Habitat associations of native and invasive snails in the San Solomon Springs complex

Background/Question/Methods

San Solomon Springs is a desert artesian spring located in Balmorhea State Park (Reeves County, TX) and fills a recreational pool, a reconstructed wetland, and a refuge canal. These habitats are home for two native snails, the Phantom tryonia (Tryonia cheatumi) and the Phantom Cave snail (Pyrgulopsis texana); both are candidates for the federal threatened and endangered species list. Two invasive snails, the red-rim melania (Melanoides tuberculata) and the quilted melania (Tarebia granifera), are also found in these three habitats and are thought to displace native species. The objectives of this study are to determine population sizes for the four mentioned snail species and document species specific habitat associations. These objectives will help us discover how invasive snails are affecting native snail microhabitat selection. Over a period of one year, snails were identified and counted using twelve randomly placed .20x.20 m² quadrats in each of the three habitats and sampling was conducted every 4-6 weeks. Several habitat parameters were documented including temperature, pH, conductivity, water depth, substrate type, water hardness, current velocity, and algal composition.

Results/Conclusions

The most abundant snail species in the refuge canal and pool was P. texana with a peak density of 56,075 individuals/m² and a calculated mean total density of 43,717 individuals/m² in the canal and a peak density of 4,450 individuals/m² and a calculated mean total density of 891 individuals/m². The most abundant species in the wetland was T. granifera with a peak density of 3,625 individuals/m² and a mean density of 1,101 individuals/m². Both invasive species and P. texana were present in all three habitats, though P. texana was only found within the first 50m stretch of wetland when water depth was at least 38cm. Occurrences of T. cheatumi were rare and no individuals were found in the wetland. Data from this study will benefit the Texas Parks and Wildlife Department by providing baseline information for future monitoring efforts.