Rapid virus production and removal as measured with fluorescently labeled viruses as tracers

Pelagic marine viruses have been shown to cause significant mortality of he terotrophic bacteria, cyanobacteria, and phytoplankton. It was previously d emonstrated, in nearshore California waters, that viruses contributed to up to 50% of bacterial mortality, comparable to protists, However, in less pr oductive waters, rates of virus production and removal and estimates of vir us-mediated bacterial mortality have been difficult to determine. We have m easured rates of virus production and removal, in nearshore and offshore Ca lifornia waters, by using fluorescently labeled viruses (FLV) as tracers. O ur approach is mathematically similar to the isotope dilution technique, em ployed in the past to simultaneously measure the release and uptake of ammo nia and amino acids, The results indicated overall virus removal rates in t he dark ranging from 1.8 to 6.2% h(-1) and production rates in the dark ran ging from 1.9 to 6.1% h(-1), corresponding to turnover times of virus popul ations of 1 to 2 days, even in oligotrophic offshore waters. Virus removal rates determined by the FLV tracer method were compared to rates of virus d egradation, determined at the same locations by radiolabeling methods, and were similar even though the current FLV method is suitable for only dark i ncubations. Our results support previous findings that virus impacts on bac terial populations may be more important in some environments and less so i n others. This new method can be used to determine rates of virus degradati on, production, and turnover in eutrophic, mesotrophic, and oligotrophic wa ters and will provide important inputs for future investigations of microbi al food webs.