The Effect of Microplastic on Mussel Biodeposit Sinking and Resuspension

Intertidal habitats are routinely exposed to varying levels of biotic and abiotic particles. As microplastics (MP, plastic < 5mm) become more prevalent in our waters, it is important examine how MP affects key ecosystem processes, such as benthic-pelagic coupling by suspension-feeders. We focused on mussels (Mytilus spp.), well-known suspension-feeder and bioindicator species, and how the sinking and resuspension rates of their biodeposits are affected by a diet that includes MP. Mussels are known to ingest MP both in natural and laboratory settings around the world but it remains unclear whether MP affects the biophysical characteristics of biodeposits. Due to the size and buoyancy of MP in seawater, we hypothesized mussel biodeposits containing MP sink at a slower rate and are more easily resuspended into the water column than biodeposits without MP. Preliminary results demonstrate biodeposits containing MP are larger and sink at a slower rate than biodeposits that do not contain MP. Further, mussels fed high quantities of MP produce larger and slower sinking biodeposits than those fed low quantities of MP. These findings suggest that mussels can effectively clear MP from the water column, but the biodeposits they produce can concentrate MP and re-introduce the pollutant into the water-column in the form of a more bio-available package.