Coral reefs across the Houtman Abrolhos archipelago off Western Australia emerged almost unscathed from a prolonged marine heatwave in early 2025 that devastated reefs elsewhere. Researchers led by Kate Quigley from the University of Western Australia found no significant bleaching or mortality during surveys in July 2025. The discovery highlights potential secrets to heat tolerance that could aid global coral protection.
Kate Quigley and her team surveyed 11 sites in the Houtman Abrolhos Islands in July 2025, expecting widespread damage after months of extreme heat. Instead, they observed virtually no signs of stress, such as fluorescing or bleached corals. “We expected to see mass bleaching with lots of white colonies, and likely mortality of reefs, given we did surveys after many months of marine heatwave. We did not see this,” Quigley said, as reported by New Scientist. In contrast, up to 60 percent of corals died at the nearby Ningaloo Reef during the same event, mirroring global losses from 2025 marine heatwaves. The heat stress, measured in degree heating weeks (DHW), reached 4 °C-weeks in early February 2025, 8 °C-weeks by early March, and peaked at 22 °C-weeks by mid-April—levels typically causing catastrophic bleaching above 8 °C-weeks. In laboratory tests, corals from the islands showed twice the survival rate and nearly four times the bleaching resistance at 8 °C-weeks compared to standard thresholds, with nearly 100 percent survival up to 16 °C-weeks. Quigley attributes the resilience to local environmental factors driving heat tolerance evolution across species, possibly involving algal symbionts. “I think this location has a particular set of environmental factors that has driven the evolution of heat tolerance generally for the species that live there,” she said. Petra Lundgren of the Great Barrier Reef Foundation called such sites natural laboratories for enhancing coral resilience through breeding and restoration, complementing efforts to cut emissions. The findings appear in Current Biology (DOI: 10.1016/j.cub.2026.04.004).