Seagrass and Plastic Are Not Friends

The year 2021’s hopeful optimism is 2024’s unfortunate reality.

In 2021, what sounded like a good news story hit the media: in the Mediterranean, seagrasses were trapping plastic waste, capturing fragments in their leaves and locking microplastics in seafloor sediments. The news cycle was spurred by a study of Neptune grass, which showed that when this seagrass species sheds its leaves each autumn some of that plastic debris is jettisoned back to shore, slightly cleaning the marine environment. At the time, scientists and reporters billed the Mediterranean seagrass as a potent ally in the fight against marine plastic pollution. But that hopeful narrative is, unfortunately, too optimistic and only tells part of the story.

In a recent meta-analysis, Alice Rotini, a marine biologist at the Institute for Environmental Protection and Research in Italy, and her colleagues comprehensively reviewed and analyzed 26 existing studies that examine how plastic pollution affects seagrasses. Rotini says that rather than filtering plastic pollution out of the water, seagrass meadows and the diverse life that depends on them may be suffering under plastic’s influence.

“I am very concerned that we don’t know the real impact,” says Rotini.

The individual studies included in Rotini’s review, for instance, show that microplastics settling on seagrass leaves can reduce plant growth, cause leaf loss, lower levels of photosynthesis and respiration, and potentially disrupt nutrient cycling. Another recently published study shows that Neptune grass meadows with high levels of microplastic pollution also have fewer crustaceans and mollusks.

For Alyssa Novak—a coastal ecologist at Boston University who was not involved in Rotini’s work but has carried out her own research on the topic—the previously lauded plastic trapping mechanism is too rife with complications to be hailed as a solution to humanity’s ocean trash problem.