Microplastic changes the sinking and resuspension rates of marine mussel biodeposits

Microplastic (MP; < 5 mm) is ubiquitous in marine environments and is likely transported by biotic benthic-pelagic coupling. Mussels are key benthic-pelagic couplers, concentrating particles from the water column into dense and nutrient rich biodeposits. This study examined how MP affects benthic-pelagic coupling processes of mussels exposed to feeding regimes with and without MP by measuring four attributes of biodeposits: 1) morphology, 2) quantity of algal and MP particles, 3) sinking rate, and 4) resuspension velocity. We found interacting effects of particle treatment and biodeposit type on biodeposit morphology. Biodeposits from the algae treatment contained more algal cells on average than biodeposits from the MP treatment. Biodeposits from the MP treatment sank 34-37% slower and resuspended in 7-22% slower shear velocities than biodeposits from the algae treatment. Decreases in sinking and resuspension velocities of biodeposits containing MP may increase dispersal distances, thus decreasing in-bed nutrient input and increasing nutrient subsidies for other communities.