Failed recruitment of southern toads (Bufo terrestris) in a trace element-contaminated breeding habitat: direct and indirect effects that may lead to a local population sink.

We conducted a transplant study in which embryonic southern toads (Bufo terrestris) were held in a site polluted with coal ash (site AB; containing As, Cd, Cr, Cu, Se, and other elements) and a reference site (site R) through hatching and early larval development. To examine the remainder of the larval period, surviving larvae in AB were then transplanted to R and back-transplanted to AB, whereas surviving larvae from R were back-transplanted to R. Survival through early larval development was lower in AB than in R (34% versus 50%). However, site of hatching did not influence traits later in development (larval metabolic rate, larval morphology, duration of larval period, size at metamorphosis, or average hopping distance by metamorphs). Toads that spent the entire larval period in R had high rates of survival (70-94% of individuals transplanted after the embryonic period) regardless of where they spent the embryonic and early larval period. However, toads held in AB for the duration of the larval period suffered 100% mortality. Algal resources were scarce and their trace element concentrations high in AB compared to R, suggesting that mortality of larval toads resulted from a combination of direct toxicity (via sediment- and foodborne exposure) and indirect effects on resource abundance. The study suggests that the widespread practice of disposing of coal ash in open aquatic basins may result in sink habitats for some amphibian populations.