Differential sensitivity to natural ultraviolet radiation among phytoplankton species in Arctic lakes (Spitsbergen, Norway)

Incubation experiments demonstrated a differential sensitivity to natural UV-radiation among the dominant phytoplankton species from three Arctic lakes, situated near Ny-Ålesund, Spitsbergen (79° N). The growth of small chlorophytes, diatoms and picocyanobacteria from two oligotrophic lakes was inhibited primarily by the shorter wavelength UV components, while the growth of the larger colony-forming species (cyanobacteria, Planktothrix sp., Woronichinia sp. and the chrysophyte, Uroglena americana Calkins) apparently was stimulated. These colonies (not easily eaten by daphnids) dominated at the end of the experiment in those treatments where the short wavelength UV components were not excluded. For the two oligotrophic localities, 70 and 61%, respectively, of total phytoplankton biovolume were edible in the treatments excluding short wavelength UV, compared to only 13 and 19%, respectively, in the treatments including such radiation. For the third, more productive and less transparent lake, the percentage of edible species in the treatments with and without short wavelength UV radiation did not differ (ca. 75% for both treatments).