Examining Threats to Cryptic Cave Salamanders in Central Texas to Petition for their Protection

Abstract

Background and Context. The Edwards-Trinity aquifer system in Texas Hill Country is one of the most biodiverse ecosystems in the world. Made of karst that was formed by tectonic plates millions of years ago when Hill Country was submerged by an ocean, this region is geologically unique and characterized by its underwater caves and aboveground springs formed when limestone rocks are dissolved by carbonic acid when it interacts with water. This karstic region provides habitat to stygobites, or species that are restricted to life in caves, and have very limited ranges due to high isolation and extreme endemism. With 60 species of invertebrates identified alone in the Edwards aquifer in 2019, there are also species of benthic blind fish, bacteria, and a genus of plethodontid or lungless salamanders–Eurycea. Eurycea Conservation. Coordinates are known for 14 species of Eurycea salamanders in Texas Hill Country that are adapted to aquatic life. Most are state and/or federally endangered or threatened due to high sensitivity of anthropogenic activities like habitat destruction. Of the 14 species we analyzed, there are three species of undescribed salamanders whose life histories are uncertain, given the inaccessibility of many Eurycea habitats as well as complicated genetic lineages and unreliable morphologies. Our client, Save Our Springs (SOS) Alliance, a central Texas nonprofit dedicated to protecting these karstic ecosystems and the species that inhabit them, is in the process of petitioning to the U.S. Fish and Wildlife Service (USFWS) for the protection of the Pedernales River Springs salamander. SOS Alliance aims to petition for the protection of additional Eurycea species under the same premises. Significance and Objectives. Our main objective is to find which salamanders should be most prioritized by our client to petition for federal protection based on our analyses. Our sub-objectives are to find which environmental variables are posing the most threat to Eurycea spp. and to suggest several management actions SOS can take to improve habitat quality. Protecting cryptic cave salamanders not only helps their population abundances, but also improves ecosystem health in karstic ecosystems by promoting these indicator species. Methods. Using locations of Eurycea salamanders found by scholars and researchers and a list of 13 threats suggested by our research, we conduct species distribution models to suggest species that should be most prioritized by SOS to petition to the USFWS. Results. MaxEnt results identified base flow index, or rate of groundwater discharge, as . Other variables with strong influence included runoff, base flow index, and soil permeability. Based on our environmental ordination in NMS, our results mostly fit our second hypothesis that samples of the same species sort similarly in the ordination, and there are also clusters of different species that occupy similar space in the ordination and are thus found in similar habitats. But not all species do this suggesting that they are not associated with habitat conditions or the variables we used. Samples are clearly clustered in geographic space suggesting that genetic isolation plays more of a role in where these species are found. We found that undescribed species 2 and 3 were associated with increases base flow index. We also found that samples of all undescribed species and Eurycea troglodytes, only a state protected species, are all likely to be found in areas of higher runoff and soil permeability, and could be weakly associated with elevation, precipitation, and in the case of species 3, pesticides. Implications. We find that E. sp 2 and E. sp 3 meet most of the criteria to create an effective petition as they meet the requirements for listing under the Endangered Species Act of 1973. Although they are not found in urbanized areas or in proximity to roads like other Eurycea that are protected at the state or federal level, their habitats should be protected to prevent anthropogenic encroachment and future habitat destruction. SOS Alliance could utilize several management techniques to improve habitat quality if found lacking such as regular water testing, incorporating and training volunteers to limit costs, increase salamander observational studies like visual encounter surveys, and developing a way to report unsuitable water quality to SOS Alliance or USFWS biologists. Conclusion. Eurycea salamanders are isolated, karstic-associated herpetofauna in central Texas. Due to tectonic plate actions millions of years ago and bedrock characteristics, these salamanders are geographically isolated. Our analyses support that Eurycea are found where they are due to evolutionary processes rather than habitat selection methods. Protection by SOS Alliance should thus seek to conserve individual habitats to avoid local extinctions. Although this is rather intuitive, petitioning to the USFWS for Eurycea protection with our analyses may improve a petition that may rely solely on general characteristics of herpetofauna in research to make a case for protection.