The trophic contributions of rotifers in tidal freshwater and estuarine habitats

Distribution patterns and trophic contributions of rotifers from freshwater through polyhaline estuarine waters were examined in the southern Chesapea ke Bay and its major tributaries for a two-year period. Trichocerca marina and Synchaeta spp. were the major taxa in abundance, followed by Polyarthra vulgaris, Keratella cochlearis and Brachionus spp. There was a significant negative correlation between salinity and rotifer density, biomass, and nu mber of species. Rotifers were a component of the microzooplankton biomass during specific periods and at particular sites, dominating summer assembla ges in tidal freshwater and river-estuary transition sites, plus the winter communities in estuarine waters. This observation indicates that rotifers may play an important trophic role by seasonally replacing metazoan nauplii as a biomass source in both tidal freshwater and estuarine ecosystems. The annual contribution of rotifers to the total microzooplankton biomass excl usive of heterotrophic dinoflagellates was brief but intensive, achieving o ver 50% of annual biomass during a 2-3 month period. Despite the small annu al mean contribution of rotifers to the total microzooplankton biomass, rot ifers may have a limited, but significant impact on the trophic dynamics of the zooplankton community in Chesapeake Bay and its major tidal tributarie s. (C) 2000 Academic Press.