Effects of Road Salts on Seasonal Wetlands: Poor Prey Performance May Compromise Growth of Predatory Salamanders

Road deicing agents that enter wetlands can affect amphibians both directly via their toxic effects and indirectly by altering food web interactions. We conducted experiments to determine whether larvae of the spotted salamander (Ambystoma maculatum) are more strongly influenced by direct versus indirect effects of salt concentration. Using outdoor mesocosms, we exposed salamanders and their prey to experimental salinities that were representative of values reported from salt contaminated breeding sites in North America. Increasing salinity depressed salamander growth but did not affect survival. Cladocerans were numerical dominants in samples taken 2 weeks after the experiment began, and markedly declined with increasing salinity. The number of cladocerans and total number of all invertebrates on this date were positively correlated with the mean mass of salamanders at the termination of the experiment. In a laboratory experiment where food was supplied in excess, increasing salinity did not affect the growth or survival of spotted salamanders that were chronically exposed to salinities that paralleled those in the mesocosm experiment. Our results suggest that spotted salamander larvae are more salt-tolerant than their prey, and that salamander growth may be compromised via indirect effects when breeding sites experience moderate salt contamination (i.e., < 1,000 mg L-1 of salts).