Corals Seem to Like the “Taste” of Plastic

Corals are attracted to the material not for its coloring, but for one of its many chemicals

A coral polyp chowing down on a flake of white plastic Alex Seymour, Duke University

One of the problems with plastic in the oceans is that when it breaks down into tiny bits of microplastic, it looks like fish food. Then, marine creatures swallow it, thinking it is prey. But as Ben Guarino at The Washington Post reports, researchers have discovered that, at least when it comes to coral, the animals may eat plastic for another reason: They think it tastes delicious.

Researchers at Duke University hand fed corals in a saltwater tank collected off the Carolina coast, feeding them tiny grains of sand and plastic. During the study, when the bits of sand came near a coral polyp’s mouth, it would close the orifice and use the cilia on its body to brush the sand way. When a bit of plastic floated by, however, they brought it to their mouth using their tentacles. While the coral ate 80 percent of the six varieties of plastic grains dropped on them, they only ate sand 1 in 10 times.

The researchers performed a second experiment, offering the coral bits of plastic covered with a biofilm. It turned out, the corals preferred the raw plastic to the bio-contaminated bits, suggesting that there’s something in the plain plastic bits they find appealing. The study appears in the journal Marine Pollution Bulletin.

“Corals in our experiments ate all types of plastics but preferred unfouled microplastics by a threefold difference over microplastics covered in bacteria,” study co-leader Austin S. Allen, a Duke Ph.D. candidate says in a press release. “This suggests the plastic itself contains something that makes it tasty.”

The researchers aren't sure yet what that substance is. “When plastic comes from the factory, it has hundreds of chemical additives on it. Any one of these chemicals or a combination of them could be acting as a stimulant that makes plastic appealing to corals,” Duke GIS analyst and study co-lead Alexander C. Seymour adds.

This is just one more wrinkle in the complicated relationship between ocean life and plastics. As Veronique Greenwood at The New York Times reports, over 200 species of sea life—including turtles (who mistake bags as jellyfish), birds, and now corals—have been recorded eating plastic. Researchers are just beginning to understand how plastic consumption is impacting creatures. These plastics can enter into the food chain—possibly even working their way up to humans. And there is still many unknowns about what those plastic compounds do to different animals. One recent study suggests that nanoparticles of plastic can make it into the brains of fish, causing behavioral changes.

Plastic in the ocean is a massive problem. A study from 2015 estimated there are between 15 and 51 trillion bits of plastic in the oceans, creating a plastic soup. There’s so much plastic it’s even making it to pristine areas of the Arctic once believed to be free from pollution.

While the coral might find the plastic bits tasty, their guts do not. Within 24 hours, most of the corals had expelled the indigestible plastic grains, but 8 percent got stuck in their intestines, which could lead to fatal blockages and the leaching of chemicals from the plastic, which could have hormonal effects.

As Guarino reports, it's possible that the situation at sea may be different—coral in the wild may avoid tiny plastic pieces. The lab is currently working to find out if other marine invertebrates also find the plastic bits appealing, according to Greenwood. If it turns out that coral and other creatures are being impacted in the wild because of plastic’s tasty chemicals, it could lead to calls to change the way the stuff is made. “If we could manufacture plastic to taste attractive, maybe we can manufacture plastic to taste repulsive,” Seymour tells Greenwood. “Maybe we can prevent critters from eating plastic in the first place.”

The best solution, of course, is keeping plastic out of the ocean. But that’s easier said than done: 9 million tons of plastic enter the ocean each year. And human trash has made it all the way to the bottom of Earth’s deepest spots in the Mariana Trench.