Antarctic krill (Euphausia superba) is a small crustacean that plays a central role in the Southern Ocean ecosystem. Although individuals typically reach only about 4 to 6 centimeters in length, the species is among the most abundant animal populations on Earth, with an estimated biomass of hundreds of millions of tons.
Krill feed mainly on microscopic algae (phytoplankton), converting this primary production into biomass that can be used by larger animals. In doing so, they form a crucial link between the base of the food web and higher predators. Many species, including whales, seals, penguins, seabirds and fish, depend heavily on krill, and for some it represents the dominant component of their diet. This central role makes krill a so-called keystone species, a term used for species that have a disproportionately large impact on their ecosystem compared to their abundance.
Krill are known for forming dense swarms that can extend over large areas and contain thousands of individuals per cubic meter. These aggregations support efficient feeding and play an important role in predator–prey interactions.
The life cycle of Antarctic krill is closely adapted to the seasonal conditions of the Southern Ocean. Spawning typically takes place during the austral summer. Eggs sink to deeper waters, where they hatch, and the larvae then develop through several stages as they slowly rise back toward the surface. This early development can take several weeks and depends strongly on temperature and food availability.
Juvenile krill rely heavily on sea ice during their first winter. The underside of the ice provides both shelter and a habitat for algae, which serve as an important food source. Survival during this stage is critical, and variations in sea ice extent can strongly influence recruitment from year to year.
Krill also undertake daily vertical movements in the water column, typically rising toward the surface at night to feed and descending during the day. This behavior reduces predation risk and contributes to the transport of carbon from surface waters to deeper layers of the ocean.
Antarctic krill typically live for around five to seven years and reach maturity after two to three years. Throughout their lives, they grow by repeatedly shedding their external skeleton in a process known as molting. Growth rates can vary depending on environmental conditions, particularly food availability and sea ice dynamics.
Because many species depend on krill, changes in their distribution or abundance can affect feeding conditions for predators. In particular, variations in sea ice and ocean conditions influence where krill are available at different times of the year.
The importance of krill is reflected in long-term scientific monitoring in the Southern Ocean, where researchers study their abundance, distribution and role in the food web. These observations support a better understanding of ecosystem dynamics and help inform the management of human activities in the region.
Léa Zinsli, PolarJournal