Antarctic krill

Antarctic krill (Euphausia superba) is a small type of krill that lives in the cold waters of the Antarctic in the Southern Ocean. These tiny crustacean creatures grow up to about 6 centimetres long and can weigh as much as 2 grams. They are very numerous, often forming huge groups called swarms that can contain thousands and thousands of them in just one cubic metre.

Antarctic krill eat tiny plants called phytoplankton, which get their energy from the sun. By eating these plants, krill help move energy through the ocean’s ecosystem. They are very important for many other animals that depend on them for food.

Even though krill are small, there are huge numbers of them in the Antarctic. Scientists think there may be around 500 million metric tons of krill in total. However, people have been catching krill for food and other uses, which is causing some concern about their future numbers.

Life cycle

Antarctic krill have a special way of having babies. The time when they lay eggs is mostly from January to March. The male attaches something called a spermatophore to the female. Females can lay between 6,000 and 10,000 eggs at once. These eggs are fertilized as they leave the female.

The eggs develop and grow while sinking to the bottom of the ocean. After a few weeks, the eggs hatch into tiny larvae. These young krill move up towards the surface of the water. As they grow, they go through many stages and develop more legs and eyes. It takes two to three years for krill to become adults. Like many small sea animals, krill need to shed their outer shell often to keep growing.

Food

Antarctic krill have a transparent body, and you can often see their green stomachs. They mainly eat tiny plants called phytoplankton, especially very small diatoms. They use special legs to catch these plants from the water. Krill can also eat small animals like copepods, amphipods, and other tiny sea creatures called zooplankton.

In aquariums, krill have been seen eating one another. When they don’t get enough food, they get smaller after shedding their skin, which is unusual for animals their size. Their eyes don’t get smaller, so the size of their eyes compared to their body can show if they are hungry.

Filter feeding

Main article: Filter feeder

Antarctic krill can eat tiny phytoplankton cells, which no other animal their size can do. They use their front legs to form a special basket that catches these tiny plants from the water. The openings in this basket are very small, only about 1 μm across. In areas with less food, they push this basket through the water for a long distance before bringing the plants to their mouths.

Ice-algae raking

Antarctic krill can scrape green ice algae from the bottom of pack ice. They have special rows of tiny bristles on their legs that help them graze the ice in a zig-zag pattern. One krill can clear an area of a square foot in about 10 minutes.

Biological pump and carbon sequestration

Krill make daily trips from the surface to depths of about 100 m. They are messy eaters and often spit out groups of phytoplankton cells. They also produce waste that contains carbon and the glass-like shells of diatoms. Both sink quickly into the deep ocean. This process, called the biological pump, helps store carbon dioxide for about 1,000 years in the deep waters around Antarctica.

Biology

Krill are sometimes called light-shrimp because they can produce light through special organs on their bodies. These organs are found on different parts of a krill, such as near its eyes and along its body. They shine a yellow-green light for a few seconds at a time, and scientists think these lights might help hide the krill from animals that want to eat them or help them stay together in groups at night.

Krill can move very quickly to escape from animals that want to eat them. They flip their bodies and swim backward fast, reaching speeds of over half a meter per second.

The genetic code of Antarctic krill is one of the largest known, with a lot of repeated information. Scientists have identified many genes in this code, and they notice that the genes are shorter than in some other animals with large genetic codes.

Geographic distribution

Antarctic krill live all around the Southern Ocean, stretching as far north as the Antarctic Convergence. This area is huge—65 times the size of the North Sea! In winter, most of it is covered in ice, but in summer, a lot of it becomes ice-free.

The Southern Ocean has currents that flow around Antarctica. These currents help krill move around, allowing them to mix with krill from other areas. Some krill groups are so big that they can be seen from space! One group covered an area of 450 square kilometres and was estimated to contain over 2 million tons of krill.

Ecology

Antarctic krill is a key part of the Antarctic ecosystem. It serves as an important food source for many animals, including whales, seals such as leopard seals, fur seals, and crabeater seals, squid, icefish, penguins, albatrosses, and many other birds. Crabeater seals have special teeth that help them catch krill easily. These seals eat over 63 million tonnes of krill each year.

Antarctic krill feeds on tiny plants called phytoplankton, which get their energy from the sun. This makes krill an important link in the food chain, helping to move energy from the sun to larger animals. The krill lives only in the Southern Ocean, where it forms large groups called swarms.

The amount of Antarctic krill in the ocean was estimated in 2009 to be similar to the total amount of humans on Earth. This is possible because the waters around Antarctica have lots of tiny plants and animals that krill eat. Even though the amount of food made by these plants is not extremely high, it happens over a very large area, making krill very important for the ecosystem.

However, changes in the environment, such as less ice in the ocean and changes in the water's chemistry, may affect krill populations in the future. Scientists are watching these changes closely because krill plays such an important role in the Antarctic food web.

Biomass and production

Decline with shrinking pack ice

Ocean acidification

Fisheries

Main article: Krill fishery

Viruses