Antarctic Krill (Euphausia superba) is a shrimp-like crustacean that forms enormous swarms in the Southern Ocean around Antarctica. Despite being small—typically 4–6 cm long—it is one of the most influential animals on Earth because it converts microscopic algae into food for larger wildlife.
Its global importance is also numerical: estimates commonly place Antarctic krill biomass in the hundreds of millions of tonnes, with many assessments citing roughly 300–500 million tonnes in the Scotia Sea–Atlantic sector alone. Because so many predators depend on it, Antarctic krill is often described as the “keystone” species of the Antarctic food web.
Antarctic krill belongs to the order Euphausiacea, a group distinct from true shrimp but similar in appearance. Its scientific name, Euphausia superba, reflects both its genus (Euphausia) and species (superba), and it is adapted for cold, seasonal waters and life in massive aggregations.
Adult Antarctic krill typically measure 4–6 cm in body length (about 1.6–2.4 inches), with large individuals reaching around 6.5 cm. Most adults weigh roughly 0.5–2 grams depending on season and body condition, as lipid stores can swell after summer feeding.
They have a semi-transparent body with a segmented exoskeleton, feathery swimming legs, and prominent compound eyes. Antarctic krill also possess bioluminescent organs (photophores) that can produce light, which may help with schooling, communication, or countershading in dim water.
Antarctic krill is distributed circumpolarly around Antarctica, most abundant in regions such as the Scotia Sea and Antarctic Peninsula, but it can occur from near the continent out into sub-Antarctic waters. It occupies surface waters to several hundred meters deep, with much of its daily activity concentrated in the upper ~0–200 m where food is richest.
Sea ice is a critical habitat, especially for juveniles: algae growing on the underside of ice can provide winter nutrition when phytoplankton in open water is scarce. In summer, krill concentrate where currents and fronts aggregate phytoplankton, helping create swarms that can extend for kilometers and contain tens of thousands of individuals per cubic meter.
Antarctic krill primarily grazes on phytoplankton, especially diatoms, using specialized basket-like feeding appendages to filter particles from the water. It is also opportunistic and can eat sea-ice algae, zooplankton, and detritus, a flexibility that improves survival through the dark Antarctic winter.
One of its most important behaviors is diel vertical migration: swarms often rise toward the surface at night to feed and descend during daylight to reduce predation risk. Individuals can move hundreds of meters vertically in a day, and their swimming speeds are typically on the order of a few body lengths per second (roughly 5–10 cm/s), enough to keep cohesive swarms and respond to predators.
Antarctic krill is a cornerstone prey for Baleen whales, which can consume hundreds to several thousand kilograms of krill per day during feeding seasons. It is also essential to seabirds such as the Emperor penguin and marine mammals like the Crabeater seal, which has specialized teeth for filtering krill from the water.
Antarctic krill is not currently listed as threatened on the IUCN Red List; it is commonly assessed as Least Concern (most recently evaluated in 2010). That said, its regional abundance can fluctuate strongly year to year, and long-term risks are tied to sea-ice change, ocean warming, and shifting phytoplankton productivity.
Industrial krill fishing—used for aquaculture feed and omega-3 supplements—removes a comparatively small fraction of total biomass but is concentrated in hotspots that overlap predator foraging areas, particularly near the Antarctic Peninsula. Management is coordinated by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which sets catch limits and applies an ecosystem-based approach intended to protect dependent predators as well as krill itself.
Because Antarctic krill can live about 5–7 years in the wild (and typically no more than about a year in captivity due to husbandry challenges), consecutive poor recruitment years can matter. Monitoring programs track biomass, sea-ice conditions, and predator performance to detect when local depletion or climate-driven habitat changes may be reducing food availability.