‘Krill’ is a general term used to describe about 85 species of free-swimming, open-ocean crustaceans known as euphausiids. Antarctic krill is one of the 85 species of krill that lives in the Southern Ocean.
With their large black eyes, krill are mostly transparent, although their shells have a bright red tinge from small pigment spots. Their digestive system is usually visible and this is often a vivid green from the pigment of microscopic plants they have eaten. Adult Antarctic krill are approximately six centimetres in length and weigh over a gram.
Distribution and abundance
Antarctic krill are one of the most abundant and successful animal species on Earth. Scientists estimate there are about 500 million tonnes of Antarctic krill in the Southern Ocean. The biomass of this one species may be the largest of any multi-cellular animal species on the planet.
As krill come to resemble adults they begin to aggregate into huge schools or swarms, sometimes stretching for kilometres in every direction, with many thousands of krill packed into each cubic metre of water, turning the water red or orange.
Most of the time the schools stay deep in the water during daylight hours and only rise to the surface at night. It is not known why swarms are occasionally seen at the surface during broad daylight.
Commercial krill fishing began in the early 1970s and the prospect of a free-for-all fishery for Antarctic krill led to the signing of a unique fishing treaty in 1981. The Convention on the Conservation of Antarctic Marine Living Resources is designed to protect the Antarctic ecosystem from the consequences of rapidly-expanding fisheries, and to aid recovery of the great whales and some of the overexploited species of fish.
The fishery is managed through an international body (CCAMLR) which sets limits on the krill catch taking into account the needs of other elements of the ecosystem.
Scientists at the Australian Antarctic Division study krill to provide a better understanding of krill life cycles so that the fishery can be better managed.
Female Antarctic krill lay up to 10,000 eggs at a time, sometimes several times a season.
Diet and feeding
Antarctic krill are mainly herbivorous, feeding mostly on the phytoplankton (microscopic suspended plants) of the Southern Ocean and, to a lesser extent, planktonic animals (zooplankton).
In winter, they have to use other food sources such as the algae which grows on the underside of the pack ice, detritus on the sea-floor or the other animals in the water. Krill can survive for long periods (up to 200 days) without food and can shrink in length as they starve.
Most of the larger Antarctic animals, the seals, whales, seabirds, fish and squid, depend directly or indirectly on Antarctic krill.
The Convention on the Conservation of Antarctic Marine Living Resources is designed to protect the Antarctic ecosystem from the consequences of rapidly expanding fisheries, and to maintain ecological relationships of the Southern Ocean ecosystems including aiding in the recovery of some of the over-exploited species of fish. The fishery is managed through an international body (CCAMLR) which sets limits on the krill catch taking into account the needs of other elements of the ecosystem.
Scientists at the Australian Antarctic Division study krill to provide a better understanding of krill life cycles so that the fishery can be better managed, and to understand the impact of environmental changes such as ocean acidification on the ecosystem.