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Great Barrier Reef Braces for Another Massive Bleaching Event

After the worst die-off in the reef’s history in 2016, scientists are worried that high sea temperatures will affect the area again

Bleached coral discovered earlier this month at Maureen's Cove in the Great Barrier Reef (Australian Marine Conservation Society)
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2016 was a rough year for the Great Barrier Reef; an increase in sea temperatures last March and April led to a massive bleaching event up and down the 1,400-mile long reef system. According to the BBC, the bleaching event—in which the algae called zooxanthellae which give coral polyps their vibrant colors are expelled during times of stress—led to the death of 63 percent of the corals in the northern reef and six percent in the central section of the reef. Though bleaching is not inherently fatal, if the algae and coral do not re-establish their symbiotic relationship relatively quickly, the coral will eventaully die. Now, scientists are warning that another round of severe bleaching may happen over the next few months.

Harry Pearl at Seeker reports that sea level temperatures in the region have stayed above normal over the last year. A heat wave has hit the Australian mainland, and cloud cover has been low. “I think the next two weeks are going to be absolutely critical to see whether this really becomes a severe event or not,” Imogen Zethoven of the Australian Marine Conservation Society tells Pearl. “Right at the moment there hasn't been much rainfall; there hasn't been a normal wet season. There is not much cloud cover; it's very hot, and there is a lot of sunshine.”

Joshua Roberts at The Guardian reports that in a government briefing released earlier this month, researchers raised alarm bells, and reported seeing the beginnings of bleaching and coral disease in areas south of the main bleaching events last year. In fact, the report says that the reef is warmer than it was this time last year and the reef is showing more heat stress than before the 2016 bleaching began.

In some areas, the bleaching has already begun in earnest. During spot checks at six reefs last Friday, the Great Barrier Reef Marine Park Authority found bleaching on some of the more sensitive coral species in the northern portion of the reef, with some areas experiencing 60 percent bleaching. “We are having major bleaching in places that were bleached last year and areas that escaped bleaching last year,” John Rumney, a tour operator on the reef, tells Pearl.

According to Robertson, critics place the blame for the bleaching on climate change and the Australian government. Though Australia has a 35-year plan for protecting the reef, a recent UN study says Australia hasn’t done enough and the recent bleaching events will hurt their future efforts.  “[U]nprecedented severe bleaching and mortality of corals in 2016 in the Great Barrier Reef is a game changer,” says the study. “Given the severity of the damage and the slow trajectory of recovery, the overarching vision of the 2050 Plan, to ensure the Great Barrier Reef continues to improve on its [outstanding universal values, like its beauty and unique ecosystem] every decade between now and 2050, is no longer attainable for at least the next two decades.”

The Great Barrier Reef is not alone in seeing devastating bleaching and die-offs. In fact, its problems are part of a four-year-long global bleaching event, reports Michael Le Page at New Scientist. The bleaching has been driven by an El Niño warming pattern that began to develop in 2014 and continued through 2015 and 2016. So far, warming temperatures have bleached about 32 percent of the world’s reefs and 60 percent may be impacted by the time the extended bleaching event ends. A small La Niña event, in which deeper ocean water cools the warmer surface temperatures, began in November and is already dissapating with little impact on ocean temperatures. As a result, NOAA now predicts that more severe bleaching will take place over the next three months.

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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