AME 31:137-144 (2003)  -  doi:10.3354/ame031137

Comparing the effects of resource enrichment and grazing on viral production in a meso-eutrophic reservoir

Markus G. Weinbauer1,2,*, Urania Christaki3, Jirí Nedoma4, Karel Simek4,5

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

ABSTRACT: As viral production depends on bacteria, factors which influence bacterial production should also impact viral production. Likewise, viruses and heterotrophic nanoflagellates (HNF) both exploit bacterial prey, so HNF grazing could influence interactions between viruses and bacteria. To examine these relationships, we examined samples from experiments in which natural bacterial populations were subjected to relaxation of nutrient limitation and different levels of grazing pressure from HNF. We observed that stimulation of bacterial production and abundance with the relaxation of nutrient limitation resulted in a higher standing stock of viruses, higher viral production and also a higher virus-induced lysis rate of bacterioplankton. These relationships suggest that the relative effect of virus-induced mortality is higher in more productive environments. We found that viral abundance, viral production and virus-induced mortality of bacteria was highest in the treatments in which grazing rates on bacteria by HNF were highest, and lowest in the treatments where no eukaryotic predators were present. Thus, high grazing rates were associated with high virus production rates. The resource enrichment had a stronger effect on viral production and infection of bacteria than grazing. Averaged over time for single treatments, viruses lysed a significant portion (range, 18 to 66%) of the bacterial production per day.


KEY WORDS: Viral lysis · Bacterial production · System productivity · Dialysis bag incubation


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