Neptune seagrass balls retain millions of plastic particles from water, study finds | Plastics

Underwater seagrasses in coastal areas appear to trap plastic pollution in natural fiber bundles known as “Neptune balls”, the researchers found.

Without the help of humans, oscillating plants – anchored in shallow seafloor – can collect nearly 900 million plastic items in the Mediterranean alone each year, said a study published in the journal Scientific Reports.

“We have shown that plastic debris on the seabed can get trapped in seagrass scraps, eventually leaving the marine environment across the beach,” author Anna Sanchez-Vidal, a marine biologist at the University of Barcelona, ​​told AFP.

This cleaning “represents a continuous elimination of plastic debris from the sea,” she added.

The study adds to the long list of services that seagrass provides – for ocean ecosystems and for humans who live near the water’s edge. They play a vital role in improving water quality, absorb CO2 and exhale oxygen, and are a natural pond and refuge for hundreds of fish species. They are also the basis of coastal food webs.

Anchoring in shallow water, they help prevent beach erosion and cushion the impact of destructive storms.

There are 70 species of marine seagrass, grouped into several families of flowering plants that – originally on land – recolonized the ocean 80m to 100m years ago.

Growing from the Arctic to the tropics, most species have long, grass-like leaves that can form vast underwater meadows.

It is unclear whether collecting the plastic damages the seagrass itself.

To better understand the seaweed’s plastic packaging capabilities, Sanchez-Vidal and his team studied a species found only in the Mediterranean Sea, Posidonia oceanica.

In 2018 and 2019, they counted the number of plastic particles found in sea balls that had reached four beaches in Mallorca, Spain, which have large seagrass meadows at sea.

There was plastic debris in half of the loose leaf samples of seagrass, up to 600 bits per kilogram of leaves.

Only 17% of the more compact seagrass fiber, known as Neptune balls, contained plastic, but in a much higher density – almost 1,500 pieces per kilogram of sea ball.

Using estimates of seagrass fiber production in the Mediterranean, the researchers worked out an estimate of how much plastic can be filtered across the basin.

Oval orbs – shaped like a rugby ball – are formed from the base of leaves that have been cut up by the action of ocean currents, but remain attached to the stems, called rhizomes.

As they are slowly buried by sedimentation, the damaged leaf sheaths form rigid fibers that intertwine in a ball, collecting plastic in the process.

“We don’t know where they travel to,” said Sanchez-Vidal. “We only know that some of them run aground during storms.”

In 2018, WWF estimated that in a matter of weeks during the Mediterranean holiday season, increased marine plastic pollution contributed to around 150 million tonnes of plastic in the ocean.