Antarctic krill
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{{Taxobox
| name = Antarctic krill
| image = Krill.jpg
| image_width = 200px
| regnum = [[Animal]]ia
| phylum = [[Arthropod]]a
| subphylum = [[Crustacea]]
| classis = [[Malacostraca]]
| ordo = [[Euphausiacea]]
| familia = [[Euphausiidae]]
| genus = ''[[Euphausia]]''
| species = '''''E. superba'''''
| binomial = ''Euphausia superba''
| binomial_authority = [[James Dwight Dana|Dana]], 1850
}}
'''Antarctic krill''' (''Euphausia superba''{{ref_label|fn_1|a|a}}) is a [[species]] of [[krill]] found in the [[Antarctica|Antarctic]] waters of the [[Southern Ocean]]. Antarctic krill are [[shrimp]]-like [[invertebrate]]s that live in large schools, called [[swarm]]s, sometimes reaching densities of 10,000–30,000 individual animals per [[cubic metre|cubic meter]].<ref name="H+83">{{cite journal |quotes=no |author=Hamner, W. M., Hamner, P. P., Strand, S. W., Gilmer, R. W. |title=Behavior of Antarctic Krill, ''Euphausia superba'': Chemoreception, Feeding, Schooling and Molting' |journal=[[Science (journal)|Science]] |volume=220 |pages=433–435 |year=1983 |doi=10.1126/science.220.4595.433 |pmid=17831417}}</ref> They feed directly on minute [[phytoplankton]], thereby using the [[primary production]] [[energy]] that the phytoplankton originally derived from the sun in order to sustain their [[pelagic]] (open [[ocean]]) [[biological life cycle|life cycle]].<ref name="KK79">{{cite journal |quotes=no |author=Kils, U., Klages, N |title=Der Krill |journal=Naturwissenschaftliche Rundschau |volume=10 |pages=397–402 |year=1979}}</ref> They grow to a length of 6 cm (2.4 in), weigh up to 2 [[gram|g]] (0.7 oz), and can live for up to six years. They are a key species in the Antarctic [[ecosystem]] and are, in terms of [[biomass (ecology)|biomass]], probably the most successful animal species on the planet (approximately 500 million tonnes).<ref name="NE97">{{cite book |author=Nicol, S., Endo, Y. |url=http://www.fao.org/documents/show_cdr.asp?url_file=//DOCREP/003/W5911E/w5911e00.htm |title=Fisheries Technical Paper 367: Krill Fisheries of the World |publisher=[[Food and Agriculture Organization|FAO]] |year=1997}}</ref>
==Systematics==
All members of the [[euphausiacea|krill order]] are shrimp-like animals of the crustacean superorder [[Eucarida]]. Their breastplate units, or [[thoracomer]]s, are joined with the [[carapace]]. The short length of these thoracomers on each side of the carapace makes the [[gill]]s of Antarctic krill visible to the human eye. The [[thoracopod|legs]] do not form a [[gnathopod|jaw structure]], which differentiates this order from the [[decapoda|crabs, lobsters and shrimp]].
{{seealso|Wikispecies:Euphausia superba}}
==Life cycle==
[[Image:Krillhatchingkils.gif|thumb|200px|left|The eggs are spawned close to the surface and start sinking. In the open ocean they sink for about 10 days: the nauplii hatch at around 3000 m depth]]
The main [[spawning]] season of Antarctic krill is from January to March, both above the [[continental shelf]] and also in the upper region of deep sea oceanic areas. In the typical way of all euphausiaceans, the male attaches a sperm package to the genital opening of the female. For this purpose, the first [[pleopod]]s (legs attached to the abdomen) of the male are constructed as mating tools. Females lay 6,000–10,000 [[egg (biology)|eggs]] at one time. They are [[fertilisation|fertilized]] as they pass out of the genital opening by sperm liberated from [[spermatophore]]s which have been attached by the males.<ref name="RQ86">{{cite journal |author=Ross, R. M., Quetin, L. B. |title=How Productive are Antarctic Krill? |journal=Bioscience |volume=36 |pages=264–269 |year=1986 | doi = 10.2307/1310217 <!--Retrieved from CrossRef by DOI bot-->}}</ref>
According to the classical hypothesis of Marr,<ref name="Marr62">{{cite journal |quotes=no |author=Marr, J. W. S. |title=The natural history and geography of the Antarctic Krill ''Euphausia superba'' |journal=Discovery report |volume=32 |pages=33–464 |year=1962}}</ref> derived from the results of the expedition of the famous British research vessel ''[[RRS Discovery]]'', egg development then proceeds as follows: [[gastrulation]] (development of egg into embryo) sets in during the descent of the 0.6 mm eggs on the shelf at the bottom, in oceanic areas in depths around 2,000–3,000 m. From the time the egg hatches, the 1<small><sup>st</sup></small> [[Nauplius (larva)|nauplius]] (i.e., larval stage) starts migrating towards the surface with the aid of its three pairs of legs; the so-called ''developmental ascent''.
