It’s no secret that trash ends up in the stomachs of animals. Photos of dead albatrosses filled to bursting with bright-colored bottle caps and knickknacks have become iconic in recent years, and one study even projected that nearly 99 percent of all seabirds will have eaten plastic by 2050.
New research from the University of California Davis’s Bodega Marine Lab gives an explanation: Some seabird species may be gobbling up ocean plastics because they smell appetizing.
Scientists examined data on plastic ingestion patterns and how they relate to the scents these birds use to track down food. They found a sensory trap: Algae-coated plastic in the ocean breaks down and emits the same odorous chemical that some seabirds normally use to find and eat zooplankton. That chemical is called dimethyl sulfide, or DMS.
“Before this, we sort of assumed that it was accidental ingestion,” said Lindsay Young, a wildlife biologist in Honolulu and the executive director of Pacific Rim Conservation. “This study is unique in that they’re looking at why [seabirds] are ingesting plastic in the first place.”
In a natural scenario, DMS gets released into the water when zooplankton or other forces break down microscopic marine plants, called phytoplankton. Imagine a hungry cow catching a whiff of freshly mowed grass. “They’re like bloodhounds over the ocean, tracking down food based on a sense of smell,” said Gabrielle Nevitt, head of the UC Davis lab that conducted the study.
But instead of eating just zooplankton, several seabird species are duped into swallowing plastic shards. The toss and turn of ocean waves ultimately causes the algae coating on plastic to break down into DMS, triggering the familiar scent of a proper meal.
“The analogy is that, in our society, we eat a lot of nutritionless junk food with chemicals that smell really attractive to us,” Nevitt said. “Birds themselves aren’t attracted to plastic at all. . . . It’s the stuff growing on the plastic that’s attractive.”
The study points to possible solutions. If plastics were designed and engineered to resist algae growth, for example, some seabirds might start turning their beaks away.
“If there were a way to simply physically alter the surface of plastic so that these things grow less readily on them, that could be a solution,” Young said. “We obviously want to reduce the amount of plastic in the first place, but maybe we can do something on the manufacturing end to stop the ingestion in the first place.”Kelly Kasulis is a journalist living in Boston and the deputy digital editor of The GroundTruth Project. Follow her on Twitter @KasulisK.