed by cnidarians (22%), fish (17%) and macroalgae (15%). Chondrichthyes (cartilaginous fishes with skeletons made of cartilage instead of bone, e.g. sharks, skates, rays and chimeras) is the taxonomic group with the most ecoregional and extensive extinctions. An example is the Chinese paddlefish, see Fig. 1.

While there are no doubts about the global decline of marine biodiversity, this is less apparent on a local scale. Studies of local marine habitats do not provide clear evidence of a reduction in species richness[12][13][14]. Although these studies may not provide a complete representative picture, they provide a strong indication that changes in biodiversity on a global scale are not automatically reflected on a local scale.


Causes of species extinction

The dominant drivers of extinction mentioned in the literature differ by taxonomic group. High mobility taxa are driven extinct mainly by overexploitation, whereas low mobility taxa from pollution, climate change and habitat destruction. Most of these extinctions are recorded in the Temperate Northern Atlantic (41%) and the Central Indo-Pacific (30%). The main driver of global marine extinctions is overexploitation (in 13 cases reported as a possible driver), followed by invasive species (seven times reported), habitat destruction (five times reported), trophic cascades (three times reported), and pollution (one time reported) [8]. Overexploitation was historically the primary driver of marine local extinctions. However, in the last three decades, other drivers, such as climate change, climate variability, and pollution, prevail in the published literature[8].

Overexploitation

The intensive exploitation of marine organisms has a short history in comparison with the terrestrial organisms, only commencing in the last few hundred years. Initially, marine animals were not obviously threatened by the wave of extinction that land species were subjected to. However, marine species have been put under great pressure since humans became able to travel over the sea. In this short period, human exploitation of marine resources has been a major factor of extinction, both through direct mortality of target species and multiple collateral effects on non-target species (bycatch). For example, exploitation is responsible for 55% of the main extinction threat to North American marine fishes[15]. Fisheries are also indirectly responsible for biodiversity loss and ecosystem disturbance by abandoning huge amounts of derelict fishing gear in the ocean, which is deadly to many marine top predator species. See also the articles Overexploitation and Effects of fisheries on marine biodiversity.

Habitat Disturbance

Figure 2: Beam trawling is one of the fishing activities that greatly destruct marine habitats. Photo credit Government of Flanders.

Biological, physical and chemical factors in most ecosystems are tightly intertwined. Hence changes in one of these factors can result in changes of others. Exploitation of habitat can therefore profoundly influence many components of a system. Examples of habitat destruction are:

Physical alterations:

Chemical alterations:

Biological alterations:

Climate Change

Recent climate change such as global warming has increased local water temperatures beyond the suitable range of many species. Such changes have made highly productive areas, such as up-welling regions, become less productive due to changes in the food web. Lower primary production supports a lower biomass of primary consumers. In the oceans, krill are major primary consumers that support many important ecosystems. Therefore climate change will inevitably impact food webs based on krill and this will be reflected in the reduction of top level consumer such as large plankton-grazing fish and sea mammals[16]. See also Climate-induced regime shifts.


Habitat destruction is the primary cause for the decline of biodiversity in the East Indian and Central Pacific marine regions. The annual global loss of coastal habitat has been estimated to be between 1–9% for coral reefs, around 1.8% for mangroves and about 7% for seagrass beds[4].

Overexploitation appears to be the primary cause in the Atlantic and Mediterranean regions. Important, but relatively lesser causes of biodiversity loss are pollution, eutrophication, climate change and invasive species, see Fig. 3.


Fig. 3. Major threats of species loss for different marine regions. From Luypaert et al. (2020[4]) Creative Commons licence.


Vulnerability of species

Although every species contributes to the ecosystem function, some species are more vulnerable to extinction and have a greater impact than others. These include:

Species at the top of food chains, such as large carnivores.

Top predators (also called 'apex predators') play a critical role in ecosystems, by regulating directly and indirectly all underlying trophic levels. They need a large territory to get sufficient prey and their abundance is relatively low. Reproduction and growth is slower than for smaller species and so is their recovery after partial depletion. They are a favorite target of the fishery and therefore prone to overfishing[17][18]. Top predators are therefore a vulnerable group of which most species have declined sharply, in some cases more than 90%[19]. For example, even light fishing pressure is sufficient to cause strong population declines in many large shark species[20]. This 'trophic downgrading' has generated widespread concern because of the fundamental role that apex predators can play in ecosystem functioning, disease regulation, and biodiversity maintenance[21]. See also the article Trophic cascade.

