The original idea of the pelagic trophic structure was a linear chain from autotrophic phytoplankton as primary producers via microzooplankton through to mesozooplankton as top predators. We now know that this is not a linear interaction but rather constitutes a complex food web. In-situ measurements of microzooplankton and mesozooplankton grazing have demonstrated the importance of these groups as phytoplankton grazers. A trophic overlap between micro- and mesozooplankton can also be expected. Still, not much is known about the species-specific feeding preferences and the dietary competition of dominant ciliates, dinoflagellate and copepod species on the phytoplankton species that dominate natural assemblages.Investigations on micro- and mesozooplankton grazing were conducted using the dilution technique and additional mesozooplankton treatments.The aim of these grazing experiments was to clarify which algae are preyed upon by both micro- and mesozooplankton, to estimate their relative contribution to phytoplankton grazing and to show selectivity patterns.