Ocean heat waves becoming more frequent and killing coral instantly

Marine heatwaves more devastating to coral reefs than previously thought: Australian research - Xinhua | English.news.cn

Marine heatwaves more devastating to coral reefs than previously thought: Australian research - Xinhua | English.news.cn

Increasingly frequent marine heatwaves can lead to the nearly instant death of corals, scientists working on the Great Barrier Reef have found.

As the human-caused climate crisis drives up ocean temperatures at a rate that has scientists anxious, a study published Thursday in the journal Current Biology reveals that warming waters are an even bigger threat to coral reefs than experts previously realized.

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. These increasingly severe thermal conditions are causing an unprecedented increase in the frequency and severity of mortality events in marine ecosystems, including on coral reefs. If sea temperatures ease, some bleached corals are able to regenerate. This means that the 3D coral framework which provides home to many other animals on the reef is also at risk.

"Now, we see there is also a temperature at which the coral animal itself suffers from heat-induced mortality. 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.

The findings revealed that extreme heat waves go beyond just causing a process known as "bleaching", a coral-related event that occurs when water temperatures get so warm that they expel algae from their tissues, forcing them to turn white.

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"Until now, we have described coral bleaching as an event where the symbiotic relationship between coral and its microbes breaks down and corals lose their main source of nutrition, and the coral can die if the symbiosis is not restored", author associate professor Tracy Ainsworth from UNSW said.

The study revealed that corals became as much as 15% weaker after an extreme heat occasion, causing some fragments actually to break off from the reef. "We show that this process is devastating not just for the animal tissue, but also for the skeleton that is left behind, which is rapidly eroded and weakened". This discovery fits into this category.

Scott Heron from James Cook University said the rapid dissolving of coral skeletons after severe heatwaves came as a surprise.

Commenting on the analysis, Dr James Guest from Newcastle University in the United Kingdom, who has been researching coral reef habitats for more than 15 years, said: "It is onerous to know how a lot we've got to keep saying that this is a huge problem before policy-makers resolve to do something about it".

In addition to being critical habitats for marine life, coral reefs are essential to people in coastal communities, who depend upon them for fishing, tourism, and beach protection.

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