Selective feeding and biodeposition by zebra mussels and their relation tochanges in phytoplankton composition and seston load

We examined the ability of zebra mussels (Dreissena polymorpha) to preferen tially infest or reject various phytoplankton species and nonliving particl es. Our objective was to determine if preferential ingestion by zebra musse ls could explain the changes observed in the Hudson River since their invas ion: (1) decline of cyanobacteria, Microcystis in particular, (2) rise to d ominance by diatoms, and (3) very small change in total seston load. We fou nd that zebra mussels are capable of efficiently sorting and rejecting part icles. Not only were clearance rates higher when the cyanobacterium Microcy stis was present in suspension, but Microcystis was preferentially ingested over almost all other particle types tested. Diatoms were generally reject ed as diffuse pseudofeces which were easily resuspended, even in still wate r. The rejection of cattail (Typha) detritus by zebra mussels corresponds t o the rejection by oysters (Crassostrea virginica) of cord grass (Spartina) detritus particles (Ward et al. 1998). Pseudofeces of clay or detritus par ticle types were also very diffuse. In a few cases, however, clay or detrit us particles, rather than phytoplankton cells, were preferentially ingested by zebra mussels. The interaction of selective feeding by zebra mussels wi th resuspension of diffuse biodeposits by tidal mixing may explain the diff erential decline of phytoplankton groups and nonliving particles in the Hud son River.