Habitat associations and abundance estimates of native and exotic freshwater snails in a West Texas Spring
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Isolated springs in West Texas are fragile systems often with high levels of endemism. The two biggest threats to these systems are habitat loss and invasion by nonnative species. San Solomon Springs, located in Balmorhea State Park, is a refuge for native and endangered aquatic species. Two native snail species, which are candidates for federal listing, the Phantom Cave Snail (Pyrgulopsis texana) and the Phantom Spring tryonia (Tryonia cheatumi), have a very limited distribution and rely on the springs at Balmorhea. Two exotic snails have established populations in San Solomon Springs, the red rim melania (Melanoides tuberculata) and the quilted melania (Tarebia granifera). Snails are important components of freshwater systems and understanding habitat usage is necessary for recognizing community patterns and improving conservation efforts of native species. We conducted a field study looking at habitat associations of the two native and two exotic snails at San Solomon Springs from May 2010 to May 2011. Our goals were to (1) measure habitat parameters, (2) measure snail density, and (3) determine the habitat associations among the four snail species. We also conducted a lab experiment to confirm our findings in the field study. We found that P. texana was associated with harder substrate, higher temperatures, and faster water velocity. M. tuberculata and T. granifera were both associated with deeper water and softer substrate. Habitat parameters did not account for much of the variation in T. cheatumi density. Data from this study will serve as a baseline for future studies.