Dredging link to WA coral disease

Barrow Island dredging
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A new study that's linked dredging turbidity and sediment plumes to increased coral disease may have significant implications for major export developments on either side of the country.

The breakthrough study published in July said it provided 'the first evidence linking dredging-associated sedimentation and turbidity with elevated coral disease prevalence in situ'.

The study was carried out near WA's Barrow Island, a class-A conservation reserve. The island hosts a small oil refinery and construction has begun on Chevron's Gorgon gas development that will pipe up to four trains of Browse Basin gas to the island for processing and export.

Surveys confirmed 'chronic exposure to dredging-associated sediment plumes significantly increase the prevalence of white syndromes, a devastating group of globally important coral diseases', the paper said. Lead author Joe Pollock is a PhD candidate at James Cook University's ARC Centre of Excellence for Coral Reef Studies and the Australian Institute of Marine Science. He said the study had 'found more than twice as much coral disease' at dredging sites than at control sites.

'Coral health surveys were conducted along a dredging-associated sediment plume gradient to assess the relationship between sedimentation, turbidity and coral health. Reefs exposed to the highest number of days under the sediment plume (296 to 347 days) had two-fold higher levels of disease, largely driven by a 2.5-fold increase in white syndromes, and a six-fold increase in other signs of compromised coral health relative to reefs with little or no plume exposure (0 to 9 days),' the paper said. The findings were backed up by further modelling, it said.

Dredging impact on coral
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Pollock said corals needed light and food to survive, and likely suffered from chronic stress due to dredging. The water turbidity meant 'less light for photosynthesis, while increased levels of sediment falling onto the coral can interfere with their ability to feed'. Coral had to spend more time cleaning extra sediment from their surface causing an energy imbalance that could 'lead to chronic coral stress'.

The results suggested 'minimising sedimentation and turbidity associated with coastal development will provide an important management tool for controlling coral disease epizootics [epidemic disease outbreaks in an animal]', it said.

The paper noted hard coral cover had declined on average by 50% on Indo-Pacific reefs and 80% on Caribbean reefs over the past 30 years. That was likely due to pollution, habitat destruction, overfishing, invasive species and climate change. But coral diseases have recently emerged as a significant driver of global coral reef decline'.

The paper was published on July 17 in PLoS ONE the Public Library of Science's open access peer-reviewed scientific journal.

More at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0102498