Krill are small, shrimp-like crustaceans that play an important role in the marine food web. They are a major source of food for whales, penguins, squid, and fish. Krill are found in all oceans of the world.
The word krill comes from the Norwegian word krill, meaning “small fry of fish”, which is also often used to refer to young herring. Krill are born as nauplii, tiny larvae with six legs and a single eye. They grow rapidly and molt (shed their exoskeleton) several times before reaching adulthood. Adult krill measure 2–3 cm (0.79–1.18 in) long and weigh up to 2 g (0.071 oz).
Krill are filter feeders – they strain plankton and other tiny organisms out of the water using their two front claws (chelae). Krill typically eat microscopic algae known as diatoms or zooplankton such as copepods and amphipods. Some species of krill are known to eat small fish and squid.
Krill reproduce rapidly – a female can produce over 10 million eggs in a single spawning season! After fertilization, eggs float freely in the ocean until they hatch into nauplii larvae about 10 days later. These nauplii go through 5-6 molts before reaching maturity at around 6 months old.
Predation is one of the biggest risks faced by krill – they are eaten by just about everything that lives in the ocean! Their main predators include baleen whales, seals, penguins, squids, fishes, and seabirds like albatrosses and petrels. To avoid being eaten, krill form large swarms called shoals that can number in the billions of individuals! When danger is near, krill will sink down deep into the water column where predators cannot reach them – some species can dive down over 600 meters (2000 feet)!
Climate change poses a threat to krill populations because it is causing changes in sea ice cover and ocean temperature which impacts their habitat and food availability . For example , warming waters caused by climate change may lead to more frequent algal blooms which could deplete oxygen levels at depth , making it difficult for krill to survive .