The study, just published in Science, suggests that because plastic debris is heavily inhabited by bacteria, when it comes into contact with coral the likelihood of disease increases twenty-fold, from 4 to 89%.

Such contact intensifies the effects of a group of devastating coral diseases that include “white syndromes”.

Over four years the scientists surveyed 159 coral reefs in the Asia-Pacific region, in Indonesia, Australia, Burma and Thailand, visually examining almost 125,000 reef-building corals for tissue-loss and disease lesions.

They found that the number of plastic items on reefs varied widely, from 0.4 items per 100sq m in Australia rising to 25.6 items in an equivalent area in Indonesia.

The scientists estimate that some 11.1 billion plastic items are already entangled on reefs across the Asia-Pacific region, and expect the figure to rise by 40% in the next seven years.

“Plastic debris acts like a marine motorhome for microbes,” said lead author Joleah Lamb, a post-doctoral research fellow at Cornell who began collecting the data while she was at James Cook University in Australia.

“Plastics make ideal vessels for colonising microscopic organisms that could trigger disease if they come into contact with corals.”

Polypropylene items such as bottle-tops and toothbrushes that can become heavily inhabited by bacteria were a particular threat.

“What’s troubling about coral disease is that once the coral tissue loss occurs, it’s not coming back,” said Lamb. “It’s like getting gangrene on your foot, and there is nothing you can do to stop it from affecting your whole body.

“This study demonstrates that reductions in the amount of plastic waste entering the ocean will have direct benefits to coral reefs by reducing disease-associated mortality.”

The report “Plastic Waste Associated with Disease on Coral Reefs” can be found here.

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