Antarctic krill (Euphausia superba) are small, shrimp-like crustaceans found in immense swarms throughout the Southern Ocean. Growing up to 6 centimeters long, they represent one of the planet’s largest animal biomasses, estimated at 379 to 500 million metric tons. Krill feed directly on minute phytoplankton, converting the sun’s energy into a protein-rich food source. This foundational position makes them the primary energy source for the entire Southern Ocean ecosystem, sustaining nearly all the larger marine life in the region.
Marine Mammal Predators
The largest consumers of krill are the baleen whales, whose sheer size and specialized feeding mechanisms allow them to ingest staggering quantities. Blue whales, the largest animals on Earth, can consume approximately 16 metric tons of krill in a single day during their feeding season. Humpback whales, another massive filter feeder, can eat up to 9 metric tons of krill daily in similar regions.
These whales use baleen plates, which are keratin structures hanging from the upper jaw, to filter the crustaceans from the water. They take in huge gulps of water dense with krill and then push the water out through the baleen sieve, trapping the prey inside. Recent studies indicate that these whales consume up to three times more prey than previously estimated, emphasizing krill’s importance to their metabolism.
Seals also rely heavily on krill, most notably the Crabeater Seal (Lobodon carcinophaga). Despite its misleading name, the Crabeater Seal’s diet consists almost exclusively of krill, often making up over 90% of its food intake. This seal has evolved a unique, sieve-like tooth structure with finely lobed teeth that interlock to strain krill from the water.
The Leopard Seal (Hydrurga leptonyx), a major predator of Crabeater Seal pups, is also an opportunistic krill consumer. Krill can account for about 45% of the Leopard Seal’s diet, demonstrating a reliance that is second only to the Crabeater Seal among pinnipeds. All seals in the Antarctic region combined consume a vast amount of krill, estimated to be between 63 and 130 million metric tons annually.
Avian Predators
Krill provides the energy for massive colonies of Southern Ocean seabirds, particularly the three most common krill-dependent penguin species. Adélie, Chinstrap, and Gentoo penguins all rely on krill availability, which directly affects their annual breeding success and population health. The diet of Adélie and Chinstrap penguins is tightly linked to krill, and their populations often decline when krill stocks are low.
Gentoo penguins are generally more opportunistic feeders but still consume large amounts of krill, especially during the breeding season. They can switch to small fish or other crustaceans if krill is scarce, giving them an advantage over more krill-specialized species. Krill makes up 96% of the calories consumed by certain seabirds and mammals in the Antarctic Peninsula region.
Flying seabirds, known as Procellariiformes, including Albatrosses and Petrels, also forage for krill near the ocean surface. Albatrosses use surface seizing and shallow dives to catch krill, often supplementing their diet with squid and fish. Petrels, such as the White-chinned Petrel, are members of a group known as “tubenoses” that possess an acute sense of smell.
These birds can detect the scent of krill and other prey from long distances, which helps them locate the dense swarms. Smaller diving petrels, adapted with short wings, are capable of plunging beneath the surface to pursue krill and copepods. These varied avian feeding strategies allow birds to collectively consume an estimated 15 to 20 million metric tons of krill each year.
Other Aquatic Consumers
Beyond the warm-blooded predators, a wide array of fish, cephalopods, and invertebrates also depend on krill. The Antarctic Silverfish (Pleuragramma antarcticum) is a primary example, linking krill to higher trophic levels in the continental shelf environment. This fish consumes krill as a major part of its diet, and in turn, becomes prey for seals, penguins, and other larger fish. Krill can dominate the silverfish diet by mass, particularly for juvenile and smaller adult fish.
Mesopelagic fish, such as Lantern Fish (Myctophids), also consume krill in deeper, offshore waters. These fish are significant krill consumers and represent an alternative energy pathway in the food web for predators not operating near the coast. Cephalopods, primarily various species of Antarctic squid, are also substantial krill predators.
Squid collectively consume between 30 and 100 million metric tons of krill annually, capturing the crustaceans in the dark water column. Invertebrates, while often overlooked, also play a role in krill dynamics. Larger invertebrates like crabs and sea stars feed on krill, including those that sink to the seafloor, contributing to nutrient recycling.
Krill’s Central Role in the Antarctic Ecosystem
The widespread consumption of krill across nearly all Antarctic predator groups confirms their status as a keystone species in the Southern Ocean. Krill are the primary mechanism for transferring energy from the base of the food web—the phytoplankton—to seals, whales, and birds. This efficient energy transfer is possible because krill aggregate in massive swarms, providing a concentrated food source for diverse predators.
Krill also contribute to the biological carbon pump, a process that helps regulate the global climate. After feeding on phytoplankton, krill excrete fecal pellets that sink rapidly to the deep ocean, effectively sequestering carbon. The health of all krill-dependent species is directly threatened by changes in krill distribution and abundance. Loss of sea ice due to warming waters negatively impacts krill survival, causing population declines among the predators that rely on them.