Krill may be tiny, but their presence in the ocean is mighty. They exist in huge numbers worldwide, provide an essential link in the marine food chain, and even help regulate global climate. Not bad for a shrimp-like creature that measures about 6 cm (2.4 inches).
In terms of sheer biomass, krill are some of the most successful creatures on the planet. Antarctic Krill alone weigh in at an estimated 379 million tons of biomass, and swarms of krill can be seen swimming in the Southern Ocean from outer space.
It’s fortunate that there are so many of them, because squid, penguins, seals and baleen whales gulp down krill by the mouthful. They’re also increasingly targeted by humans to use as raw material for fish meal and Omega-3 supplements. That’s why some species hide out in the cool, dark waters of the ocean twilight zone by day and only swim up to the surface at night to feed on phytoplankton.
Most krill are filter feeders, and use their front legs to comb through the water for food. Their favorite meals include plant-like phytoplankton, single-celled algae called diatoms, and sometimes even tiny animals like zooplankton and fish larvae. Antarctic krill especially enjoy the phytoplankton they find on the underside of ice—a unique adaptation in what might otherwise be considered a food desert.
Krill’s place on the food chain gives them a starring role in the ocean’s biological pump, the process by which carbon and nutrients move from surface waters to the deep ocean. By feeding on phytoplankton—which grow in the presence of sunlight and carbon dioxide—krill essentially remove carbon from the atmosphere. When krill poop falls to the sea floor, or when they’re eaten by larger species, the carbon from their bodies remains at the bottom of the ocean for years, if not centuries. Scientists are closely studying krill populations, their feeding behavior, and—yes—their pooping patterns to get a better estimate of just how much carbon they take up each year.
|Scientific Name||There are many different Krill species, all under the order Euphausiacea.|
|Other Names||Commonly fished types incllude Antarctic krill, Pacific krill, and Northern krill.|
|Size||Up to 6 cm (2.4 inches)|
|Discovery||James Dwight Dana, 1852|
|Eats what?||Most eat phytoplankton and algae, but some also prey on zooplankton and fish larvae|
|Eats how?||Filter feeding, or (in some species) combing through water with front legs|
|Is eaten by?||Fish, birds, marine mammals, and humans|