Difference between revisions of "Antarctic krill"
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==Ecology== | ==Ecology== | ||
Antarctic krill | 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. | ||
The size step between krill and its prey is unusually large: generally it takes three or four steps from the | 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. | |||
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. | |||
===Biomass and production=== | ===Biomass and production=== | ||
The | 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. | ||
Thus | 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. | ||
===Decline with shrinking pack ice=== | ===Decline with shrinking pack ice=== | ||
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]]. | |||
===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. | 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. | ||
===Fisheries=== | ===Fisheries=== | ||
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. | |||
The fishery of Antarctic krill is on the order of 100,000 | |||
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. | 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. | ||
==Future visions and ocean engineering== | ==Future visions and ocean engineering== |