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| ==Ecology== | | ==Ecology== |
| Antarctic krill is the [[keystone species]] of the [[Antarctic]] ecosystem beyond the coastal shelf,<ref>{{cite book |editors=Guido di Prisco, Cinzia Verde |series=Adaptation and Evolution in Marine Environments |volume=1 |title=The Impacts of Global Change on Biodiversity |publisher=Springer Science & Business Media |year=2012 |isbn=9783642273513 |chapter=Sea-ice interactions with polar fish: focus on the Antarctic silverfish life history |authors=Mario Vacchi, Philippe Koubbi, Laura Ghigliotti & Eva Pisano |pages=51–73<!-- at p. 63 --> |doi=10.1007/978-3-642-27352-0_4}}</ref> and provides an important food source for [[whale]]s, [[Seal (mammal)|seals]], [[leopard seal]]s, [[fur seal]]s, [[crabeater seal]]s, [[squid]], [[Notothenioidei|icefish]], [[penguin]]s, [[albatross]]es and many other species of [[bird]]s. Crabeater seals have even developed special teeth as an adaptation to catch this abundant food source: its unusual multilobed teeth enable this species to sieve krill from the water. Its dentition looks like a perfect strainer, but how it operates in detail is still unknown. Crabeaters are the most abundant seal in the world; 98% of their diet is made up of '' E. superba''. These seals consume over 63 million [[tonne]]s of krill each year.<ref name="Bon95">{{cite book |author=B. Bonner |chapter=Birds and Mammals – Antarctic Seals |pages=202–222 |editor=R. Buckley |title=Antarctica |publisher=[[Pergamon Press]] |year=1995 |isbn=0-08-028881-2}}</ref> [[Leopard seal]]s have developed similar teeth (45% krill in diet). All seals consume 63–130 million tonnes, all whales 34–43 million tonnes, birds 15–20 million tonnes, squid 30–100 million tonnes, and fish 10–20 million tonnes, adding up to 152–313 million tonnes of krill consumption each year.<ref name="MH89">{{cite book |author1=D. G. M. Miller |author2=I. Hampton |year=1989 |title=Biology and ecology of the Antarctic krill (''Euphausia superba'' Dana): a review |series=BIOMASS Scientific Series |volume=9 |pages=1–66 |isbn=0-948277-09-2 |publisher=[[Scientific Committee on Antarctic Research]]}}</ref> | | Antarctic krill are the keystone species of the [[Antarctica|Antarctic]] ecosystem beyond the coastal shelf, and provides an important food source for whales, [[leopard seal]]s, [[fur seal]]s, [[crabeater seal]]s, [[squid]], [[icefish]], penguins, albatrosses and many other species of birds. |
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| The size step between krill and its prey is unusually large: generally it takes three or four steps from the 20 μm small [[phytoplankton]] cells to a krill-sized organism (via small [[copepod]]s, large copepods, [[mysid]]s to 5 cm [[fish]]).<ref name="KK79"/> ''E. superba'' lives only in the Southern Ocean. In the North Atlantic, ''[[Meganyctiphanes norvegica]]'' and in the Pacific, ''[[Euphausia pacifica]]'' are the dominant species. | | Crabeater seals have even developed special teeth as an adaptation to catch this abundant food source: its unusual multilobed teeth enable this species to sieve krill from the water. Its dentition looks like a perfect strainer, but how it operates in detail is still unknown. Crabeaters are the most abundant seal in the world; 98% of their diet is made up of '' E. superba''. These seals consume over 63 million tonnes of krill each year. |
| | [[Leopard seal]]s have developed similar teeth and consume approximately 45% krill in their diets. All seals combined consume 63–130 million tonnes, all whales 34–43 million tonnes, birds 15–20 million tonnes, squid 30–100 million tonnes, and fish 10–20 million tonnes, adding up to 152–313 million tonnes of krill consumption each year. |
