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Krill are shrimp-like marine invertebrate animals. These small crustaceans are important organisms of the zooplankton, particularly as food for whales, mantas, baleen whales, seals, seabird, fishes and squid. Krill are member of taxonomic order Euphausiacea. They are distinguished among the eucarids by the absence of maxillipeds, the exposure of the thoracic gills external to the carapace, and the possession of biramous thoracopods. These thoracic legs include the feeding legs and the grooming legs. Additionally all species have five swimming legs called pleopods or "swimmerets". Most of them have photophores that are able to emit light on the eyestalks, the bases of the second and seventh thoracopods, and between the first 4 pairs of abdominal limbs. The precise function of these organs is as yet unknown; they might have a purpose in mating, social interaction, orientation and counter-illumination camouflage. Krill are pelagic and known from all oceanic environments to depths of 5,000 m. Commercial fishing of krill is done in the Southern Ocean and in the waters around Japan. The total global production amounts to 150 - 200,000 tonnes annually, most of this from the Scotia Sea. Most krill is used for aquaculture, sport fishing, and in the pharmaceutical industry. The Antarctic krill Euphausia superba have a circumpolar distribution with the highest concentrations in the Atlantic sector of the Southern Ocean. It is a keys species of the Antarctic ecosystem and plays an important role both as feeder of algae, bacteria and micro-zooplankton and as a prey of vertebrates. E.superba displays a large daily vertical migration that occurs generally within the upper 200 m water column making a significant amount of biomass available as food for predators near the surface at night and in deeper waters during the day. Antarctic krill makes up a biomass of over 500 million tons, roughly twice that of humans. (http://en.wikipedia.org/wiki/Antarctic_krill) | |
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