Ecology: Stress-resistant corals maintain heat tolerance under cooler temperatures

Heat-resistant corals can maintain their health and resistance to heatwaves at cooler temperatures, a study in Nature Communications reports. However, these corals cannot increase their bleaching threshold after acclimatizing to warmer conditions. The findings suggest that corals from thermally extreme conditions could be used to help restore cooler reefs degraded by bleaching, but they will have limited ability to adapt to a rapidly warming environment.

The presence of reefs thriving in highly variable temperatures has fuelled hope that some corals may be able to adapt to warmer oceans, but whether they can do so fast enough to keep up with climate change is uncertain.

Verena Schoepf and colleagues performed thermal experiments on coral colonies from reefs in the Kimberley region of northwest Australia that can tolerate extreme temperature fluctuations. They transplanted colonies into water tanks with either temperatures similar to their native habitat, 4°C cooler or 1 °C warmer under stable or fluctuating temperatures. The corals acclimatized to both cooler (over 9 months) and warmer (over 6 months) conditions, but their health began to decline once maximum temperatures exceeded the normal seasonal range. When the authors subjected the colonies to two-week heat-stress tests, they were unable to increase their bleaching threshold.

These findings suggest that even coral reefs adapted to extreme environments have a limited ability to acclimatize to ocean warming in the future. However, the ability of the corals to retain their heat tolerance, despite exposure to cooler temperatures, suggests that such colonies could provide natural refuges from which larvae may colonize cooler, bleaching-sensitive regions.