Bioassay of the seasonal ability of water from a eutrophic Alberta lake to promote selective growth of strains of Anabaena flos-aquae and other blue-green algae

Abstract

Significant differences were observed in the capacity of samples of filtered, unautoclaved water from Hastings Lake, Alta., to support growth of two strains of Anabaena flos-aquae (A-l 13-9q2, NRC-445-i), a strain of Aphanizomenon flos-aquae (NRC-568), and a culture of Anabaena sub-cylindrica isolated from Hastings Lake when tested by a 2-week, 1-L standard bioassay in aerated hydrometer cylinders at 20 °C with photosynthetically active radiation (400–700 nm) of 60 μE m−2 s−1. Growth was measured by two independent methods, optical density at 750 nm and mean filament length × mean filament number, and analyzed by fitting logistic curves to the data for comparisons of yields, lag phases, and growth rates. Anabaena A-113-9q2 grew best in spring and fall, poorest in summer, and the growth was always much lower than the controls in ASM-1-TR minus nitrogen (NO3) medium. The results support the hypothesis that nutrient variability in the water column contributes to the selection and growth of dominant species and strains and is one of the factors (along with buoyancy and other concentrating mechanisms) which cause observed successional changes and localized differences in composition of bloom-forming populations and scums. Inhibitors along with nutrient deficiencies may have caused the low biomass densities supported by the lake water. Buoyancy can best account for the 10-fold higher biomass densities observed for heavy bloom-forming populations collected from the top 0.25 m of the water column of Hastings Lake.