SYDNEY • Marine heatwaves are killing coral reefs far more quickly than previously believed, according to a new study released yesterday.
Scientists have known that rising sea temperatures blamed on global warming can severely damage reefs through a process of "bleaching", where the high temperatures kill the colourful algae that nourish the coral animals. Coral anemones build calcium carbonate skeletons that create the reefs and rely on algae for most of their food. In return, the algae get a home to live in.
Repeated "bleaching events", such as ones that hit Australia's Great Barrier Reef in 2016 and 2017, can eventually kill the coral in a process which takes months or years. If sea temperatures ease, some bleached corals are able to regenerate.
But the new study found that severe marine heatwaves can actually degrade the skeletal structure of the coral, potentially killing the organisms in a matter of days or weeks.
"The severity of these heatwave events is beyond the bleaching process, it's actually a point where the coral animal itself is dying," said Dr Tracy Ainsworth, a co-author of the study from the University of New South Wales.
The study also involved researchers from James Cook University, the University of Newcastle, the University of Technology Sydney and the US National Oceanic and Atmospheric Administration and was published in the journal Current Biology.
The researchers used CT scans of coral reefs to monitor the impact of extreme temperatures.
Dr Scott Heron from James Cook University said the rapid dissolving of coral skeletons after severe heatwaves came as a surprise.
"Climate scientists talk about 'unknown unknowns' - impacts that we haven't anticipated from existing knowledge and experience," he said. "This discovery fits into this category. As we begin now to understand this impact, the question is how many more of these 'unknown unknowns' might there still be that could bring faster and greater damage to coral reefs from climate change," he said.
The back-to-back bleachings in 2016 and 2017 caused the death of about half of all shallow water corals in the northern and central sections of the 2,300km reef, a United Nations-listed World Heritage site off the east coast of Australia.