Conservation Physiology of the Plethodontid Salamanders Eurycea nana and E. sosorum: Response to Declining Dissolved Oxygen

Abstract

Eurycea sosorum and E. nana are plethodontid salamanders endemic to several karst springs in central Texas. Landscapes around these habitats are increasingly urbanized. At the Barton Springs complex, where E. sosorum occurs, average dissolved oxygen (DO) in the main flow is approximately 6.5 mg L−1. However, DO is quite variable, ranging between 2.4 and 10 mg O2 L−1, and recent data suggest a positive relationship between DO and spring discharge in Barton Springs Pool, though this relationship may not be as strong under extreme low-flow conditions. Here we examine sensitivity of a surrogate species, E. nana, to experimental variation in oxygen availability (DO); due to limited availability of E. sosorum, they were examined in only a subset of experiments. A suite of traits was measured on adults: spontaneous activity, metabolic rate, and mortality during 28 days of exposure. A separate experiment examined growth of juveniles across levels of DO during 60 days of exposure. Levels of DO below 3.4 mg O2 L−1 appeared to pose a grave threat to salamander survival over a 28-day study, whereas DO above 4.5 mg O2 L−1 gave no observable effects in any experiment. Between these values is a critical range in which salamanders became progressively compromised. An ambient water quality criterion for DO in lentic systems (5 mg O2 L−1, 24 hour minimum) appears adequate to protect Eurycea.