Joleah Lamb and colleagues surveyed 124,000 reef-building corals on 159 reefs across Indonesia, Myanmar, Thailand and Australia, recording plastic debris and signs of disease.
The likelihood of disease rose from 4% in corals with no plastic contact to 89% in corals in contact with plastic. Plastic can cut coral tissue, block light and carry disease-causing bacteria. The team estimated 11.1 billion plastic items were snagged on Asia-Pacific reefs and projected a 40% increase by 2025.
The finding matters because coral reefs support a quarter of marine species and hundreds of millions of people, and plastic is a stressor that can be reduced locally, unlike ocean warming.
The study shows a strong association; the exact mechanisms are inferred rather than experimentally proven for each disease.