MARINE VIRAL ECOLOGY - INCORPORATION OF BACTERIOPHAGE INTO THE MICROBIAL PLANKTONIC FOOD-WEB PARADIGM

In the decade since the microbial loop was defined by Azam et al. (Mar . Ecol. Prog. Ser., 59, 1-17, 1983), the importance of the interaction between microbial organisms and the larger planktonic animals has bee n a subject of controversy. Until recently, grazing was considered to be the major fate of bacterial production. Now, however, viruses are s een to have an important role in microbial processes. We describe how growth and recycling parameters affect the transfer of bacterial produ ction through a microbial loop model that includes viruses. The loop i s very inefficient for all reasonable conditions, but its relative imp ortance as a source of mesozooplankton nutrition is variable. The mode l demonstrates that in mesotrophic coastal waters, the microbial loop is unlikely to supply more than a minor component of mesozooplankton n utrition, a proposition that is supported by accumulating evidence. Fo r oligotrophic pelagic waters, the model indicates that in the absence of viruses the microbial loop, despite its low efficiency, may provid e an important resource for mesozooplankton. Bacterial production, wit hout viral mortality, is also relatively important in the case of dire ct exploitation by salps. Under these conditions, bacteria account for 10-30% of mesozooplankton nutrition. With high levels of bacteriophag e activity, zooplankton production is generally reduced by 5-15%. We t hus conclude that bacteriophages could significantly affect mesozoopla nktonic and, hence, exploitable marine production.