Specialized endemic species.

Specialized species with a small geographic range are especially vulnerable to disturbance by invasive species and human intervention. These species can fulfill important functions for the local ecosystem, which are lost when they are replaced by non-native generalist species that compete more efficiently on a larger scale[22].

Several species such as damselfish (Azurina eupalama), the Mauritius green wrasse (Anampses viridis) and two corals (Millepora boschmai and Siderastrea glynni), the Turkish towel algae (Gigartina australis) and Bennett’s seaweed (Vanvoortsia bennettiana) are highly endangered or extinct throughout their small distribution areas.

Migratory species.

Migratory species need suitable habitats to feed and rest in widely spaced locations. Such species, for example, Dugong (Dugong dugon), Loggerhead turtle (Caretta caretta), Hawksbill turtle (Eretmochelys imbricata) and Mediterranean Monk Seal (Monachus monachus) are very vulnerable if one of their habitats is lost.

Species with exceptionally complex life cycles.

Species such as a Tunicate (Ciona intestinalis) and a Brown bryozoan (Bugula neritina) normally need several different elements to be in place at very specific times to complete their life cycles, making them vulnerable if there is disruption of any single element in the cycle.


Consequences of species extinctions at local or regional scales

Species extinction at local or regional scales implies in general a decline in species richness (number of species) and a decline in biodiversity. There is strong evidence that species richness in an area enhances ecosystem productivity and stability [23][24][25][26]. The loss of any species can be detrimental to the ecosystem. This is especially true of the loss of species from the higher trophic levels that suffer the greatest risk of (local) extinction as a result of hunting by humans, loss of habitat or bioaccumulation of toxins. Loss of top predators can result in a so-called trophic cascade - a complete restructuring of the ecosystem and the food web relationships. Reintroduction of lost species is not always possible, as return is prevented by species that have taken their niche in the food web (see the article Trophic cascade for an example).

Invasion of alien species can in some cases compensate for a decline in species diversity (see the article Non-native species invasions). However, most alien invasions are by species from lower trophic levels. The structure of marine food webs then changes from a trophic pyramid covered by a diverse array of predators and consumers to a shorter, squatter configuration dominated by filter feeders and scavengers[27].

A review of global databases related to the impact of biodiversity loss on marine ecosystem services shows that the number of viable fisheries has declined by -33%, the provision of nursery habitats such as oyster reefs, seagrass beds and wetlands has declined by -69% and filtering and detoxification services provided by suspension feeders, submerged vegetation and wetlands has declined by -63% [28]. The loss of filtering services has the potential to increase the risks of harmful algal blooms (e.g. ‘red tide’), oxygen depletion and declining water quality. Moreover, the loss of coastal habitats has also resulted in historical losses of floodplain buffer area and loss of erosion control from coastal wetlands, thus increasing flooding risks to coastal inhabitants[29]. Analysis of the FAO Global Catch Database shows that the rate of fishery collapses, defined here as catches falling below 10% of the recorded maximum, has accelerated over time, with 29% of currently fished species considered to have collapsed in 2003[28].


Mitigation of species extinction

The importance of biodiversity in maintaining a stable ecosystem implies that species extinction should be avoided. Several measures can contribute to this objective.

The most practiced measure to protect marine ecosystems is the instauration of Marine Protected Areas (MPAs). These designated areas help to protect depleted, threatened, rare or endangered species and populations, as well as to preserve habitats of critical species. Currently (2020) MPAs cover about 4% of the oceans; the target of 10% formulated in the Convention on Biological Diversity is still a long way off. In addition, only part of the MPAs offer full protection. These fully protected MPAs, where any kind of resource removal is prohibited, are often referred to as Marine Reserves. A study of 44 Marine Reserves shows an average increase of 23% in species richness. This increase in biodiversity coincides with a sharp increase in fishery productivity[28]. MPAs cover different habitats (e.g sandbank, mudflat, lagoon, mangrove and reef) and therefore provide protection to different assemblages of species (e.g. Lamprey, Bottlenose Dolphin and Loggerhead Turtle), according to the needs and natural states in different countries.

Also crucial to the conservation of species is the elimination, as far as possible, of the various causes of species extinction, by measures such as:

Above all, great efforts should be made to increase public awareness of the urgent need for action. People around the world should understand the causes and consequences of extinctions and the fact that loss of diversity is happening everywhere.

