Great Basin Naturalist


The major hanging gardens and associated water seeps in Zion National Park were surveyed for the presence of the Zion Snail (Physa zionis). Environmental parameters, including water depth, water velocity, substrate slope, and algal cover, were measured to determine their effect on the local distribution of the snail. Large populations (densities 125 to 250/m2) were found in the Virgin River Narrows area of the park and at a hanging garden and seep located 1.0 km north of Scout Lookout. Densities in other localities were low in comparison. Snails were not found in all hanging gardens or seeps. The major factor controlling within seep distribution was determined to be water velocity. Experiments were conducted to test the ability of the snail to remain attached during differing water flows. The snail showed an ability to remain attached during high flows, but few snails were found in areas of high flow.