Reproduction rates and secondary production of three species of the rotifer genus Synchaeta in the estuarine Potomac River

Rotifers are a relatively well-studied component of lacustrine systems but their role is only poorly understood in estuaries. Three species of the genus Synchaeta—S. baltica, S. triophthalma and S.cecilia —dominate the cold-water assemblage of rotifers in Chesapeake Bay. Laboratory experiments were conducted to determine the temperature dependence of egg development time (EDT) for each species; EDT varied over an approximate range of 90–9 h as temperature ( T ) varied from 2 to 22°C. The EDT/temperature relationships could be closely fitted by a simple polynomial equation of the form log(EDT) = a + b (log T ) + c (log T ) 2 for each species. Natural populations of these three rotifers were sampled during a cruise in the Potomac River (7–11 March 1983). Estimates of specific reproductive rates ( b ) were calculated based on the previously defined EDT/temperature relationship and the observed ratio of eggs/rotifers for each species. The two most abundant species, S.triophthalma and S.cecilia , showed a clear dependence of b on the observed chlorophyll a concentrations. Maximum reproductive rates (˜0.015 h −1 ) were attained only at relatively high phytoplankton densities within a bloom of Heterocapsa triquetra where the chlorophyll a concentrations exceeded 10 μg l −1 . Estimates of secondary production suggest that Synchaeta spp. may contribute to the trophic flow of carbon in this system with a significance at least similar to that of the planktonic copepods.