Coral bleaching

Coral bleaching hits 93% of Great Barrier Reef: scientists

Sydney: Australia’s Great Barrier Reef is suffering its worst coral bleaching in recorded history with 93 per cent of the World Heritage site affected, scientists said on Wednesday, as they revealed the phenomenon is also hitting the other side of the country.

After extensive aerial and underwater surveys, researchers at James Cook University said only 7 per cent of the huge reef had escaped the whitening triggered by warmer water temperatures.

“We’ve never seen anything like this scale of bleaching before,” Terry Hughes, convener of the National Coral Bleaching Taskforce, said.

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-kilometre site off the east coast.

Hughes said of the 911 individual reefs surveyed, only 68 (or 7 per cent) had escaped the massive bleaching event, which has also spread south to Sydney Harbour for the first time and across to the west.

Researcher Verena Schoepf, from the University of Western Australia, said coral was already dying at a site she had recently visited off the state’s far north coast.

“Some of the sites that I work at had really very severe bleaching, up to 80 to 90 per cent of the coral bleached,” she said. “So it’s pretty bad out there.”

Australia’s Environment Minister Greg Hunt said it was “absolutely clear that there is a severe coral bleaching event occurring not just in the Great Barrier Reef but throughout many parts of the Pacific”.

Hughes said the bleaching began in Hawaii late last year and had already affected several Pacific islands.

“Right now, New Caledonia, the Coral Sea, the northern half of the Barrier Reef and New South Wales are bleaching severely, and Western Australia is quickly catching up,” he said.

What is coral bleaching?

Bleaching occurs when abnormal environmental conditions such as warmer sea temperatures cause corals to expel tiny photosynthetic algae, draining them of their colour.

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.

Hughes said while bleaching had been linked to El Ninos, which generally occur every four to six years, “it wasn’t until 1998 that one finally caused a bleaching event to happen” on the Great Barrier Reef.

“So the issue is global warming,” Hughes said, saying the link between water temperature and the severity of the bleaching was clear.

Hughes said the impact on the Great Barrier Reef would have been even worse had not a tropical cyclone that smashed into the Pacific island of Fiji in February brought rain and cooler weather to parts of Queensland.

“If you think about it, being rescued by the vagaries of a cyclone is a fairly precarious place to be,” he added.

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 said. 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 said.

“And again the big question is how many of these events can it handle? And I think the answer is not many more.”

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