The influence of viruses on phytoplankton and bacterial productivity in Hamilton Harbour, an impaired embayment of Lake Ontario

Abstract

Abstract This study investigated the ecological effects of viruses on the microbial community in Hamilton Harbour, a Lake Ontario embayment. A modified Landry-Hassett style dilution assay was used to assess the relative impact of microzooplankton grazers and viruses on phytoplankton community and population growth and mortality in August 2013. Although viral effects were not observed in this experiment, significant grazing mortality was detected in all instances. Similar dilution methodology was then applied in conjunction with standard bacterial and size-fractionated primary productivity assays (using 3 H–leucine and Na 14 CO 3 , respectively). The first iteration of this experiment (August 2013) involved the use of a single dilution treatment with grazer-and-virus-free filtrate, and led to the observation that the combined activity of grazers and viruses appeared to stimulate productivity for phytoplankton 20 μm may have first been limited by viral infection/lysis and then stimulated by grazer dynamics. Our results provide the first evidence that viruses can actively affect microbial productivity in the Harbour.