Krill

Presentation

Krill are small marine crustaceans resembling tiny shrimp that live in swarms, sometimes vast in number, in cold and temperate oceans. Antarctic krill (Euphausia superba) is the most widely known and studied species because of its central role in the Southern Ocean ecosystem. These animals filter phytoplankton and provide essential food for numerous marine predators, from fish to whales. Their total biomass ranks among the largest in the animal kingdom. Krill undertake daily vertical migrations through the water column. They are also harvested commercially for krill oil and aquaculture feed.

Krill have a segmented translucent to reddish body, a thin shell and photophore organs that emit faint bioluminescence. Their compound eyes are well developed and adapted to life in dimly lit waters. They measure several centimetres and move by means of several pairs of thoracic and abdominal legs.

Characteristics

Indicative values: they vary by subspecies, sex and region.

Habitat and distribution

Krill occupies the water column of the oceans, from the surface to several hundred meters deep. It is particularly abundant in cold, nutrient-rich waters such as the Southern Ocean. Some species are also found in temperate or coastal waters.

Behaviour

Krill live in dense swarms that can number millions of individuals; this behaviour provides them with some protection from predation. They perform daily vertical migrations, rising toward the surface at night to feed and descending to deeper water during the day. This gregarious organisation also facilitates reproduction and larval dispersal.

Reproduction

The female releases thousands of eggs that sink to the depths before larvae hatch. The larvae then gradually rise toward the surface while passing through several developmental stages. Sexual maturity is reached after approximately two to three years depending on the species and environmental conditions.

Peculiarities

Antarctic krill forms one of the largest known animal biomasses on Earth, estimated at several hundred million tons. It plays a crucial role in the ocean carbon cycle through its carbon-rich droppings that settle into the depths. Its natural bioluminescence is a distinctive trait among planktonic crustaceans.

Threats and conservation

Climate warming and the melting of sea ice are changing habitats favorable to Antarctic krill. Commercial fishing, expanding for krill oil and aquaculture, is subject to international regulation to prevent overexploitation. Ocean acidification may also affect the survival of larvae.

References

Profile updated 29 August 2026 · Reviewed by the TunisieVet editorial team.

CONSERVATION STATUS

Least concern (LC)

IUCN source, latest published assessment.

Documented diseases for this species.

This information is provided for educational purposes only and is not a substitute for a veterinary consultation. If you have any concerns about your animal's health, consult a veterinarian.

Related species