A Simple In Vivo Fluorescence Method for the Selective Detection and Quantification of Freshwater Cyanobacteria and Eukaryotic Algae

A method for the rapid detection of cyanobacteria (blue‐green algae) and their differentiation from eukaryotic algae in natural phytoplankton assemblages is presented. Fluorescence emission of photosynthetic pigments at 670 nm was measured using a microplate fluorescence reader when excited at two different wavelengths – 485 nm and 590 nm. The ratio of fluorescence excited at these wavelengths (590 nm/485 nm) was proportional to the ratio of cyanobacteria and eukaryotic algae, which was determined by the in situ spectrofluorometer for the phytoplankton quantification. The fluorescence intensity was equal to the total chlorophyll‐a content. These two fluorescence values can provide the first warning on a development of potentially toxic cyanobacteria in water.