Knowledge of life on Earth is far from complete. In the past 250 years of research, taxonomists have named about 1.78 million species of animals, plants and micro-organisms, yet the total number of species is unknown and probably between 5 and 30 million. Taxonomy provides a major foundation of conservation practice and sustainable management of the world living resources. Worldwide research on taxonomy is fostered by the Global Taxonomy Initiative.


Related articles

Overexploitation
Effects of fisheries on marine biodiversity
Measurements of biodiversity
Ecological thresholds and regime shifts
Resilience and resistance
Trophic cascade


References

  1. ↑ Herringshaw, L.G. and Davies, N.S. 2008. Bioturbation levels during the end-Ordovician extinction event: a case study of shallow marine strata from the Welsh Basin. Aquatic Biology 2: 279–287
  2. ↑ Kaufman, L. and Mallory, K. (eds.) 1986. The Last Extinction. 2nd Edition. The MIT Press. 242 p
  3. ↑ 3.0 3.1 Baille, J.E.M., Hilton-Taylor, C. & Stuart, S. 2004. IUCN Red List of Threatened Species: a global species assessment
  4. ↑ 4.0 4.1 4.2 4.3 Luypaert T., Hagan J.G., McCarthy M.L., Poti M. 2020. Status of Marine Biodiversity in the Anthropocene. In: Jungblut S., Liebich V., Bode-Dalby M. (eds) YOUMARES 9 - The Oceans: Our Research, Our Future. Springer, Cham. https://doi.org/10.1007/978-3-030-20389-4_4
  5. ↑ Rounsevell, M.D.A., Harfoot, M., Harrison, P.A., Newbold, T., Gregory, R.D. and Mace, G.M. 2020. A biodiversity target based on species extinctions. Science 368: 1193–1195
  6. ↑ McCauley, D.J., Pinsky, M.L., Palumbi, S.R., Estes, J.A., Joyce, F.H. and Warner, R.R. 2015. Marine defaunation: Animal loss in the global ocean. Science 347: 1255641
  7. ↑ Carlton, J.T., Geller, J.B., Reaka-Kudla, M.L. and Norse, E.A. 1999. Historical extinctions in the sea. Annual Review of Ecology and Systematics 30: 525-538
  8. ↑ 8.0 8.1 8.2 8.3 8.4 Nikolaou, A. and Katsanevakis, S. 2023. Marine extinctions and their drivers. Regional Environmental Change 23: 88
  9. ↑ Dulvy, N.K., Sadovy, Y. and Reynolds, J.D. 2003. Extinction vulnerability in marine populations. Fish and Fisheries 4: 25-64
  10. ↑ Wilson, E.O. and Frances, M.P. 1988. Biodiversity. National Academy Press. 521p
  11. ↑ The Chinese paddlefish
  12. ↑ Elahi, R., O’Connor, M.I., Byrnes, J.E., Jarrett, E. K., Dunic, J., Eriksson, B.,K., Hensel, M.J. S. and Kearns, P.J. 2015. Recent trends in local-scale marine biodiversity reflect community structure and human impacts. Curr. Biol. 25: 1938–1943. https://doi.org/10.1016/j.cub.2015.05.030
  13. ↑ Hillebrand, H., Blasius, B., Borer, E.T., Chase, J.M., Downing, J.A., Eriksson, B.K., Filstrup, C.T., Harpole, W.S., Hodapp, D., Larsen, S., Lewandowska, A.M., Seabloom, E.W., Van de Waal, D.B and Ryabov, A.B. 2018. Biodiversity change is uncoupled from species richness trends: consequences for conservation and monitoring. J Appl Ecol 55:169–184. https://doi.org/10.1111/1365-2664.12959
  14. ↑ Pilotto, F. et al. 2020. Meta-analysis of multidecadal biodiversity trends in Europe. Nature Communications 11: 3486 https://doi.org/10.1038/s41467-020-17171-y
  15. ↑ Musick, J.A., Harbin, M.M., Berkeley, S.A., Burgess, G.H., Eklund, A.M., Findley, L., Gilmore, R.G., Golden, J.T., Ha, D.S., Huntsman, G.R., McGovern, J.C., Parker, S.J., Poss, S.G., Sala, E., Schmidt, T.W., Sedberry, G.R., Weeks, H. and Wright, S.G. 2000. Marine, estuarine, and diadromous fish stocks at risk of extinction in North America (exclusive of Pacific salmonids). Fisheries 25: 6-30
