Krill is the Norwegian word for whale food. It is also used as synonym for euphausiids, which are shrimp-like marine invertebrates, important organisms of the plankton (zooplankton).

In the literal sense krill is used as common name for the most spectacular species: the Antarctic Krill (Euphausia superba) of the Antarctic waters in the Southern Ocean. It is an euphausiid (Arthropoda / Crustacea / Malacostraca / Euphausiacea) [1] (http://www.biosis.org.uk/zrdocs/zoolinfo/grp_crus.htm#Euphausiacea). Krill live in large schools (swarms) and convert the primary production directly into a relatively large animal [2] (http://www.ecoscope.com/naturwie.htm)[3] (http://www.ecoscope.com/polarbe2.htm): they grow to a length of 6 cm, weigh 2 grammes, and live probably for 6 years.

Krill is the keystone species of the ecosystem of Antarctica, and is an important food organism for whales, seals, Leopard Seals, fur seals, Crabeater Seals, squid, icefish, penguins, albatrosses and many other birds. Their biomass is estimated to be between 100 and 800 million tonnes, making E. superba probably the most successful animal on the planet; for comparison, the total non-krill yield from all world fisheries is about 100 million tonnes per year. The fishery of krill is on the order of 90,000 tonnes per year.

The gut of E. superba can often be seen shining in green through its transparent skin, an indication that this species feeds predominantly on phytoplankton, e.g. diatoms, which it filters from the water with a "feeding basket" [4] (http://www.ecoscope.com/krill/filter/index.htm). Antarctic krill can also scrape algae from the undersurface of the pack ice [5] (http://www.ecoscope.com/icecave2.htm) and prey on copepods. Krill is also called light-shrimp because it can produce a yellow green light with light-organs at the eyes and base of the swimming legs (bioluminescence).