Just how 'green' is the grass on the other side? Particulate carbon and microplastic capture potential by seagrass meadows in Wales

Seagrasses are important ecosystem engineers, providing food and crucial refugia for a wide range of species. Seagrass beds are a conservation priority, listed as habitats of principle importance for biodiversity under the Environment (Wales) Act 2016, and targets of the UK Blue Carbon Evidence Needs Statement (2023). Evidence suggests seagrasses capture significant amounts of carbon directly through photosynthesis, and indirectly through entrainment of allochthonous material.

This material is of interest because it may include recalcitrant organics and microplastics. Microplastic capture by seagrasses is particularly understudied, and research on the synergies between multiple simultaneous ecosystem services provided by a single biogenic habitat are also lacking.

The primary threats to UK seagrasses are eutrophication and light reduction associated with declining water quality and increased turbidity, causing reduced biomass, higher epiphyte loads (further reducing light levels), and greater vulnerability to pressures from storms, anchor drops, persistent pollutants, and novel macroalgae. Research on tropical seagrasses suggests carbon capture potentially changes with structure and condition (meadow density, aboveground biomass, rhizome depth, epiphyte load) and environmental drivers such as substrate grainsize, presence of bioturbators and herbivores, nutrient input, physical disturbance, and macroalgae in and around the meadows.

However, the interactions between these factors are not clear and we lack sufficient information to maximise ecosystem service provision by temperate seagrasses. How these factors change the capture of microplastics is also unclear, although recent Envision REP work at Bangor suggests seagrass microplastic capture is also affected by meadow structure and condition.

This PhD will elucidate the environmental factors that change particulate carbon and microplastic capture potential in temperate seagrasses, to better inform management. The PhD will use broad-scale surveys and manipulative in-situ and ex-situ experiments to test the hypothesis that carbon and microplastic capture potential changes with meadow structure, condition, and environmental context.