| Abstract: | In a limnocorral (LC) experiment performed in mesotrophic Lake Lucerne, Switzerland, a control LC containing a planktonic community similar to that in the lake was compared with a LC where the large zooplankton had been removed by filtration at the beginning of the experiment. The herbivorous zooplankton (mainly Daphnia galeata and D. hyalina) reduced algal biomass and primary production, however did not influence the size structure of the phytoplankton and the relative amount of different size classes contributing to the total primary production. Likewise, the seston (POC and PP) concentrations were diminished without changes in particle size composition. Since herbivorous zooplankton transform smaller particles into larger particles (fecal aggregates) through their grazing activity and thus enhanced particle formation owing to coagulation and microbial activity, sedimentation losses of POC and PP were increased in the LC with zooplankton. The importance of planktonic and sestonic particle size structure in aquatic ecosystems is stressed, as the smallest algae (< 12 μm) contributed 80 % of the primary production, which is in contrast to the 33 % contributed to the total POC sedimentation by this particle size class. |
