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Antarctica and Southern Ocean BiodiversityThe ocean surrounding Antarctica is perhaps the last true marine wilderness on the planet providing essential nutrients to the rest of the world's oceans, supporting life systems thousands of kilometres away from the South Pole.The ocean surrounding Antarctica is perhaps the last true marine wilderness on the planet providing essential nutrients to the rest of the world's oceans, supporting life systems thousands of kilometres away from the South Pole. Some 95 per cent of the Antarctic landmass is covered by permanent ice or snow, that’s 90 per cent of the world's ice, with an average thickness of about 2,300 metres. The Antarctic marine ecosystem is biologically rich and diverse. Microscopic plankton are at the base of the food chain and are, in turn, eaten by vast shoals of small crustacean-like shrimps (krill) and a wide range of fish. Krill are food for penguins and other birds, seals and sea-lions, and even for many of the great whales. Fish of the Southern Ocean Of the 20,000 known species of fish in the world, only 120 live in the Southern Ocean. Throughout the past 40 million years they have adapted to the freezing conditions by developing a special 'anti-freeze' component in their body fluids. Antarctic fish are especially vulnerable to overfishing because most species take a long time to become sexually mature and are long lived. Like many deep-sea species, little is known about the Patagonian toothfish. However, they are known to grow slowly to more than two metres long, can live for 50 years and do not breed until it is at least 10 years old. The toothfish lives in deep waters (from 300 to 3500 metres) and is found on seamounts and continental shelves around most sub-Antarctic islands. Birds of Antarctica and the Southern Ocean While the bird species from this region are highly adapted to a marine existence, they come ashore to land or ice to breed and raise their young. During the breeding season, millions of adelie (Pygoscelis adeliae) and emperor (Aptenodytes forsteri) penguins (accounting for almost 85% of the biomass of Antarctica's birds) form noisy rookeries on beaches and sheltered inland sites. Birdlife includes a number of petrels - a diverse group of birds characterised by tube-like nostrils on the upper beak. Giant petrels (Macronectes giganteus) are mainly carrion feeders, removing dead chicks from penguin rookeries, or feeding on casualties at seal nurseries. Other species, such as the Antarctic petrel (Thalassoica antarctica) and Wilson's storm petrel (Oceanites oceanicus) feed mainly on plankton, small fish and krill. The largest bird species, the Wandering albatross (Diomedea exulans), with a wingspan up to 3.5 metres, spends much of the year aloft riding the ocean thermals returning to land only to breed. These great ocean wanderers fly thousand of kilometres in search of food. Once they have left the nest, they spend between five and eight years at sea, feeding in key commercial fishing grounds.
Longline fishing is the driving force in albatross declines. The biology of the birds further complicates their plight, as they are long lived creatures that mate for life and do not reach breeding age until they are at least 10 years of age. Depending on the species, only one chick is produced every one to three years and is tended by both parents for at least nine months. Adult survival rates must be high to ensure chick survival and stable populations. If one of the adults dies, it is more than likely that the chick will perish as well. Marine Mammals The productive marine environment also sustains a wide range of marine mammals - seals and whales - at far greater levels than are found in the Arctic region. The population of the Crabeater seals (Lobodon carcinophagus) alone accounts for about half of the world's seals with an estimated population of 12 million. Other fish-eating species include the Weddell seal, Ross seal (Ommatophoca rossii), Antarctic fur seal (Arctocephalus gazella) and the largest species of all, the Southern Elephant seal (Mirounga leonina) - adult males of which may weigh up to 2,200 kilogrammes. The predatory Leopard seal (Hydrurga leptonyx) feeds on penguins and young seals, but may also eat fish and krill. The monarchs of the southern oceans, the great whales, are now formally protected from commercial whaling, but their numbers remain considerably depressed compared with years past. Many of the largest species, blue (Balaenoptera musculus), fin (B. physalus) and humpback (Megaptera novaengliae) whales, feed by filtering plankton from the surface waters using specialised horny plates (baleen) which hang from their upper jaws. Other species, such as the sperm whale (Physeter catodon), feed primarily on squid while the much smaller killer whales (Orcinus orca) frequently prey on seals and penguins. |
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