PRIMARY RESEARCH PAPER The role of environmental parameters in the structure of phytoplankton assemblages and cyanobacteria toxins in two hypereutrophic lakes L. Xie • R. R. Rediske • Y. Hong • J. O’Keefe • N. D. Gillett • J. Dyble • A. D. Steinman Received: 13 April 2011 / Revised: 20 February 2012 / Accepted: 7 March 2012 / Published online: 27 March 2012 Ó Springer Science+Business Media B.V. 2012 Abstract We evaluated the variability of cyanotox- ins, water chemistry, and cyanobacteria communities in two hypereutrophic drowned river mouth lakes (Spring Lake and Mona Lake; summer 2006) in west Michigan, USA. Even with considerable geographical and watershed similarity, local variations in nutrient concentrations and environmental factors were found to influence the differences observed in cyanobacteria assemblages and cyanotoxins levels between the two lakes. Limnothrix sp. dominated the phytoplankton community in Spring Lake (82% of biovolume) and was negatively correlated with total phosphorus (TP) concentrations. Although Spring Lake was treated with alum during the previous year, Limnothrix sp. was able to bloom in the lower P environment. In contrast, the N 2 -fixing cyanobacterium, Anabaena flos-aquae, dominated the phytoplankton in Mona Lake (64% of biovolume). N 2 -fixing cyanobacteria dominance in Mona Lake was correlated with higher TP lower dissolved nitrogen levels. Cylindrosperm- opsis raciborskii was found in both systems; however, the toxin-producing polyketide synthetase gene was not present in either population. The higher TP in Mona Lake appeared to account for the 3-fold increase in cyanobacteria biovolume. Restoration plans for both lakes should include assessments of internal loading and continued phytoplankton monitoring to track the temporal distribution of cyanobacteria species and cyanotoxin concentrations. Keywords Limnothrix Á Planktothrix Á Microcystins Á Environmental parameters Á Cylindrospermopsis Introduction The toxicity of cyanobacteria blooms has drawn worldwide attention by scientists. Environmental conditions such as nutrient enrichment, light, temper- ature, essential metal availability, and the activity of selective grazers are all thought to initiate bloom growth and toxin production (Paerl, 1988; Long et al., 2001). In freshwater bodies, the most recognized causative agents for cyanobacterial mass occurrences are eutrophication, warm water temperatures, high light intensity and stable weather conditions (Francis, 1878; Pearson et al., 1990), however, no one factor is clearly responsible. Handling editor: David Philip Hamilton. L. Xie Á R. R. Rediske (&) Á Y. Hong Á J. O’Keefe Á N. D. Gillett Á A. D. Steinman Annis Water Resources Institute, Grand Valley State University, 740 West Shoreline Drive, Muskegon, MI 49441, USA e-mail: redisker@gvsu.edu J. Dyble National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, 4840 South State Rd., Ann Arbor, MI 48108, USA 123 Hydrobiologia (2012) 691:255–268 DOI 10.1007/s10750-012-1077-1