Krill is despite its small size one of the world’s biggest biomasses. The Antarctic krill, Euphausia superba, lives in the cold and pristine waters of Antarctica, and feed on plankton.
Krill are shrimp-like crustaceans mostly found in the Northern (Arctic) and Southern (Antarctic) circumpolar seas of the earth. The most abundant species of krill and the world largest single species biomass, Euphausia superba, is found in Antarctic waters, and is believed to amount to the order of up to 400 million metric tons (human biomass is 250 million metric tons). Thus, Krill play a key role in the ecosystems of the Arctic and Antarctic seas. Krill feed on phytoplankton and algae, but they have an opportunistic feeding pattern and may feed on almost any available plankton. However, Krill is eaten by many larger creatures such as seals, penguins, fish, squid and sea birds and is the favorite and exclusive food source for many of the baleen whales.
Euphausia superba has a length up to 6.5 cm and have a chitinous exoskeleton. The Krill anatomy have a few characteristic features such as combined filter legs and ice rakes attached to their head, unlike shrimps they have externally visible gills. They can swim at a speed of a few centimeters per second and like lobsters are able to flip their tail to escape by scuttling quickly backwards. Special light organs with muscles and lenses can illuminate the surroundings, confuse predators or send out signals to other individuals for social grouping or mating.
Krill (Euphausia superba) is found in the Antarctic waters to a depth of approx 100 meters south of the 55°S latitude between the coast and the seasonal pack ice edge. During the winter it feeds on ice-imbedded algae. In the summer the krill distribution coincide with the phytoplankton blooms. Thus, sea ice is an important factor for feeding, shelter and rest for the Krill; the more ice the better conditions for survival.
The life cycle of Krill is amazing. Its life span may be between 6-8 years and the animals reach maturity only after three to four years. After mating the eggs sink in depths around 1000-2000 meters where they start their development. They go through different stages of development as they ascend towards the surface. They must live through the first stages on their yolk reserves avoiding predators until they reach the growth zone. The success of reproduction is positively correlated with early spawning followed by extensive ice cover in the preceding winter. Thus, Krill is truly adapted to the cold and austere winters of the Antarctic, enjoying their success in the temperate summers and harsh winters of the Southern seas.