As the industrial production of nanoplastic and the degradation of microplastic into smaller particles at sea increase, the potential amount of nanoplastics in the marine environment rises. It has been reported that mussels uptake 100-nm polystyrene (PS) beads; to date, however, the effects of this uptake on the organism are unknown. In the present study, the authors investigated the effects of 30-nm PS on the feeding behavior of the blue mussel (Mytilus edulis) by exposing the organism to different nano PS and different algae (Pavlova lutheri) concentrations. The state of nano PS aggregation in the exposure medium was assessed using dynamic light scattering. In all treatments that contained nano PS, M. edulis produced pseudofeces. The total weight of the feces and pseudofeces increased with increasing nano PS and increasing algae concentration. Furthermore, M. edulis reduced its filtering activity when nano PS was present but still caused a decrease in the apparent nano PS concentration in the water. The presence of nano PS around the foot of M. edulis after the bioassay confirmed that the organism removed nano PS from the water. Chronic effect studies are therefore needed to investigate the effects of nanoplastics in M. edulis and possible consequences for its predators, including humans.