As if the world's coral reefs weren't already in enough danger due to bleaching, a new study indicates that water-borne plastic trash is also killing them off. According to the study, when such debris comes into contact with corals, the likelihood of disease increases from 4 to 89 percent.

"Plastic items – commonly made of polypropylene, such as bottle caps and toothbrushes – have been shown to become heavily inhabited by bacteria," says lead scientist Joleah Lamb, a postdoctoral research fellow at Cornell University who began her research while she was a doctoral candidate at Australia's James Cook University. "This is associated with the globally devastating group of coral diseases known as white syndromes."

For the study, Lamb and her team surveyed 159 coral reefs in Indonesia, Australia, Myanmar and Thailand. They visually examined approximately 125,000 corals, checking for tissue loss and lesions. The greater the amount of plastic that was present, the more evidence they found of disease.

The prevalence of plastic varied greatly, depending on the location. In Australia, for instance, it was 0.4 items per 100 square meters, while in Indonesia it was 25.6 items per 100 square meters. All told, the scientists estimate that roughly 11.1 billion plastic items are present on reefs throughout the Asia-Pacific region – over the next seven years, that figure will likely increase by 40 percent.

"Our work shows that plastic pollution is killing corals," says Cornell's Prof. Drew Harvell, senior author of a paper on the study. "Our goal is to focus less on measuring things dying and more on finding solutions. While we can't stop the huge impact of global warming on coral health in the short term, this new work should drive policy toward reducing plastic pollution."

The paper was recently published in the journal Science.