Researchers have found that underwater seaweed in coastal areas traps plastic pollution in bundles of natural fibers known as “Neptune balls.”
A study published in Scientific Reports reports that swaying plants – anchored at the bottom of shallow seas – may collect nearly 900 million pieces of plastic in the Mediterranean alone every year without the help of humans.
Lead author Anna Sanchez Vidal, a marine biologist at the University of Barcelona, told AFP: “We are showing that plastic debris on the sea floor can get trapped in seaweed remnants and ultimately leave the marine environment through the beaches.”
She added that this cleaning process “represents a continuous clean-up of plastic debris at sea.”
The study adds to the long list of services that seaweed provides – to ocean ecosystems, and to humans who live near the water’s edge. They play a vital role in improving water quality, absorbing carbon dioxide and producing oxygen, and they are a natural nursery and refuge for hundreds of species of fish. They are also the basis of coastal food webs.
By fixing them in shallow water, they help prevent beach erosion, and mitigate the impact of destructive storms.
There are 70 species of seaweed, grouped into several families of flowering plants that – originally on land – re-colonized the ocean from 80 meters to 100 million years ago.
Most species grow from the arctic to the tropics, and have tall, grass-like leaves that can form vast underwater lawns.
It’s unclear if collecting the plastic harms the seaweed itself.
To better understand the gathering capabilities of seaweed, Sanchez Vidal and her team have studied a species only found in the Mediterranean. Posidonia Oceanica.
In 2018 and 2019, they counted the number of plastic particles in the sea balls that were washed away by the water on four beaches in Mallorca. SpainWhich contains large seaweed meadows outside.
There was plastic debris in half of the bulk seaweed leaf samples, up to 600 bits per kilogram of leaves.
Only 17% of the tighter bulk seaweed fibers known as Neptune balls contain plastic, but at a much higher density – roughly 1,500 pieces per kilogram of sea ball.
Using estimates of seaweed fiber production in the Mediterranean, the researchers worked to estimate how much plastic could be filtered into the entire aquarium.
The elliptical orbs – the rugby ball shape – form at the base of leaves that have been torn apart by ocean currents but remain attached to the stems, and are called roots.
When it is slowly buried by sedimentation, the damaged leaf bindings form stiff fibers that cross into a ball, collecting plastic in the process.
“We don’t know where they are going,” said Sanchez Vidal. “We only know that some of them went ashore during the storms.”
In 2018, the WWF estimated that within weeks of the holiday season in the Mediterranean, plastic marine pollution had risen Contributed about 150 million tons of plastic to the ocean.