Bleached staghorn coral on the Great Barrier Reef between Townsville and Cairns, March 2017BETTE WILLIS, ARC CENTRE OF EXCELLENCE FOR CORAL REEF STUDIES

Australia’s Great Barrier Reef is undergoing its third mass bleaching episode, which began in 2016. These events, which are spurred by warming waters, pose a dire threat to coral life, researchers reported Wednesday (March 15) in Nature.

When ocean waters warm, coral start to expel photosynthetic algae, a major energy source for the animal colonies. Such algal loss is known as bleaching, as it leaves the reefs an eerie white. If the waters cool, the polyps can recover their algae; otherwise, they will starve and die.

“If you think about it, on a really hot day, it’s hot out, it’s not a big deal. But when it goes on and on through time, that’s when people without air conditioning start dying,” Mark Eakin, a coral...

See “Bleached Corals “Sickest” Scientists Have Ever Seen” 

For to the new study, Eakin and colleagues examined the current bleaching episode in the Great Barrier Reef, which was triggered by the record-setting temperatures in 2015 and again in 2016 (the hottest year since scientists started keeping records in 1880). The team conducted aerial surveys of the reefs in 2016 and compared the results to data from two previous bleaching events (1998 and 2002). This revealed that the ongoing event is much more widespread and damaging than the previous ones: only around 9 percent of the 1,156 surveyed reefs showed no signs of bleaching in 2016, compared with 42 percent of 631 reefs in 2002 and 45 percent of 638 reefs in 1998.

“We didn’t expect to see this level of destruction to the Great Barrier Reef for another 30 years,” study coauthor Terry Hughes, director of a government-funded center for coral reef studies at James Cook University in Australia, told The New York Times. “In the north, I saw hundreds of reefs—literally two-thirds of the reefs were dying and are now dead.”

While some factors, such as reduced water pollution and restricted fishing, may help save the reefs, these efforts will not be enough to counter the effects of warming waters, the authors say. “Climate change is not a future threat,” Hughes told The New York Times. “On the Great Barrier Reef, it’s been happening for 18 years.”

See “Changing Oceans Breed Disease

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