Demography and habitat use of the Badwater snail (Assiminea infima), with observations on its conservation status, Death Valley National Park, California, U.S.A.

Abstract

Cultural use of spring-fed wetlands in Death Valley National Park, California has reduced populations of endemic macroinvertebrates. Studies were conducted during the spring and late autumn of 1994 to assess demography and habitat use by the Badwater snail (Assiminea infima), which is endemic to low-elevation, spring-fed habitats in Death Valley where its abundance is believed to be adversely affected by municipal diversions and habitat trampling by Park visitors. Effects on demography and habitat were examined at sites highly, lightly, and unaffected by these activities. Field experiments examined the response of its habitat and abundance to trampling. Snail density ranged from 0 to 19 000 m−2 along the banks of seven springs sampled at Badwater and Cottonball Marsh. Springbrooks with high, steep, and overhanging banks were preferred A. infima habitat. Mean distance of snails from water ranged from 1 mm at Badwater to 39 mm at Cottonball Marsh, and distance from water was greater in autumn than spring. Frequency distributions of shell height showed each population was comprised of several cohorts during spring and autumn, suggesting that reproduction occurs several times a year. Field experiments demonstrated that trampling reduces bank heights, angles and overhangs, and A. infima population density. Actions are required to manage public use at Badwater to arrest declines in abundance and distribution of A. infima, and to allow for recovery. Historical diversion of springs for irrigation and municipal uses have reduced and dried many aquatic and riparian habitats in the Funeral Mountains, causing current distribution in these springs to be approximately 15% of historical levels.