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| | The size step between krill and its prey is unusually large: generally it takes three or four steps from the small phytoplankton cells to a krill-sized organism (via small copepods, large copepods, mysids to 5 cm fish. ''E. superba'' lives only in the Southern Ocean. In the North Atlantic, ''Meganyctiphanes norvegica'' and in the Pacific, ''Euphausia pacifica'' are the dominant species. |
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| ===Biomass and production=== | | ===Biomass and production=== |
| The [[Biomass (ecology)|biomass]] of Antarctic krill is estimated to be 125 to 725 million [[tonne]]s.<ref name="FAO05">{{cite web |publisher=[[Food and Agriculture Organization]] |url=http://www.fao.org/figis/servlet/species?fid=3393 |title=Species Fact Sheet ''Euphausia superba'' |accessdate=June 16, 2005}}</ref> The reason Antarctic krill are able to build up such a high biomass and production is that the waters around the icy Antarctic continent harbour one of the largest [[plankton]] assemblages in the world, possibly ''the'' largest. The ocean is filled with [[phytoplankton]]; as the water rises from the depths to the light-flooded surface, it brings [[nutrient]]s from all of the world's oceans back into the [[photic zone]] where they are once again available to living organisms. | | The biomass of Antarctic krill is estimated to be 125 to 725 million tonnes. The reason Antarctic krill are able to build up such a high biomass and production is that the waters around the icy Antarctic continent harbor one of the largest plankton assemblages in the world, possibly ''the'' largest. The ocean is filled with phytoplankton; as the water rises from the depths to the light-flooded surface, it brings nutrients from all of the world's oceans back into the photic zone where they are once again available to living organisms. |
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| Thus [[primary production]]—the conversion of sunlight into organic biomass, the foundation of the food chain—has an annual carbon fixation of 1–2 g/m<sup>2</sup> in the open ocean. Close to the ice it can reach 30–50 g/m<sup>2</sup>. These values are not outstandingly high, compared to very productive areas like the [[North Sea]] or [[upwelling]] regions, but the area over which it takes place is enormous, even compared to other large primary producers such as [[rainforest]]s. In addition, during the Austral summer there are many hours of daylight to fuel the process. All of these factors make the plankton and the krill a critical part of the planet's ecocycle. | | Thus primary production—the conversion of sunlight into organic biomass, the foundation of the food chain—has an annual carbon fixation of 1–2 g/m in the open ocean. Close to the ice it can reach 30–50 g/m. These values are not outstandingly high, compared to very productive areas like the North Sea or upwelling regions, but the area over which it takes place is enormous, even compared to other large primary producers such as rainforests. In addition, during the Austral summer there are many hours of daylight to fuel the process. All of these factors make the plankton and the krill a critical part of the planet's ecocycle. |
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| ===Decline with shrinking pack ice=== | | ===Decline with shrinking pack ice=== |
| [[File:Krillicekils.gif|thumb|Temperature and pack ice area over time, after data compiled by Loeb ''et al.'' 1997.<ref name="L+97">{{cite journal |author1=V. Loeb |author2=V. Siegel |author3=O. Holm-Hansen |author4=R. Hewitt |author5=W. Fraser |author6=W. Trivelpiece |author7=S. Trivelpiece |year=1997 |title=Effects of sea-ice extent and krill or salp dominance on the Antarctic food web |journal=[[Nature (journal)|Nature]] |volume=387 |issue=6636 |pages=897–900 |doi=10.1038/43174 |url=http://www.magazine.noaa.gov/stories/pdfs/loeb.nature.paper.1997.pdf |format=[[Portable Document Format|PDF]] |bibcode=1997Natur.387..897L}}</ref> The scale for the ice is inverted to demonstrate the correlation; the horizontal line is the freezing point—the oblique line the average of the temperature.]]
