The Great Barrier Reef’s management authority is preparing to carry out aerial surveys across the entire length of the marine park after helicopter flights confirmed extensive coral bleaching across the southern section of the world’s biggest coral reef.
The Guardian reported last week that bleaching was being reported in all regions of the reef from Lizard Island in north to the Keppel islands in the south – a distance of more than 1,100 kilometres.
Conservationists fear a seventh mass bleaching event could be unfolding on the reef.
On Wednesday, the Great Barrier Reef Marine Park Authority said helicopter flights had covered 27 inshore reefs and 21 offshore reefs in the southern region off the Queensland coast and found bleaching was “extensive and fairly uniform” at all surveyed spots.
Dr Mark Read, the authority’s director for reef health, said most corals were showing signs of heat stress and were either bleaching white or were showing fluorescent colours. Some coral species fluoresce under heat stress.
Bleaching is caused when corals sit in unusually warm water for several weeks. Corals can recover if bleaching is mild and if water temperatures drop off. But coral scientists also say bleaching can make corals more susceptible to disease and affect their ability to reproduce.
Reefs surveyed were in the Keppel Islands and Gladstone region and a group of offshore reefs known as the Capricorn Bunkers.
Dr Neal Cantin, a senior research scientist at the Australian Institute of Marine Science, who was in the helicopter, said: “We were able to see bleached corals at depth quite clearly across the reef slope from the air.”
Limited bleaching was also seen on some reefs north of Mackay and the Whitsunday islands.
The authority said while the southern section of the reef appeared to most affected, it had reports of bleaching from all other regions.
Teams of scientists and park managers would be carrying out in-water surveys over the coming month.
Cantin said: “Aerial surveys are an ideal tool to assess the spatial extent of bleaching, but we need to go under the water to understand more about the severity of bleaching and how deep the bleaching extends.”
More helicopter surveys were planned, and Read said: “We are also preparing for broadscale surveys by fixed wing aircraft which will cover the central and northern regions, should conditions indicate these are required.”
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The reef has been through six previous mass bleaching events in 1998, 2002, 2016, 2017, 2020 and 2022.
Any reef-wide surveys would be timed to coincide with the peak of heat stress “to provide us with the best understanding of the event’s extent and severity,” added Read.
Read said it was important anyone using the marine park should know where they could fish, avoid anchoring on coral and taking all rubbish home.
“Most importantly do what you can to contribute to the global effort to reduce greenhouse gas emissions,” he said.
Forecasts from the US government’s Coral Reef Watch program suggests the heat stress currently across the reef could begin to dissipate by mid-March.
Richard Leck, head of oceans at WWF Australia, said the reef was “on the precipice” of a potential seventh mass bleaching event.
“The heat stress caused by this underwater heatwave is continuing to accumulate and we’re incredibly concerned that the reef is still some way off being out of the woods.”
Dr Lissa Schindler, a reef campaigner at the Australian Marine Conservation Society, said seeing bleaching unfolding across the souther region was a worry. “The next few weeks will tell us if this is another mass bleaching event.”