The conservation of native snails within a Chihuahuan desert spring system

Aquatic biodiversity in the Chihuahuan Desert of West Texas is an important national resource and conservation concern because of the high levels of endemism, limited distributions of natural communities, and the continuing decline of water resources. The Diamond Y Spring preserve located in Pecos County, Texas contains two endemic springsnails (Tryonia circumstriata=stocktonensis and Pseudotryonia=Tryonia adamantia, family Hydrobiidae), one federally endangered snail (Assiminea pecos), one common pond snail (Physella spp.), and one invasive snail (Melanoides tuberculatus, family Thiaridae). The potential impact of this invasive snail is of concern as it has been documented to outcompete and eradicate populations of native snails. In addition, the red-rimmed melania snail also poses the potential threat of introducing non-native parasites into novel environments. Our study objectives were to determine the habitat associations, distribution, and densities of each of the snail species within the Diamond Y Spring preserve and investigate how the invasive Melanoides affects native species.

We conducted a field study over the course of one year (June 2009 to July 2010) at three spring systems (Diamond Y, Bird, and Euphrasia) within the preserve. Only two snails, Assiminea pecos and Physella spp. were found throughout all three spring systems. Melanoides tuberculatus and T. circumstriata were found only within Diamond Y Spring, while P. adamantia was found only within Euphrasia Spring. The invasive Melanoides tuberculatus was the most abundant snail within the Diamond Y Spring preserve and the endemic T. circumstriata was the least abundant snail within the preserve.

We found that the variation in snail densities was strongly associated with one or two habitat variables. However, species distributions can be driven by a multitude of factors such as the utilization of different habitats, competition for resources, and differences in environmental tolerances. Therefore, we concluded that follow up laboratory investigations would be useful in determining which factors drive the unique distribution of the snail species within the Diamond Y Spring preserve.

We conducted laboratory experiments to determine how the invasive Melanoides may be affecting native populations within the preserve. Our first laboratory investigation consisted of surveying M. tuberculatus for exotic trematodes. Our second experiment determined if M. tuberculatus predated upon the eggs of a native snail species. We did not find any evidence of introduced parasites within the Diamond Y Spring system and using a computer simulation, concluded that parasite prevalence is likely less than 5%. Melanoides tuberculatus did prey upon native snail eggs and may be a mechanism that directly effects native snail populations. However, more research focusing on M. tuberculatus?s feeding preferences in natural settings would be helpful to determine the exact mechanisms of native snail displacement by M. tuberculatus.

Our study will be useful for future researchers studying or monitoring the native snail species within the Diamond Y Spring preserve. Successful conservation of the native snail population within the preserve will require more basic research on the life histories and ecology of each of the native species. In addition, more research is needed to determine how the invasive Melanoides tuberculatus impacts aquatic communities. Practical benefits from this knowledge will benefit resource managers and planners charged with managing this spring preserve and its unique snail community.