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May 31, 2016

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Bleaching killing Great Barrier Reef

MASS bleaching has killed more than a third of the coral in the northern and central parts of Australia’s Great Barrier Reef, though coral to the south has escaped with little damage, scientists said yesterday.

Researchers who conducted months of aerial and underwater surveys of the 2,300-kilometer reef off Australia’s east coast found that around 35 percent of the coral in the northern and central sections of the reef dead or dying, said Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University in Queensland. Some parts of the reef had lost more than half of the coral to bleaching.

The extent of the damage, which has occurred in the past couple of months, has serious implications, Hughes said. Though bleached coral that hasn’t died can recover if the water temperature drops, older coral takes longer to bounce back and likely won’t have a chance to recover before the next bleaching event occurs, he said. Coral that has died is gone for good, which affects other creatures that rely on it for food and shelter.

“Is it surprising? Not anymore. Is it significant? Absolutely,” said Mark Eakin, the coral reef watch coordinator for the US National Oceanic and Atmospheric Administration. “We’re talking about losing 35 percent of the population of coral in some of these reefs — that’s huge.”

The damage is part of a massive bleaching event that has been impacting reefs around the world for the past two years. Experts say the bleaching has been triggered by global warming and El Nino, a warming of parts of the Pacific Ocean that changes weather worldwide. Hot water puts stress on coral, causing it to turn white and become vulnerable to disease. Other reefs have suffered even more severely. Some Pacific islands, for example, have reported over 80 percent of their coral dead, Eakin said.

This is the third and most extreme mass bleaching event in 18 years to strike the Great Barrier Reef, and in each case, the areas that suffered the worst were the areas where the water was hottest for the longest period of time, Hughes said.

This time, the southern half of the reef was spared largely due to a tropical cyclone. The remnants of the storm which had lashed the South Pacific brought cloud cover and heavy rain, cooling the ocean enough to stop the bleaching in the south. About 95 percent of the coral in the southern portion of the reef has survived.

Storms have previously proved very helpful for heat-stressed reefs, Eakin said. In 2005, for example, the quick succession of Hurricane Katrina and Hurricane Rita cooled the water, sparing the Florida Keys from a serious coral bleaching event affecting the Caribbean.

Experimental approaches to the bleaching dilemma have included attempts to lower temperatures by using shades to cover coral, Eakin said. But such efforts require massive amounts of preparation and can only be done in small areas. Other solutions may lie in finding ways to minimize additional stressors to the already fragile reef.

“Anything you can do to reduce the level of injury and stress coming from other sources, the better the chance that the corals are going to survive,” Eakin said. “Those reefs that have recovered after events like this are the ones that are the most protected, least visited and least disturbed.”




 

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