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An empty, plastic rice bag is nestled between corals. (Credit: Kathryn Berry/James Cook University)

corals

Watch: Plastic trash makes diseases worse for corals

Plastic trash—widespread throughout the world’s oceans—intensifies disease for coral and so puts reefs in peril, a new study suggests.

“Plastic debris acts like a marine motor home for microbes,” says the study’s lead author Joleah Lamb, a postdoctoral research fellow at Cornell University who began collecting this data as a doctoral candidate at James Cook University in Australia.

“Plastics make ideal vessels for colonizing microscopic organisms that could trigger disease if they come into contact with corals,” Lamb says. “Plastic items—commonly made of polypropylene, such as bottle caps and toothbrushes—have been shown to become heavily inhabited by bacteria. This is associated with the globally devastating group of coral diseases known as white syndromes.”

When plastic debris meets coral, the authors say, the likelihood of disease increases from 4 to 89 percent—a 20-fold change. 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 percent over the next seven years.

“It’s like getting gangrene on your foot and there is nothing you can do to stop it from affecting your whole body.”

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,” says Lamb. “It’s like getting gangrene on your foot and there is nothing you can do to stop it from affecting your whole body.”

Lamb and colleagues surveyed 159 coral reefs from Indonesia, Australia, Myanmar, and Thailand, visually examining nearly 125,000 reef-building corals for tissue loss and disease lesions. The number of plastic items varied widely, from 0.4 items per 100 square meters (about the size of a two-bedroom Manhattan flat) in Australia, to 25.6 items per 100 square meters in Indonesia. This is significant given that 4.8 million to 12.7 million metric tons of plastic waste are estimated to enter the ocean in a single year, Lamb says.

trash on the shore
A thick blanket of plastic debris covers the beach in Sulawesi, Indonesia, near where scientists conducted inspections of coral. (Credit: Joleah Lamb/Cornell)

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.

“Our work shows that plastic pollution is killing corals. Our goal is to focus less on measuring things dying and more on finding solutions,” says senior author Drew Harvell, professor of ecology and evolutionary biology. “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.”

Researcher Joleah Lamb dives in Australia
Joleah Lamb surveys the coral at the Great Barrier Reef in Australia. (Credit: Yui Sato/Cornell)

Coral reefs are productive habitats in the middle of nutrient-poor waters, Harvell says. Thanks to the symbiotic relationship between corals and their solar-powered algae, “this miracle of construction creates the foundation for the greatest biodiversity in our oceans,” she says. “Corals are creating a habitat for other species, and reefs are critical to fisheries.”

“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,” says Lamb.

Corals eat plastic for the taste, not by accident

Additional coauthors of the paper are from the University of Washington; the University of Hawaii, Manoa; James Cook University; the Environmental Defense Fund; Prince of Songkla University; Thailand; the Nature Conservancy; and Hasanuddin University, Indonesia.

Funding for the research came from the National Science Foundation, the National Oceanic and Atmospheric Administration, the Nature Conservancy, the Environmental Defense Fund, the World Bank, the Australian Research Council, and Cornell’s Atkinson Center for a Sustainable Future.

Source: Cornell University

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