Competition between benthic and pelagic microalgae for phosphorus and light – long-term experiments using artificial substrates

Abstract.

Benthic and pelagic microalgae inhabiting shallow lakes compete mainly for the limiting resources phosphorus and light. The availability of these resources depends on the spatial structure of the algal habitats. Pelagic microalgae use phosphate that is dissolved in the water column, and in turn their biomass affects the light intensity that reaches benthic microalgae. Benthic algae are able to use sediment-associated nutrients and nutrients that are recycled within the algal mats. To investigate competition between benthic and pelagic microalgae in shallow lakes, we performed two microcosm experiments with a three-factorial design. Phosphorus concentration in both the artificial substrates and the water column as well as light intensity were manipulated. The manipulated factors significantly affected Chl a and particulate phosphate concentrations of the experimental communities. In both experiments, benthic algae dominated during the entire time. Irrespective of light intensity, phosphate concentrations in the sediments and in the water column, pelagic algae were unable to become competitively superior by producing a biomass that was dense enough to shade the benthic algal community. Nutrients dissolved in the water column were effectively used by benthic microalgae, which reduced their availability for pelagic algae. The assumption that increasing the nutrient concentration in the water column would result in the loss of benthic communities was not confirmed.