Embryonic mortality also contributed to the observed reduction in hatching success, with mortality significantly correlating with increasing egg THg concentrations. Clutches collected from females inhabiting contaminated portions of the South River had 154−425% higher frequencies of embryonic mortality than those clutches collected from reference females. Mercury is an embryotoxicant that is known to reduce hatchability and cause malformations in multiple vertebrate
species. However, our results suggest that maternally transferred Hg is more embryotoxic than teratogenic in snapping
turtles, as malformation frequencies were uniformly low across sites and were not correlated with egg THg. Similarly, Bergeron et al. found teratogenicity to be lower than embryotoxicity in American Toad larvae (Bufo americanus) exposed to high concentrations of maternal Hg. Embryotoxicity has also been observed in female American kestrels (F. sparverius), with eggs laid by females exposed to dietary Hg showing decreased hatching and lower fledging rates than those produced by mothers that were not exposed during nesting. Additionally, availability of lipids, micronutrients, and hormones that are important for embryonic and hatchling quality and development can be affected by Hg exposure. Thus, it also remains possible that female turtles living in Hg contaminated areas allocated inappropriate quantities of important resources to their eggs, contributing to the reductions in embryonic survival.