Influence of Ultraviolet Radiation on UVR-Absorbing Compounds in Freshwater Algal Biofilms and Scenedesmus vacuolatus Cultures

Abstract

There is considerable concern about increasing levels of solar ultraviolet radiation (UVR) and the potential harmful effects of UVR on living organisms. Microcosm studies were conducted with algal biofilms and Scenedesmus vacuolatus cultures to examine the effects of increased UVR on freshwater algae. Because algae have evolved various strategies to minimize the potential damage induced by UVR, the sensitivity of an UVR ratio was evaluated using absorbance characteristics of algal extracts to short- and long-term responses of algae to UVR exposure. The effects of UVR on the photosnthetic activity of periphyton also were determined by fluorometry. Results showed various patterns: (1) a short-term decrease in the UVR ratio between UVR-absorbing compounds and chlorophyll-a that reflect damage from UVR, and (2) a long-term increase in the UVR ratio as communities change their photosystems by increasing UVR absorbance capabilities, and thereby cell protection. Results include (1) validation of the UVR ratio, (2) allowing assessment of different UVR exposure-induced effects to algae, and (3) providing mechanistic information on cellular strategies used by algae to reduce UVR-induced damages.

We thank Carsten Riemeier, Regula Illi, and Richard Illi for assistance in sampling and laboratory analysis, and Ylenia Maniglio and Lucca Rossi for providing environmental data of the Chriesbach River. This work was supported by the project “Linking Ecology and Ecotoxicology: Response of River Biofilms to Simultaneous and Sequential Exposure to UV-Radiation and Cadmium,” from the Velux Foundation.