Coral cover on two-thirds of Australia’s Great Barrier Reef has reached its highest level since records began 36 years ago, according to marine scientists who monitor the ecosystem.
But the coral remains highly vulnerable to mass bleaching events, which are occurring more frequently as human activity warms the oceans, the Australian Institute of Marine Sciences (AIMS) said in its annual report.
The recovery in the central and northern regions of the UNESCO World Heritage Site did not extend to the southern region, which lost coral cover amid an outbreak of crown-of-thorns starfish.
The Great Barrier Reef remains a “forty system” that “still retains that ability to recover from disturbances,” said Mike Emslie, AIMS monitoring program leader.
“But the concern is that the frequency of these disruption events is increasing, especially the massive coral bleaching events,” he added.
Earlier this year saw the first mass bleaching during a La Niña year, a natural climate cycle that typically brings cooler temperatures that allow the coral to recover. It was the fourth mass bleaching event in seven years.
Dr Emslie said climate change is driving more frequent and longer lasting marine heat waves.
“The increasing frequency of warming ocean temperatures and the magnitude of mass bleaching events highlight the critical threat climate change poses to all reefs, particularly as starfish outbreaks and tropical cyclones also occur,” he said.
He warned: “Future disruption could reverse the observed recovery in a short time.”
AIMS chief executive Dr Paul Hardisty said the increasing frequency of such events is “uncharted territory” for the reef.
“In our 36 years of monitoring the condition of the Great Barrier Reef, we have not seen bleaching events so close together,” he said.
The report comes as UNESCO considers whether to list the Great Barrier Reef as “in danger”, following a visit by the United Nations body in March.
The matter was to be discussed at a meeting of the World Heritage Committee in Russia in June, which was then postponed.
In an important measure of reef health, AIMS defines hard coral cover of more than 30% as high value, based on its long-term
surveys of the reef.
In the northern region, average hard coral cover grew to 36% in 2022, while in the central region hard coral cover increased to 33% – the highest levels recorded for both regions since the institute began monitoring the reef in 1985.
But in the southern region, which generally has higher hard coral coverage than the other two regions, coverage fell to 34% in 2022 from 38% a year earlier.
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Record high coral on parts of Australia’s Great Barrier Reef, although the ecosystem remains vulnerable to warming Climate News
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