Experimental studies on habitat preference and tolerances of three species of snails from the Snake River of southern Idaho, U.S.A.

In laboratory experiments we studied the habitat preferences and physical tolerances of two endangered snails, the Utah valvata (Valvata utahensis) and the Idaho springsnail (Pyrgulopsis idahoensis), and the non-native snail Potamopyrgus antipodarum, from the Snake River of southern Idaho, U.S.A., in an attempt to understand habitat use and potential limiting factors in nature. Snails were tested for habitat preference in custom, 1 L aquaria that presented four substrates simultaneously. We tested the snail's tolerance to stream velocity in a laboratory flume capable of delivering water at velocities of approximately 0.15 m/s to 1.0 m/s. We observed tolerance to desiccation and loss of mass in snails by exposing animals to one of three moisture treatments and measuring mass over 50 h. Results show that in laboratory tests individuals of V. utahensis prefer pebble substrate types (χ² = 20.72, p < 0.0001), individuals of P. idahoensis use sand substrates most often (χ² = 2.20, p = 0.53) but preference could not be assigned, and individuals of P. antipodarum prefer gravel substrate types (χ² = 13.58, p = 0.004). Median detachment velocities for snails were significantly different (χ²₍₂₎ = 6.19, p = 0.045) being greatest for P. antipodarum (0.24 m/s) compared to V. utahensis (0.20 m/s) and P. idahoensis (0.17 m/s). Tolerance to desiccation differed between treatments of dry, damp, and wet moisture (F = 80.06, p < 0.0001). Snails lost significant mass in dry treatments after one hour of exposure to desiccating conditions (Dunnett's p > t < 0.0001). Very little is known regarding factors controlling the presence of many western North American snail species. Ours is the first experimental study to address habitat use and potential limiting factors controlling the presence of these federally protected snails.