Great Barrier Reef "dead or dying" ?

After extensive aerial and underwater surveys, researchers at James Cook University said only seven percent of the huge reef had escaped the whitening triggered by warmer water temperatures.

"We've never seen anything like this scale of bleaching before. Our estimate at the moment is that close to 50 percent of the coral is already dead or dying," said Terry Hughes, convenor of the National Coral Bleaching Taskforce.

The damage ranges from minor in the southern areas - which are expected to recover soon - to very severe in the northern and most pristine reaches of the 2,300 kilometres (1,430 miles) site off the east coast. Hughes said of the 911 individual reefs surveyed, only 68 (or seven percent) had escaped the massive bleaching event which has also spread south to Sydney Harbour for the first time and across to the west.

Corals can recover if the water temperature drops and the algae are able to recolonise them, but scientists warned last year that the warming effects of a El Nino weather pattern could result in a mass global bleaching event.

Andrew Baird, from James Cook University's centre for coral reef studies, said he had been surprised by the scale and severity of the event on the major tourist drawcard which is teeming with marine life. "We've been expecting a really big event for a while I suppose and here it is," he told AFP. Baird said because the bleaching was far less serious in the southern reaches "lots of the reef will still be in good shape". "But the reef that's been badly affected - which is a third to a half of it - is going to take a while to recover," he told AFP. "And again the big question is how many of these events can it handle? And I think the answer is not many more."

The Great Barrier Reef is the world's largest coral reef ecosystem and one of the main sources of tourism in the region. The reef is some 2,300 kilometers (1,429 miles) in length and is made up of around 3,000 individual reefs.They are home to over 600 different corals and thousands of animal species. The Great Barrier Reef was declared a UNESCO World Heritage site in 1981.

is/at (dpa, afpe, rtre)