The impacts of the 2017 heat wave on the Great Barrier Reef were dependant on the impacts from the heat wave in the previous year, reports a paper published online this week in Nature Climate Change. These findings shed light on the extent to which the impacts of marine heat waves on coral reefs may be influenced by previous warming events - a phenomenon known as ‘ecological memory’.

Terry Hughes and colleagues analysed aerial surveys to assess the severity of bleaching in individual reefs along the length of the Great Barrier Reef. They surveyed the severity of coral bleaching on 1,135 reefs in 2016, and 742 in 2016, with 606 surveyed in both years. The authors combined these data with satellite-based temperature measurements of the entire Great Barrier Reef, which showed that 2017 had hotter or longer-lasting summer sea-surface temperatures on around 80% of the individual reefs compared to the previous year. The authors then used a generalized linear model to show that the corals were more resistant to bleaching in 2017 than the year before. Between the two events, severe bleaching affected two-thirds of the world’s largest reef system.

The ecological memory of the 2016 heat wave, despite exposure to higher temperatures in 2017, demonstrates that studying individual events may be insufficient for understanding climate impacts. With climate-driven events increasing in frequency, it is imperative to examine the interactions of successive disturbances, the authors conclude.