Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


The Asian clam, Corbicula fluminea, is one of the most invasive bivalves in the world but there is limited research on its presence in tidal freshwater systems. Despite its introduction into Chesapeake Bay tributaries in the 1970s, the initial colonization and subsequent development of populations of C. fluminea in the Mattaponi and Pamunkey sub-tributaries of the York River, Virginia, is mostly undocumented. This study assessed the spatial distribution and population structure of C. fluminea in tidal freshwater sections of these rivers (~45km) with benthic surveys during summer 2011 – 2012. Benthic grabs (2.4L, 0.023m2) taken at 40 sites in each river were analyzed for clam abundance and size. In addition, relationships between abiotic factors and clam distribution within each river were evaluated using Akaike’s Information Criterion (AIC) to compare a set of generalized linear models. C. fluminea was present at the majority of sites in both rivers during both years, with mean densities (m-2) during 2011 and 2012 of 660 and 410 for Mattaponi River; 1,451 and 834 for Pamunkey River. Populations were dominated by > 90% juvenile clams (< 6mm shell length), which is common for C. fluminea populations during recruitment periods. Both rivers had lower abundance during 2012, suggesting that C. fluminea is actively reproducing but not necessarily accumulating in the system. High juvenile and adult mortality are characteristic of C. fluminea populations. Compared to other invaded systems, C. fluminea in Mattaponi and Pamunkey Rivers is a low-to-moderate level invasion based on clam density. Using AIC analysis, the bestsupported models included factors of distance upriver (km), % sand, depth (m), and year. Distance and % sand showed positive relationships with C. fluminea abundance and had significant parameter estimates in all models (" = 0.05). Spatial analysis in GIS showed 3 that C. fluminea was widely distributed throughout the rivers but achieved higher densities further upriver and in sandier habitats. Despite these trends, Corbicula densities were highly variable, highlighting eurytopic habitat preferences of this species that have led to its successful invasion of tidal freshwater habitats. Populations may also be controlled by the high degree of physical disturbance in tidal freshwater systems and predation by fish and waterfowl.



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