The next two larval stages, termed 2<small><sup>nd</sup></small> nauplius and metanauplius, still do not eat but are nourished by the remaining [[yolk]]. After three weeks, the little krill has finished the ascent. They can appear in enormous numbers counting 2 per [[litre|liter]] in 60 m water depth. Growing larger, additional larval stages follow (2<small><sup>nd</sup></small> and 3<small><sup>rd</sup></small> calyptopis, 1<small><sup>st</sup></small> to 6<small><sup>th</sup></small> furcilia). They are characterized by increasing development of the additional legs, the compound eyes and the setae (bristles). At 15 mm, the juvenile krill resembles the habitus of the adults. Krill reach maturity after two to three years. Like all [[crustacean]]s, krill must [[ecdysis|molt]] in order to grow. Approximately every 13 to 20 days, krill shed their [[chitin]]ous [[exoskeleton]] and leave it behind as [[exuvia]].
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==Food==
[[Image:Kilsheadkils.jpg|200px|right|thumb|The head of Antarctic krill. Observe the [[bioluminescence|bioluminescent organ]] at the [[eyestalk]] and the [[nerve]]s visible in the [[Antenna (biology)|antennae]], the [[gastric mill]], the filtering net at the [[thoracopod]]s and the rakes at the tips of the thoracopods.]]
The gut of ''E. superba'' can often be seen shining green through the animal's transparent skin, an indication that this species feeds predominantly on [[phytoplankton]]—especially very small [[diatom]]s (20 [[micrometre|μm]]), which it filters from the water with a ''feeding basket''.<ref>[http://www.ecoscope.com/krill/filter/index.htm Ecoscope.Com<!-- Bot generated title -->]</ref> The glass-like shells of the [[diatom]]s are cracked in the "[[gastric mill]]" and then digested in the [[hepatopancreas]]. The krill can also catch and eat [[copepod]]s, [[amphipod]]s and other small [[zooplankton]]. The gut forms a straight tube; its digestive efficiency is not very high and therefore a lot of [[carbon]] is still present in the [[feces]] (see "[[#The biological pump and carbon sequestration|the biological pump]]" below).
In [[aquarium|aquaria]], krill have been observed to eat each other. When they are not fed in aquaria, they shrink in size after [[ecdysis|molting]], which is exceptional for animals the size of krill. It is likely that this is an [[adaptation]] to the seasonality of their food supply, which is limited in the dark winter months under the ice.
===Filter feeding===
{{main|Filter feeder}}
[[Image:Krill filter feeding.jpg|left|thumb|180px|Krill feeding under high phytoplankton concentration. A [[:Image:Filterkrillkils2.gif|slow motion video]] (from 300 frame/s; 490 kB) is also available.]]
Antarctic krill manages to directly utilize the minute [[phytoplankton]] cells, which no other animal of krill size can do. This is accomplished through [[filter feeding]], using the krill's highly developed front legs, providing for an efficient filtering apparatus:<ref name="Kils83">{{cite book |author=Kils, U. |url=http://wikisource.org/wiki/Author:Uwe_Kils/polar/part1 |title=Swimming and feeding of Antarctic Krill, ''Euphausia superba'' - some outstanding energetics and dynamics - some unique morphological details}} In '{{cite journal |quotes=no |title=On the biology of Krill ''Euphausia superba'' |publisher=[[Alfred Wegener Institute for Polar and Marine Research]], |volume=Special Issue 4 |year=1983 |journal=Proceedings of the Seminar and Report of Krill Ecology Group |author=Editor: S. B. Schnack |pages=130–155 and title page image}}</ref> the six [[thoracopod]]s (legs attached to the [[thorax]]) form a very effective "feeding basket" used to collect phytoplankton from the open water. In the finest areas the openings in this basket are only 1 μm in diameter. In the movie linked to the left, the krill is hovering at a 55° angle on the spot. In lower food concentrations, the feeding basket is pushed through the water for over half a meter in an opened position, as in the ''in situ'' image below, and then the algae are combed to the mouth opening with special [[setae]] (bristles) on the inner side of the thoracopods.
