Optical characteristics of natural waters protect amphibians from UV-B in the U.S. Pacific Northwest: Reply

Few ecologists would dispute that exposure to high levels of ultraviolet-B radiation (UV-B) is detrimental to organisms. It is well established that UV-B has been a critical factor shaping the physiology (Blum et al. 1949, Hansson 2000), behavior (Pennington and Emlet 1986, van de Mortel and Buttemer 1998), and distribution (Williamson et al. 2001, Leavitt et al. 2003) of many aquatic species. Recently, increasing UV-B caused by stratospheric ozone depletion has stimulated much research on the UV-B sensitivity of a wide variety of taxa, and has been found to cause direct mortality (Calkins and Thordardottir 1980, reviewed by Siebeck et al. 1994), elevate developmental abnormalities (Ankley et al. 2002), increase susceptibility to disease (Little and Fabacher 1994, Kiesecker and Blaustein 1995), and change the strength of species interactions (Sommaruga 2003). Increasing levels of UV-B have also been invoked as an explanation for the decline of some amphibian species, and support for this hypothesis has been extrapolated from many laboratory experiments and field studies at individual sites that indicate ambient or enhanced levels of UV-B can increase mortality of embryos and larvae (but see Licht 2003). This has been an especially attractive hypothesis for amphibian populations in alpine environments where direct anthropogenic impacts such as habitat modification are limited and ambient levels of UV-B are high (Blaustein and Wake 1990, Blaustein et al. 1994, Alford and Richards 1999). However, for all the attention UV-B has received in the context of declining amphibian populations, there is little evidence linking the physiological sensitivity of individuals to actual population dynamics (Licht 2003).