Microplastics suppress copepod grazing of the harmful algal bloom-forming dinoflagellate, Alexandrium catenella

While harmful algal blooms (HABs) are prominent occurrences in coastal zones where microplastic concentrations are maximal, the manner in which microplastics influence food webs and HABs are poorly understood. This study explored how polystyrene microplastics effected copepod grazing of the saxitoxin-synthesizing harmful dinoflagellate, Alexandrium catenella, as well as a non-toxic dinoflagellate, Gymnodinium aureolum. Experiments were performed using multiple densities of microplastics (250– 10,000 mL-1) of differing sizes (4 and 10 µm), as well as multiple densities of microalgae. The addition of 10 µm microplastics at densities of 1,000 – 10,000 beads mL-1 consistently and significantly reduced grazing on A. catenella while 10,000 µm beads mL-1 (10 µm diameter) consistently and significantly increased grazing on G. aureolum (p