Antarctic krill (Euphausia superba)
|Size||Length: 6.2 cm (2)|
This species has yet to be classified by the IUCN.
One of the most abundant organisms in Antarctic waters, the Antarctic krill is a ‘keystone species’ of the Southern Ocean ecosystem, playing a crucial role within the food chain as the main prey for a wide variety of predators, including fish, penguins, seals and whales (3) (4). A small crustacean which is relatively shrimp-like in appearance, the Antarctic krill has a hard, calcified exoskeleton which is divided into three sections: the head and the thorax (which are fused into what is known as the cephalothorax), and the abdomen. Each section is further divided up into individual segments, with many of the segments having a pair of appendages. At the end of the abdomen, the appendages are flattened and form the tail fin, or ‘telson’ (2) (5).
The Antarctic krill occurs across a large geographic area throughout the Southern Ocean, in a wide belt between the Antarctic continent and the polar front (the boundary where polar air and tropical or subtropical air meet). Its range includes the British Antarctic Territory, and the waters surrounding South Georgia and the South Sandwich Islands, the tip of South America and the Falkland Islands (2) (6) (7).
The Antarctic krill inhabits a variety of habitats throughout its life cycle, with adults more often associated with deeper waters, especially during winter, while juveniles are usually found at the surface of inshore waters, beneath the sea ice (5) (8). The Antarctic krill is also commonly found in dense aggregations, where surface currents bring together many individuals to form patches or swarms, although groups are capable of migrating up and down the water column. These large groupings can span from a few square metres to more than 100 square kilometres, and are most often associated with islands, continental shelves and slopes, and zones of mixing water (2).
The Southern Ocean is a highly seasonal environment, and the life cycle of the Antarctic krill is closely linked to these changing conditions. Spawning occurs mainly during the summer, when several thousand eggs are laid by the female within the upper 100 metres of water. The eggs sink, sometimes to depths of 2,000 metres, where they hatch into ‘nauplii’ (the first of several larval stages). The nauplii begin what is known as the ‘developmental ascent’ and migrate up towards the surface, during which time the young krill passes through many different larval phases, before becoming a juvenile in the following spring. The juvenile continues to mature, with the adult form able to mate at two years of age (2) (3). The likelihood of the Antarctic krill surviving to the adult life stage is closely linked to the extent of sea ice during the winter. Survival is much greater when ice develops early in the year and remains for a long period of time, as the area directly under the ice provides the larvae with refuge from predators and a stable source of food (3) (8).
The adult Antarctic krill feeds preferentially on phytoplankton; however, it is also able to depend on a wide variety of alternative food sources during the winter months, which may include its own eggs and larvae, as well as other zooplankton, detritus and other materials. As an adult, the Antarctic krill is also capable of shrinking in body size during periods when food is scarce, by consuming its own tissues and by reversing or halting development (6) (8). The larval feeding stage of Antarctic krill is largely dependent on algae and the microbial community beneath the sea ice (3) (5) (8).
Although the Antarctic krill population is currently estimated to have an incredible total mass of between 100 and 500 million tonnes, over the last 30 years the abundance of krill has seriously declined (3). Several threats to Antarctic krill have been identified, including increasing commercial demand for krill oil and meal for the aquaculture, medical and cosmetic industries, as well as advancing technologies which enable much greater catches and quicker processing (9). Over recent years, the Antarctic region has also seen significant increases in temperature as a result of climate change, which is affecting the extent and duration of the winter sea ice on which successful krill reproduction is so dependent (3) (8) (9) (10).
An additional concern is that Antarctic krill is the main food source for many predators, which are increasingly having to compete with fisheries that target krill aggregations on island shelves close to breeding sites. Over-fishing of these vital food sources will alter the whole Antarctic ecosystem, with localised depletions likely to have a severe knock-on effect for many predator populations (9) (11).
Because the Antarctic krill is such a critical component of the Antarctic ecosystem, as well as a valuable resource for humans, there are many organisations committed to ensuring that krill fisheries are sustainable and have minimal impact on other animals that depend on krill for food. The Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) was established in 1982, as part of the Antarctic Treaty System, in response to concerns about the effect of krill fishing on marine life. As a result, CCAMLR has introduced several precautionary conservation measures to minimise the risk of unsustainable practices, including catch quotas which are considered low enough not to compromise future sustainability of the targeted krill stocks (11). Other organisations dedicated to ensuring sustainable krill fisheries include the Antarctic Krill Conservation Project (AKCP), which is a network of organisations committed to krill conservation, and the Antarctic and Southern Ocean Coalition (ASOC), with both acting as key partners to CCAMLR (9) (12).
To find out more about conservation issues surrounding the Antarctic krill, see:
Antarctic Krill Conservation Project:
Antarctic and Southern Ocean Coalition:
To find out more about other conservation work in this area, see:
The British Antarctic Survey:
The UK Overseas Territories Conservation Forum:
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- Algae: simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
- Aquaculture: the cultivation of marine or freshwater food fish or shellfish under controlled conditions.
- Calcified: hardened by the deposition of calcium carbonate.
- Continental shelf: a region of relatively shallow water, not usually deeper than 200 metres, surrounding each of the continents.
- Crustaceans: diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, slaters, woodlice and barnacles.
- Detritus: litter formed from fragments of dead material.
- Exoskeleton: an external skeleton that supports and protects an animal’s body.
- Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Larval: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Plankton: aquatic organisms, usually tiny, that drift passively with water movements; may be phytoplankton (plants), zooplankton (animals), or other organisms such as bacteria.
- Spawning: the production or depositing of eggs in water.
ITIS (September, 2010)
Food and Agriculture Organisation of the United Nations – Fisheries and Aquaculture Department (September, 2010)
Alfred Wegener Institute, Bioscience Research Division (September, 2010)
British Antarctic Survey (September, 2010)
Marinebio (September, 2010)
- Alonzo, S.H. and Mangel, M. (2001) Survival strategies and growth of krill: avoiding predators in space and time. Marine Ecology Progress Series, 209: 203-217.
The UK Overseas Territories Conservation Forum (September, 2010)
- Nicol, S. (2006) Krill, currents, and sea ice: Euphausia superba and its changing environment. BioScience, 56(2): 111-120.
Antarctic Krill Conservation Project (September, 2010)
- Nicol, S. and Foster, J. (2003) Recent trends in the fishery for Antarctic krill. Aquatic Living Resources, 16: 42-45.
Convention on the Conservation of Antarctic Marine Living Resources (September, 2010)
Antarctic and Southern Ocean Coalition (September, 2010)