Acoustic observation of the spatial and temporal distribution of zooplankton in Lake Constance: The driving mechanisms and ecological consequences of patchiness

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The spatial and temporal scales of variability of phytoplankton, zooplankton and fish abundances will be investigated simultaneously by combining different remote sensing techniques. Major technological advances will be achieved by the evaluation and calibration of the acoustic backscatter signal from common Acoustic Doppler Current Profilers (ADCPs) for the in situ observation of zooplankton. Typical scales of horizontal patchiness will be estimated from the measurements. The formation, maintenance and dynamics of the patches will be investigated with special emphasize on the relative importance of abiotic (currents, large-scale circulation, internal waves, turbulence and diffusion) and biotic (swimming, shoaling, swarming, migration, differential growth) mechanisms. Further, the ecological consequences of the patchiness in all three food-web compartments will be discussed in terms of trophic interactions as well as in terms of predator-prey encounter rates and avoidance strategies. The measurements will cover the seasonal variability of the physical forcing and the biological activity, and they will be supplemented by numerical modeling and simulations.