Photoorientation, motility and pigmentation in a freshwater peridinium affected by ultraviolet radiation.

The effects of ultraviolet radiation on orientation, motility and pigmentation were measured in the freshwater dinoflagellate, Peridinium gatunense. Histograms of the positive phototactically oriented cells showed a decrease in the degree of orientation even after short exposure times. Quantification of the orientation revealed a significant inhibition after 2 h exposure. Similarly, the percentages of motile cells and the mean linear velocity of the cells was strongly affected. UV radiation also caused a massive bleaching of the cellular pigments as shown by absorption spectra determined after increasing exposure times. The ecological consequences of these effects are discussed.