Corals Are Eating Plastic Because They’re Delicious, Study Says
Corals are an important part of Earth's marine ecosystem, but their lives are in grave danger.
Corals have declined in a staggering scale — and they continue to face threats of extinction. They are living organisms made up of thousands upon thousands of tiny creatures called polyps that attach to rocks or skeletons of dead corals. To most humans, they look like vibrant swathes of tentacles and color that sway gracefully underwater.
The Importance Of Corals In Marine Life
But besides being beautiful, corals serve an important purpose in the grand scale of marine life, providing shelter and food for millions of tiny marine creatures roaming Earth's oceans. But the growing number of plastic in oceans is a cause for concern.
Plastic in oceans is an indiscriminate hazard. It endangers fish and kills seabirds. Turtles swallow it because they think it's jellyfish. It also ends up wedged in corals and plankton, disrupting their ecosystem.
Marine Life Eats Plastic Because They Confuse It With Food, But Do They?
For years, marine biologists assumed that, like turtles, sea creatures, including corals, ate plastic by accident. In general, the intelligence of underwater creatures is thought to be far too weak to recognize plastic as hazardous.
But a new study by Duke University researchers published in the Marine Pollution Bulletin suggests there might be another reason why corals love eating plastic.
Studying coral from an estuary on the North Carolina coast, the researchers found that corals overwhelmingly preferred to eat plastic particles instead of plain sand — regardless if the plastic was factory-made or weathered for several years.
The team was surprised to learn that the corals might prefer plastic because humans have found a way to make it appetizing.
Corals Think Plastic Is Tasty
"Plastics may be inherently tasty," said Austin Allen, one of the lead authors of the study alongside Alexander Seymour.
Allen, Duke, and marine ecologist Daniel Rittschof demonstrated that corals eat microplastic fragments as if they were food.
The study involved two experiments: In the first one, the researchers gave corals microbe-free, pre-production plastic in addition to organic-free sand.
In the second one, they put them in a feeding chamber and exposed them to both clean plastic and plastic covered in biofilm. Afterward, they moved the corals to another chamber to see if they'd spit the plastic out.
They discovered that corals aren't eating plastic because it looked like prey. They're eating it because it's delicious.
"Corals discriminate between particles of plastic and sand, and they greatly prefer the plastic when given these two things," said Seymour.
Initially, the researchers thought corals would prefer the plastic that was covered with a bacterial film. But the results showed the exact opposite: they liked the biofilm-free plastic five times as much as those applied with it.
Corals can't digest plastic. That's why the experiment involved putting them in a separate chamber to see if they'd expel it eventually. They did, but only about 90 to 92 percent, meaning roughly 10 percent of the consumed plastic remained in their gut.
Ingestion of microplastic could potentially impair coral health, according to a study published in 2015.
While the researchers didn't go as far as study the effects of microplastic ingestion, Seymour said that any leftover plastic could be making the corals feel full, resulting in a lack of food. It might also lead to blockages, a phenomenon that's been found to be present on other creatures that also eat plastic.