Michael Staniewski (Department of Biology)

Abstract for Oral Presentation for 2011 CSM Conference: 

Grazer and virus mediated mortality of freshwater phytoplankton

M. A. Staniewski¹, C. M. Short¹, S. M. Short^1
1University of Toronto Mississauga


In this study, grazing and virus-induced mortality of phytoplankton was investigated in a freshwater pond at the University of Toronto Mississauga, Canada, during September 2009. Species-specific primers and probes were designed and used for quantitative real-time PCR (qPCR) together with a modified dilution-based assay which partitions phytoplankton mortality into virus and grazing-induced fractions. Growth and mortality rates for both the entire phytoplankton community and four distinct phytoplankton populations were investigated to determine whether a community based approach of assessing mortality sufficiently reflects the interactions occurring between the constituent populations of phytoplankton and their viruses and grazers. Change in total phytoplankton biomass was estimated via fluorometric determination of Chlorophyll a (Chl a) concentrations, whereas change in the abundance of the individual phytoplankton populations studied was estimated via qPCR. It was found that the sources and amounts of mortality for individual phytoplankton populations differed from those of the whole community, as well as from each other. Our results suggest that whole community-based methods of assessing mortality may overlook valuable information about carbon flow in aquatic microbial food webs. Our results also suggest that the combination of qPCR and a modified dilution method can be used to efficiently estimate both viral lysis and grazing pressure on several different phytoplankton populations within a community. Further, the results of our analyses may address some of the classical limitations associated with such dilution methods, in regards to the dilution of specific phytoplankton populations at low abundances.