Life in a cold environment - Antarctica: Global Science from a Frozen Continent - page 168

Box 6.2 The essential link: krill

Within the pack ice zone one animal is dominant, though it is rarely as
visible as the animals that depend on it. This animal is krill, a pelagic shrimp-like
crustacean that occurs in abundance in south polar waters. Krill are relatively
large (up to 6 cm long) for pelagic herbivores and are highly nutrient rich, and
these two features, together with their aggregating habit and their huge
abundance in some localities, make them the preferred food for most of the
vertebrate species of the region sh. Once

thought to be short-lived animals, they are now known to be able to live to
11 years old, which makes them considerably older than many of the animals
that prey upon them. Krill live in schools or swarms that can extend for many
kilometres and contain millions of tonnes of crustacean biomass. Not
surprisingly, they have been commercially

- the baleen whales, seabirds, seals and

fished for the last 40 years, with a
current annual catch of 210 000 tonnes being taken from the South Atlantic. The

fishery appears to be in an expansion phase following a period of stable catches.
The catch is used as aquaculture feed, and for a variety of medical and
pharmaceutical uses, including the production of omega 3 oils for human
consumption. The global demand for farmed fishery into

more rapid expansion and this will require careful management to ensure the
needs of other elements of the ecosystem (see Chapter 10 ). Not only are krill
vitally important for the wellbeing of the vertebrates of the Antarctic region, they
also exert a major in

fish may drive the krill

uence on the microscopic organisms in the water as the
huge schools move around and strain out most of the particulate organic matter.
It has also recently been discovered that krill may regularly migrate and
presumably forage across great depth ranges of several thousand metres.
There are suggestions that the waste produced by krill schools fertilises the
ocean and encourages phytoplankton growth once they have moved on.

the sub-Antarctic. In addition there are cormorants, skuas, gulls and terns, as well
as sheathbills, the latter the only Antarctic birds without webbed feet. Seabirds
forage in the surface of the water with the smaller species, such as the snow petrel,
dipping their prey from the surface flying birds plunging into the top

10m or so and the penguins diving to great depths (up to 50m) in search of their
prey, which consists of krill, squid and

film, larger

fish. During their breeding seasons, birds
are tied to the colonies to which they have to return regularly with food for their
offspring, whereas in winter they can disperse more widely. Modern studies using
satellite trackers have demonstrated that birds such as Adélie penguins can cover
thousands of kilometres on their winter feeding trips, but return faithfully to their
natal colonies in spring in time to breed.