Over 70% of the world’s amphibian populations are in decline, in part due to decreased recruitment rates to the mating population (2). Future saltwater intrusion into near-coast freshwater breeding sites from sea level rise is likely to contribute to population declines, as increased salinity has been seen to delay metamorphosis and limit size in adults (1,3). This thesis is investigating how increasing frequency and intensity of saltwater intrusion in freshwater tidal wetlands of the Oregon coast will affect three native amphibians.
The main question examined by this thesis is "To what degree does salinity impact breeding site selection of the Pacific treefrog, Northern red-legged frog, and Roughskin newt?" Additional questions for investigation include "How are these species developmentally affected by differing salinities that are found in their natural habitats?" and "Do these species have any tolerance to salt in their larval stages given their coastal breeding habitats?"
Investigations are being performed at 12 field sites on the Oregon Coast. Field methods are described in Sampling Amphibians in Lentic Habitats (5) for complete surveys collecting abundance data with two observers. Laboratory experiments exposing study species to 3 experimental salinity treatments of environmentally relevant concentrations are being conducted.
We are ascertaining the ways increasing intensity and frequency of salinity gradients in the study species' natural breeding grounds may affect these species, and the degree to which these species have the natural variation and potential to adapt to changing salinity regimes.
Preliminary surveys indicate that Rana aurora tends to lay eggs further away from intertidal areas, while Taricha granulosa adults have been seen closer to areas of tidal influence. It is too early in the season to observe Psuedacris regilla eggs. It has been suggested that caudates are more susceptible to increased salinities due to road salt runoff (4). If this trend holds true for saltwater, then Taricha granulosa may experience population declines in the future. If it is found that Rana aurora prefers to lay in lower salinity habitats, then this species may experience range changes in the future.