As reported in The Guardian, researchers have discovered that seagrass beds along the Spanish coast seem to trap ocean plastic in natural fibre-bundles known as ‘Neptune Balls’.

The oval-shaped orbs form out of old and shredded seagrass leaves that are still attached to their stems. As they are buried, the stems become stiff and matted together, collecting plastic fibres in the process.

Neptune Balls
The 'Neptune Balls'. Photo by: Marta Veny, University of Barcelona

Published in the journal Scientific Reports, the study suggests that the shallow seagrass beds might collect around 900 million plastic items in the Mediteranean every year.

“We show that plastic debris in the seafloor can be trapped in seagrass remains, eventually leaving the marine environment through beaching,” - Anna Sanchez-Vidal, marine biologist at the University of Barcelona

Seagrass beds play a vital role in coastal ecosystems, providing protection against erosion and storm surges, as well as absorbing CO2 and expelling oxygen, and acting as a nursery for hundreds of species. This latest study also suggests they provide a “continuous purge of plastic debris out of the sea,” Sanchez-Vidal added.

Originating on land, these flowering plants colonised the ocean up to 100 million years ago, and now boast 70 distinct species. Found anywhere from the Arctic to the tropics, most species feature long blade-like leaves that form grass-like meadows beneath the sea.

Posidonia Oceanica Seagrass
Posidonia oceanica seagrass meadow in the Mediterranean sea. Photo by: Jordi Regas, University of Barcelona

Between 2018 and 2019, Sanchez-Vidal and her team counted the number of plastic particles in seagrass bundles that had washed up on beaches in Mallorca. The researchers found plastic debris in 50% of the loosely-packed bundles - around 600 bits of plastic per kilogram of leaves. Only 17% of tightly-packed seagrass bundles contained plastic particles. But those that did, collected it at a much higher density - nearly 1,500 pieces per kilogram of seagrass.

Using this data, along with estimates of seagrass fibre production in the Mediterranean the researchers were able to estimate how much plastic might be filtered throughout the entire basin.

But Sanchez-Vidal suggested more research might be needed to track the movements of seagrass bundles. “We don’t know where they travel,” said Sanchez-Vidal. “We only know that some of them are beached during storms.”