Phytoplankton community dynamics

Phytoplankton in the reference Paul Lake, Wisconsin, were dominated by gelatinous colonial algae throughout the seven-year study. Small, edible algae had relatively stable concentrations, whereas dinoflagellates and colonial chrysophytes and variable concentrations. The phytoplankton of Peter Lake were far more variable. Brief periods of high planktivory that caused decreases in grazer size were followed by increases in biovolume of colonial algae in 1985 (large bass year class followed by blooms of Sphaerocystis), 1988 (stocking of rainbow trout (Oncorhynchus mykiss followed by blooms of Aphanocapsa) and 1990 (stocking of golden shiners Notemigonus crysoleucas followed by blooms of Botryococcus). Decreases in cladoceran length were followed by increases by phytoplankter size and biovolume of total algae, gelatinous colonies, and edible algae (<20μm). The transformation of Tuesday Lake from planktivore domination to piscivore domination in 1985 caused dramatic changes in the phytoplankton. Reductions occurred in total biovolume and biovolume of dinoflagellates, colonial chrysophytes, and edible algae (<20μm). However, there were no significant changes in the algal community after the removal of piscivores and reestablishment of planktivores in 1987. The failure of large dinoflagellates, especially Peridinium limbatum, to recover their abundance was notable. Slow dynamics of this phytoplankter limited the community recovery and ecosystem resilience of Tuesday Lake. -from Authors