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Survey: 93 percent of Great Barrier Reef affected by bleaching

"When bleaching is this severe it affects almost all coral species," said researcher Andrew Baird.

By Brooks Hays
Survey: 93 percent of Great Barrier Reef affected by bleaching
Coral along Australia's Great Barrier Reef are experiencing record amounts of bleaching. Photo by Wagsy/Shutterstock

CAIRNS, Australia, April 20 (UPI) -- Just 7 percent of the Great Barrier Reef has avoided bleaching. It's the worst coral bleaching event in Australia's history.

"We've never seen anything like this scale of bleaching before," Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies, said in a news release.

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Hughes convened the National Coral Bleaching Taskforce to survey the damage both by plane and boat. The research team returned with alarming news: some 93 percent of the reef is suffering from the coral bleaching event.

Coral depends on its symbiotic relationship with algae-like organisms known as zooxanthellae, which give coral their color and perform photosynthesis. Coral expel their zooxanthellae in times of stress, such as prolonged periods of unusually warm water temperatures. Coral can recover from brief and moderate coral bleaching, but severe bleaching events can damage reefs beyond repair.

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The Great Barrier Reef has suffered significant coral bleaching events in the past, the largest in 1998 and 2002. Researchers say each event is different, with the most severe bleaching occurring where the warmest water sits the longest.

In this instance, the most damage is being done along the northern third of the Great Barrier Reef.

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"Tragically, this is the most remote part of the Reef, and its remoteness has protected it from most human pressures: but not climate change," said ARC researcher Andrew Baird.

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Some reefs are already suffering a more than 50 percent mortality rate for bleached corals. Researchers expect many of the northern reefs to experience 90 percent mortality rates before the bleaching event dissipates.

"When bleaching is this severe it affects almost all coral species, including old, slow-growing corals that once lost will take decades or longer to return," Baird said.

Reefs to the south have experienced more moderate bleaching and are expected to recover rather quickly as water temperatures there cool in the coming weeks and months, but only time will reveal the resilience of more damaged reefs.

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"We thought the corals there are tough "super corals" because they can normally cope with big swings in temperature," Verena Schoepf, of the University of Western Australia, said of coral off the continent's opposite coast where bleaching is also occurring. "So, we're shocked to see up to 80 percent of them now turning snow-white. Even the tougher species are badly affected."

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