OMG: Heatwaves kill coral reefs far faster than thought says study

Rodiano Bonacci
Agosto 10, 2019

In fact, though the study focused on the effects of ocean heatwaves during the heatwave that hit Australia's Great Barrier Reef in 2016, researchers determined that this heatwave phenomenon affected 37% of coral reefs globally between 2014 and 2017.

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.

This bleaching and skeletal decay risks the lives of the many other sea creatures call the coral framework home.

In 2016 the team's research showed that just a 0.5C increase in ocean temperature changes the extent of mortality that happens in coral during bleaching.

To better understand this phenomenon in the new study, Ainsworth and colleagues simulated the severe heatwave conditions seen on the GBR in 2016 with two coral species that showed high mortality that year.

"The severity of these heatwave events is beyond the bleaching process, it's actually a point where the coral animal itself is dying", said Tracy Ainsworth, a co-author of the study from the University of New South Wales.

"We are just going so far beyond what's normal". After the heatwave, the corals showed rapid degradation and mortality as microbial biofilms took over.

CT scanning of the coral skeleton as would be used in medical imaging shows that the skeleton left behind is rapidly eroded and weakened. The heat kills the tissue on the coral reefs, leaving them vulnerable to microbes which then cover the stripped skeletons, dissolving them within as little as a few days.

"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.

Heatwave conditions lead to an immediate heat-induced mortality of the coral colony, as the coral skeleton rapidly dissolves and its structure is lost.

"Climate scientists talk about "unknown unknowns" - impacts that we haven't anticipated from existing knowledge and experience". 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", says James Heron, a scientist at James Cook University.

"We already use climate models and satellite data to predict and detect conditions that cause coral bleaching".

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