Effects of the benthic suspension feeder Dreissena polymorpha on zooplankton in a large river

We conducted a series of in situ enclosure experiments to assess the impact of zebra mussels (Dreissena polymorpha) on the plankton of the Ohio River. Adult mussels were suspended in pelagic enclosures (‘potamocorrals’) at three densities (0, 1000, 2500 mussels per corral) and incubated for 6 days with daily plankton and physiochemical sampling. 2. The presence of adult zebra mussels was correlated with a shift in composition of the phytoplankton community and a severe reduction in some rotifers. The effects of zebra mussels on the larger zooplankton were taxon‐dependent, but bacterial density showed no trend among treatments. 3. Zebra mussels may have significant negative impacts on zooplankton, which may in turn alter riverine food webs.