Second Year of Severe Bleaching for Great Barrier Reef

PHOTO: Coral bleaching at Cairns Townsville along the Great Barrier Reef. (Photo courtesy of ARC Centre of Excellence for Coral Reef Studies/Ed Roberts}[/IMAGECAPTION

It looks like there's more bad news for the Great Barrier Reef. Scientists conducting aerial studies of the entire reef have found a severe case of coral bleaching, marking the second time in as many years the reef has been affected by the phenomenon.

While the popular diving site off the coast of Australia has experienced severe bleaching before, this is the first time such incidences have occurred over consecutive years according to scientists at the ARC Centre of Excellence for Coral Reef Studies.

During the two-year period, nearly two-thirds of the reef were been affected by significant bleaching incidences. This year the middle-third section was hardest hit, while last year the northern third of the reef recorded the worst cases of bleaching.

“The combined impact of this back-to-back bleaching stretches for 1,500 km (900 miles), leaving only the southern third unscathed,” says Prof. Terry Hughes, Director of the ARC Centre of Excellence for Coral Reef Studies, who conducted the aerial surveys of the reef.

This is the fourth time in 20 years the reef has been subject to such extreme bleaching.

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“The Great Barrier Reef has bleached severely[in] 1998, 2002, 2016, and now in 2017,” said Dr. James Kerry, a senior research officer with the ARC, who also led the aerial surveys. “Bleached corals are not necessarily dead corals, but in the severe central region we anticipate high levels of coral loss.”

Read more: Australia must act to save the Great Barrier Reef

Bleaching occurs when corals expel tiny algae called ‘zooxanthellae,’ which causes them to turn white, or bleach, usually in response to environmental conditions.

“The bleaching is caused by record-breaking temperatures driven by global warming,” said Kerry. “This year, 2017, we are seeing mass bleaching, even without the assistance of El Niño conditions.”

Although bleached coral can recover if water temperatures decrease, their survival is not guaranteed. Last year, the scientists determined that nearly two-thirds of the affected coral in the northern-most 700-km section of the Great Barrier Reef were lost during the six-month period following the peak March bleaching.

“It takes at least a decade for a full recovery of even the fastest growing corals, so mass bleaching events 12 months apart offers zero prospect of recovery for reefs that were damaged in 2016,” said Kerry.

This year’s aerial surveys encompassed more than 5,000 miles and some 800 individual coral reefs and were designed to closely replicate the methods used during last year’s surveys, which were conducted by the same two researchers.

In addition to the bleaching events, the reef could is also facing pressure from the effects of Tropical Cyclone Debbie, which struck the Great Barrier Reef late last month. According to the ARC Centre, the system cut a path that was as large as 100 km in width and struck a relatively healthy section of the reef that was largely free of the effects of the worst of the coral bleaching.

“Clearly the reef is struggling with multiple impacts,” said Prof. Hughes. “Without a doubt, the most pressing of these is global warming. As temperatures continue to rise the corals will experience more and more of these events: 1 degree Celsius of warming so far has already caused four events in the past 19 years.”

“Ultimately, we need to cut carbon emissions, and the window to do so is rapidly closing.”

For more information, visit www.coralcoe.org.au. 

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