===Ice-algae raking===
[[Image:Krillicekils.jpg|right|thumb|200px|Antarctic krill feeding off [[ice algae]]. The surface of the ice on the left side is colored green by the algae.]]
Antarctic krill can scrape off the green lawn of [[ice-algae]] from the underside of the [[pack ice]].<ref>[http://www.ecoscope.com/icecave2.htm Ecoscope.Com<!-- Bot generated title -->]</ref><ref name="Mar88">{{cite journal |author=Marschall, P. |title=The overwintering strategy of Antarctic krill under the pack ice of the Weddell Sea |journal=Polar Biology |volume=9 |pages=129–135 |year=1988 | doi = 10.1007/BF00442041 <!--Retrieved from CrossRef by DOI bot-->}}</ref> The image to the right, taken via a [[ROV]],<ref name="KM95">{{cite journal |quotes=no |author=Kils, U., Marshall, P. |url=http://wikisource.org/wiki/Author:Uwe_Kils/hempel/part1 |title=Der Krill, wie er schwimmt und frisst - neue Einsichten mit neuen Methoden ("Antarctic krill - feeding and swimming performances - new insights with new methods") |pages=201–210}} In {{cite book |author=Hempel, I., Hempel, G. |title=Biologie der Polarmeere — Erlebnisse und Ergebnisse (Biology of the polar oceans) |publisher=Fischer |year=1995 |id=ISBN 3-334-60950-2}}</ref> shows how most krill swim in an upside-down position directly under the ice. Only a single animal (in the middle) can be seen [[hover]]ing in the free water. Krill have developed special rows of rake-like setae at the tips of the [[thoracopod]]s, and graze the ice in a zig-zag fashion, akin to a lawnmower. One krill can clear an area of a square foot in about 10 minutes (1.5 cm²/s). It is relatively new knowledge that the film of ice algae is very well developed over vast areas, often containing much more carbon than the whole water column below. Krill find an extensive energy source here, especially in the spring.
===The biological pump and carbon sequestration===
[[Image:Krillspitballkils3.jpg|thumb|200px|left|''In situ'' image taken with an [[ecoSCOPE]]. A green spit ball is visible in the lower right of the image and a green fecal string in the lower left.]]
The krill is a highly untidy feeder, and it often spits out aggregates of [[phytoplankton]] (spit balls) containing thousands of cells sticking together. It also produces fecal strings that still contain significant amounts of [[carbon]] and the [[glass]] shells of the [[diatom]]s. Both are heavy and sink very fast into the abyss. This process is called the [[biological pump]]. As the waters around [[Antarctica]] are very deep (2,000–4,000 m), they act as a [[carbon dioxide sink]]: this process exports large quantities of carbon (fixed [[carbon dioxide]], CO<small><sub>2</sub></small>) from the biosphere and [[Carbon Sequestration|sequesters]] it for about 1,000 years.
If the phytoplankton is consumed by other components of the pelagic ecosystem, most of the carbon remains in the upper strata. There is speculation that this process is one of the largest biofeedback mechanisms of the planet, maybe the most sizable of all, driven by a gigantic biomass. Still more research is needed to quantify the Southern Ocean ecosystem.{{clear}}
==Biological peculiarities==
===Bioluminescence===
[[Image:Bioluminescencekils.jpg|thumb|200px|right|Watercolor of bioluminescent krill]]
Krill are often referred to as ''light-shrimp'' because they can emit light, produced by [[bioluminescence|bioluminescent]] organs. These organs are located on various parts of the individual krill's body: one pair of organs at the [[eyestalk]] (cf. the image of the head above), another pair on the hips of the 2<small><sup>nd</sup></small> and 7<small><sup>th</sup></small> [[thoracopod]]s, and singular organs on the four [[pleonsternite]]s. These light organs emit a yellow-green light periodically, for up to 2 to 3 seconds. They are considered so highly developed that they can be compared with a torchlight: a concave reflector in the back of the organ and a lens in the front guide the light produced, and the whole organ can be rotated by muscles. The function of these lights is not yet fully understood; some hypotheses have suggested they serve to compensate the krill's shadow so that they are not visible to predators from below; other speculations maintain that they play a significant role in [[mating]] or [[schooling]] at night.
