Sensitivity of amphibian embryos, tadpoles, and larvae to enhanced UV-B radiation in natural pond conditions

Abstract

Temperate zone amphibians are exposed to the maximum change in UV-B radiation influx during early stages of their development. Embryos and tadpoles of six anurans, Bufo americanus, Rana sylvatica, Rana pipiens, Rana clamitans, Rana catesbeiana, and Hyla versicolor, and embryos and larvae of two salamanders, Ambystoma maculatum (the yellow-spotted salamander) and Ambystoma laterale (the blue-spotted salamander), were exposed to different UV-B radiation regimes in containers (12 cm in diameter and 4.5 cm deep) with Nitex screening (1 mm) on the sides to permit natural exchange with pond water. The containers were secured to a floating structure in a small natural pond in south-central Ontario, where most of the species tested lived and successfully recruited offspring. Three exposure conditions were evaluated: (i) natural incident light, (ii) incident light with the UV-B radiation filtered out, and (iii) incident light with the UV-B radiation enhanced by UV-B lamps. Embryos of all species hatched successfully under enhanced and incident UV-B radiation conditions. However, salamander larvae and anuran tadpoles were sensitive to enhanced UV-B radiation conditions and a differential sensitivity was observed based on developmental stage. When 2 weeks old, anuran tadpoles showed greater sensitivity than when newly hatched. Incident levels of UV-B radiation had no significant effect on tadpoles or larvae. Because of the tolerance of the embryos and the very rapid attenuation of UV-B radiation in the water of small ponds (high in dissolved organic carbon (DOC)), little direct damage is likely to occur during the aquatic stages of these amphibians.