Evaluating ultraviolet radiation exposure with satellite data at sites of amphibian declines in Central and South America

Many amphibian species have experienced substantial population declines or have disappeared altogether during the last several decades at a number of amphibian survey sites in Central and South America. Our study addresses the use of trends in solar UV-B radiation exposure (280-320 mn) tit these sites over the last two decades, derived from the Total Ozone Mapping Spectrometer satellite data. It is intended to demonstrate a role for satellite observations In determining whether UVB radiation is a contributing factor in amphibian declines. We used these data to calculate the daily erythemal (sunburning) UV-B or UV-B-ery, exposure at the latitude, longitude, and elevation of each of 20 survey sites. The annually average UV-B-ery dose, as well as the maximum values, have been increasing in both Central and South America, with higher levels reached at the Central American sites. The annually averaged UV-B-ery exposure increased significantly from 1979-1998 at all 11 Central American site; we examined (r(2) = 0.60-0.79; p less than or equal to0.015), with smaller but significant increases at five of the nine South American sites (r(2) = 0.24-0.42- p less than or equal to0.05). The number of days having the highest UV-B exposure (greater than or equal to6.75 kJ/m(2)/day) increased in both regions from <40 days per year to approximately 58 days per year in 1998 (r(2) = 0.24-0.42- p 0.001). In Central America, the contribution of these very, high UV-B-ery exposure levels to the annual UV-B-ery total increased from approximately 5 to approximately 15% over the 19-year period, but actual daily exposures for each species are unknown, A UV-B ratio, the highest monthly UVB exposure relative to the annual average for the highest UV-B category (greater than or equal to6.75 kJ/m(2)), increased in both regions over this time period (r(2) = 0.73; p less than or equal to0.001). This UV index was consistently higher for Central America, where species declines have been the most severe. These results should justify further research into whether UV-B-ery radiation plays a role in amphibian population declines and extinctions. We discuss synergy among UV-B radiation and other factors, especially those associated with alterations of water chemistry (e.g., acidification) in aqueous habitats.