Krill are small, shrimp-like crustaceans that swarm in enormous numbers, especially in the Southern Ocean. They feed on phytoplankton and, in turn, are the primary food for whales, seals, penguins, and many fish. Their collective biomass is among the largest of any multicellular animal species on Earth.

Antarctic krill (Euphausia superba) grow to about six centimeters and live for several years. They undertake daily vertical migrations and can form surface swarms visible from ships and satellites. Because they occupy such a central position in the polar food web, changes in krill abundance or distribution reverberate through the entire ecosystem.

Krill are also harvested commercially for aquaculture feed and human supplements. Management seeks to balance the fishery with the needs of dependent predators. Climate-driven changes in sea ice, which provides nursery habitat for larval krill, are a major concern for the future of Antarctic krill populations.

• Small shrimp-like crustaceans
• Key prey for whales, seals, and penguins
• Form massive swarms in polar waters
• Subject to commercial harvest and climate pressure