There have been more than enough horrific viral videos of the turtles with straws stuck in their noses to show that plastic is a threat to them (I’ll spare you by not linking them). Studies have found that every minute, the equivalent of one dump truckload of plastic gets into the ocean, and researchers estimate every species of sea turtle in the world is full of microplastic. Eating all that plastic is often fatal.
Scientists have long thought that sea turtles eat plastic because it looks like their prey – plastic bags, for instance, resemble jellyfish. But sea turtles’ attraction to plastic may have more to do with smell than sight, according to a new study.
“This ‘olfactory trap’ might help explain why sea turtles ingest and become entangled in plastic so frequently,” says Joseph Pfaller, a biologist from the University of Florida who worked on the study, in a statement.
To be clear, the turtles weren’t tempted by plastic because it carried the odours of the human food it was wrapped around. Rather, turtles seem to be seduced by the smell of “biofouled” plastic, or plastic covered in microbes, algae, plants, and small animals on wet surfaces. That’s what happens to plastics that end up in waterways.
Pfaller and his co-authors examined 15 young loggerhead turtles’ reactions to smells sprayed through a pipe in a study released on Monday in Cell. They exposed each turtle to four odours: turtle food containing fish and shrimp meal, “biofouled” plastic that mimicked how it smelled in the ocean, and two controls: deionised water and clean plastic. They found that the turtles responded to the smells of biofouled plastic and turtle food in much the same way. In other words, it seems like turtles think plastic in the ocean smells like a tasty treat.
One of the scientists’ turtle subjects. Photo: Joseph Pfaller
The turtles in the test were bred in captivity and have consistently eaten one kind of food. That led the scientists to expect they’d have stronger responses to the smell of it than to the smell of biofouled plastic. Alas, that’s not what happened – the turtles were equally interested in both odours.
It’s not totally clear why turtles find the smell of biofueled plastic so appetising, which means it will be an area for future research. It’s possible that they were responding to dimethyl sulphide, a substance with a particular smell that emanates from the algae and microbes that accumulates on marine plastic. They may have also been enticed by the smells of the tiny animals that accumulate on marine plastic, such as bryozoans, hydrozoans, and crustaceans.
But the preliminary findings are important, because they show that all kinds of plastic in the ocean pose problems for sea turtles, not just the ones that are shaped perfectly to clog their orifices (like straws), the ones they can get stuck in (like soda can holders), or the ones that look like jellyfish and other prey (like shopping bags). No matter what shape it is, plastic becomes biofouled once it’s in the ocean. As if we needed another reason to force the fossil fuel industry to stop producing so much plastic.