They live in large groups, called swarms. Sometimes these swarms have a density of 10,000–30,000 individual animals per cubic meter.
They feed directly on very small phytoplankton, so they can use the energy that the phytoplankton originally got from the sun in order to sustain their life in the open ocean. They grow to a length of 6cm, weigh up to 2g, and can live for up to six years. They are a key species in the Antarctic ecosystem and are, in terms of biomass, probably the most successful animal species on the planet (approximately 500 million tonnes).
In aquaria, krill have been observed to eat each other.
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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
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.
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)
"Virtual microscope"Archived 2002-12-18 at the Wayback Machine of Antarctic krill for an interactive tour of their morphology and behavior, along with other peer-reviewed information.