In late 2018, researchers announced that they had found synthetic particles like microplastics in the intestinal tracts of every single sea turtle they’d studied in the Atlantic and Pacific Oceans and the Mediteranean Sea. New research might help to explain why turtles are consuming plastic in the first place.

The way plastic looks might be one of its attractive features for marine species — for example, a plastic bag floating in the ocean might be mistaken for a tasty jellyfish by a hungry turtle.

A study published in the journal Current Biology last week might point to another answer, at least when it comes to sea turtles: After just seven days in the ocean, plastic particles become so coated with algae and other microorganisms that they begin to smell like food.

In late 2018, researchers announced that they had found synthetic particles like microplastics in the intestinal tracts of every single sea turtle they’d studied in the Atlantic and Pacific Oceans and the Mediteranean Sea. New research might help to explain why turtles are consuming plastic in the first place.

Hundreds of marine wildlife species, including many endangered species of sea turtles, filter-feeders, and whales, are at risk of ingesting or becoming entangled in the incredible amounts of plastic debris humans dump into Earth’s oceans. Though it’s a widespread problem, scientists know little about what entices animals to interact with plastic in the oceans.

It’s suspected that the way plastic looks might be one of its attractive features for marine species — for example, a plastic bag floating in the ocean might be mistaken for a tasty jellyfish by a hungry turtle. A study published in the journal Current Biology last week might point to another answer, at least when it comes to sea turtles: After as little as seven days in the ocean, plastic particles become so coated with algae and other microorganisms that they begin to smell like food.

“The same airborne odorants used by marine predators to identify prey and locate areas of elevated ocean productivity also emanate from marine-conditioned or ‘biofouled’ plastic debris,” write the study’s authors, a team of researchers led by Joseph Pfaller of the Savannah, Georgia-based Caretta Research Project.

To test whether or not the odors emanating from biofouled plastic debris are capable of luring unsuspecting turtles into ingesting indigestible plastic, the researchers conducted experiments with 15 captive-reared loggerhead turtles collected from Bald Head Island, North Carolina. The turtles were placed in tanks that allowed the researchers to pipe in scents and videotape their reactions to four different odors — deionized water, turtle food, clean plastic, and biofouled plastic.

The odors of food and biofouled plastic elicited nearly identical responses from the loggerheads, who kept their noses out of the water, a key foraging behavior, more than three times as long for food and biofouled plastic as they did for water and clean plastic.

“These results indicate that sea turtles can detect airborne odorants emanating from biofouled plastic and respond to them in the same way that they respond to food odors,” the researchers write in the study. “Moreover, these findings are consistent with the hypothesis that odors emanating from biofouled plastic stimulate foraging behavior in sea turtles and contribute to turtles’ attraction to marine plastic debris.”

“This finding is important because it’s the first demonstration that the odor of ocean plastics causes animals to eat them,” Kenneth J. Lohmann, a distinguished professor of biology at University of North Carolina, Chapel Hill and study co-author, said in a statement. “It’s common to find loggerhead turtles with their digestive systems fully or partially blocked because they’ve eaten plastic materials. There also are increasing reports of sea turtles that have become ill and stranded on the beach due to their ingestion of plastic.”

Exactly which odor acquired by biofouled plastic is so alluring to sea turtles could not be determined by the study, but one culprit could be dimethyl sulfide, “a volatile odorant perceived by turtles and that emanates from the algal and microbial biofouling community associated with marine plastic,” according to the study. But plastic debris in the oceans can also accumulate what the researchers call “other fouling organisms such as encrusting bryozoans, hydrozoans, and crustaceans,” which might produce volatile organic compounds and become similarly attractive to sea turtles. It’s also possible that water-born chemicals associated with plastic give off a scent that elicits foraging behavior in turtles, or that airborne and waterborne smells act in concert to whet turtles’ appetite. “Further research will be needed to identify the precise odorants to which turtles respond and the effects that they have on turtle behavior,” the researchers write.

The most important thing people can do to eliminate the threat of plastic ingestion for marine wildlife is to prevent plastic waste from ever even making its way into the ocean, the researchers note. They urge everyone to recycle plastic waste or otherwise properly dispose of it, especially after a trip to the beach or after a boat trip, to use reusable or paper shopping bags, and to avoid buying small drink containers held together with plastic rings.

One particular concern, Lohmann noted, is that regions where plastic debris is concentrated in the oceans, like the Great Pacific Garbage Patch, could become harmful or even lethal “olfactory traps” for marine predators.

“In parts of the Pacific Ocean there are huge areas covered with floating plastic debris,” he said. “These areas may draw in marine mammals, fish and birds because the area smells like a good foraging ground. Once these plastics are in the ocean, we don’t have a good way to remove them or prevent them from smelling like food. The best thing we can do is to keep plastic from getting into the ocean at all.”

CITATION

• Pfaller, J. B., Goforth, K. M., Gil, M. A., Savoca, M. S., & Lohmann, K. J. (2020). Odors from marine plastic debris elicit foraging behavior in sea turtles. Current Biology, 30(5), R213-R214. doi:10.1016/j.cub.2020.01.071

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