[Sampling method adapted for colonial cyanobacteria in a lake environment. Case study of Microcystis aeruginosa in the Grangent reservoir (Loire, France)].

New method of sampling adapted to colonial cyanobacteria was developed on the Grangent reservoir (Loire, France). These prokaryotes were sampled using a filtering pump and were counted at laboratory under epifluorescence microscope. This method allowed us to follow the annual cycle of Microcystis aeruginosa, since benthic spring recruitment (cyanobacteria being used as inoculum) until autumnal sedimentation, and even revealed the presence of this cyanobacterian species in winter in the epilimnion. Our study also showed the inadequacy of the standard sampling methods used in limnology, which badly underestimate colonial cyanobacteria.