Krill are eaten by an enormous range of ocean predators, from the largest animal on Earth to relatively small fish and seabirds. In Antarctic waters alone, baleen whales, seals, penguins, squid, and fish all depend on krill as a primary food source. With a global biomass estimated between 300 and 500 million metric tons, Antarctic krill may be the most abundant wild animal species on the planet, and that abundance is what makes them the foundation of one of Earth’s most productive food webs.
Baleen Whales: The Biggest Krill Eaters
Baleen whales are the single largest consumers of krill. Blue whales, fin whales, humpback whales, sei whales, and minke whales all feed heavily on krill, using plates of baleen (a comb-like structure in their mouths) to filter massive volumes of seawater and trap the tiny crustaceans inside. A blue whale can eat roughly 16 metric tons of krill in a single day during peak feeding season. That’s about 35,000 pounds of food every 24 hours, consumed by lunging into dense swarms with its mouth open and then pushing the water out through its baleen.
Fin and humpback whales are especially abundant in the areas where krill concentrate around the Antarctic Peninsula and sub-Antarctic islands. These species are considered the most significant mammalian krill predators in those regions, and their recovery from 20th-century whaling has increased predation pressure on krill stocks considerably.
The relationship between whales and krill also works in reverse. When whales digest krill, they release iron, manganese, and other trace nutrients back into surface waters through their feces. These nutrients fertilize the growth of phytoplankton, which is exactly what krill eat. So whales don’t just consume krill. They help sustain the conditions krill need to thrive.
Seals That Specialize in Krill
Crabeater seals, despite their misleading name, eat almost no crabs at all. They feed almost exclusively on krill. Their teeth have evolved into elaborate, interlocking lobes that work like a sieve. A crabeater seal dives into a krill swarm, sucks in a mouthful of water and krill, then pushes the water out through its teeth while trapping the krill inside. Its tongue scrapes the krill off the teeth before swallowing. A single crabeater seal can eat up to 20 kilograms (about 44 pounds) of krill per day.
Crabeater seals are the most abundant seal species in the world, with population estimates in the tens of millions, so their collective krill consumption is staggering. Antarctic fur seals also depend on krill. Around South Georgia Island alone, approximately 3.5 million fur seals compete with about 1 to 2 million krill-eating penguins for the same food supply. Leopard seals eat krill too, though they’re better known for hunting penguins and other seals.
Penguins and Other Seabirds
Several penguin species rely on krill as their dominant food source. Chinstrap, Adélie, Gentoo, and Macaroni penguins are all classified as krill-dependent species. Around the Antarctic Peninsula and the South Orkney Islands, krill-dependent penguins vastly outnumber resident fur seals, making them the most numerous warm-blooded krill predators in those areas.
The proportion of krill in a penguin’s diet varies by location. Adélie penguin chicks at Cape Hallett in the Ross Sea get about 65% of their food from Antarctic krill. At other sites closer to the coast, the same species shifts to a mix of silverfish and ice krill (a smaller, related species) depending on what’s locally available. Chinstrap penguins tend to be the most krill-specialized of the group, with some populations getting over 90% of their calories from krill.
Beyond penguins, petrels, albatrosses, and other seabirds also feed on krill, though most of these species take krill as part of a broader diet rather than depending on it exclusively.
Fish and Squid
Dozens of fish species eat krill, particularly in the Southern Ocean. Antarctic silverfish, lanternfish (myctophids), and icefish all consume krill at various life stages. Lanternfish are especially important because they eat krill near the surface at night and then migrate to deeper water during the day, transferring energy from the upper ocean to the deep sea. This vertical migration makes lanternfish a critical link in moving krill-derived nutrients through the water column.
Several species of squid also prey on krill. In the Southern Ocean, squid occupy a middle position in the food web, eating krill and then being eaten by sperm whales, elephant seals, and large fish. Outside of Antarctic waters, krill species in the North Pacific and North Atlantic are consumed by commercially important fish like herring, mackerel, salmon, and cod.
Why So Many Animals Depend on Krill
Krill occupy a unique position in ocean ecosystems because they convert the energy stored in microscopic phytoplankton into a food source large enough for whales to bother eating. A single Antarctic krill is only about 6 centimeters long, but they form swarms so dense they can be detected by satellite. This concentration of biomass makes them extraordinarily efficient to harvest. A whale doesn’t need to chase individual prey; it simply opens its mouth in the middle of a swarm.
Krill also concentrate nutrients at rates far beyond what you’d find in surrounding seawater. Iron levels in krill tissue are roughly 3 times higher than in the phytoplankton they eat, and concentrations of other trace metals like copper and zinc can be hundreds of thousands to millions of times higher than ambient seawater levels. This means that every animal eating krill gets a nutrient-dense meal packed with essential minerals, not just calories. When predators like whales release those nutrients back through their waste, the cycle continues: phytoplankton bloom, krill eat the phytoplankton, and predators eat the krill.
This is why krill are often described as a keystone species. Remove them from the Southern Ocean, and the entire food web collapses. Whales, seals, penguins, fish, squid, and seabirds all converge on this single group of small crustaceans, making krill one of the most ecologically important animals on Earth.