Applicability of Littoral Food-web Biomanipulation for Lake Management Purposes: Snails, Macrophytes, and Water Transparency in Northeast Ohio Shallow Lakes

Abstract

Seven shallow-to-intermediate-depth, meso-eutrophic lakes in northeast Ohio were surveyed July-August 1998 to evaluate a macrophyte-based littoral food-web (and its possible manipulation) role in increasing or maintaining water transparency. Macrophyte and periphyton growth were determined from pre-weighed C. demersum sprigs and biomass developed on glass tiles, respectively; littoral snail densities were estimated from assemblages in large-mesh cages at 1-m depth. Other variables were monitored weekly in situ. Lakes were generally phosphorus (P)-limited, but differed significantly in perceived state (turbid, stable or unstable clear-water), water transparency (SD), total phosphorus (TP) and chlorophyll a concentration (chla), vegetation cover (VC), snail density, sprig growth and periphyton biomass. The most richly vegetated lake was also the most stable (seasonally and long-term) clear-water lake, but midsummer SD was more strongly correlated with watershed:lake surface area. C. demersum growth was negatively correlated with periphyton biomass; meristem production was lower in turbid lakes, but was influenced by TP. Snail abundance tended to follow food (periphyton) and substrate (VC) availability, but was lower in crayfish-present lakes. Correlations between lake-describing variables were nonlinear with frequent outliers. When integrated with information from the literature, the results suggest that littoral food-web biomanipulation may be employed as a management technique in some cases. More often, macrophytes and the macrophyte-driven, snail-mediated clear-water stable state may (re)establish naturally in suitable lakes after conditions are brought above a “threshold” for plant growth. Frequent exceptions in observed patterns in this study and elsewhere suggest that applicability of littoral food-web biomanipulation should be evaluated on a case-by-case basis.