HATCHING SUCCESS AND LARVAL SURVIVAL OF THE FROGS HYLA-REGILLA AND RANA-AURORA UNDER AMBIENT AND ARTIFICIALLY ENHANCED SOLAR ULTRAVIOLET-RADIATION

The aquatic stages of amphibians may be sensitive to increased levels of solar ultraviolet B radiation (UV-B, 280-320 nm) that have been obs erved at higher latitudes over the past several decades, but the effec ts on most species are unknown. We exposed eggs and larvae of Hyla reg illa and Rana aurora to three experimental treatments: (1) solar UV <4 50 nm blocked (control), (2) ambient solar UV, and (3) solar UV-B enha nced 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 re gimes. Hatching success of H. regilla did not differ among the treatme nts 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 enha nced UV-B treatment (56.0%) was lower than in the ambient UV (89.8%) a nd 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. au rora in the enhanced UV-B treatment compared with the ambient UV and c ontrol treatments. We conclude that ambient UV levels at the study sit e did not affect the embryonic or early larval survival of either of t he species tested under the experimental conditions, but both species are potentially vulnerable to increases in solar UV-B.