Annual cycle of Planktothrix agardhii (Gom.) ANAGN. & KOM. Nature population

Changes in abundance, biovolume and morphology of Planktothrix agardhii in a natural population were followed over one year period in shallow fishpond Bila Lhota (Central Moravia, Czech Republic). The selected environmental parameters (pH, oxygen, temperature, conductivity, nutrients, light) were measured at the surface and at the bottom of the fishpond, together with the Planktothrix abundances and filament morphology - filament length, width, shape, aerotopes (gas vacuoles) formation. The annual cycle of P. agardhii in this hypertrophic fishpond starts in March with the germination of hormogonia and the growth of overwintered filaments. The filament length quickly increases to a maximum length in April. The following summer period can be characterized by filament shortening and by changes in the aerotopes shape. On the other hand the abundance and biomass of P. agardhii is increasing until the maximum in August. Further shortening of filaments, loss of aerotopes and hormogoniae formation is typical for the autumn (October) with the average temperature of 9.4 degreesC. The population overwinters near the pond bottom in the form of hormogonia (60%) and filaments (40%).