Salinity Characteristics of Rocky Cliff Pools Used as Breeding Habitat by Spotted Salamanders (Ambystoma maculatum)

Ambystoma maculatum (Spotted Salamander) is a widely distributed species in the eastern United States whose aquatic breeding habitat has been well documented as being hydrologically diverse but always freshwater in chemical composition. On Mount Desert Island, ME, a population of Spotted Salamanders breed in an aggregation of pools located atop a coastal rock cliff that is subject to seawater intrusion from nearby wave action. We periodically measured salinity concentrations (in ppt) of 7 pools with the highest breeding activity from 2016 to 2021 to quantify pool salinities within and between 5 breeding seasons. Our findings confirm that this breeding habitat experiences sporadic and extreme bouts of salt intrusion from the adjacent ocean, causing salinity levels to vary markedly and unpredictably (0.1 ppt to 32.5 ppt) on a spatiotemporal scale. The presence of salamanders exhibiting apparent normal behavior in salinities greater than 12 ppt suggest an upper threshold of salt tolerance in this population that exceeds purported upper thresholds for the majority of amphibians studied to date. Future experimental work on this population holds great promise to deepen our understanding of the underlying mechanisms of salt tolerance in coastal populations of amphibians from both a physiological and evolutionary perspective.