The krill's bioluminescent organs contain several fluorescent substances. The major component has a maximum [[fluorescence]] at an excitation of 355 [[Nanometre|nm]] and emission of 510 nm.<ref name="HS01">{{cite book |author=Harvey, H. R., Se-Jong Ju |url=http://www.ccpo.odu.edu/Research/globec/3sciinvest/harvey.htm |title=Biochemical Determination of Age Structure and Diet History of the Antarctic Krill, ''Euphausia superba,'' during Austral Winter'' |publisher=[http://www.ccpo.odu.edu/Research/globec/3sciinvest/menu.html Third U.S. Southern Ocean GLOBEC Science Investigator Meeting], Arlington |year=2001}}</ref>
===Escape reaction===
[[Image:Krilllobsterkils.gif|thumb|200px|left|Lobstering krill]]
Krill use an [[escape reaction]] to evade [[predator]]s, swimming backwards very quickly by flipping their [[telson]]. This swimming pattern is also known as [[Caridoid escape reaction|lobstering]]. Krill can reach speeds of over 60 cm/s.<ref name="Kils82">{{cite journal |author=Kils, U. |url=http://wikisource.org/wiki/Author:Uwe_Kils/biomass3/part1 |title=Swimming behavior, Swimming Performance and Energy Balance of Antarctic Krill ''Euphausia superba'' |journal=BIOMASS Scientific Series |volume=3, BIOMASS Research Series |pages=1–122 |year=1982}}</ref> The [[induction (biology)|trigger]] time to optical [[stimulus (physiology)|stimulus]] is, despite the low temperatures, only 55 [[millisecond|ms]].
===The compound eye===
[[Image:Krilleyekils.jpg|right|thumb|200px|[[Electron microscope]] image of the compound eye — the eyes are deep black in the living animal]]
Although the uses for and reasons behind the development of their massive black [[compound eye]]s remain a mystery, there is no doubt that Antarctic krill have one of the most fantastic structures for [[visual perception|vision]] seen in nature{{Fact|date=September 2007}}.
As mentioned above, krill can shrink in size from one molt to the next, which is generally thought to be a survival strategy to adapt to scarce food supplies (a smaller body needs less energy, i.e., food). However, the animal's eyes do ''not'' shrink when this happens. The ratio between eye size and body length has thus been found to be a reliable indicator of starvation.<ref name="SN02">{{cite journal |author=Hyoung-Chul Shin, Nicol, S. |url=http://www.int-res.com/abstracts/meps/v239/p157-167/ |title=Using the relationship between eye diameter and body length to detect the effects of long-term starvation on Antarctic krill ''Euphausia superba'' |journal=Marine Ecology Progress Series (MEPS) |volume=239 |pages=157–167 |year=2002 |doi=10.3354/meps239157}}</ref>
==Geographical distribution==
[[Image:krilldistribution.jpg|thumb|200px|left|Krill distribution on a [[NASA]] [[SeaWIFS]] image — the main concentrations are in the [[Scotia Sea]] at the [[Antarctic Peninsula]]]]
Antarctic krill are found thronging the surface waters of the [[Southern Ocean]]; they have a circumpolar distribution, with the highest concentrations located in the [[Atlantic Ocean|Atlantic]] sector.
The northern boundary of the Southern Ocean with its Atlantic, [[Pacific|Pacific Ocean]] and [[Indian Ocean]] sectors is defined more or less by the Antarctic convergence, a circumpolar front where the cold Antarctic surface water submerges below the warmer [[subantarctic]] waters. This front runs roughly at 55° South; from there to the continent, the Southern Ocean covers 32 million [[square kilometer]]s. This is 65 times the size of the [[North Sea]]. In the winter season, more than three quarters of this area become covered by ice, whereas 24 million square kilometers become ice free in summer. The water temperatures range between −1.3 and 3 [[Celsius|°C]].
