An enclosure experiment was conducted to assess the effects of a zooplankton elimination on the structure of a phytoplankton community. Phytoplankton biomass and production were higher in grazer-free enclosures, while the productivity per unit biovolume was lower. Exclusion of zooplankton favoured the majority of algal species, especially chrysophyceans (Dinobryon spp.) and the diatom Rhizosolenia, while mucilagineous green-algae were disfavoured. Middle sized algae (ESD 15–50 µm) and those with the largest Surface Area/Volume ratio were proportionally most favoured by the elimination of grazers.