Life at turbulent sites : benthic communities in lake littorals interacting with abiotic and biotic constraints ; field and mesocosm investigations

Abstract

The central issue of this doctoral thesis is an evaluation of abiotic and biotic constraints on benthic communities in lake littoral zones. The thesis concentrates on various aspects of hydrodynamics, i.e. wave exposure, as a major abiotic force within the upper eulittoral zone of a large lake and its potential influence on taxa occurrence and habitat parameters and further its interference with biotic interactions. The importance of another abiotic factor water level fluctuations for the benthic community within the upper eulittoral zone of unregulated pre-alpine lakes is also emphasised. The thesis summarises results from standardised field, enclosure and mesocosm experiments and from a field sampling at Lake Constance, a large pre-alpine lake.<br />In order to understand the impact of abiotic disturbance processes, the colonisation abilities of macroinvertebrates were studied under field conditions. The effects of wave propagation and dissipation on behaviour and growth of the herbivorous snail Radix ovata were studied within an outdoor mesocosm deployed with a newly developed pneumatic wave machine. The determination of benthic variability was the central focus of a one-year field study at three representative sites. The understanding of the mechanism influencing the spatial and temporal patterns of benthic communities is an important background information on the system itself.<br />The present work involves two studies with emphasis on predator prey interactions between benthivorous fish and their macroinvertebrate food source. The predation impact of the most abundant fish taxa in Lake Constance, perch (Perca fluviatilis) and ruffe (Gymnocephalus cernuus), as well as of juvenile cyprinids [dace (Leuciscus leuciscus), bream (Abramis brama, Blicca bjoerkna)] were studied in enclosure experiments. Despite the direct impact of fish on benthic variability, wave exposure was expected to interfere with such food web interactions.