Ambient Levels of Ultraviolet-B Radiation Cause Mortality in Juvenile Western Toads, Bufo boreas

—Numerous anthropogenic and natural factors affect living organisms in nature. Anthropogenic factors include a wide array of contaminants and processes that alter the habitat on both local and global scales. For example, chlorofluorocarbons (CFCs) and other industrial gases contribute to the depletion of the earth’s protective ozone layer, resulting in increased amounts of cell damaging ultraviolet-B (UV-B) radiation reaching the surface of the earth. Recent experiments provide evidence that increasing ambient levels of UV-B radiation harm many amphibian species. UV-B radiation can kill amphibians and can cause sublethal damage to them. However, most studies that have examined the effects of UV-B radiation on amphibians have focused on developing embryos. There is little information on how UV-B radiation affects amphibians at later stages of development. In experimental laboratory tests, we exposed one group of juvenile western toads (Bufo boreas) to full spectrum lighting with ambient levels of UV-B radiation and control toads to full spectrum lighting excluding most UV-B. Juvenile toads exposed to ambient levels of UV-B radiation showed significantly greater mortality rates compared with controls. These results add to a growing body of literature demonstrating that UV-B is harmful to amphibians. Furthermore, our results suggest that investigators should look at the effects of UV-B radiation on different life stages before making conclusions about the overall impact of UV-B on amphibians.