AME 31:123-135 (2003)  -  doi:10.3354/ame031123

Comparing the effects of resource enrichment and grazing on a bacterioplankton community of a meso-eutrophic reservoir

Karel Simek1,2,*, Karel Hornák2, Michal Masín2, Urania Christaki3, Jirí Nedoma1, Markus G. Weinbauer4,5, John R. Dolan5

1Hydrobiological Institute of the Academy of Sciences of the Czech Republic, and
2University of South Bohemia, Faculty of Biological Sciences, Na sádkách 7, 37005 Ceské Budejovice, Czech Republic
3Institute of Oceanography, National Centre for Marine Research, PO Box 712, Anavìssos 19013, Attiki, Greece
4Netherlands Institute for Sea Research (NIOZ), Department of Biological Oceanography, POB 59, 1790 AB Den Burg, Texel, The Netherlands
5Marine Microbial Ecology Group, Laboratoire d¹Océanographie de Villefranche (LOV), UMR 7093 CNRS-UPMC, BP 28, 06234 Villefranche-sur-Mer, France

ABSTRACT: We examined changes in a microbial community in reaction to shifts in predation pressure and resources in a meso-eutrophic reservoir. Manipulations consisted of size fractionation and either in situ incubation or transplantation from the dam area to the river area, which differed in P-availability. Three treatments, in which samples were incubated for 96 h in dialysis bags, were used: a bacterivore-free (<0.8 μm) treatment, an enhanced flagellate grazing (<5 μm) treatment and a control treatment (all bacterivores present). We monitored bacterial abundance, mean cell volume (MCV), bacterial production, protistan grazing, as well as bacterial community composition (BCC) using fluorescence in situ hybridisation (FISH) with oligonucleotide probes with different levels of specificity. Populations transplanted to the relatively P-rich river area showed a 3- to 6-fold increases in bacterial and heterotrophic nanoflagellates (HNF) abundance and bacterivory compared to the corresponding treatments incubated at the dam area. In the transplanted community, nearly all phylogenetic groups of bacteria distinguished showed increased growth rates, even in the top-down manipulation treatments of increased bacterivory. In contrast, at the more resource-limited dam, the top-down manipulations induced significant changes in bacterial community composition. Thus, we found that BCC changes with predation in resource-limited bacteria but that predation plays a minor role when resource limitation is relaxed.

KEY WORDS: Reservoir · Top-down and bottom-up control · Dialysis bags · Microbial food webs · Bacterivory · Bacterial community composition · RNA-targeted oligonucleotide probes

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