We conducted feasibility assessments for reintroduction of extirpated spotted salamanders following a large scale habitat restoration effort. Blue-spotted salamanders persisted in the study site despite habitat degradation. We compared hatching success of spotted salamanders with blue-spotted salamanders as a control, to determine if restored vernal pools would support the reintroduction effort. We monitored hatching success of both species with in situ pond enclosures over three field seasons. Hatching success appeared to be limited by dissolved oxygen saturation in vernal pools. To isolate dissolved oxygen as a deterministic factor in hatching success, we created dissolved oxygen gradients in the laboratory. The laboratory experiment allowed us to determine a threshold level of oxygen necessary for hatching success. This information can be applied to guide vernal pool restoration efforts. We included the levels 0, 2, 4, 5, 6, 7, and 8 mg/l of dissolved oxygen in the spotted salamander hatching experiment. We used the levels 2, 4, and 6 mg/l dissolved oxygen for the blue-spotted salamander hatching experiment. Spotted salamanders were expected to require greater dissolved oxygen levels than blue-spotted salamanders because the eggs differ in structure and oxygen delivery mechanisms.
Results/Conclusions
In the field experiments, hatching failure was correlated with hypoxic conditions. Vernal pools with a mean dissolved oxygen level < 50% saturation had consistent hatching failure with spotted salamanders and low to moderate blue-spotted salamander hatching success. In the laboratory experiment, spotted salamander hatching was only successful in levels greater than 50% saturation, supporting the field observations. Blue-spotted salamanders hatched successfully in all dissolved oxygen treatments. Spotted salamanders have cohesive egg masses surrounded by a thick jelly coating. Oxygen is delivered convectively through small channels in the jelly. Oxygen subsidies are thought to be provided by the endogenous alga, Oophilia amblystomatis. In contrast, blue-spotted salamanders lay single eggs or small clumps of eggs and oxygen is delivered by diffusion. These differences may explain the persistence of blue-spotted salamanders in hypoxic pools where spotted salamanders have been extirpated. Using the results from the laboratory experiments, restoration management was applied to improve dissolved oxygen levels through prescribed burns in dried pool basins and selective canopy thinning. These restoration management prescriptions resulted in increased dissolved oxygen levels and increased hatching success in successive field seasons.
