Temporal variation in microcystin production by Planktothrix agardhii (Gomont) Anagnostidis and Komárek (Cyanobacteria, Oscillatoriales) in a temperate lake

¹ Collegium Polonicum, Adam Mickiewicz University, ul. Kościuszki 1, 69-100 Słubice, Poland
² Department of Hydrobiology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
³ Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
⁴ International Institute of the Polish Academy of Sciences, European Regional Centre of Ecohydrology u/a UNESCO, Tylna 3, 90-364 Łódź, Poland
⁵ Department of Applied Ecology, University of Łódź, 12/16 Banacha Str. - 90-237 Łódź, Poland
⁶ Department of Environmental Sciences, University of Helsinki, Niemenkah 73, 15140 Lahti, Finland

^* Corresponding author: kok@amu.edu.pl

Received: 13 January 2011
Accepted: 30 May 2011

Abstract

Eutrophication of freshwater lakes has led to blooms formed by cyanobacteria often associated with toxins harmful to livestock and humans. Environmental conditions that favor toxin production during cyanobacterial blooms are, however, not well understood. Moreover, the ability to use cyanobacteria quantity to assess the level of threat associated with toxin production is a topic of discussion. The purpose for this study was to examine Planktothrix agardhii dynamics in a shallow, temperate hypertrophic lake and to determine the factors that affect microcystin production. In addition, the relationship between P. agardhii morphology and microcystin production was examined. The study spanned 2 years, and we documented a perennial P. agardhii bloom that contributed up to 99% of the total biomass. Intracellular microcystins were primarily detected throughout the study, with the highest concentration in October. Microcystin concentrations ranged from 3.4 to 71.2 μg.L⁻¹, and they had a strong, positive correlation with P. agardhii biomass. In contrast, the levels of weight-specific microcystin were relatively stable throughout the entire study, ranging from 0.23 to 1.18 μg.mg⁻¹. We also found that environmental factors, such as water temperature, phosphate level, ammonium nitrogen and transparency, were the most related to microcystin production. Furthermore, a significant relationship between filament morphology and toxin concentration suggested that there were different morphotypes within the toxic and non-toxic populations of P. agardhii. Our study showed that P. agardhii biomass and filament morphology may be useful characteristics for the identification of threats associated with cyanotoxins.