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Abstract

Microphytobenthos represents an important component in freshwater and marine habitats as it contributes significantly to the primary production in shallow-water ecosystems and benthic microalgae biomass supports higher trophic levels. This study had the main aim of elucidating which microphytobenthic community structures and key organisms were important in situ and then, based on this, to differentiate key grazer-microalgae interactions. Because of the man-hour problems associated with differentiating the variability of microphytobenthos populations spatially in situ a new multi-algal fluorometer was devised and tested. This probe enabled a rapid evaluation of microphytobenthic communities, instantaneous monitoring of total chlorophyll concentrations and differentiation of major taxonomic groups on an non-retrospect approach. The information on community structures gleaned from the in situ investigations was then used as a fundament to carry out three types of grazer-microphytobenthos experiments: (1) Investigations on the grazer efficiency and active selectivity of the freshwater snail Potamopyrgus antipodarum, (2) Experiments on the functional role of consumer presence and nutrient supply on microphytobenthic assemblages in macrophyte ecosystems and (3) Labelling experiments on selectivity patterns and competitive interactions between coexisting benthic grazers.