A Symposium on Amphibian Declines and Habitat Acidification

Abstract

A symposium was held 8 August 1991, at the annual meeting of the Society for the Study of Amphibians and Reptiles and The Herpetologists' League in University Park, Pennsylvania. The topic, Amphibian Declines and Habitat Acidification was selected for its relevance to the topical issues of a precipitous drop in many amphibian populations, and possible causation by acidic atmospheric deposition. As organizers, we felt that a rigorous approach to these issues requires meticulous field documentation of population fluctuations and correlated environmental measures of pollution, along with an experimental ecotoxicological analysis of possible anthropogenic causation. Because of the potential for large-scale environmental change acting synergistically with pollution across landscapes, the experimental elucidation of cause and effect will be extremely difficult. It appears that some amphibian populations fluctuate in an episodic fashion, but there are no long-term data bases adequate to determine whether particular declines are uniequivocally due to acidic deposition from non-point sources, other anthropogenic causes, natural causes, or interactions among them. This series of papers deals with the effects of acidic waters and soils on amphibians in England and North America. It is very clear that acidic habitats of natural and polluted origin exclude certain species and cause sub-lethal and lethal effects. However, no data are at hand which show directly that anthropogenic acidification causes amphibian populations to decline. There is consid- erable interest in the development of bioindicators of habitat decline. Net loss of body sodium and the embryonic curling defect in amphibians are examples of the best of such direct bioassays in acidified aquatic and terrestrial habitats. There is a strong need for standardization of test conditions so that better comparisons can be made among results from laboratories in different geographic regions. We recommend that a number of sites be chosen for long-term (10 year minimum) study of the relation between amphibian population cycles and anthropogenic change. This research would provide data not only specifically pertinent to the issue of amphibian declines, but would also provide valuable tests of the usefulness of amphibians as general bioindicators of ecosystem decline in response to anthropogenic stress. These issues are complex and are not amenable to quick solutions. A sustained commitment is needed by researchers and funding agencies to provide long-term monitoring and rigorous experimental tests of the causes of any declines in especially sensitive biotic components of ecosystems.