Landscape-scale Risk Assessment for Current and Future UV-B Exposure of Alpine Amphibians of the Pacific Northwest

Wendy J. Palen

Department of Integrative Biology

University of California, Berkeley, CA

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ABSTRACT

PALEN, WENDY J.
Department of Integrative Biology, University of California, Berkeley, CA
wpalen@berkeley.edu

Landscape-scale Risk Assessment for Current and Future UV-B Exposure of Alpine Amphibians of the Pacific Northwest

Increasing ultraviolet-B radiation (UV-B, 290-320nm) as a result of stratospheric ozone depletion has been proposed as a leading explanation for declining amphibian populations for almost ten years. It is not until recently however that we have begun to examine the likelihood that UV-B could influence amphibians at the large spatial scales relevant to populations declines and species conservation. A key limitation to these has been in understanding how results from a variety of single experimental sites relate to the effect of UV-B more generally across many sites. Here I present the results of a series of field experiments testing the importance of UV-B exposure for the hatching success of two species of montane amphibians, Ambystoma macrodactylum and Rana cascadae, at sites spanning agradient of UV-B exposure. Using the existing variation in the concentration of UV-B attenuating optical color (dissolved organic matter, DOM) present in the water at different amphibian breeding sites, I find the ambient levels of UV-B only negatively affect amphibian egg survival in the clearest of sites when compared to embryos shielded from UV-B. Secondly, I used the level of UV-B exposure associated with significant mortality from these field experiments to evaluate the relevance of the total dose of UV-B received by embryos surveyed across a large number of montane breeding sites. By combining data onthe timing of incubation, measured incident UV-B, optical properties of the water, and the depth distribution and light exposure of embryos at each site I find that 0.4% of A. macrodactylum and 0% of R. cascadae embryos across a landscape of breeding sites are exposed to doses of UV-B exceeding lethal levels in our field experiments. These results and extend earlier predictions that ambient levels of UV-B are not likely to cause widespread embryonic mortality.