Seasonal variations of virus- and nanoflagellate-mediated mortality of heterotrophic bacteria in the coastal ecosystem of subtropical western Pacific

[摘要] Since viral lysis and nanoflagellate grazing differ in their impact on theaquatic food web, it is important to assess the relative importance of bothbacterial mortality factors. In this study, an adapted version of themodified dilution method was applied to simultaneously estimate the impact ofboth virus and nanoflagellate grazing on the mortality of heterotrophicbacteria. A series of experiments was conducted monthly from April toDecember 2011 and April to October 2012. The growth rates of bacteria wemeasured ranged from 0.078 h⁻¹ (April 2011) to 0.42 h⁻¹(September 2011), indicating that temperature can be important in controllingthe seasonal variations of bacterial growth. Furthermore, it appeared thatseasonal changes in nanoflagellate grazing and viral lysis could account for34% to 68% and 13% to 138% of the daily removal ofbacterial production, respectively. We suggest that nanoflagellate grazingmight play a key role in controlling bacterial biomass and might exceed theimpact of viral lysis during the summer period (July to August) because ofthe higher abundance of nanoflagellates at that time. Viral lysis, on theother hand, was identified as the main cause of bacterial mortality betweenSeptember and December. Based on these findings in this study, the seasonalvariations in bacterial abundance we observed can be explained by a scenarioin which both growth rates and loss rates (grazing + viral lysis)influence the dynamics of the bacteria community.

[学科分类] 地球化学与岩石