Predation of epipelic diatoms by the amphipod Corophium volutator and the polychaete Nereis diversicolor

Abstract

The effects of Corophium volutator (Pallas) and Nereis diversicolor [O. F. Muller) on the densities and specific compositions of epipelic diatom assemblages were investigated experimentally, in the laboratory and in an estuary. In laboratory experiments cores containing no macrofauna had significantly higher densities of diatoms than cores with C. volutator and cores with N. diversicolor after 8 d. In field experiments the densities of diatoms increased where G. volutator were removed, by spraying with insecticide, and where N. diversicolor were prevented from surface deposit feeding, by the insertion of porous mats under the surface. The mean daily rates of consumption of diatoms by individual C. volutator and N. diversicolor in the field were estimated to be 2150 to 3767 and 5476 to 12 184 cells respectively. In the laboratory the effects of C. volutator and N. diversicolor on the species composition of the diatom assemblage were similar. In the field the assemblages that developed where predation was reduced were different because of initial differences in diatom assemblage structure in the 2 experimental areas. The laboratory results showed that C. volutator and N. diversicolor may feed on the same species of diatoms when presented with the same diatom assemblage, indicating that interspecific competition for food may be important under some natural conditions.