The waters of the Southern Ocean form a system of currents. Whenever there is a [[Antarctic Circumpolar Current|West Wind Drift]], the surface strata travels around Antarctica in an easterly direction. Near the continent, the [[Antarctic Coastal Current|East Wind Drift]] runs counterclockwise. At the front between both, large [[eddy (fluid dynamics)|eddies]] develop, for example, in the [[Weddell Sea]]. The krill schools drift with these water masses, to establish one single stock all around Antarctica, with gene exchange over the whole area. Currently, there is little knowledge of the precise migration patterns since individual krill cannot yet be tagged to track their movements.
===Position in the Antarctic ecosystem===
Antarctic krill is the [[keystone species]] of the [[Antarctica]] ecosystem, and provides an important food source for [[whale]]s, [[Seal (mammal)|seals]], [[Leopard Seal]]s, [[fur seal]]s, [[Crabeater Seal]]s, [[squid]], [[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 most unusual [[Crabeater Seal|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=Bonner, B. |title=Birds and Mammals — Antarctic Seals |pages=202–222}} In {{cite book |author=Buckley, R. |title=Antarctica |publisher=[[Pergamon Press]] |year=1995}}</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 journal |author=Miller, D. G., Hampton, I. |title=Biology and Ecology of the Antarctic Krill (''Euphausia superba'' Dana): a review |journal=BIOMASS Scientific Series |volume=9 |pages=1–66 |year=1989}}</ref>
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"/> The next size step in the [[food chain]] to the [[whale]]s is also enormous, a [[phenomenon]] only found in the [[Antarctic ecosystem]]. ''E. superba'' lives only in the Southern Ocean. In the North Atlantic, ''[[Meganyctiphanes norvegica]]'' and in the Pacific, ''[[Euphausia pacifica]]'' are the dominant species.
===Biomass and production===
The biomass of Antarctic krill is estimated to be between 125 to 725 million [[tonne]]s,<ref name="FAO05">{{cite web |publisher=[[Food and Agriculture Organization|FAO]] |url=http://www.fao.org/figis/servlet/species?fid=3393 |title=Species Fact Sheet ''Euphausia superba'' |accessmonthday=June 16 |year=2005}}</ref> making ''E. superba'' the most successful animal species on the [[Earth|planet]]. It should be noted that of all animals visible to the naked eye some biologists speculate that [[ant]]s provide the largest biomass (but this speculation adds up hundreds of different species) whilst others speculate that it could be the [[copepod]]s, but this too would be the sum of many hundreds of species that exist over the planet. To get an impression of the biomass of ''E. superba'' against that of other species: The total non-krill yield from all world fisheries, finfish, [[shellfish]], [[cephalopod]]s and plankton is about 100 million tonnes per year whilst estimates of the Antarctic krill production are between 13 million to several billion tonnes per year.
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 [[nutrient]]s from all of the world's oceans back into the [[photic zone]] where they are once again available to living organisms.
Thus [[primary production]] — the conversion of sunlight into organic biomass, the foundation of the food chain — has an annual carbon fixation of between 1 and 2 g/m² in the open ocean. Close to the ice it can reach 30–50 g/m². 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 just 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.
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===Decline with shrinking pack ice===
[[Image:Krillicekils.gif|thumb|240px|right|after data compiled by Loeb et al. 1997<ref name="L+97">{{cite journal |quotes=no |author=Loeb, V., Siegel, V., Holm-Hansen, O., Hewitt, R., Fraser, W., ''et al.'' |title=Effects of sea-ice extent and krill or salp dominance on the Antarctic food web |journal=[[Nature (journal)|Nature]] |volume=387 |pages=897–900 |year=1997 |doi=10.1038/43174}}</ref> — temperature and pack ice area — 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 — in 1995 the temperature reached the freezing point]]
There are concerns that the overall biomass of Antarctic krill has been declining rapidly over the last few decades. Some scientists have speculated this value being as high as 80%. This could be caused by the reduction of the [[pack ice]] zone due to [[global warming]].<ref name="Gr05">{{cite journal |quotes=no |author=Gross, L.|doi= 10.1371/journal.pbio.0030127 |title=As the Antarctic Ice Pack Recedes, a Fragile Ecosystem hangs in the Balance |journal=PLoS Biology |volume=3 |issue=4 |pages=127 |year=2005}}</ref> The graph on the right depicts the rising temperatures of the Southern Ocean and the loss of pack ice (on an inverted scale) over the last years 40 years. 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 |author=Atkinson, A., Siegel, V., Pakhomov, E., Rothery, P. |title=Long-term decline in krill stock and increase in salps within the Southern Ocean |journal=[[Nature (journal)|Nature]] |volume=432 |pages=100–103 |year=2004 |doi=10.1038/nature02996}}</ref> a barrel-shaped free-floating [[filter feeder]] that also grazes on plankton.
