Antarctic krill (Euphausia superba) are small, shrimp-like crustaceans that inhabit the cold waters of the Southern Ocean. These organisms are typically only about six centimeters long but gather in massive, dense swarms, sometimes reaching tens of thousands of individuals per cubic meter of water. The sheer quantity of krill forms the base of the entire Antarctic marine food web, transferring energy from the microscopic algae they eat to a diverse array of larger animals. This immense biomass sustains nearly all the iconic wildlife of the region, making the small crustacean a foundational pillar of the ecosystem.
Baleen Whales and Seals: The Largest Consumers
The enormous filter-feeding baleen whales represent the largest consumers of Antarctic krill, consuming tens of millions of tonnes annually. Species like the Blue, Fin, Humpback, and Antarctic Minke whales rely heavily on these dense swarms during their feeding season in the Southern Ocean. Baleen whales use specialized plates made of keratin to strain vast quantities of krill from the seawater in a single gulp. Recent research suggests that before commercial whaling drastically reduced their populations, these whales may have consumed over 400 million tonnes of krill each year, which is roughly equivalent to the entire current krill population estimate.
Blue whales, the largest animals on Earth, can eat as much as 16 tonnes of krill in a single day. Fin whales and Humpback whales also feed on krill in impressive amounts, demonstrating the scale of consumption required to fuel these massive bodies. The collective consumption by all seal species in the region is also substantial, estimated to be between 63 and 130 million tonnes of krill annually.
The Crabeater seal (Lobodon carcinophaga) is the most abundant seal species globally and is an extreme specialist, with krill making up over 90% of its diet. This seal has uniquely adapted, sieve-like, multi-lobed teeth that interlock to strain krill from the water, much like a miniature baleen plate. Crabeater seals can consume up to 20 kilograms of krill per day, feeding mostly at night when krill migrate closer to the surface. Another major predator, the Leopard seal, also includes a significant amount of krill in its diet, sometimes comprising up to 45% of its food intake.
Krill Consumption by Penguins and Flying Birds
Penguins are highly specialized krill predators, with their local populations often tracking the availability of the crustacean. Adélie and Chinstrap penguins are particularly krill-dependent, with krill making up nearly all of their diet, especially during the crucial summer breeding season when they are feeding chicks. The health of these penguin colonies is closely tied to the localized abundance of krill, which provides the necessary energy for successful reproduction. A single Adélie or Chinstrap penguin can consume about one kilogram of krill daily while provisioning its young.
Emperor penguins, while their diet can include a greater proportion of fish and squid in some areas, still consume Antarctic krill and are sensitive to its availability. Flying seabirds like various petrels and albatrosses also target krill, which they often catch closer to the ocean surface. Black-browed Albatrosses are known to forage on krill, and the overall consumption by flying birds is recognized as a significant component of the krill food web.
Fish and Invertebrates That Target Krill
A host of smaller, less visible predators also consume Antarctic krill, acting as a crucial intermediate link in the food chain. Various species of squid are significant predators of krill, with consumption estimates ranging between 30 and 100 million tonnes annually. These cephalopods are preyed upon by seals and whales, effectively passing the krill’s energy up to the higher trophic levels.
Antarctic silverfish (Pleuragramma antarcticum) are a prominent fish species that relies on krill, particularly as they mature. Juvenile silverfish have been found to consume krill for up to 46% of their diet by mass, while small adults consume it for about 37%. These fish themselves are a major food source for many penguins, seals, and other toothed whales, highlighting how krill’s energy is transferred through multiple steps to the top predators. Other fish, including icefish larvae and myctophids (lanternfish), also feed on krill.
Krill’s Role as a Keystone Species
Antarctic krill’s importance to the ecosystem extends beyond merely being a food source; it is considered a keystone species. A keystone species is one whose influence on its environment is disproportionately large compared to its abundance. Krill’s massive biomass, estimated to be several hundred million metric tons, connects the bottom of the food web—the phytoplankton—to almost every higher-level predator.
The health and population dynamics of krill directly dictate the stability and diversity of the entire Southern Ocean ecosystem. Krill also play a role in global biogeochemical cycles, particularly the biological carbon pump. By feeding on carbon-rich surface algae and then excreting the waste as pellets that sink to the deep ocean, krill actively help sequester carbon. The availability of krill is therefore a fundamental determinant of the entire Antarctic ecosystem’s structure and function.