Abstract
Summary When exposed to solar radiation in a slanting groove placed in a pond for 4 h the cyanobacteria Phormidium uncinatum (Tubingen and Baikal strains), Anabaena variabilis and Oscillatoria tenuis migrated from the water surface to lower levels in order to avoid high solar irradiance. The organisms accumulated at depths between 40 and 60 cm. Fluorescence emission spectra indicated that solar radiation caused an impairment of energy transfer from the accessory pigments to the photosynthetic reaction centers in the organisms found in the first 10 to 20 cm of the water column after 4 h of irradiation. Prolonged exposure of the organisms to artificial solar radiation from a Honle lamp induced the production of sunscreening pigments absorbing at 312 and at shorter wavelengths between 250 and 300 nm. In the marine cyanobacteria Nodularia harveyana and N. spumigena , only the production of the pigment absorbing at shorter wavelengths was observed.
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