Antarctic krill (Euphausia superba): biology, ecology, and human relevance

Physical characteristics and behaviour

Antarctic krill are euphausiids, not true shrimps, and possess a segmented body with compound eyes, a carapace, and multiple pairs of thoracic legs for feeding and swimming. Many individuals produce bioluminescent light through specialised organs. They are strong swimmers for their size and form dense swarms that can persist for hours to days. Reported local swarm densities can be extremely high, and observers have recorded thousands to tens of thousands of animals per cubic metre in concentrated aggregations.

Feeding, life cycle, and reproduction

Krill are primarily grazers of phytoplankton and small zooplankton, capturing food with thoracic legs and filtering particles through feeding setae. By consuming microscopic algae, they convert solar energy captured by primary producers into biomass accessible to larger predators. Reproduction involves seasonal spawning: females release eggs that develop through planktonic larval stages before growing into juveniles. Development and recruitment are influenced by sea-ice conditions, food availability, and ocean temperature.

Ecological role and human uses

Antarctic krill are a keystone species: they are a major food source for whales, seals, penguins, fish, and seabirds. Their estimated total biomass has been described as one of the largest of any animal species on Earth, and their population dynamics affect many higher trophic levels. Krill are also harvested commercially for use in aquaculture feed, human dietary supplements rich in omega-3s, and bait. Fisheries are managed to balance use with conservation, and their catches are subject to international regulation.

Research, threats, and notable facts

Scientists study Antarctic krill to understand ecosystem energy flow, the effects of climate change, and polar food webs. Warming waters, changing sea-ice extent, and changes in phytoplankton communities can alter krill distribution and abundance, with cascading impacts on predators. In captivity krill sometimes display opportunistic feeding including cannibalism, especially when food is scarce. Their ability to form large swarms and to store lipids for overwintering are notable adaptations to a seasonal polar environment.

Further information and resources

• Species overview: Euphausia superba
• General information on krill
• Southern Ocean habitats
• Regional oceanography
• Comparisons with shrimp
• Invertebrate biology resources
• Swarms and collective behaviour
• Reported swarm densities and studies
• Phytoplankton as a food source
• Energy transfer in marine food webs
• Primary production and sunlight
• Open ocean ecology
• Typical adult size and growth
• Individual mass and biomass estimates
• Role in Antarctic ecosystems
• Observation notes: krill in aquaria

Note: Many aspects of Antarctic krill biology and abundance are the subject of ongoing research; population estimates and ecological consequences are refined as new observations and models become available.