===Ocean acidification===
[[ocean acidification|Acidification of the oceans]] due to increased levels of carbon dioxide appears to be another challenge to Antarctic Krill as it will be for many calcifying organisms such as corals or bivalve mussels or snails.{{Fact|date=June 2008}} The krills exoskeleton contains carbonate, which is susceptible to dissolution under low [[pH]] conditions. It is however not currently know whether [[calcium carbonate]] or the less stable [[aragonite]] form of carbonate forms the exoskeleton of the krill. Little is currently know about the effects that ocean acidification could have on the krill but it is feared that it could significantly impact on its distribution, abundance and survival as it appears to have effects on its ability to moult and grow or its behavioural patterns.
===Fisheries===
{{Main|Krill fishery}}
[[Image:krillcatch.gif|thumb|240px|left|Annual world catch of ''E. superba'', compiled from [[Food and Agriculture Organization|FAO]] data.<ref name="FAO05"/>]]
The fishery of Antarctic krill is on the order of 100,000 tonnes per year. The major catching nations are [[Japan]] and [[Poland]]. The products are used largely in [[Japan]] as a [[delicacy]] and worldwide 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. Additionally, fine nets also tend to be very delicate, and the first krill nets tore apart while fishing through krill shoals.
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. Processing aims are splitting the muscular hind part from the front part and separating the [[chitin]] armor, in order to produce frosted products and concentrate powders. 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 |author=Everson, I., Agnew D. J., Miller, D. G. M. |title=Krill fisheries and the future |pages=345–348}} In {{cite book |author=Everson, I. (ed.) |title=Krill: biology, ecology and fisheries |publisher=Oxford, Blackwell Science |year=2000}}</ref>
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==Future visions and ocean engineering==
Despite the lack of knowledge available about the whole Antarctic ecosystem, large scale experiments involving krill are already being performed to increase [[carbon sequestration]]: in vast areas of the Southern Ocean there are plenty of nutrients, but still, the phytoplankton does not grow much. These areas are termed [[HNLC]] (high nutrient, low carbon). The phenomenon is called the [[Antarctic Paradox]], and occurs because [[iron]] is missing.<ref>[http://www.palomar.edu/oceanography/iron.htm The Iron Hypothesis<!-- Bot generated title -->]</ref> Relatively small injections of iron from research vessels trigger very large blooms, covering many miles. The hope is that such large scale exercises will draw down [[carbon dioxide]] as compensation for the burning of [[fossil fuel]]s.<ref>[http://www.chooseclimate.org/cleng/cleng.html Climate Engineering<!-- Bot generated title -->]</ref> Krill is the key player in this process, collecting the minute plankton cells which fix carbon dioxide and converting the substance to rapidly-sinking carbon in the form of spit balls and fecal strings.
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==Notes==
<div class="references-small">
# {{note_label|fn_1|a|a}} This species is often misspelled ''Euphasia superba'' [http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&safe=off&q=%22euphasia+superba%22&btnG=Google+Search] or ''Eupausia superba'' [http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&safe=off&q=%22eupausia+superba%22&btnG=Google+Search].
</div>
==References==
{{reflist|2}}
==Further reading==
<div class="references-small">
* Hempel, I.; Hempel, G.: ''Field observations on the developmental ascent of larval ''Euphausia superba'' (Crustacea)''. Polar Biol 6; pp. 121 – 126; 1986.
* Hempel, G.: ''Antarctic marine food webs''. In Siegfried, W. R.; Condy, P. R.; Laws, R. M. (eds): ''Antarctic nutrient cycles and food webs''. Springer-Verlag, Berlin, pp. 266 – 270; 1985.
