For the first time, researchers have described the natural mechanism of a marine seagrass that can filter and trap plastics in coastal areas. The posidonia oceanica seagrass, an endemic marine phanerogam, or seed-bearing plant, performs many important ecological roles in the marine environment: it provides shelter, nutrition and habitat through its dense prairies.
But in a recent study, researchers from the University of Barcelona have shown how this seagrass can take and remove plastic material that has been left in the sea. The findings of this study were recently published in the journal Scientific Reports. As part of the study, the team analysed the seagrass’ ability to trap and extract plastic in the coasts of Majorca, Spain.
This marine phanerogam has a vegetative structure made by a modified stem with a rhizome shape, from which the roots and leaves appear. When the leaves fall, its bases or pods are added to rhizomes and give them a feather-like appearance. Due to the mechanical erosion in the marine environment, the foliage from this seagrass releases a fibrous material, which slowly intertwines to form ball-like structures known as ‘Neptune balls’ or aegagropilae. The seagrass, which is endemic to the Mediterranean Sea, is also commonly known as the ‘Neptune grass’.
These ‘Neptune balls’ are often expelled from the prairies during periods of strong waves or storms and wash up on the beaches. Although there are no studies that quantify the amount of aegagropilae expelled from the marine environment, it is estimated that about 1,470 pieces of microplastics are taken per kg of plant fibre, which is significantly higher than those captured through leaves or sand.
“According to the analyses, the trapped microplastics in the prairies of the Posidonia oceanica are mainly filaments, fibers and fragments of polymers which are denser than the sea water such as polyethylene terephthalate or PET,” Anna Sànchez-Vidal, member of the Department of Ocean and Earth Dynamics at the University of Barcelona, says in a news release. Sànchez-Vidal is also one of the authors of the study. “We cannot completely know the magnitude of this plastic export to the land. However, first estimations reveal that Posidonia balls could catch up to 867 million plastics per year,” she adds.
Decades of marine plastic pollution has now slowly found its way to the sea and ocean floors in the form of microplastics. Ocean currents, waves and winds often transport these small pieces of plastics over long distances. “The plastics we find floating in the sea are only a small percentage of everything we have thrown onto the marine environment”, Sànchez-Vidal adds.