Heatwaves kill coral reefs far faster than thought

James Marshall
August 10, 2019

This dissolution results in the entire structure of the coral reef collapsing, decimating an entire ecosystem nearly immediately.

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.

"But what we are now seeing is that severe marine heatwave events can have a far more severe impact than coral bleaching - the water temperatures are so warm that the coral animal doesn't bleach, in terms of a loss of its symbiosis, the animal dies and its underlying skeleton is all that remains". "We still see the coral become white as the animal dies and its skeleton is exposed to the water, and then we see it very rapidly become overgrown by colonizing algae from both the inside out and the outside in".

The study published in journal Current Biology on Friday says a temperature increase of half-a-degree Celsius in the ocean changes the extent of mortality in coral during bleaching.

At that time, reefs of the northern GBR were exposed to a rapid and severe rise in sea surface temperatures, with more than 30% experiencing temperatures above the established threshold for coral survival. After the heatwave, the corals showed rapid degradation and mortality as microbial biofilms took over.

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.

Their research showed that while it was previously understood that coral bleaching can lead to a break down of symbiosis, marine heatwaves can lead directly to heat-induced mortality of the coral animal as well.

Scott Heron from James Cook University said the rapid dissolving of coral skeletons after severe heatwaves came as a surprise. "Corals can survive a bleaching event, but they are under more stress and are subject to mortality", the US' National Oceanic and Atmospheric Administration (NOAA) explains on its website. Due to their severity and rapid effects, the study argues that these climate change-induced ocean heatwaves are a phenomenon distinct from normal coral reef bleaching, and considers these events to be further compelling evidence that something must be done to drastically lessen global heating in order to control these deadly events.

Researchers from Australia, the United Kingdom and the USA studied the impact of global warming in Australia's Great Barrier Reef and published their findings on Friday in the Current Biology journal. The authors declare no competing interests.

Other reports by Click Lancashire

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