Evaluating Ultraviolet Radiation Exposure with Satellite Data at Sites of Amphibian Declines in Central and South America

Abstract

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 nm) at 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 UV-B radiation is a contributing factor in amphibian declines. We used these data to calculate the daily erythemal (sunburning) UV-B, or UV-Bₑᵣᵧ, exposure at the latitude, longitude, and elevation of each of 20 survey sites. The annually averaged UV-Bₑᵣᵧ 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-Bₑᵣᵧ exposure increased significantly from 1979–1998 at all 11 Central American sites we examined (r² = 0.60–0.79; p≤ 0.015), with smaller but significant increases at five of the nine South American sites (r² = 0.24–0.42; p≤ 0.05). The number of days having the highest UV-B exposure (≥6.75 kJ/m²/day) increased in both regions from <40 days per year to approximately 58 days per year in 1998 (r² = 0.24–0.42; p≤ 0.001). In Central America, the contribution of these very high UV-Bₑᵣᵧ exposure levels to the annual UV-Bₑᵣᵧ 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 UV-B exposure relative to the annual average for the highest UV-B category (≥6.75 kJ/m²), increased in both regions over this time period (r² = 0.73; p≤ 0.001). 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-Bery 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.