Life in a cold environment - Antarctica: Global Science from a Frozen Continent - page 172

Figure 6.7 Penguin guano, the distinctive colour is due

to the high krill content. (Credit: Steve Nicol)

Flying seabirds can range over great
distances in the Southern Ocean but still have to
return to colonies on the continent or on islands
to breed. Unlike the seals and penguins, flying

seabirds are restricted to feeding in the very
surface layer of the ocean and some species,
such as snow petrels, are adapted to feeding in
the leads between the floes in the disintegrating

pack ice. Some, such as sooty shearwaters, migrate out of the region to breed, using
the rich waters of the sea ice zone in summer merely as a fattening zone.
Life on the Antarctic continent occurs largely around the coastline and this is
because the nutrients that support most forms of Antarctic life arise from the
surrounding ocean. The most highly visible signs of life on land, the penguin
and seal colonies, are entirely dependent on the pelagic food web for their diet,
and their guano provides the major nutrient source for many terrestrial food
chains.

Seals

Colonies of fur seals and Weddell seals face the same constraints as the land-
breeding penguins, although fur seals are generally found breeding in the north
of the region where persistent ice is less of a problem, while Weddell seals are
able to maintain holes in the ice so that they can get to their food (mainly sh and

other benthic organisms) despite the presence of unbroken fast ice. The seals of the
pack ice are thought to spend their entire lives in

the sea ice zone using the ice as a platform in winter from which they can access
the concentrations of over-wintering krill,

- the Ross and the crabeater -

fish and squid that persist over the
continental shelf and slope. Fur, Weddell and elephant seals, being larger animals,
which return to colonies to breed, present opportunities to study the feeding
behaviour of pelagic predators. Using satellite trackers and a variety of advanced
electronics, it has been possible to determine the foraging behaviour of these
wide-ranging animals. Elephant seals have been shown to dive to great depths
(at least 1.5 km) in search of fish and squid, ranging in latitude from temperate

waters to the frigid sea ice zone. Fur seals regularly travel from the sub-Antarctic
where they breed to the ice edge where they feed. Crabeaters are thought to be the
most numerous seal on the planet because of their extensive habitat amongst the
circumpolar ring of sea ice. Recent results from a global census of pack ice seals