| | A possible decline in Antarctic krill biomass may have been caused by the reduction of the [[pack ice]] zone due to [[global warming]]. Antarctic krill, especially in the early stages of development, seem to need the pack ice structures in order to have a fair chance of survival. The pack ice provides natural cave-like features which the krill uses to evade their predators. In the years of low pack ice conditions the krill tend to give way to [[salp]]s, a barrel-shaped free-floating filter feeder that also grazes on plankton. |
| A possible decline in Antarctic krill biomass may have been caused by the reduction of the [[pack ice]] zone due to [[global warming]].<ref name="Gr05">{{cite journal |author=Liza Gross |year=2005 |title=As the Antarctic ice pack recedes, a fragile ecosystem hangs in the balance |journal=[[PLoS Biology]] |volume=3 |issue=4 |page=e127 |doi=10.1371/journal.pbio.0030127 |pmid=15819605 |pmc=1074811}}</ref> Antarctic krill, especially in the early stages of development, seem to need the pack ice structures in order to have a fair chance of survival. The pack ice provides natural cave-like features which the krill uses to evade their predators. In the years of low pack ice conditions the krill tend to give way to [[salp]]s,<ref name="A+04">{{cite journal |author1=Angus Atkinson |author2=Volker Siegel |author3=Evgeny Pakhomov |author4=Peter Rothery |year=2004 |title=Long-term decline in krill stock and increase in salps within the Southern Ocean |journal=[[Nature (journal)|Nature]] |volume=432 |issue=7013 |pages=100–103 |doi=10.1038/nature02996 |pmid=15525989 |bibcode=2004Natur.432..100A}}</ref> a barrel-shaped free-floating [[filter feeder]] that also grazes on plankton. | |
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| ===Ocean acidification=== | | ===Ocean acidification=== |
| Another challenge for Antarctic krill, as well as many calcifying organisms (corals, bivalve mussels, snails etc.), is the [[Ocean acidification|Acidification of the oceans]] caused by increasing levels of carbon dioxide.<ref name="ACECRC">{{cite book |authors=Australian Antarctic Climate and Ecosystems, Cooperative Research Centre |lastauthoramp=yes |title=Position analysis: CO<sub>2</sub> emissions and climate change: OCEAN impacts and adaptation issues |issn=1835-7911 |year=2008}}</ref> Krill exoskeleton contains carbonate, which is susceptible to dissolution under low [[pH]] conditions. It has already been shown that increased carbon dioxide can disrupt the development of krill eggs and even prevent the juvenile krill from hatching, leading to future geographically widespread decreases in krill hatching success.<ref>{{cite journal |author1=So Kawaguchi |author2=Haruko Kurihara |author3=Robert King |author4=Lillian Hale |author5=Thomas Berli |author6=James P. Robinson |author7=Akio Ishida |author8=Masahide Wakita |author9=Patti Virtue |author10=Stephen Nicol |author11=Atsushi Ishimatsu |year=2011 |title=Will krill fare well under Southern Ocean acidification? |journal=[[Biology Letters]] |volume=7 |issue=2 |pages=288–291 |doi=10.1098/rsbl.2010.0777 |url=http://www.webpages.uidaho.edu/envs501/downloads/Kawaguchi%20et%20al.%202010.pdf |format=[[Portable Document Format|PDF]]}}</ref><ref>{{cite journal |author1=So Kawaguchi |author2=Akio Ishida |author3=Robert King |author4=Ben Raymond |author5=N. Waller |author6=A. Constable |author7=Stephen Nicol |author8=Masahide Wakita |author9=Atsushi Ishimatsu |year=2013 |title=Risk maps for Antarctic krill under projected Southern Ocean acidification |journal=[[Nature Climate Change]] |volume=3 |issue=9 |pages=843–847 |url=https://www.researchgate.net/profile/Atsushi_Ishimatsu/publication/249009598_Risk_maps_for_Antarctic_krill_under_projected_Southern_Ocean_acidification/links/540f9c9f0cf2f2b29a3de215.pdf |format=[[Portable Document Format|PDF]]|bibcode=2013NatCC...3..843K |doi=10.1038/nclimate1937 }}</ref> The further effects of ocean acidification on the krill life cycle however remains unclear but scientists fear that it could significantly impact on its distribution, abundance and survival.