Plastic in our oceans has become a major problem, with microplastics making their way everywhere, from in seafood to polluting the Arctic. The seafloor is often the final resting place for plastics that make their way into the sea. A new study published in Scientific Reports has revealed that the seagrass Posidonia oceanica may help reduce the burden of these plastics in the ocean, trapping it and causing it to be washed ashore.
Lush meadows of P. oceanica are found in the seas of the Mediterranean and southern Australia, 0.5 to 40 meters (1.6 to 131 feet) underwater. They are an important part of the ecosystem, improving water quality and forming refuge and nursery areas for a variety of species. They also absorb carbon dioxide and help protect the coast. P. oceanica loses its leaves in autumn, which are then washed onto beaches by waves and currents. The leaf sheaths remain attached to the stem, releasing fibers that intertwine to form spheres of material called "Neptune balls". These balls are also washed ashore, mainly during stormy weather.
Researchers examined Neptune balls and seagrass leaves on four beaches in Mallorca, the largest of Spain's Balearic Islands. This location was chosen as the nearshore has the highest location of floating plastic debris in the Mediterranean sea, and also has plenty of seagrass meadows. They found that the balls and leaves contained plastic.
Around 1,470 pieces of plastic debris were found per kilogram of Neptune balls, with an average size of 9.48 millimeters (0.37 inches). The types of plastic found in the balls were PET, PVC, PE, PP, and PA. There was less plastic found in loose seagrass leaves than in the Neptune balls, 613 pieces per kilogram, mostly the low-density polymers PVC, PE, and PP.
The researchers theorize that seagrass meadows trap plastic on the seabed, which is then ejected and washed ashore, escaping the ocean. They also claim that Neptune balls may protect plastic pieces from abrasion and UV radiation, preventing them from breaking down into even smaller particles. Each year, 867 million plastic items may be trapped in Neptune balls alone. These results are an argument for the conservation of seagrass meadows, which, according to the study, in the Mediterranean Sea have decreased by 13-50 percent since 1960.