ABSTRACT
As a result of stratospheric ozone depletion, concerns about increasing levels of solar ultraviolet (UV) radiation gave impetus for research to determine the impact of UV exposure to amphibians. Worldwide observations of declining amphibian populations were considered, in part, as outcomes potentially linked to changes in solar irradiance that have occurred over large landscapes during the past 25 to 30 years (Blaustein et al. 1994a; Carey 1994). Ozone concentrated in the stratosphere partially absorbs and ultimately governs the amount of solar ultraviolet B (UV-B) over the wavelength range of 290 to 320 nm radiation penetrating to the earth’s surface. Ozone has little effect on the ultraviolet A (UV-A) wavelength range (320 to 400 nm) and visible (400 to 800 nm) radiation. The amount of UV radiation reaching the earth’s surface is strongly influenced by diurnal, seasonal, and latitudinal variations in solar angle, which determines the thickness of ozone column traversed by UV radiation. Stratospheric contamination by chloroflurocarbons (Rowland 1982), brominated hydrocarbons (Wuebbles et al. 1999), and contamination associated with volcanic eruptions (Sigurdsson 1990) has resulted in ozone depletion evident as reduced ozone concentrations and concomitant increases in UV-B, especially in early spring over large areas of Antarctica and to a lesser extent over Arctic regions (Blumthaler 2003). Sulfer dioxide, nitrogen dioxide, and other greenhouse gases absorb UV light in the upper atmosphere. The intensity of UV penetrating the lower atmosphere is also influenced by cloud cover, aerosols, and altitude (Herman et al. 1996). In northern temperate latitudes, average surface exposure to biologically damaging UV-B radiation has increased by about 3 and 6% in south temperate latitudes since 1980 (McKenzie et al. 2006), with the greatest increases occurring in the spring when amphibians breed. Transient changes in
13.1 Mitigating Factors in UV Exposure ................................................................................... 452 13.1.1 Climate Conditions ............................................................................................... 452 13.1.2 Habitat Characteristics .......................................................................................... 454
13.2 Photoprotective Defenses of the Organism ........................................................................ 456 13.2.1 Behavioral Mechanisms ........................................................................................ 456 13.2.2 Photoprotective Substances in Aquatic Organisms .............................................. 458 13.2.3 Egg Jelly ................................................................................................................ 462 13.2.4 Photoreactivation and Photorepair ........................................................................464
