Adult blue mussels (Mytilus spp.) were exposed to microplastic particles in a controlled laboratory experiment. The effect of PS beads on the filtration was assessed by measuring the clearance rates. Clearance rate of the food algae Rhodomonas baltica was measured during the first hour of exposure and standardized by shell length. Since the reproductive status of the mussels can have an influence on the feeding activity, this factor was taken into account. Therefore, the mussels were inspected for the presence or absence of gonads at the end of the experiment. This resulted in four different treatment groups: control group with or without gonads and the microplastic-exposed group with or without gonads. Presence of PS beads and the reproductive status had a significant influence on the clearance rates.