New research has found that some reefs play host to heat-tolerant corals, highlighting the importance of identifying and protecting these reefs as an insurance policy against future bleaching.
The team of scientists from James Cook University, University of Western Australia and Edith Cowan University surveyed coral reefs in the West Australian Houtman Abrolhos group of islands (HAI), publishing their findings on the extraordinary heat resilience of its corals in the journal Current Biology.
Western Australian reefs experienced massive and deadly marine heat waves throughout 2025 that resulted in widespread coral bleaching and death.
Despite being exposed to extreme heat, researchers found there was minimal coral bleaching on HAI reefs, part of an archipelago of hundreds of islands in the Indian ocean off the coast of WA.
"This marine heat wave was likely one of the worst in Western Australian history. The temperatures have been off the scale for eight months … what we would call catastrophic," said the paper's first author and JCU Research Fellow Dr Kate Quigley.
"Other locations in WA have completely fried and died.
"But when we surveyed the HAI reefs there was really no to little sign of bleaching … it was very unexpected."
Scientists took a selection of three different coral species from the HAI reefs and put them through laboratory trials to test their heat resistance under controlled conditions.
"We investigated corals that build the foundation of the reef, corals that cement and hold the reef's structural complexity together, and corals that fill it in," said Dr Quigley.
"It's a classical framework for reef function and we had species from all three of those functions. All three did much better than expected when we exposed them to extreme heat stress."
In the laboratory, researchers measured coral death, photosynthetic efficiency, and the extent of coral bleaching as function of degree heating weeks (DHW), a standard indicator of heat stress in marine ecosystems.
"In the lab trials, they survived a lot longer compared to expected values. Their bleaching resistance was 3.7 times higher, they lasted 3.8 times longer, and thresholds for declining photosynthetic efficiency were up to 22 times higher than expected," Dr Quigley said.
"Bringing them back to the lab allowed us to take a deeper dive and confirm the observations we saw in the field.
"We were also able to get at some of the mechanisms that could explain this incredible resistance."
Dr Quigley explained that the improved photosynthetic efficiency seen in the HAI corals, compared to other reef's corals, could be associated with the symbiotic algae – symbionts – that live inside the corals and provide corals with energy.
"The photosynthetic measures we recorded here for these symbionts show they are particularly tough," she said.
"The HAI reefs lie at the junction between temperate and tropical regions. This may also be driving the incredible resistance."
The researchers emphasise how important it is to protect refuge reefs like those in the Houtman Abrolhos group of Island's, suggesting that there may be less than ten locations like this in the world.
"While reducing greenhouse gas emissions still has to be our number one priority, we should also be doubling down on our efforts to protect these special places … they give us hope for a better future," said Dr Quigley.
