Long Term Fluctuations in the Microbial–Planktonic Food Web of Lake Ontario

Session: State of Lake Ontario: 2003-2018 CSMI Overview (1)

Mark Fitzpatrick, Fisheries & Oceans Canada, [email protected]
Mohiuddin Munawar, Fisheries & Oceans Canada, [email protected]
Heather Niblock, GLLFAS, DFO, [email protected]

Abstract

In Lake Ontario, studies of the lower trophic levels were first implemented on a lakewide basis beginning in 1970 with an emphasis on phytoplankton and zooplankton populations.  By 1990, the concept of ‘lower trophic levels’ had been expanded to include microbial populations (bacteria, heterotrophic nanoflagellates and ciliates) and more holistic food web studies were developed and implemented.  Our research has shown that the relative importance of autotrophic and heterotrophic organisms varies considerably in time and space.  For example, during the summer of 1990 we observed that the organic carbon pool was approximately 520 mg C m^-3 and about 95% was composed of autotrophic organisms (phytoplankton and picoplankton).  In 2003 by contrast, the organic carbon pool was only 270 mg C m^-3 and about 60% heterotrophic (mostly nanoflagellates).  For the current paper, we will consider the structure and function of the microbial-planktonic food web during 2013 CSMI survey of Lake Ontario – including primary productivity and bacterial growth experiments in addition to food web composition – and compare with previous studies in order to assess the longer term implications for ecosystem health.