Abstract:
Land-use practices in karst can threaten aquatic subterranean species (stygobionts). However, since their habitat is mostly inaccessible, baseline ecological data such as distribution and population size are not known, making monitoring and risk assessment difficult. Wells provide easy and inexpensive access for sampling subterranean aquatic habitats. Over three years, including a two-month period of intensive sampling, the authors sampled sixteen wells (ten repeatedly) in Jefferson County, West Virginia, USA, for a threatened stygobiont, the isopod crustacean Antrolana lira Bowman, in two areas where the species was known to occur. A. lira was collected during 21 of 54 sampling events. A. lira was collected from 6 wells in which a total of 31 of the sampling events took place. Borehole logs suggest that only these 6 wells intersected appropriate habitat. Using the binomial approximation, the authors conclude that a random well has a 29% to 91% chance of intersecting appropriate habitat. In a well that intersects appropriate habitat, a single sampling event has a 51% to 85% chance of successful capture. The species occurs heterogeneously throughout the aquifer both in space and time, and thus, repeated sampling of multiple wells is needed to confidently establish presence or absence. In a contiguous block of phreatic carbonate- aquifer habitat analogous to that in the study area, at least 6 wells need to be sampled at least one time each to determine absence or presence of A. lira with 95% confidence. Additional studies with larger sample size would better constrain confidence intervals and facilitate refinement of minimum sampling requirements. In one well that consistently yielded from 8 to 19 animals, the population was estimated by mark- recapture methods. The limited data only allowed a very rough result of 112.3 6 110 (95% CI) individuals. Successful recapture suggests that animals are largely stationary when a food source is present. Animals were collected at depths below the water surface from ,1m (hand-dug well and cave) to , 30 meters in drilled wells. No migration of animals between wells was observed.