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 th e use of trends in solar UV-B radiation exposure (280-320 mn) tit these sit es over the last two decades, derived from the Total Ozone Mapping Spectrom eter satellite data. It is intended to demonstrate a role for satellite obs ervations In determining whether UVB radiation is a contributing factor in amphibian declines. We used these data to calculate the daily erythemal (su nburning) UV-B or UV-B-ery, exposure at the latitude, longitude, and elevat ion 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 Amer ica, with higher levels reached at the Central American sites. The annually averaged UV-B-ery exposure increased significantly from 1979-1998 at all 1 1 Central American site; we examined (r(2) = 0.60-0.79; p less than or equa l to0.015), with smaller but significant increases at five of the nine Sout h American sites (r(2) = 0.24-0.42- p less than or equal to0.05). The numbe r 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 approximatel y 58 days per year in 1998 (r(2) = 0.24-0.42- p <less than or equal to>0.00 1). In Central America, the contribution of these very, high UV-B-ery expos ure levels to the annual UV-B-ery total increased from approximately 5 to a pproximately 15% over the 19-year period, but actual daily exposures for ea ch species are unknown, A UV-B ratio, the highest monthly UVB exposure rela tive to the annual average for the highest UV-B category (greater than or e qual 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 high er for Central America, where species declines have been the most severe. T hese results should justify further research into whether UV-B-ery radiatio n plays a role in amphibian population declines and extinctions. We discuss synergy among UV-B radiation and other factors, especially those associate d with alterations of water chemistry (e.g., acidification) in aqueous habi tats.