By Alice Klein
Australia’s Great Barrier Reef has experienced its third mass bleaching event in five years. For the first time, all three sections of the reef have been severely affected.
The damage occurred in February when the reef was exposed to the hottest month of water temperatures on record.
Aerial surveys conducted by Terry Hughes at James Cook University in Australia and his colleagues during the last two weeks of March revealed that 25 per cent of the reef had been severely bleached and 35 per cent moderately bleached. The northern, central, and southern sections of the reef were all hit.
Severe bleaching also struck in 1998, 2002, 2016 and 2017, but was confined to one or two sections. This is the first time that all three sections have simultaneously experienced severe bleaching, says Hughes. “It’s heartbreaking.”
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Some of the damaged corals will survive, including more heat-resistant species and those that have only been lightly bleached. But many others were probably “literally cooked” at the peak of the country’s heatwave in early 2020.
Others will die more slowly from stress over the next few months, says Hughes. His team will conduct underwater surveys in October and November to assess the death toll.
Hughes has particularly grave fears for the southern reef, which has mostly been spared in previous bleaching events and hasn’t developed the same heat resistance as the northern and central parts.
After the combined 2016 and 2017 bleaching events, about half the coral on the Great Barrier Reef died. It normally takes a decade for even the fastest-growing corals to recover, meaning the latest damage will cripple the reef’s ability to bounce back, says Hughes. “Having three events in five years is very bad news,” he says.
The high frequency of mass bleaching in recent years has been driven by human-induced climate change, which is steadily raising global ocean temperatures. The only way to tackle the problem is to urgently reduce greenhouse gas emissions, says Hughes.
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