BRISBANE, AAP – Another significant bleaching event is unfolding on the Great Barrier Reef ahead of a key international visit to take the ecosystem’s pulse.

Early results from monitoring work along the length of the 2300km World Heritage-listed reef show it is in trouble again.

“Bleaching has been detected across the marine park – it is widespread but variable, across multiple regions, ranging in impact from minor to severe,” the Great Barrier Reef Marine Park Authority said on Friday.

There are some instances of whole colonies bleaching but most observations are of early stage bleaching.

“The most heavily impacted reefs are around the Townsville region. There have also been reports of early mortality where heat stress has been the greatest,” the authority said.


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“Corals across the Marine Park remain vulnerable to the ongoing elevated temperatures.”

In the past week, sea surface temperatures have ranged between 0.5-2C above average throughout the marine park.

But parts of the far north and inshore areas between Townsville and Rockhampton have been as much as 2-4C above average.

There will be further updates as scientists analyse the results of aerial and in-water surveillance.

Leading coral scientist Terry Hughes, from James Cook University, has said the reef appears to be in the grip of its sixth mass bleaching event, driven by an end-of-summer heatwave.

If he is right, it will be the fourth such event in just six years.

Scientists agree greenhouse gas emissions are pushing up ocean temperatures, which in turn caused mass bleaching events on the reef in 1998, 2002, 2016, 2017 and 2020.

Earlier this month, a major report by the Intergovernmental Panel on Climate Change said the reef was in crisis and facing the prospect of irreversible damage.

It warned a high-emissions future could see the reef bleaching twice every decade from 2035, and every year after 2044.

That would be a death sentence for the reef because it takes about 10 years for decent recovery of fast-growing corals, and longer for slow-growing species.

The new bleaching coincides with a United Nations monitoring mission due to arrive next week, at Australia’s request, to check on the health of the ecosystem and report back to the World Heritage Committee.

Tony Fontes is a dive operator and climate advocate based in the Whitsundays.

He said the bleaching now being documented is gravely concerning because its happening under the La Nina weather phenomenon that typically keeps ocean temperatures lower.

“The fact we can still see bleaching in a La Nina is just mind boggling and as depressing a story as I’ve ever heard,” he said.