Abstract
Abstract. Since viral lysis and nanoflagellate grazing differ in their impact on the aquatic food web, it is important to assess the relative importance of both bacterial mortality factors. In this study, an adapted version of the modified dilution method was applied to simultaneously estimate the impact of both virus and nanoflagellate grazing on the mortality of heterotrophic bacteria. A series of experiments was conducted monthly from April to December 2011 and April to October 2012. The growth rates of bacteria we measured ranged from 0.078 h−1 (April 2011) to 0.42 h−1 (September 2011), indicating that temperature can be important in controlling the seasonal variations of bacterial growth. Furthermore, it appeared that seasonal changes in nanoflagellate grazing and viral lysis could account for 34% to 68% and 13% to 138% of the daily removal of bacterial production, respectively. We suggest that nanoflagellate grazing might play a key role in controlling bacterial biomass and might exceed the impact of viral lysis during the summer period (July to August) because of the higher abundance of nanoflagellates at that time. Viral lysis, on the other hand, was identified as the main cause of bacterial mortality between September and December. Based on these findings in this study, the seasonal variations in bacterial abundance we observed can be explained by a scenario in which both growth rates and loss rates (grazing + viral lysis) influence the dynamics of the bacteria community.
Highlights
Hydrology andIt is well recognized that EboathrvthiralSlyysisstaendmprotozoan grazioncgeaanreicimsypsotermtans t(tPoapc-ed,o1w9n88c;onWtSriolhclseileomfnbecatceatles.r,ia2l0m02o;rtTaaliitrya in et al, 2009)
Seasonal variations of Pigmented nanoflagellates (PNFs) abundance were similar to that of heterotrophic nanoflagellates (HNFs) throughout the study period, though HNF abundance was lower than PNF in the summer (Fig. 2b)
Viral lysis was found to be the main cause of bacterial mortality between September and December, when it removed between 53 % and 137 % of the potential bacterial production (Fig. 5)
Summary
Hydrology andIt is well recognized that EboathrvthiralSlyysisstaendmprotozoan grazioncgeaanreicimsypsotermtans t(tPoapc-ed,o1w9n88c;onWtSriolhclseileomfnbecatceatles.r,ia2l0m02o;rtTaaliitrya in et al, 2009). (Weinbauer and Peduzzi, 1995; Steward et al, 1996; Weinbauer and Hofle, 1998; Pedros-Alio et al, 2000; Jacquet et al, 2005; Fischer et al, 2006; Wells and Deming, 2006). These studies have shown that both viral lysis and grazing can cause significant mortality, but that the impact of each varies by season, host organism, and environmental conditions.
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