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Biodiversity: Great Barrier reef has lost half its coral cover

Outbreaks of the coral eating crown of thorns starfish have been responsible for 42 percent of the over 50 percent decline in coral cover on the Great Barrier Reef between 1985 and 2012. Photo courtesy Katharina Fabricius, Australian Institute of Marine Science.

Multiple short-interval disturbances causing long-term decline, with southern areas hit hardest

By Summit Voice

SUMMIT COUNTY — Australian researchers say the Great Barrier Reef has lost half its coral cover in the past 27 years, with more impacts expected as the climate warms in coming decades. About half (46 percent) of the loss was from storm damage, with another 42 percent attributed to crown of thorns starfish and 10 percent lost to bleaching.

“We can’t stop the storms but, perhaps we can stop the starfish. If we can, then the reef will have more opportunity to adapt to the challenges of rising sea temperatures and ocean acidification, says John Gunn, CEO of the Australian Institute of Marine Science in Townsville.

“This finding is based on the most comprehensive reef monitoring program in the world. The program started broadscale surveillance of more than 100 reefs in 1985 and from 1993 it has incorporated more detailed annual surveys of 47 reefs,” said  Dr. Peter Doherty, one of the program’s original creators and a research fellow at AIMS.

“Our researchers have spent more than 2,700 days at sea and we’ve invested in the order of $50 million in this monitoring program,” Doherty said. “Interestingly, the pattern of decline varies among regions. In the northern Great Barrier Reef coral cover has remained relatively stable, whereas in the southern regions we see the most dramatic loss of coral, particularly over the last decade when storms have devastated many reefs.” he said.

The study clearly shows that three factors are overwhelmingly responsible for this loss of coral cover. Intense tropical cyclones have caused massive damage, primarily to reefs in the central and southern parts of the Great Barrier Reef, while population explosions of the coral-consuming crown-of-thorns starfish have affected coral populations along the length of the reef. Two severe coral bleaching events have also had major detrimental impacts in northern and central parts of the reef.

“Our data show that the reefs can regain their coral cover after such disturbances, but recovery takes 10-20 years. At present, the intervals between the disturbances are generally too short for full recovery and that’s causing the long-term losses,” said Dr. Hugh Sweatman, one of the study’s authors.

“We can’t stop the storms, and ocean warming, the primary cause of coral bleaching, is one of the critical impacts of the global climate change,” said Gunn. “However, we can act to reduce the impact of crown of thorns. The study shows that in the absence of crown of thorns, coral cover would increase at 0.89 percent per year, so even with losses due to cyclones and bleaching there should be slow recovery.

“We at AIMS will be redoubling our efforts to understand the life cycle of crown of thorns so we can better predict and reduce the periodic population explosions of crown of thorns. It’s already clear that one important factor is water quality, and we plan to explore options for more direct intervention on this native pest.”

The study was published this week in the  Proceedings of the National Academy of Sciences.

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