Das Projekt "Spatial and temporal distribution patterns of plankton in lakes: Abiotic forcing and organismic interactions with special emphasis on Planktothrix rubescens" wird vom Umweltbundesamt gefördert und von Universität Konstanz, Fachbereich Biologie, Limnologisches Institut, Arbeitsgruppe Umweltphysik durchgeführt. The aim of the project is to investigate the role of physical forcing, resource availability, and organismic interactions for the spatial and temporal distribution patterns of plankton in lakes. The research is focused on the distribution patterns of the buoyant cyanobacterium Planktothrix rubescens in Lake Ammer and compares the abundance of P. rubescens with the temporal and spatial variability of abiotic conditions and of phyto- and zooplankton. The main hypotheses are that (1) transport by internal wave motions has a substantial influence on the horizontal distribution patterns of P. rubescens and also affects the distribution of other phyto- and zooplankton; (2) vertical water column motions associated with internal waves cause fluctuations in the vertical layering of P. rubescens and thus alters its competitive abilities; (3) horizontal differences in habitat conditions, i.e. limited vertical water column depth in bays and resource. gradients near river inflows, result in longer-term characteristic horizontal distribution patterns of P. rubescens and other plankton; (4) layers of toxic P. rubescens may interfere with the vertical migration of zooplankton. These research questions will be addressed in extensive field experiments measuring horizontal and vertical distribution patterns of plankton and abiotic conditions at temporal scales ranging from minutes to several weeks. In-situ measuring techniques for plankton and abiotic parameters, providing sufficient temporal and spatial resolution, will be combined with water sample analyses to support them. The distribution of P. rubescens will be measured by using our newly developed in-situ technique that combines information from optic and acoustic instruments. The field experiments will be complemented with 3D and 1D model approaches. The intension of the modeling work is to support the interpretation of the field data by performing numerical experiment. s that investigate the response of horizontal distribution pat. terns of P. rubescens to physical forcing, patchy nutrient distribution (e.g. river inflow) or the presence of a shallow bay and by studying the implications of water column depth, internal wave induced fluctuations in light intensity, and grazing for the layering of P. rubescens in a vertical water column.
Das Projekt "Chemische Kontrolle von Weidern durch Futterorganismen" wird vom Umweltbundesamt gefördert und von Universität Zürich, Institut für Pflanzenbiologie, Limnologische Station durchgeführt. It is now generally acccepted that higher plants have developed chemical defence mechanisms against grazer and pathogenic micro-organisms. The existence of molecules with similar features that may regulate aquatic ecosystems have frequently been proposed and many experiments clearly show the presence of such molecules but up to now in no single case has the structure of such a compound been determined. In the current research programme we will capitalize on our experience on ultratrace analysis of odour and allelopathic compounds. Our interest focuses on the chemical interactions between grazers and food organisms in the aquatic environment and the chemical analysis of compounds responsible for these interactions. Planktothrix rubescens is the major cyanobacterium in Lake Zuerich and exhibits high resistance against grazers. Experiments with an axenic strain have shown two different strategies of the grazers to avoid the toxicity of this cyanobacterium. Either ingestion of Planktothrix filaments is rejected (food selection takes place by perception of Planktothrix specific compounds that are different from the microcystins) or the grazers have developed resistence against the toxins. The chemical characterization of the responsible compounds is under investigation.