Heatwaves kill coral reefs faster than you think

  • Heatwaves kill coral reefs faster than you think

Heatwaves kill coral reefs faster than you think

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

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.

In the past 20 years, the reef has suffered from four mass bleaching events due to global warming.

The report showed that a severe marine heatwave will not only trigger bleaching events, but can lead to heat-induced death of the coral itself.

University of Technology Sydney scientists A/Professor David Suggett and Dr Emma Camp explain how they were also able to use novel bio-optical techniques that allow them to visualise and study the rapid transition in the coral microbiome for the first time. Within days, a complex microbial biofilm encases the exposed coral skeleton, further accelerating the loss of calcium carbonate from the reef to weaken it even further.

Researchers suggest that "severe heatwave-induced mortality events" should therefore be considered a separate phenomenon to coral bleaching, and one which causes more damage. They say that such heatwave mortality events, and the rapid reef decay that results, likely will become more frequent as the intensity of marine heatwaves increases in the coming years.

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