AME 34:247-261 (2004)  -  doi:10.3354/ame034247

ABSTRACT: From 1987 to 1998, ciliates and their prey and predator communities in Lake Constance (which is large, deep and meso-eutrophic) were intensively studied as the lake underwent re-oligotrophication. Ciliate biomass exhibited the bimodal seasonal distribution typical for meso-eutrophic lakes, with high biomass in spring and summer and low biomass in winter and during the clear-water phase. Cluster analysis produced 9 groups of temporally co-occurring ciliate morphotypes with potentially similar ecological characteristics. The clusters exhibited a larger seasonality than found in the size distribution, showing that size alone failed to capture some ciliate seasonal dynamics. Ciliate biomass declined by approx. 30% during the 12 yr of study, i.e. considerably less than daphnids (and total phosphorus). This yielded a significant increase in the ratio between summer ciliate and daphnid biomass as re-oligotrophication progressed, in contrast to previous studies. Few indications for a mechanistic link between phosphorus concentrations (which declined 3-fold during the study period) and ciliate biomass or community composition via group-specific food concentrations were found. The relative contribution of 3 of the 9 clusters changed as re-oligotrophication progressed. Ciliate size distribution was related to re-oligotrophication and daphnid biomass in summer. The smallest and largest ciliates gained importance when daphnids decreased, whereas the biomass of large ciliates declined. Generally, summer daphnid biomass had a greater predictive power for attributes of the ciliate community than the other factors studied (phosphorus, prey biomass, copepod biomass). The extent of bottom-up and top-down control of ciliates appeared to be time- and group-specific. Overall, the ciliate community exhibited remarkably recurrent seasonal patterns, despite major alternations in abiotic and biotic conditions.

KEY WORDS: Ciliates · Long-term observations · Bottom-up control · Top-down control · Eutrophication · Daphnids · Copepods