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Aquatic Microbial Ecology

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AME 35:153-162 (2004)  -  doi:10.3354/ame035153

Control of epibenthic ciliate communities by grazers and nutrients

Stephen A. Wickham1,3,*, Simone Nagel1, Helmut Hillebrand2,4

1Zoological Institute, University of Cologne, Weyertal 119, 50923 Cologne, Germany
2Erken Laboratory, Department of Limnology Evolutionary Biology Centre, University of Uppsala, Norr Malma 4300, 76173 Norrtälje, Sweden
3Present address: Department of Organismal Biology, University of Salzburg, Hellbrunnerstr. 34, 5020 Salzburg, Austria
4Present address: Institute for Botany, University of Cologne, Gyrhofstrasse 15, 50931 Cologne, Germany

ABSTRACT: Four in situ experiments were conducted to examine the potential top-down and bottom-up control of epibenthic ciliate communities. The experiments were run in the littoral of Lake Erken and at a brackish water site on the island of Väddö on the Baltic coast of Sweden, during the spring of 2000. The experimental manipulations were the presence/absence of the natural macrozoobenthos grazer community, cross-classified with the presence/absence of additional nutrients. Epibenthic ciliates responded to both manipulation of grazers and resources, but the response was group specific. Total ciliate abundance decreased when macrozoobenthos (largely chironomids, gastropods, trichopteran larvae, isopods and amphipods) were removed, thus excluding a direct predation effect of the macrozoobenthos community on ciliates. Total ciliate biomass, but not abundance, tended to increase in the presence of additional nutrients; an effect weakly dependent on season and site. The disparity between effects of nutrients on biomass and abundance was due to effects on heterotrichs, a group of large but relatively rare algivorous ciliates. The manipulations altered the ciliate community composition, and between lakes there were differences in species richness and diversity and experiments. However, neither the removal of macrozoobenthos nor the addition of nutrients changed species richness or diversity. This runs counter to work with other taxonomic groups, which shows maximal diversity at an intermediate level of resources or predation. This can only be partially explained by the lack of direct predation effects and the open nature of the experimental system.

KEY WORDS: Benthic · Ciliate · Top-down · Bottom-up · Diversity

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