GREAT BARRIER REEF GRIEF
The Great Barrier Reef has experienced “probably the most intense and widespread bleaching event recorded to date”, the head of the reef’s aerial monitoring program has confirmed.
The latest snapshot, released on Wednesday, found a range of stressors affected the Great Barrier Reef over what reef experts said was the “worst summer on record”, with elevated water temperatures, two tropical cyclones, extreme rainfall in December, January, February and March, and continuing outbreaks of the crown of thorns starfish.
The snapshot found: evidence of bleaching on 73 per cent of reefs surveyed; “very high” levels of bleaching (between 61–90 per cent of coral affected) in 31 per cent of reefs surveyed; and evidence of “extreme” levels of bleaching (more than 90 per cent of coral affected) in 8 per cent of reefs surveyed.
Researchers monitored 1080 individual reefs from the air, over 10 clear days with low wind and low wave activity, starting towards the end of summer. They flew at low altitudes of about 500 feet, enabling visibility down to 6m-10m.
Dr Neal Cantin from the Australian Institute of Marine Science, who led the aerial survey work, said this was probably going to be the “most intense and widespread bleaching event recorded to date”.
“We’re seeing high levels of bleaching in all three regions of the marine park, from Lady Elliot Island all the way to Princess Charlotte Bay,” he said.
In the official research paper underpinning the snapshot, Dr Cantin and his team said the corals were experiencing “the highest levels of thermal stress on record”.
The snapshot, produced by the AIMS, along with the Great Barrier Reef Marine
Park Authority (the Reef Authority) and the Commonwealth Scientific and Industrial Research Organisation, synthesises observations made by researchers every week in the summer.
Despite the widespread bleaching, Dr Cantin said there were still healthy corals to be found.
“The Barrier Reef is a very large ecosystem, and there are locations that are less bleached and that won’t
have mortality from this event,” he said.
The Reef Authority confirmed the reef was undergoing a mass bleaching event on March 8. It was the fifth such event since 2016.
Dr Cantin has helped develop a scale from one to five to denote the severity of a bleaching event, but the summer assessment would not be made until after the results of water quality tests were known.
The past few summers on the Reef have been strikingly different. In the 2021-22 summer, bleaching was reported on 91 per cent of all reefs surveyed, but in the “benign” 2022-23 season, coral was reported to be at record levels in the northern and central parts of the Reef.
The report comes two days after the US National Oceanic and Atmospheric Administration confirmed tropical reefs around the world were experiencing a fourth mass bleaching event, the second in a decade.
Since early 2023, NOAA said bleaching had been detected across the Pacific, Atlantic and Indian Oceans, as well as the Caribbean, the Persian Gulf and other areas.
Great Barrier Reef Foundation managing director Anna Marsden said this week’s reports were “devastating milestones for our Great Barrier Reef and the world’s coral reefs”.
“Coral reefs are on the frontline of climate change,” she said.
“If we do not take immediate action to reduce global emissions and implement effective conservation measures, we risk losing these irreplaceable ecosystems forever.”
Australian Marine Conservation Society campaign manager Dr Lissa Schindler said coral could bounce back after bleaching events, “but climate change is driving more frequent and severe events, meaning reefs aren’t being given the chance to recover”.
If we do not take immediate action ... we risk losing these irreplaceable ecosystems forever Anna Marsden Great Barrier Reef Foundation managing director