Coral reefs are meant to be riots of color, but those that Joleah Lamb studied in the Indo-Pacific were colorful for all the wrong reasons. Their branches and crevices were frequently festooned with plastic junk. “We came across chairs, chip wrappers, Q-tips, garbage bags, water bottles, old nappies,” she says. “Everything you see on the beach is probably lying on the reef. And it seems like it’s getting worse.”

Whenever Lamb or her colleagues from Cornell University found a piece of plastic, they would lift it up to study the health of the coral underneath. And almost every time, that coral would be riddled with disease. “It’s just a disaster under there,” she says.

The Nike logo next to a coral afflicted by white syndrome (Kathryn Berry)

Over four years, the team analyzed more than 124,000 corals, spanning 159 reefs in four countries: Myanmar, Thailand, Indonesia, and Australia. They found that under normal circumstances, just 4 percent of corals are afflicted by some kind of disease. But infections strike down 89 percent of corals that come into contact with plastic.

“I didn’t think we would be the ones to write this study,” says Lamb, because other scientists have already done so much research on plastic pollution. They’ve estimated that 5 trillion tiny pieces of plastic float in the seas. They’ve shown that some gets swallowed by seabirds because it smells like food. They’ve documented plastic waste on the shores of the world’s remotest islands.

But to Lamb’s surprise, no one had really estimated the extent of plastic junk on coral reefs, or studied how that junk relates to disease. Indeed, when people think about the many ills befalling reefs—rising temperatures, acidifying waters, overfishing, nutrient pollution, ravenous starfish—plastic rarely gets a mention.

Worse still, plastic-induced ailments disproportionately affect the corals that provide important habitats for fish—the ones that create intricate branches and layers. That same architectural complexity becomes easily filled and entwined with plastic, so these corals are eight times more likely to be diseased than simpler ones with rounded shapes.

Plastic on a beach in Sulawesi, Indonesia (Joleah Lamb)

In fairness, not all reefs are strewn with plastic. Lamb never saw much of it in the Great Barrier Reef, for example. But “in Indonesia, we were seeing 26 pieces of plastic in an area the size of a Manhattan two-bedroom apartment,” she says. The Asia-Pacific region is home to eight of the world’s top 10 plastic-polluting countries, and more than half of the world’s coral reefs. According to estimates from Lamb’s team, those reefs are currently covered with around 11 billion pieces of plastic—and that’s likely a gross underestimate because it doesn’t account for contributions from China, the world’s top plastic polluter.

This problem is only going to get worse. Half of all the plastic that has ever existed was made in just the last 13 years, and production is still accelerating. Around nine tons are created every second. By 2025, Lamb’s team estimated that around 15.7 billion pieces will be entangled in Asia-Pacific reefs.

It’s not clear how that plastic actually leads to disease, and the exact route probably differs from one infection to the other. In black-band disease, a mat of dark algae moves across a coral, leaving dead white tissue in its wake. Those algae thrive in dark, low-oxygen environments—the kind you’d find under a piece of plastic. Skeletal eroding band disease also involves a spreading wave of death with a white trail, but it is caused by a protozoan that invades through wounded tissue. Perhaps sharp plastic fragments are cutting the corals, giving the protozoan an easy entrance.

Other diseases, like the aptly named white syndrome, are caused by opportunistic bacteria like Vibrio, which have a penchant for hitchhiking on plastic debris. “Plastic could be perfect rafts, full of pores and pits that are beneficial to the Vibrio, which they then introduce into the corals,” says Lamb.

A plastic bottle on a reef (Kathryn Berry)

“This is a very important study for coral-reef biologists and managers, as it evaluates a driver of disease that has never been addressed,” says Rebecca Vega Thurber, from Oregon State University, who studies the microbes that live on corals.

“Threats to coral reefs come in many forms, but many occur simultaneously,” Vega Thurber adds. For example, many reefs have been hit by several consecutive years of severe bleaching, where unusually warm temperatures force them to expel the algae that provide them with nutrients and color. They then turn ghostly white—hence, bleaching—and risk starving to death. Bleaching is fundamentally a problem of climate change, but its effects can be exacerbated by, say, pollution or overfishing, which reduce the resilience of reefs. Diseases are especially problematic. “Corals can recover their algae after bleaching,” says Lamb. “But with diseases, they lose their tissues, and they aren’t getting those back.”

“Given that damage from plastics can increase the likelihood of disease, this suggests an easy target for reducing this effect,” says Vega Thurber. “Plastics are something that can be managed at the local level, with greater success than perhaps efforts to reduce global warming. And unlike with climate change, the reduction of plastic pollution is not a controversial topic and might be an issue that could garner international support.”

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