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

The effects of Corophium volutator (Pallas) and Nerefs djversicolor (0. F. hluller) on the dcnslties and specific compositions of epipel~c diatom assembldges were investigated experimentally, in the laboratory and in an estuarb-.In laboratory experiments cores contaming no macrofauna hdd sign~ficantly h ~g h e r dens~ties of d~dtonis than cores w ~t h C volutator and cores with N. d i r ~r s ~c o l o r after 8 d.In field exper~ments the densit~es of diatoms increased where C, volutator were removed, by spraying with insecticide, ~l n d wherc..V diversicolor were prevented from surface deposit feeding, by the ~nsertion of porous mats under the .The mean d a ~l y rates uf consumption of diatonls by individual C'.volutator and N. d ~v e r s ~c o / o ~-In the f~eld we]-c estimated to bc 2150 to 3767 and 5476 to 12 184 cells respect~vely.In the laboratory the effects of C. vol~ltator and N. diversrcolor on the specles composition of the dlatom assernblage were similar.In the field the assemblages that developed where predation tvas reduced were different because of in~tial difforrnces in diatom assemblage structure in the 2 experlment~~l areds.Thc laboratory results sho\.ved that C' .volutator and h'.dlver~icolor Inay feed on the same species of diatoms when presented -11th the same diatom assemblage, indicat~ng that interspwific competition for food may be important under some natural conditions.