* Hempel, G.: ''The krill-dominated pelagic system of the Southern Ocean''. Envir. Inter. 13, pp. 33 – 36; 1987.
* Hempel, G.: ''Life in the Antarctic sea ice zone''. Polar Record '''27'''(162); pp. 249 – 253; 1991
* Hempel, G.; Sherman, K.: ''Large marine ecosystems of the world: trends in exploitation, protection, and research''. Elsevier, Amsterdam: Large marine ecosystems 12, 423 pp; 2003
* Mauchline, J.; Fisher, L.R.: ''The biology of euphausiids.'' Adv. Mar. Biol. 7; 1969.
*Nicol, S. & de la Mare, W. K. Ecosystem management and the Antarctic krill. American Scientist 81 (No. 1), pp. 36–47. Biol 9:129–135; 1993.
* Nicol, S.; Foster, J.: ''[http://www.edpsciences.org/articles/alr/pdf/2003/01/alr3065.pdf?access=ok Recent trends in the fishery for Antarctic krill]'', Aquat. Living Resour. '''16''', pp. 42 – 45; 2003.
* Quetin, L. B., Ross, R. M. and Clarke, A.: ''Krill energetics: seasonal and environmental aspects of the physiology of ''Euphausia superba. In El-Sayed, S. Z. (ed.): ''Southern Ocean Ecology: the BIOMASS perspective'', pp. 165 – 184. Cambridge University Press, 1994.
* Sahrhage, D.: ''Antarctic Krill Fisheries: Potential Resources and Ecological Concerns.'' In Caddy, J. F. (ed.): ''Marine Invertebrate Fisheries; their assessment and management''; pp. 13 – 33. Wiley, 1989.
*Ikeda, T. (1984) The influence of feeding on the metabolic activity of Antarctic krill (''Euphausia superba'' Dana). Polar Biology 3(1)
*Clarke, A. (1983) Towards an energy budget for krill: The physiology and biochemistry of ''Euphausia superba'' Dana. Polar Biology 2(2)
*Ishii, H. (1987) Metabolic rates and elemental composition of the Antarctic krill, ''Euphausia superba'' Dana. Polar Biology 7(6)
*Kils, U., (2006) So frisst der Krill <nowiki>[</nowiki>[[wikisource:How Krill feeds|How krill feeds]]]. In: Hempel, G., Hempel, I., Schiel, S., Faszination Meeresforschung, Ein oekologisches Lesebuch. Hauschild Bremen, 112–115
</div>
{{wikispecies|Euphausia superba}}
== External links ==
{{Commonscat|Euphausia superba}}
{{Spoken Wikipedia|Antarctic krill.ogg|2005-09-03}}
* [http://www.marinebio.com/species.asp?id=518 ''Euphausia superba''] from ''MarineBio''.
* [http://www.ecoscope.com/krill "Virtual microscope"] of Antarctic krill for an interactive tour of their morphology and behavior, along with other peer-reviewed information.
* [http://earthobservatory.nasa.gov/Study/UpperCrust/ "Krill fights for survival as sea ice melts"] from the [[NASA]]'s "Earth Observatory".
* [http://news.nationalgeographic.com/news/2003/08/0805_030805_antarctic.html "Antarctic Wildlife at Risk From Overfishing, Experts Say"], from ''[[National Geographic]]'' News, [[August 5]] [[2003]].
* [http://www.antarctica.ac.uk/Living_and_Working/Diaries/RRS_James_Clark_Ross/antarctic2002_2003/jrupdate12_16.html Diary] of the [[RRS]] ''James Clark Ross'', giving a popular introduction to the Antarctic krill.
*[http://news.bbc.co.uk/1/hi/sci/tech/1445754.stm "Climate row touches blue whales"], from the [[BBC]], [[July 19]] [[2001]].
* [http://www.aad.gov.au/default.asp?casid=1143 A time to krill]
* [http://wikisource.org/wiki/Wikisource:Miscellaneous_material/krill_literature Extensive bibliography].
* [http://www.krillcount.org/ Krill Count Project]
* [http://de.wikiversity.org/wiki/Kurs:Biologie_der_Antarktis WIKIversity Lecture "Biology of Antarctica"]
{{featured article}}
[[Category:Krill]]
[[Category:Spoken articles]]
[[Category:Fauna of Antarctica]]
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