Effects of incident UV-B radiation on periphyton in four alpine freshwaterecosystems in central Colorado: Impacts on boreal toad tadpoles (Bufo boreas)

Field experiments using mylar shielding were conducted to determine the imp acts of UV-B on food quality in four western boreal toad breeding ponds loc ated in central Colorado. The breeding ponds were located at elevations ran ging from 2971 m to 3272 m, an elevational range associated with at least a 5% change in UV-B exposure. The protein concentration in algae decreased w ith increased exposure to UV-B, chlorophyll a concentration was not affecte d by UV-B exposure, and community composition of algae was affected. Densit ies of Chlorophyta and Xanthophycease increased and densities of Diatomacea e and Cyanophyta decreased under mylar shielding. Not all members of taxono mic groups reacted the same. These data are interpreted to mean that food q uality available to boreal toad tadpoles is poorer as a result of increased exposure to UV-B. Poorer food quality can impact the ability of these toad s to complete their life cycle and thus can impact recruitment to adult pop ulations.