Factors influencing ultraviolet radiation dose to developing frogs in northern vernal pools

Ultraviolet-B (UV-B) radiation exposure is one hypothesized mechanism explaining amphibian population declines and malformations, but it is rarely quantified in amphibian habitats. We measured spatial and temporal variations in northern vernal pools with UV-B attenuation through the water column, incident UV-B across pool surfaces and seasons, and cumulative UV-B dose. Atmospheric, local, and landscape effects were compared with variances across spatial and temporal scales, plus influence on exposure risk. Risk was evaluated using published reports on detrimental levels for amphibian survival and health, with life history and behavior of vernal pool breeding Rana sylvatica L. (wood frog). Pools were exposed to sufficiently high UV-B at or near the surface for developing amphibians to be at risk of reduced survival, altered growth, and malformation. Atmospheric conditions, vegetative cover, and water column properties significantly influenced UV-B levels, with oviposition and larval behavior controlling actual embryonic and larval exposure. UV-B risk to vernal pool species is greater than predicted in previous studies. Given changes in light regimes, climate change, and forest harvesting, amphibian UV-B exposure could reach levels of great concern.