Krill (order Euphausiacea) are small crustaceans found in all the oceans of the world. The name krill comes from the Norwegian word krill, meaning 'young fry of fish', which is also often attributed to other species of fish. Krill are considered an important trophic level connection near the bottom of the food chain because they feed on phytoplankton and to a lesser extent zooplankton, converting these into a form suitable for many larger animals for whom krill makes up the largest part of their diet. In the Southern Ocean, one species, the Antarctic krill, Euphausia superba, makes up an estimated biomass of over 500,000,000 tonnes (490,000,000 long tons; 550,000,000 short tons), roughly twice that of humans. Of this, over half is eaten by whales, seals, penguins, squid and fish each year, and is replaced by growth and reproduction.
Contributions by Lupo, Stemonitis, and Kils.