There is strong evidence that the seafloor constitutes a final sink for plastics from land sources. There is also evidence that part of the plastics lying on the shallow seafloor are washed up back to the shoreline. However, little is known on the natural trapping processes leasing to such landwards return.

This study investigated microplastics and larger plastic debris within beached seagrass remains including balls (aegagropilae) made of natural aggregates of vegetal fibres intertwined by seawater motion.

Up to 1470 plastic items per kilogram of plant material were found, which were mainly composed of negatively buoyant polymer filaments and fibers. The authors highlight that their findings show that seagrass meadows promote plastic debris trapping and aggregation with natural lignocellulosic fibers, which are then ejected and escape the coastal ocean.

It is concluded that seagrasses, one of the key ecosystems on Earth in terms of provision of goods and services, also counteract marine plastic pollution, and the authors underline that, in view of their findings, the regression of seagrass meadows in some marine regions acquires a new dimension.

https://www.nature.com/articles/s41598-020-79370-3

Sánchez-Vidal et al. (2021) Seagrasses provide a novel ecosystem service by trapping marine plastics. Scientific Reports 11: 254.