In contrast to the sparsely vegetated, barren, and ice-covered continent, the oceans surrounding Antarctica support a wealth of plant and invertebrate animal life.
The cold waters are about four times as productive, acre for acre, as the other oceans of the world. The first link in this immense food chain is the microscopic algae which drift in the ocean and are eaten by zooplankton, of which krill is the most prominent, as well as being the principal food supply for whales. Krill are shrimp-like crustaceans that grow to 7 or 8 centimeters in length, and form enormous schools, which color the sea red.
Squid and octopus are also important to the Antarctic ecosystem, providing food for sperm whales, seals, penguins, sea birds, and fishes (see Wildlife Section). It has been estimated that about 55 million tons of squid is consumed annually by the whales of the Southern Hemisphere; this is about 75 percent of the world’s current total fisheries catch.
Seals are one of the most fascinating and unique of Antarctic marine mammals. Seals are aquatic but, unlike whales, must return to the land or pack ice to breed. The Antarctic supports a much larger seal population than does the Arctic, due to larger and more productive feeding areas and a lack of native predators.
With the end of the long polar winter comes the arrival of millions of sea birds to breed. Probably 100 million or more birds breed along the coast and offshore islands of Antarctica. Most of the sea birds belong to the species Procellariiformes, which include the albatross (largest flying sea bird, with the wingspan of some species exceeding 4 meters, the fulmers, prions, petrels, and shearwaters. The remaining regular sea bird species encompass shore birds, skuas, gulls, terns, and the penguin. Most sea birds breed in large concentrations, owing to the scarcity of snow-free ground used for nesting. The chicks develop quickly and soon fend for themselves until the approach of winter, when most species migrate north in pack ice or the open sea–some even to Arctic waters–in which they spend most of their lives.
Many fish of Antarctica are the only vertebrates that entirely lack red oxygen-carrying pigment (hemoglobin) in their blood. This adaptation to the cold conditions allows a decrease in blood viscosity and in the amount of energy required to circulate blood. Most research has concentrated on the two most abundant groups: the Antarctic cod Nototheniidae and the ice fish Channichthyidae. Initial interest focused on the evolution of the groups, their ability to survive in icy waters, their reproduction and growth rates and their population age structure. Much current research is concerned with making more accurate estimates of growth and population size.