Antarctic Krill
Euphausia superba
Antarctic Krill (Euphausia superba): The Swarm That Feeds the Whales
Antarctic krill (Euphausia superba) are small, shrimp-like crustaceans of the Southern Ocean. They live in enormous swarms, their total weight is estimated at hundreds of millions of tonnes, and whales, seals, penguins, fish and squid all depend on them.
- Habitat
- Open Southern Ocean around Antarctica, often near sea ice
- Size
- Adults about 6 cm long
- Diet
- Phytoplankton, especially diatoms, and algae under sea ice
- Range
- Circumpolar, south of the Antarctic Polar Front
- Conservation
- Least Concern (IUCN)
- Authority
- Dana, 1850
Habitat & range
Antarctic krill live only in the Southern Ocean, in a ring of cold water around Antarctica. They are most abundant in the southwest Atlantic sector, around the Antarctic Peninsula and South Georgia, and many spend winter beneath the sea ice (Atkinson et al. 2009; Australian Antarctic Division). They are among the most abundant animals on Earth. A 2009 re-analysis of net surveys put the total stock at about 379 million tonnes, and the Australian Antarctic Division gives a figure of about 400 million tonnes. Swarms are so dense that they can colour the sea a reddish brown.
Diet & feeding
Krill are filter feeders. Their feathery front legs form a feeding basket that sieves microscopic plants, mostly diatoms, out of the water. In winter, when there is little food in open water, they graze the algae that grows on the underside of sea ice (Australian Antarctic Division). They can go without food for long periods, up to about 200 days in experiments. A starving krill keeps moulting but shrinks, getting smaller with each new exoskeleton, which is very unusual for an animal (Australian Antarctic Division).
Body & swarms
Adult Antarctic krill are about 6 cm long. The body is mostly transparent, with a red tinge from small pigment spots, and the gut often shows vivid green from the algae they have eaten. They have large black eyes and no claws (Australian Antarctic Division). Krill school in swarms where the density can reach 10,000 to 30,000 animals per cubic metre (Hamner et al. 1983; Australian Antarctic Division). Swarming probably helps them avoid predators and find food, and it is also why baleen whales can feed on them so efficiently.
Food web & conservation
Most large Antarctic animals depend on krill directly or indirectly, including whales, seals, penguins and other seabirds, fish and squid. NOAA notes that the biggest blue whales may eat up to 6 tons of krill a day. A 2021 study using tags on feeding whales estimated that, before industrial whaling, baleen whales in the Southern Ocean ate about 430 million tonnes of krill a year (Savoca et al. 2021). The IUCN lists Antarctic krill as Least Concern. A commercial krill fishery operates in the Southern Ocean and is managed by CCAMLR, the Commission for the Conservation of Antarctic Marine Living Resources. Warming seas and shrinking sea ice are the main long-term concerns, because young krill rely on the ice in winter.
Fun facts about Antarctic Krill
- The gut of a krill often glows vivid green through its see-through body, coloured by the algae it has eaten (Australian Antarctic Division).
- When food runs out, krill can shrink as they moult instead of growing (Australian Antarctic Division).
- Before industrial whaling, Southern Ocean baleen whales are estimated to have eaten about 430 million tonnes of krill a year (Savoca et al. 2021).
- Antarctic krill are thought to live for 5 to 10 years, a long life for such a small crustacean (Australian Antarctic Division).
Antarctic Krill vs Blue Whale (predator and prey)
The blue whale wins easily: krill are its main food, and the biggest blue whales may eat up to 6 tons of them a day.
This is a predator and its prey, not a fair fight. Blue whales feed almost entirely on krill, lunging into dense swarms with their mouths open and straining the water out through their baleen plates (NOAA Fisheries). A single krill has no defence against that. The swarm's strength is its size: there are hundreds of millions of tonnes of Antarctic krill, enough to feed the largest animals that have ever lived.
Read more about Blue Whale.
Common questions about Antarctic Krill
How much krill does a blue whale eat a day?
The biggest blue whales may eat up to about 6 tons of krill a day, according to NOAA Fisheries. A 2021 tag study found earlier estimates of baleen whale feeding were often three times too low or more (Savoca et al. 2021). See our Blue Whale card.
Is Antarctic krill the largest biomass of any animal?
It is one of the largest of any single wild animal species. A 2009 re-analysis put the total stock at about 379 million tonnes (Atkinson et al. 2009), and the Australian Antarctic Division gives about 400 million tonnes.
How many krill are in a swarm?
Up to 10,000 to 30,000 krill per cubic metre of water in the densest swarms (Hamner et al. 1983; Australian Antarctic Division). Swarms can be dense enough to colour the sea reddish brown.
Is Antarctic krill endangered?
No. The IUCN Red List lists it as Least Concern. The krill fishery is managed by CCAMLR, and warming seas and shrinking sea ice are the main long-term concerns.
Why is krill pink or red?
Krill are mostly transparent, with a red tinge from small pigment spots in the shell. Their gut often shows bright green from the algae they eat (Australian Antarctic Division).
Featured in the Field Journal
More Malacostraca animals
Malacostraca · Tundra · Cost 1