Thesis Title

Top-down Control of Algal Biomass: The Role of Snails (Elimia Potosiensis) in the James River Watershed, Missouri

Date of Graduation

Summer 2007


Master of Science in Biology



Committee Chair

John Havel


algal biomass, snail, grazing, top-down, Elimia, eutrophication

Subject Categories



Algal biomass in streams is influenced by a combination of bottom-up (nutrients) and top-down (gazers) effects. The objective of the current study was to investigate the relationship between snails and algal biomass through a survey and an in situ experiment. In Ozark streams, prosobranch snails are important grazers, and perhaps buffer the effects of eutrophication. During summer 2006, I surveyed eight streams in the James River watershed (Southwest Missouri) for snail density, species richness, and algal biomass. My survey showed a significant difference in algal biomass among the streams, with Wilson's Creek having the highest mean chlorophyll-a (172 mg/m²) and James River having the lowest (28 mg/m²). My survey also showed a negative correlation between snail (Elimia potosiensis) and algal biomass. A 1-month enclosure experiment was conducted in Wilson's Creek to test the relationship of snail density (zero, low, high, and ambient) on algal biomass through time. As time progressed, algal biomass decreased in all treatments. Snail density had no statistically discernable effects on algal biomass. The contrasting results from the survey and experiment may be due to high nutrient levels, which stimulate a high replacement rate of algae, and relatively low snail densities in Wilson's Creek.


© Angela Lee Bandy