Scientists have found that contact with plastic waste -- ubiquitous throughout the world's oceans -- massively increases the chance of disease in corals.
"We examined more than 120,000 corals, both plastic-free and with plastic present, on 159 reefs from Indonesia, Australia, Myanmar and Thailand," said lead researcher Joleah Lamb, a postdoctoral research fellow at Cornell University in New York.
She began collecting this data as a doctoral candidate at James Cook University in Australia.
"We found that the chance of disease increased from four per cent to 89 per cent when corals are in contact with plastic," Lamb said.
The findings, published in the journal Science, add to the burden of climate-related disease outbreaks that have already had an impact on coral reefs globally, James Cook University Emeritus Professor Bette Willis said.
"Bleaching events are projected to increase in frequency and severity as ocean temperatures rise. There's more than 275 million people relying upon coral reefs for food, coastal protection, tourism income and cultural significance. So moderating disease outbreak risks in the ocean will be vital for improving both human and ecosystem health," Willis added.
The scientists estimate that about 11.1 billion plastic items are entangled on reefs across the Asia-Pacific region, and that this will likely increase 40 per cent over the next seven years.
Coral are tiny animals with living tissue that cling to and build upon one another to form "apartments," or reefs. Bacterial pathogens ride aboard the plastics, disturbing delicate coral tissues and their microbiome.
"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," she said.
"We don't know the exact mechanisms, but plastics make ideal vessels for colonising microscopic organisms that could trigger disease if they come into contact with corals," Lamb said.
"For example, plastic items such as those commonly made of polypropylene, like bottle caps and toothbrushes, have been shown to become heavily inhabited by bacteria that are associated with a globally devastating group of coral diseases known as white syndromes," she added.
The scientists forecast that by 2025, plastic going into the marine environment will increase to roughly 15.7 billion plastic items on coral reefs, which could lead to skeletal eroding band disease, white syndromes and black band disease.
"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," Lamb said.
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