ANTHROPOGENIC IMPACT ON FRESHWATER BIVALVE GROWTH IN NORTHERN NEW YORK AND THE ADIRONDACK PARK

Bivalves are important ecosystem engineers in freshwater communities, but there has been a dramatic decline in freshwater bivalves throughout North America making them one of the most endangered organisms in the United States. Their close relationship to the environment makes these semi-infaunal filter-feeders good proxies for changes in their habitat. One common freshwater bivalve in the northeastern US is the unionid Elliptio complanata. Here, we use this taxon to examine the impact of anthropogenic activities on these vulnerable organisms. We hypothesis that stressors such as agricultural runoff and fine sediment input as well as other sources of contamination associated with shoreline development should negatively impact the bivalve communities in these areas resulting in overall smaller body size and slower growth.

Samples were collected from lakes in northern New York and the Adirondacks Park that have various degrees of exposure to environmental stressors. For every locality, ten individuals were selected and thin sections from the umbo to the posterior-ventral margin were cut capturing the complete live history of the individual. Growth rings were measured and von Bertalanffy growth curves were calculated. The degree of anthropogenic influence on a sampling location was quantified using ArcGIS raster analysis of land use surrounding the sampling area.

Preliminary data shows that bivalves from Black Lake, a relatively developed lake, reach an average maximum shell size of 55.4mm. The more pristine environments of Horse Shoe Lake and Mountain View Lake is home to larger individuals with an average maximum size of 61.2mm and 75.3mm respectively. Valves from Black Lake and Horse Shoe Lake reach 36% of their maximum shell growth in the first year of their ontogeny. The samples from Mountain View Lake grow slower reaching 23% of their maximum shell growth during the same growth interval. In later stages of shell development, growth slows down notably more in Black Lake and Horse Shoe Lake than in Mountain View Lake.

These preliminary results suggest that the bivalves from lakes which have greater anthropogenic pressures are smaller in maximum shell size and grow slower in the later stages of ontogeny than the bivalves which live in an environment further away from anthropogenic influences.