We know plastic trash in the oceans kills birds, turtles, and whales, but now, scientists have found it’s making corals sick, too. In reefs in Asia and Australia, corals tangled in plastic are about 90 percent more likely to get a disease, according to new research. And that can cause corals, which are already stressed by warming ocean waters, to die.
Between 2011 and 2014, researchers looked at more than 124,000 corals in 159 reefs across the Asia-Pacific region, which hosts over 55 percent of all the world’s reefs. They estimated that over 11 billion plastic items — from Q-tips to bags — are found on coral reefs in the area. And where there’s plastic, disease outbreaks are more likely, according to a study published today in Science.Spawning coral wrapped in plastic. Photo by Lalita Putchim
Around the world, coral reefs provide food, tourism income, and protection from storms for more than 275 million people, including in the US. Coral reefs in Hawaii are valued at more than $33 billion for the US economy. But corals around the world are bleaching more frequently because of warmer oceans, losing their colorful algae that provide about 90 percent of their energy. Today’s study shows that corals are threatened not just by climate change, but also by plastic pollution.
“I’d never thought of plastic rubbish as a vector of coral disease before,” Terry Hughes, a lead coral researcher in Australia, who was not involved in the study, tells The Verge in an email. “It’s a real concern because of all the other stressors corals have to deal with, especially global warming.”A plastic bottle wedged in the coral reef. Photo by Kathryn Berry
Every year, millions of metric tons of plastic trash enter the oceans from land, which ends up virtually everywhere: remote islands, down onto the seafloor, and even frozen in Arctic ice. Scientists are just starting to understand how all this plastic affects marine life. Large animals like whales and sharks are known to die tangled up in fishing nets, but until today, it wasn’t clear whether plastic could affect disease outbreaks in the ocean.
Corals — which are animals, not plants — can get sick, just like us. One coral disease, called black band disease, for instance, is caused by several microbes that eat away at the coral tissue, leaving behind the bare skeleton and killing coral colonies within months. Others, called white syndrome and skeletal eroding band disease, also destroy the coral’s tissue. “With diseases, it’s actually the skin that’s getting eaten away,” says study co-author Joleah Lamb, a marine biologist at Cornell University. “And then you only have the skeleton left.”A piece of debris bearing the Nike logo is snagged on coral, which is affected by white syndrome coral disease. Photo by Joleah Lamb
In their survey, Lamb and her colleagues found plastic on one-third of coral reefs, with Indonesia having the most plastic and Australia with the least. When plastic was present, the likelihood of coral disease increased to 89 percent from 4 percent, according to the study, particularly those deadly tissue-eating diseases. Unsurprisingly, corals with branches and complex structures were more likely to be entangled.
The plastic could be making the corals sick because of a variety of reasons, Lamb tells The Verge. The debris could stress the corals by depriving them of light and oxygen, it could damage or cut their tissue by tangling around them, or it could carry disease around because it’s easily colonized by bacteria. Previous research has shown that plastic debris is dominated by the bacterial genus Vibrio, which causes the disease white syndrome. Pieces of plastic also accumulate pollutants such as PCBs anywhere from 100,000 to 1,000,000 times the levels found in seawater. (Those chemicals — which were used in electrical switches, insulating foam, and tapes — were banned in the US in the 1970s because they can cause negative health effects, such as developmental disorders in kids.)
“What surprised us is just the extent of plastic on the reef and the likelihood of them having a disease,” Lamb says. “This is a phenomenon that was happening across the Asia-Pacific.”Plastic floating over corals. Photo by Kathryn Berry
The good news here is that this problem is solvable: implementing better waste management in developing countries like Indonesia could keep much of the plastic trash from going into the ocean. Reducing the use of disposable cups, plates, and water bottles also helps.
Coral reefs are already suffering because of global warming. Given the increasing rates of bleaching, keeping the reefs trash-free is necessary to keep them alive. “It’s essentially like if you have an autoimmune disease and then you get the flu,” Lamb says. “That flu could actually be the one that causes your death.”