Grazing and viral lysis vary for different components of the microbial community across an estuarine gradient

Abstract

The balance between grazing and viral lysis of both photosynthetic and heterotrophic microbes determines the food resources that are available, and how much of each resource is present, for higher trophic levels. Mobile Bay is the fourth largest estuary in the USA, based on river discharge, and is home to a variety of nursery habitats for larvae and juveniles of economically important species which depend for their food on production of organisms of microbial size. To characterize the patterns of growth and removal rates of this fraction of organisms in Mobile Bay, we carried out modified dilution experiments in summer and winter at 3 stations along a salinity and nutrient gradient. Rates of growth, grazing and viral lysis for prokaryotes and dominant phytoplankton (cyanobacteria, diatoms and dinoflagellates) were determined for each experiment. Grazing and viral lysis of prokaryotes did not appear to be related to season or location, and both processes were detected within the bay as well as on the shelf. For phytoplankton, grazing was the dominant removal process inshore in the summer, while viral lysis of phytoplankton was detected in the fall and in winter. In winter, an apparent increase in dinoflagellates, and in the overall biomass of phytoplankton, was concurrent with increased viral lysis, suggesting that recycling by viruses may be an important source of nutrients in coastal waters. © Inter-Research 2011.