Sommer U, Lewandowska A
climate change, mesocosm, phytoplankton, spring bloom, Zooplankton, Kiel, 1.4 m3, Germany
Indoor mesocosms were used to study the combined effect of warming and of different densities of overwinteringmesozooplankton (mainly copepods) on the spring development of phytoplankton in shallow, coastal waters. Similarto previous studies, warming accelerated the spring phytoplankton peak by ca. 1 day 1C 1 whereas zooplankton didnot significantly influence timing. Phytoplankton biomass during the experimental period decreased with warmingand with higher densities of overwintering zooplankton. Similarly, average cell size and average effective particle size(here: colony size) decreased both with zooplankton density and warming. A decrease in phytoplankton particle sizeis generally considered at typical footprint of copepod grazing. We conclude that warming induced changes in themagnitude and structure of the phytoplankton spring bloom cannot be understood without considering grazing byoverwintering zooplankton.