Frequency of bleaching alarms scientists

Looking at 100 reef locations in 54 countries around the globe over the period 1980 to 2016, the researchers concluded that, prior to 1980, while coral bleaching events were recorded at local scales (tens of kilometres in extent), regional-scale bleaching (thousands of kilometres in extent) was a rare phenomenon. The reason for the bleaching events was usually the addition or movement of sediment in an area, unusual temperatures or the influx of fresh water. During the 1980s, worldwide bleaching events became apparent as the effects of El Niño became stronger – the result of global warming. In addition, in the past 20 years more bleaching has been recorded outside of El Niño events.

The researchers believe that coral reefs are now subjected to soon-to-be unsustainable levels of bleaching intensity and frequency. These levels, they say, are indicative of the human-dominated Anthropocene era. Given that even the fastest-growing corals take between 10 and 15 years to recover after bleaching, the ever-decreasing interval is cause for alarm.

The paper by Terry Hughes and his colleagues concludes, ‘The future condition of reefs, and the ecosystem services they provide to people, will depend critically on the trajectory of global emissions and on our diminishing capacity to build resilience to recurrent high-frequency bleaching through management of local stressors before the next bleaching event occurs.’