This study concentrates on the seasonal composition and trophic dynamics of the benthic microbial community in freshwater and marine systems and on the effect of macrozoobenthos grazing on these communities. Laboratory experiments with and without added macrograzers were carried out with sediments from the North Sea, temperate lakes of Northern Germany and arctic lakes of North East Greenland. Incubation time varied between 30min and 5d. In further experiments, fluorescently labeled bacteria (FLBs) were added as food tracers in order to estimate bacterivory. The abundancec of bacteria, cyanobacteria, protists and meiofauna were determined at the beginning and in the end of all experiments. First results indicate no effect of the macrograzers Hydrobia ulvae (Gastropoda), Corophium volutator (Crustacea), Potamopyrgus antipodarum (Gastropoda), mixed polychaets (Annelida) and chironomid larvae (Insecta) on the abundance of bacteria and flagellates. However, FLB experiments revealed a removal of 40 to 60% of the standing bacterial stock per day, with no differences between the treatments with and without macrograzers. These results point a minor effect of macrograzers as bacterivores. Implications on the structure of the food web will be discussed.