5 Mass Bleachings In Rapid Succession Have Left Great Barrier Reef A "Checkerboard"
A new study reveals the impacts of multiple climate extremes on coral reefs over the past three decades, with only 2% of the Great Barrier Reef escaping bleaching in that time. Lead author Professor Terry Hughes from the ARC Centre of Excellence for Coral Reef Studies at James Cook University (Coral CoE at JCU) said the frequency, intensity and scale of climate extremes is changing rapidly due to global warming—and this includes the record-breaking marine heatwaves that cause corals to bleach and die.
"We no longer have the luxury of studying individual climate-related events that were once unprecedented or very rare," Prof Hughes said. "Instead, as the world gets hotter, we have to understand the effects of sequences of rapid-fire catastrophes, as well as their combined impacts."
The study shows only 2% of the Great Barrier Reef has escaped bleaching since the first event in 1998, then the world's hottest year on record. Bleaching is a stress response by overheated corals during heatwaves, where they lose their color and many struggle to survive. Eighty percent of reefs bleached severely in 2016, 2017 and 2020. "Five bouts of mass bleaching since 1998 have turned the Great Barrier Reef into a checkerboard of reefs with very different recent histories, ranging from 2% of reefs that have escaped bleaching altogether, to 80% that have now bleached severely at least once since 2016," Prof Hughes said.
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The scientists found the responses to extreme heat depended on the recent history of bleaching. In 2002 and 2017, it took more heat to reach similar levels of bleaching to those in 1998 and 2016. "To our surprise, we found the threshold for bleaching was much higher on reefs that had experienced an earlier episode of heat stress," Dr. Eakin said. "Consequently, the most vulnerable reefs each year were the naïve ones that had not bleached recently."
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"But," he cautioned, "more frequent, severe bleaching events will only undermine the resilience of coral reef ecosystems. Corals still need time to recover before another round of heat stress so they can make babies that will disperse, settle and recover the depleted parts of the Reef."
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https://phys.org/news/2021-11-rapid-fire-climate-extremes-great-barrier.html
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