Tens of thousands of penguins are starving to death in Antarctica because a vast iceberg has devastated the regional food chain. The B15 iceberg, which covered about 4,400 square miles when it calved in March 2000, has blocked much of the Ross Sea, preventing the growth of microscopic plants known as phytoplankton that are crucial to the entire ecosystem.
Blooms of phytoplankton, which are the first link in the Antarctic food chain, are down by 40 per cent in what is normally one of the continent?s most biologically productive areas, with dramatic consequences for larger species. Thousands of penguins have already died from a shortage of the fish called krill, which feed on phytoplankton and form a major part of the birds? diet.
The iceberg has also cut penguin rookeries off from their normal feeding grounds, leaving adults with a long walk from their nests to clear waters where they can fish. Many birds have died of exhaustion, and others have been unable to carry food back to their chicks. Some rookeries in the Ross Sea could lose up to 30 per cent of their population if access to food does not improve during the Antarctic winter. The region is home to 30 per cent of the world?s adelie penguins and to 25 per cent of all emperor penguins.
Many of them have abandoned attempts to breed this year because of food shortages. A colony of 1,200 emperors at Cape Crozier, first discovered by members of Robert Falcon Scott?s Antarctic expedition in 1911, has bred no chicks at all this year, and others that have bred, such as an adelie rookery at Cape Royds, are expected to lose all their newly hatched chicks to starvation. Whales may also be affected, although their numbers are harder to monitor closely.
The full extent of the disaster has been revealed by Kevin Arrigo, Professor of Geophysics at Stanford University in California. He has used NASA satellites to trace the iceberg?s ecological impact. The images show how B15, which has now split into four smaller but still extremely large icebergs, has restricted the normal drift of ice out into the Ross Sea, a process which generally leaves open water in which phytoplankton can breed and penguins can hunt.
?Not only do [the penguins] have to go farther to find food, but they have to swim around this enormously large iceberg that has found its way in their path,? says Arrigo. ?Some rookeries have been abandoned altogether. They left their nests exposed for longer periods of time than they normally would. That made them vulnerable to predators such as the skua, a large gull that feeds on chicks and the eggs. So penguin breeding success was much lower last year.?
See news story ?Ice Shelf Collapse May Cause Antarctica Starvation?, click here.
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