The impact of zooplankton on the dynamics of natural phytoplankton communities /

The role of crustacean zooplankton in changing the size structure of phytoplankton communities was examined in Lake Memphremagog, Quebec. The hypothesis that zooplankton have a selective effect on various algal size classes, within the net- and nannoplankton, was tested during different periods of the growing season in controlled field experiments. Depending on the pattern of loss rates imposed by zooplankton on different algal size fractions, it is shown that zooplankton can both accelerate and decelerate successional events in the phytoplankton. Manipulation of zooplankton biomass produced significant changes in algal phosphorus demand, estimated from observations on the short-term dynamics of orthophosphorus. It is shown that the presence of zooplankton reduces the phosphorus deficiency of the phytoplankton in early periods of the season. Empirical relationships are also presented, based on literature observations, to predict variation in feeding selectivity of cladocerans and variation in the biomass of zooplankton among lake ecosystems