Differences in effects of grazing by deposit-feeders Hydrobia ulvae (Pennant) (Gastropoda:Prosobranchia) and Corophium arenarium Crawford (Amphipoda) on sediment microalgal populations. 2. Quantitative effects

An earlier study showed that the growth rate of the prosobranch Hydrobia ulvae (Pennant) in microcosms is reduced at high population densities, but that the presence of the amphipod Corophium arenarium Crawford does not affect snail growth rate. In the present study, the effect of these two grazing species on sediment microalgal numbers was measured in the same microcosms. Contrary to the findings of many previous studies, low levels of grazing did not lead to an increase in microalgal standing stock.