Heatwaves kill coral reefs far faster than thought

A diver swims near the Great Barrier Reef off the coast of Australia

Marine Heat Waves Decimate Coral Reefs Much Faster Than ly Thought- Study Flickr Tchami

Marine heatwaves, which have become more frequent, intense, and have been staying longer, are playing a huge role in coral death, says new research from scientists working at the Great Barrier Reef.

Ainsworth's team earlier showed that just a 0.5C increase in water temperature changes the extent of mortality in corals during bleaching.

Their studies show that marine heatwave events on coral reefs are entirely different from the way coral bleaching has been understood.

The study, which also involved researchers from the University of Newcastle in Britain, Australia's James Cook University, the University of Technology Sydney and the US National Oceanic and Atmospheric Administration, used CT scans of coral reefs to monitor the impact of extreme temperatures. "This isn't starvation, this is the animal itself undergoing mortality directly from the heat of the water", says Tracy Ainsworth, a marine biologist at the University of New South Wales.

The skeleton is immediately overgrown by algae and bacteria, a process that was devastating not just for the animal tissue, but also for the skeleton that is left behind which is rapidly eroded and weakened, the study found. After the heatwave, the corals showed rapid degradation and mortality as microbial biofilms took over.

"It confirms that we are on a trajectory where heatwave events and heat stress is becoming so severe it's beyond the capacity of the ecosystem to withstand it", she told AAP.

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.

"Here, we show that marine heat wave events on coral reefs are biologically distinct to how coral bleaching has been understood to date, in that heat wave conditions result in an immediate heat-induced mortality of the coral colony, rapid coral skeletal dissolution, and the loss of the three-dimensional reef structure", the study explains.

"We already use climate models and satellite data to predict and detect conditions that cause coral bleaching". The report indicates that the benefits derived by humans from coral reefs "span from coastal protection to subsistence and industrial fisheries", and that these industries depend on the structural integrity of the coral reefs' 3-D structures, which are greatly compromised by ongoing climate change as well as ocean heatwaves.

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