Quantitative determination of cyanobacteria in mixed phytoplankton assemblages by an in vivo fluorimetric method

An in vivo fluorimetric method for selectively determining the concentration of cyanobacteria (blue-green algae) in mixed phytoplankton communities was developed. Excitation wavelengths of 620 nm and 440 nm were applied, the former for detecting the cyanobacteria themselves, and the latter for subtracting the interference due to eukaryotic algae present in the sample. The emission fluorescence of the cyanobacteria and eukaryotic algae was measured at 645 nm and 680 nm, respectively. In the range of 0.01 to 10 μg phycocyanin ml−1 a linear relationship between fluorescence intensity and cell concentration was established for all the species examined: Microcystis aeruginosa, Phormidium tenue, Anabaena cylindrica and Spirulina platensis.