Institut für Biochemie und Biologie
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During 1987-1998, the ciliates and their prey and predator communities in large, deep, mesotrophic Lake Constance were intensively studied as it 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 nine 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 similarly-sized ciliates had seasonally compensatory dynamics. Ciliate biomass declined by approx. 30 % during the 12 years 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 threefold during the study period) and ciliate biomass or community composition via group-specific food concentrations were found. The relative contribution of three of the nine clusters changed as re-oligotrophication progressed. Ciliate size distribution was related to reoligotrophication and daphnid biomass in summer. The smallest and largest ciliates gained in importance when daphnids decreased whereas large ciliates declined. Overall, summer daphnid biomas 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.
Biomass size spectra collate structural and functional attributes of plankton communities enabling standardised temporal and cross-system comparisons and may be rapidly obtained by automated particle counters. To examine how differences in plankton communities from highly eutrophic and more oligotrophic lakes are reflected in size spectra, a three-year time series of biomass size spectra was established for polymictic, eutrophic Lake Müggelsee, based on approximately weekly sampling and microscopic enumeration. The continuous but often bumpy size spectra reflected appropriately the seasonal and trophy-related variations in the plankton composition and growth conditions and the potential impact of daphnids on smaller plankton. We tested the hypothesis that more diverse plankton communities have smoother size spectra than impoverished ones. The spectra of L. Müggelsee and other more less eutrophic lakes covaried roughly with the functional diversity in total plankton composition but were unrelated to taxonomical diversity within the phyto- or mesozooplankton. The slopes of the normalised size spectra of Lake Müggelsee were generally more negative than -1, exhibited a recurrent seasonal pattern, and were strongly correlated with crustacean biomass. In contrast to less eutrophic systems, slopes could not be used to quantify energy fluxes within the foodweb due to highly variable algal P/B ratios and frequently bumpy size distributions. The latter indicated stronger deviations from the ideal concept of a steady energy flow along the size gradient than found in e. g. large, mesotrophic Lake Constance.
Molinio-Arrhenatheretea = Kulturgrasland und verwandte Vegetationstypen. Teil 2: Molinietalia
(2004)
Heimische Aquarienfische
(2000)