<ref>{{cite news |title=Swiss marine researcher moving in for the krill |author=Jill Rowbotham |publisher=[[The Australian]] |date=September 24, 2008 |url=http://www.theaustralian.news.com.au/story/0,25197,24392216-27703,00.html}}</ref><ref>{{cite journal |author1=James C. Orr |author2=Victoria J. Fabry |author3=Olivier Aumont |author4=Laurent Bopp |author5=Scott C. Doney |year=2005 |title=Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms |journal=[[Nature (journal)|Nature]] |volume=437 |issue=7059 |pages=681–686 |doi=10.1038/nature04095 |pmid=16193043 |bibcode=2005Natur.437..681O|display-authors=etal}}</ref> | | Another challenge for Antarctic krill, as well as many calcifying organisms (corals, bivalve mussels, snails etc.), is the [[Ocean acidification|Acidification of the oceans]] caused by increasing levels of carbon dioxide. The further effects of ocean acidification on the krill life cycle however remains unclear but scientists fear that it could significantly impact on its distribution, abundance and survival. |
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| ===Fisheries=== | | ===Fisheries=== |
| {{Main|Krill fishery}}
| | The fishery of Antarctic krill is on the order of 100,000 tonnes per year. The major catching nations are South Korea, Norway, Japan and Poland. The products are used as animal food and fish bait. Krill fisheries are difficult to operate in two important respects. First, a krill net needs to have very fine meshes, producing a very high drag, which generates a bow wave that deflects the krill to the sides. Second, fine meshes tend to clog very fast. |
| [[File:krillcatch.gif|thumb|Annual world catch of ''E. superba'', compiled from [[Food and Agriculture Organization|FAO]] data.<ref name="FAO05"/>]]
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| The fishery of Antarctic krill is on the order of 100,000 tonnes per year. The major catching nations are [[South Korea]], [[Norway]], [[Japan]] and [[Poland]].<ref>[http://www.ccamlr.org/pu/e/e_pubs/sb/sb-vol20.pdf CCAMLR Statistical Bulletin vol. 20 (1998-2007)] {{webarchive |url=https://web.archive.org/web/20090225124314/http://www.ccamlr.org/pu/e/e_pubs/sb/sb-vol20.pdf |date=February 25, 2009 }}, CCAMLR, Hobart, Australia, 2008. URL last accessed July 3, 2008.</ref> The products are used as animal food and fish bait. Krill fisheries are difficult to operate in two important respects. First, a krill net needs to have very fine meshes, producing a very high [[Drag (physics)|drag]], which generates a [[bow wave]] that deflects the krill to the sides. Second, fine meshes tend to clog very fast. | |
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| Yet another problem is bringing the krill catch on board. When the full net is hauled out of the water, the organisms compress each other, resulting in great loss of the krill's liquids. Experiments have been carried out to pump krill, while still in water, through a large tube on board. Special krill nets also are currently under development. The processing of the krill must be very rapid since the catch deteriorates within several hours. Its high protein and vitamin content makes krill quite suitable for both direct human consumption and the animal-feed industry.<ref name="E+00">{{Cite book |author1=Inigo Everson |author2=David J. Agnew |author3=Denzil G. M. Miller |chapter=Krill fisheries and the future |pages=345–348 |editor=Inigo Everson |title=Krill: Biology, Ecology and Fisheries |location=Oxford |publisher=[[Blackwell Science]] |series=Fish and aquatic resources series |year=2000 |isbn=978-0-632-05565-4}}</ref> | | Yet another problem is bringing the krill catch on board. When the full net is hauled out of the water, the organisms compress each other, resulting in great loss of the krill's liquids. Experiments have been carried out to pump krill, while still in water, through a large tube on board. Special krill nets also are currently under development. The processing of the krill must be very rapid since the catch deteriorates within several hours. Its high protein and vitamin content makes krill quite suitable for both direct human consumption and the animal-feed industry. |
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| ==Future visions and ocean engineering== | | ==Future visions and ocean engineering== |