AN EPIDEMIC of coral bleaching hitting Australia’s Great Barrier Reef has sparked fears that much of the world largest coral reef may be dying. Bleaching is also reported to be spreading through the coral islands of the South Pacific.
Coral bleaching occurs when high sea temperatures force the algae that give coral its colour out of the coral polyps. Bleached coral may recover in the next cool season, but if all the algae are lost the coral will die and reefs will crumble.
An extensive survey of the Great Barrier Reef over the past month has revealed widespread bleaching, says Terry Done, chief conservation scientist at the Australian Institute of Marine Science in Townsville, Queensland. This is the second epidemic of coral bleaching in four years.
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Thomas Goreau, president of the Global Coral Reef Alliance in Chappaqua, New York, says he has received reports in the past few days of bleached, dead coral across much of the South Pacific, including Tahiti, the Cook Islands, New Caledonia and Fiji. “It will take a long time before we have full confirmation of the magnitude of the disaster,” he says. “But I predict we will have confirmation that almost all corals across the entire South Pacific have died in the last few months.”
The bleaching follows this summer’s record sea temperatures off Australia. “Almost all the Great Barrier Reef was 2 °C or more above normal for more than two months from early January to mid-March,” says Goreau. “This was hotter and longer than the bleaching that wiped out the Maldives, Seychelles and western Australian reefs in 1998.”
The high temperatures appear to be connected to the likely onset of a new El Niño, like the one that caused the bleaching in 1998. But Goreau says global warming is a key underlying factor: “It means reefs are already under stress before El Niño starts.”
The Great Barrier Reef Marine Park Authority confirmed for the first time this week that there had been “extensive coral bleaching along much of the length of the reef”. Much of it was visible in aerial surveys and had “affected a range of reef organisms”. The aerial surveys are being followed up by detailed monitoring by divers.
Done told New Scientist that little of the coral has died yet. But Goreau remains pessimistic. He claims that the Australian government is unwilling to discuss the extent of bleaching on the reef because it is reluctant to take action on global warming.