Environmental variation and distribution patterns of freshwater snails (Family Pleuroceridae) and their trematode parasites in the rappahannock watershed
Abbie M. Tomba and Colby Croft. Biological Sciences, University of Mary Washington, 1301 College Ave., Fredericksburg, VA 22401
Snails in the family Pleuroceridae often compose a large portion of the invertebrate biomass in North American streams. They also serve as intermediate hosts to parasitic trematodes, which have been shown to affect snail feeding and reproduction. Our study investigates the environmental factors related to snail abundance and parasite prevalence of freshwater snail populations of the Rappahannock watershed in northeastern Virginia. We sampled five sites on the Rappahannock and Rapidan rivers. At each site snails were collected from 20 to 30 quadrats (surbers), and dissected for parasites. Temperature, pH and conductivity were measured at each site and flow velocity, shade, dissolved oxygen, depth, and substrate size were measured at each quadrat. Two genera (Elimiavirginica and Leptoxis carinata) were observed across the study sites. Elimia density ranged from 68.8/m² to 2.35/m² across sites, while Leptoxis densities ranged from 31.9/m² to 0.27/m². Leptoxis abundance was positively correlated with substrate size, where as Elimia abundance wasnegatively correlated with current velocity. Parasite prevalence across sites ranged form 9.8% to 0%. Parasitism was positively correlated with substrate size at the high prevalence site. Within the Rappahannock watershed, flow and substrate size were the key environmental predictors of snail and trematode abundance.