The future of the Great Barrier Reef hangs in the balance as global warming continues to affect the coral’s ability to recover, with only 2 per cent of the entire reef escaping bleaching in the past 30 years.

A new report by James Cook University finds this history of bleaching changes how the affected areas of coral respond to extreme heat. Those that have not been bleached before, or for a long time, were more vulnerable to the effects of bleaching than others.

“Five bouts of mass bleaching since 1998 have turned the Great Barrier Reef into a checkerboard of reefs with very different recent histories, ranging from 2 per cent of reefs that have escaped bleaching altogether, to 80 per cent that have now bleached severely at least once since 2016,” said lead author Professor Terry Hughes, from the ARC Centre of Excellence for Coral Reef Studies at James Cook University.

These bleaching events cannot be examined on their own but need to be considered alongside their bleaching history to indicate the likelihood of recovery, the report finds.

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Professor Hughes said coral that was first to recover after bleaching was also most likely to be impacted in extreme heat events.

“The recovery driven by heat-sensitive coral is similar to the recovery in a forest after a fire. The most flammable grasses come back faster, which can push the transition of the area from fire-resistant forest to a fire-prone grassland,” he said.

Climate change has also affected the reproductive abilities of bleached corals, with larval supply declining 71 per cent between 2016 and 2020, according to a new report by the University of Queensland, also released on Friday.

Researcher Mandy Cheung said while work was being done on how to protect the reef, more ambitious actions were needed to reduce greenhouse emissions, reduce ocean temperatures and improve larval supply.