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Aquatic Microbial Ecology

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AME 61:163-178 (2010)  -  DOI:

Effects of snail grazers and light on the benthic microbial food web in periphyton communities

Tanja Burgmer1, Julia Reiss1,2, Stephen A. Wickham3, Helmut Hillebrand1,4,*

1Erken Laboratory, Department of Limnology, Evolutionary Biology Centre, Uppsala University, Norr Malma 4200, Norrtälje 761 73, Sweden
2Department of Life Sciences, Roehampton University, London SW15 4JD, UK
3Organismal Biology, Institute for Zoology, Hellbrunnerstr. 34, Salzburg 5020, Austria
4Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl-von-Ossietzky University Oldenburg, Schleusenstr. 1, Wilhelmshaven 26382, Germany
*Corresponding author. Email:

ABSTRACT: Periphyton harbours a complex microbial food web with different trophic levels, but little is known about trophic interactions within this food web and its response to factors that potentially control the entire community. We used natural periphyton communities from Lake Erken (Sweden) in 2 experiments manipulating grazer presence. In addition to an ungrazed control, we included natural densities of either of 2 snail species (Theodoxus fluviatilis and Bithynia tentaculata) in order to test how generalist consumers affect different components of the periphyton. In the second experiment, we additionally manipulated light supply to alter the heterotroph–autotroph ratio in the periphyton and thus potentially the trophic interactions. In both experiments, grazer presence decreased algal biomass immediately and shifted the community composition from dominance of large filamentous forms to dominance of prostrate and motile unicellular species. Biomass of bacteria, heterotrophic nanoflagellates, ciliates and meiofauna also decreased with grazing, but with differentiated temporal dynamics and effect strength. In the ungrazed control, first heterotrophic protists and later meiofaunal biomass increased, indicating strong bottom-up and top-down propagation of trophic interactions in the microbial food web. High light increased the biomass of mixotrophic ciliates and nanoautotrophs but not total algal biomass. Grazer presence decreased algal richness in the second experiment, but increased evenness of the algal community under high light conditions. We conclude that grazer presence puts different pressure on the components of the periphyton, which are further linked by direct or indirect internal trophic processes.

KEY WORDS: Periphyton · Microbial food web · Protozoa · Algae · Grazer · Light

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Cite this article as: Burgmer T, Reiss J, Wickham SA, Hillebrand H (2010) Effects of snail grazers and light on the benthic microbial food web in periphyton communities. Aquat Microb Ecol 61:163-178.

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