Viruses in Marine Food Webs

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Recent evidence suggest that viruses may be very important in marine food webs, with some estimates suggesting they are responsible for the majority of bacterial mortality, and driving a significant component of nutrient cycling. If these estimates are correct, the scientific community will need a major rethinking of our conceptual models and modification of the performance and interpretation of many currently-accepted field measurements. However, the evidence to date is only from a few samples, and the methods and results are in real need of verification before they can be accepted with confidence. The objectives of this project are to use a variety of independent methods to measure from marine samples: (1) mortality rates of bacteria from viral infection in the context of bacterial growth and mortality from other sources including protistan grazers, and (2) the rates and mechanisms by which free viruses are removed or destroy. There are no known direct means to measure virus-induced bacterial mortality in natural mixed population, so two indirect methods will be used: (a) electron microscopy of field populations containing mature intracellular viruses, and (b) native virus population size changes and removal or decay rates in field samples. Rates will be compared to estimates of bacterial growth, grazing losses, and size-fractionated total mortality in an attempt to assemble a "source and sink" budget for large enclosed samples. Rates and mechanisms of viral decay and removal will be studied with both natural populations and cultured viruses. This project includes some laboratory work, but primarily field studies to be performed in nearshore and offshore environments off California. The use of multiple methods, cross-verified with each other, should greatly increase the confidence in any conclusion that are reached.