Impacts of microplastic versus natural abiotic particles on the clearance rate of a marine mussel

In coastal habitats, mussels are exposed to microplastic (MP; plastic <5mm) and silt, two abiotic particles that are similarly sized and lack nutrition. The addition of MP or silt may change the functional response of mussels. We measured clearance rate of Mytilus trossulus in three particle treatments (algae, MP + algae, and silt + algae) across four concentrations to 1) determine if the effects of MP and silt are similar and 2) disentangle the effects of particle type, particle concentration, and proportion of abiotic particles. Clearance rate decreased by 62% at high MP concentrations (>1,250 particles/ml) but was not affected at equivalent silt concentrations. These findings suggest high MP concentrations inhibit mussel clearance rate, more than expected by changes in particle concentration or the proportion of abiotic particles. As plastic production increases, mussel exposure to MP will increase, potentially reducing energy transfer, benthic-pelagic coupling, and water clarity.