The aquatic stages of amphibians may be sensitive to increased levels of solar ultraviolet B radiation (UV-B, 280–320 nm) that have been observed at higher latitudes over the past several decades, but the effects on most species are unknown. We exposed eggs and larvae of Hyla regilla and Rana aurora to three experimental treatments: (1) solar UV < 450 nm blocked (control), (2) ambient solar UV, and (3) solar UV-B enhanced 15 and 30% above ambient levels at midday to simulate conditions predicted for the next decades at midlatitudes. The rearing containers were covered with acrylic filters to provide the desired radiation regimes. Hatching success of H. regilla did not differ among the treatments and was 87.7, 71.8, and 87.1% in April 1995 and 94.0, 85.1, and 97.4% in May 1995 for the control, ambient, and enhanced UV-B treatments, respectively. In contrast, hatching success of R. aurora in the enhanced UV-B treatment (56.0%) was lower than in the ambient UV (89.8%) and control (81.0%) treatments. Larval survival over the first 2 months of development was reduced to 18.4% for H. regilla and 2.6% for R. aurora in the enhanced UV-B treatment compared with the ambient UV and control treatments. We conclude that ambient UV levels at the study site did not affect the embryonic or early larval survival of either of the species tested under the experimental conditions, but both species are potentially vulnerable to increases in solar UV-B.
