Students investigate the accumulation of microplastics in seagrass meadows

Students from the University of the West of England (UWE Bristol) are researching new ways to tackle the challenge of plastic pollution in the seas and oceans by investigating how seagrass meadows at Studland Bay in Dorset accumulate microplastics within their sediments and biomass. Here the coastline and near inshore areas are managed by the National Trust and are a designated Marine Conservation Zone due to the presence of extensive seagrass meadows, which are also home to the beautiful but endangered spiny sea horse.

Seagrass is a marine flowering plant which provides important ecosystem services. It acts as a nursery habitat for fishes of commercial importance, offers coastal protection from erosion, and stores huge amounts of carbon. Understanding how human impacts affect the functioning of these seagrass meadows is a key area of scientific research.

Through wading and snorkeling across carefully planned transects, students collected sediment cores from areas of seagrass cover and unvegetated areas. Seagrass percentage cover was estimated using quadrats and some seagrass blade samples were collected, which will be scraped to check for microplastics sticking to the blades. Water samples were also taken from sampling sites along the coastline to analyse the general microplastic loading of the water column.

All samples were returned to the labs at UWE Bristol in order to extract, identify and quantify the microplastics present using specialized equipment such as Sediment Microplastic Isolation (SMI) units. The SMI units are built on site following a standardized protocol developed at Plymouth Marine Laboratory and simplify the extraction of microplastics from sediment samples. They use high density solutions, such as concentrated salt solution, to float the microplastics to the surface while the heavier sediment particles remain at the bottom. The surface layer is then filtered and the microplastics can be easily counted.

It is crucial to understand the potential of these important habitats to accumulate microplastics as they are protected under numerous pieces of national and international legislation, demonstrating the key role they play in a healthy functioning ecosystem.

There are indications that seagrass does accumulate microplastics and therefore they may be able to provide a partial, natural solution to this very human problem. However, there are potential side effects: as some species eat seagrass or the organic matter in the sediment, microplastics may still enter marine food chain.