  16. ↑ Myers, N. 1993. Sharing the earth with whales. In: Les Kaufman and Kenneth Mallory (eds.). The Last Extinction. 2nd Edition. The MIT Press. 242 p
  17. ↑ Roberts, C.M. and Hawkins, J.P. 1999. Extinction risk at sea. Trends Ecol. Evol. 14: 241–246
  18. ↑ Olden, J.D., Hogan Z.S. and Van der Zanden, M.J. 2007. Small fish, big fish, red fish, blue fish: size-biased extinction risk of the world’s freshwater and marine fishes. Glob. Ecol. Biogeogr. 16: 694–701
  19. ↑ Worm, B., Sandow, M., Oschlies, A., Lotze, H.K. and Myers, R.A. 2005. Global Patterns of Predator Diversity in the Open Oceans. Science 309: 1365-1369
  20. ↑ Ferretti, F., Worm, B., Britten, G.L., Heithaus, M.R. and Lotze, H.K. 2010. Patterns and ecosystem consequences of shark declines in the ocean. Ecology Letters 13: 1055–1071
  21. ↑ Stier, A. C., Samhouri, J. F., Novak, M., Marshall, K. N., Ward, E. J., Holt, R. D. and Levin, P. S. 2016. Ecosystem context and historical contingency in apex predator recoveries. Science advances, 2(5), e1501769. https://doi.org/10.1126/sciadv.1501769
  22. ↑ Clavel, J., Julliard, R. and Devictor, V. 2011. Worldwide decline of specialist species: toward a global functional homogenization? Front. Ecol. Environ 9: 222–228
  23. ↑ Loreau, M., Naeem, S., Inchausti, P., Bengtsson, J., Grime, J. P., Hector, A., Hooper, D. U., Huston, M. A. ,Raffaelli, D., Schmid, B., Tilman, D. and Wardle D. A. 2001. Biodiversity and Ecosystem Functioning: Current Knowledge and Future Challenges. Science 294: 804-808
  24. ↑ Palmer, M., Bernhardt, E., Chornesky, E., Collins, S., Dobson, A., Duke, C., Gold, B., Jacobson, R., Kingsland, S., Kranz, R., Mappin, M., Martinez, M.L., Micheli, F., Morse, J., Pace, M., Pascual, M., Palumbi, S., Reichman, O.J., Simons, A., Townsend, A. and Turner, M. 2004. Ecology for a Crowded Planet. Science 304: 1251-1252
  25. ↑ Worm, B., Barbier, E.B., Beaumont, J., Duffy, E., Folke, C., Halpern, B.S., Jackson , J.B.C., Lotze, H.K., Micheli, F., Palumbi, S.R., Sala, E., Selkoe, K.A., Stachowicz, J.J. and Watson, R. 2006. Impacts of biodiversity loss on ocean ecosystem services. Science 314:787–790. https://doi.org/10.1126/science.1132294
  26. ↑ Gamfeldt, L., Lefcheck, J.S., Byrnes, J.E., Cardinale, B.J., Duffy, J.E. and Griffin, J.N. 2015. Marine biodiversity and ecosystem functioning: what’s known and what’s next? Oikos 124: 252–265. https://doi.org/10.1111/oik.01549
  27. ↑ Byrnes, J.E., Reynolds, P.L. and Stachowicz, J.J. 2007. Invasions and Extinctions Reshape Coastal Marine Food Webs. PLoS ONE 2(3): e295. doi:10.1371/journal.pone.0000295
  28. ↑ 28.0 28.1 28.2 Worm B, Barbier EB, Beaumont N, Duffy JE, Folke C, et al. (2006) Impacts of biodiversity loss on ocean ecosystem services. Science 314: 787–790
  29. ↑ Stachowicz, J.J., Whitlatch, R.B., Osman, R.W., 1999. Species diversity and invasion resistance in a marine ecosystem. Science, 286:1577–79
  30. ↑ IUCN booklet Marine Menace; Alien invasive species in the marine environment


The main author of this article is Wan Hussin, Rauhan
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Citation: Wan Hussin, Rauhan (2024): Species extinction. Available from http://www.coastalwiki.org/wiki/Species_extinction [accessed on 21-11-2024]



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