Corals that survive bleaching are more resilient to high temperatures

Increased ocean temperatures and sea level rise are wreaking havoc on marine ecosystems, and coral bleaching events are occurring at an unprecedented rate.

The Great Barrier Reef experienced two mass back to back bleaching events in 2016 and 2017, raising the number of mass bleachings for the reef to four in the past two decades.

But now, researchers from the Australian Research Council Centre of Excellence for Coral Reef Studies and the US National Oceanic and Atmospheric Administration (NOAA) discovered that corals along the Great Barrier Reef that survived 2016’s bleaching event were more resilient in 2017.

The discovery was part of a study published in the journal Nature Climate Change examining how ecological memory, or the imprint a past extreme event leaves on an ecosystem, impacts responses to future climate extremes.

With the Great Barrier Reef, the researchers found that the quick succession of back to back bleachings caused corals that survived past bleaching event to be more resistant to temperature changes.

“We were astonished to find less bleaching in 2017, because the temperatures were even more extreme than the year before,” said Terry Hughes, the lead author of the study. “The outcome in 2017 depended on the conditions experienced by the corals one year earlier. We called that ‘ecological memory,’ and show that these repeating events are now acting together in ways that we didn’t expect.”

A researcher records coral bleaching severity, Image Credit: Justin Marshall

Of the 2,300 kilometers of coral that make up the Great Barrier Reef, the researchers discovered that only seven percent escaped bleaching since 1998. After 2017, 61 percent of the reefs have experienced severe bleaching at least once.

“We found, using the National Oceanic and Atmospheric Administration’s satellite-based coral bleaching tools, that corals in the north of the Great Barrier Reef were exposed to the most heat stress in 2016,” said Mark Eakin, a co-author of the study. “A year later, the central region saw the most prolonged heating.”

The results of the study highlight the importance of understanding how climate-driven events impact future responses in an ecosystem and call for stronger measures to protect the world’s reefs from climate change.

“We need urgent global action on greenhouse emissions to save the world’s coral reefs. Australia should be – but regrettably isn’t – at the forefront of tackling global heating,” said Hughes.

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By Kay Vandette, Earth.com Staff Writer

Image Credit: Tane Sinclair-Taylor

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