LAUSR

Abstract Two Great Lake embayments, Bay of Quinte (Lake Ontario) and Maumee Bay (Lake Erie) prone to toxic cyanobacteria blooms were sampled in early and late summer in 2006 to determine which cyanobacteria genotypes were present and how many of those were capable of producing microcystins. Microcystins, chlorophyll a, soluble reactive phosphorus and stoichiometric seston ratios of carbon, nitrogen and phosphorus were measured on the same samples to provide an ecological characterization of the phytoplankton. The V3 hypervariable region of the 16S rRNA and aminotransferase (AMT) genes, microcystin (mcyE) and nodularin (nda) were analyzed with PCR-DGGE and quantitative real-time PCR to describe cyanobacterial communities. DGGE results indicated species capable of producing microcystins were present at some point in all study sites and were most likely from species within the genus Microcystis. Concentrations of microcystins were greatest when hepatotoxic cell numbers were highest and when seston stoichiometry indicated cells were not nutrient stressed. This study demonstrated the effective use of a combination of molecular and ecological monitoring of cyanobacterial communities in regions that are susceptible to toxic cyanobacteria blooms.