Coral without local stressors fare better in heatwaves: UVic study

A recent University of Victoria (UVic) study dove into the effects of marine heatwaves on the world’s coral reefs, and examined how local stressors varied those results.

According to the study, “marine heatwaves triggered by climate change pose an imminent threat to the world’s coral reefs.”

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The research paper, dubbed “Transformation of coral communities subjected to an unprecedented heatwave is modulated by local disturbance,” was released Wednesday by Science Advances.

The study found that, after a heatwave, 90 per cent of an island’s coral cover was lost. Although further findings showed other coral species “fared reasonably well,” losing just 30 per cent of their colonies.

“We might have expected almost complete coral mortality, but instead we found that despite extraordinarily long heat stress, there will still winners and losers,” said Dr. Julia Baum, the biology professor leading the project.

The coral species suffering the most lost 99 per cent of their colonies in the “unrelenting heat.”

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The study explains local stressors provide varying impacts on coral species during a heatwave. Some of these stressors include; coastal development, pollution, and overfishing.

“Few studies take into account how stressed-out reefs respond to heatwaves until now,” a excerpt from the study reads. “The study was carried out throughout the 2015-2016 El Niño on the world’s largest coral atoll, Kiritimati (also known as Christmas Island), in the central equatorial Pacific. Because villages and other infrastructure are concentrated at one end of the atoll, reefs around the atoll are exposed to vastly different levels of local stressors, and range from near pristine to highly degraded ones.”

Baum says this study “underscores” just how important it is to monitor and take care of the world’s coral species right now, and she adds reducing greenhouse gas emissions is how it needs to be done.

“Local management efforts are important, because every little bit matters right now, but without addressing the root cause of climate change, coral reefs are doomed.”

The study explains, at the current rate of climate change, between 70 and 90 per cent of the world’s coral reefs could be gone at 1.5 degrees Celsius global warming, while 99 per cent could be lost after two degrees of warming. The university notes this data comes from the The Intergovernmental Panel on Climate Change (IPCC).

“Recovery of coral reefs can take decades, and under climate change the interval between successive heatwaves has shortened to the extent that most reefs will not have sufficient time to recover,” Baum added.