The Asian Clam Corbicula fluminea: Seasonal Filtration Rates of Representative Populations in Two Tributaries of the Delaware River

The Asian clam, Corbicula fluminea, is an exotic freshwater bivalve that was first introduced to the United States in the early 1930s. Populations of C. fluminea have rapidly spread over the country due to its high reproductive output and short life cycle. Due to its numerical abundance and filter-feeding behavior, C. fluminea has the potential to impact water quality through a reduction of turbidity as well as possibly removing particulate pollutants such as nutrients. In the Delaware River system, where C. fluminea was first documented over 40 years ago, Asian clams have assumed a dominant position in the benthic community of many streams, often representing a majority of benthic faunal biomass. Despite its potential to alter stream ecology, there have been few studies regarding the clam’s feeding behavior on natural seston diets and seasonal changes in population demographics and feeding processes. Seasonal changes in natural seston quantity and quality, physiological rates including clearance rates of C. fluminea, and Asian clam size and population density were contrasted between two representative tributaries of the Delaware River basin: the Cooper River, NJ, and Red Clay Creek, DE. Data from seston analyses, physiology studies, and population surveys were coupled to estimate the importance of clam-mediated particle filtration in removing suspended matter flowing through each study stream. Seston quantity and quality were greater in the Cooper River than in Red Clay Creek during all seasons. Clearance rates (units = water volume processed) were seasonally consistent for Asian clams in the Cooper River but showed a seasonal drop for clams in Red Clay Creek. Clams from the Cooper River had greater seasonal filtration rates (units = mass of seston removed) and were larger on average than clams from Red Clay Creek. Due to greater seston quantity and quality, Asian clams in the Cooper River were able to feed during three seasons and were more likely to successfully overwinter compared to clams in Red Clay Creek, where clams appeared to be food limited. Population densities were less than 100 clams / m2 in Cooper River and Red Clay Creek and demonstrated seasonal variability. Populations of Asian clams in both streams were found to be reproductive. Asian clams in the Cooper River were estimated to remove a greater amount of suspended particulate matter in the water column than clams in Red Clay Creek. Particle removal services of Asian clams were estimated to be 5.4 and 0.4 metric tons of total suspended solids per kilometer per year in Cooper River and Red Clay Creek, respectively. Although sizeable, this represented only 1.6 and 0.13 % of the total seston flowing through each reach, averaged over the year. Additional research on population densities of clams in other reaches of both streams would support extrapolation of particle removal services to entire streams to determine the full ecosystem service potential of C. fluminea.M.S., Environmental Science -- Drexel University, 201