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Dredging near reefs increases coral disease

SYDNEY--Dredging activity near reefs can more than double the frequency of diseases affecting corals by impacting the light and food they need to survive, a study showed Thursday.

While scientists have known for decades that dredging can smother corals, researchers said this was the first time it has been linked to diseases.

“Corals require both light and food to survive,” said marine scientist Joe Pollock, who led the study for the Australian Research Council's Coral Reef Studies Centre of Excellence.

“And unfortunately, dredging impacts corals on two fronts: increased turbidity means less light for photosynthesis, while increased levels of sediment falling onto the coral can interfere with their ability to feed.”

The study compared 11 reefs and thousands of coral near Barrow Island off Western Australia, where a seven million cubic meter dredging project took place so ships could transport liquefied gas to a nearby processing plant.

“At dredging sites, we found more than twice as much coral disease than at our control site,” said Pollock.

He explained that corals must spend more energy cleaning the extra sediment from their surface that is stirred up by dredging and this energy imbalance can lead to chronic stress.

“Just like in any other organism, it seems that chronic stress can lead to increased levels of disease in corals,” he said.

He added that there were other contributing factors to coral disease including climate change, crown-of-thorns starfish and cyclones.

“But when you add another impact on top of that, there's every reason to believe that will only exacerbate the levels of disease we're already seeing.”

The study, published in the science journal PloS ONE, follows an Australian government decision in January to allow three million cubic meters of dredge waste to be disposed of in Great Barrier Reef waters in Queensland state.

Conservationists warned it could hasten the demise of the reef, which is already considered to be in “poor” health.

The most common diseases affecting corals after dredging events are “white syndromes,” where the coral tissues fall off, leaving behind exposed, white coral skeletons, the study said.

It added that the frequency of coral disease had risen across the world and become a significant factor in global coral reef decline.

Queensland Resource Council chief executive Michael Roche welcomed the report, but added that it was “essentially a laboratory-style study” that highlighted what was already known.

“That is that the impacts of dredge plume is very temporary and very localized,” he said, adding that studies had shown the biggest cause of coral disease was the crown-of-thorns starfish and cyclones.

Pollock agreed that impacts were localized — coral most affected were within 10 kilometers (six miles) of the dredging project.

“But as far as temporary, a lot of these coral diseases that we've seen, especially white syndrome, they can be quite chronic ... and in the long run it's fatal.”

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