Principal component analysis, correlation, and multiple regression were used to evaluate the relationships of 12 environmental variables to the recorded values of density and biomass of Corbicula fluminea (Asian clam) collected in a 13-km segment of the lower Roanoke River delta, NC, in 1992–1993. Sediment fractions, pH, conductivity, and oxygen saturation accounted for the most variance in density, and, with the addition of shell length, water temperature, and river kilometer, accounted for the most variance in biomass. Similar variables were important in principal component analysis and multiple regression, although regression was less useful due to lower tissue weights of clams at two stations, which resulted in low predictive power for some regressions. The results of this preliminary census indicate that there were relationships among Asian clam density and biomass and various environmental factors. Higher density and biomass were found where the substrate was > 40% fine sand, < 45% silt, and < 8% organic content. This habitat type was limited in the study area and resulted in the majority of Asian clams living in a 4-km segment. Seasonal extremes in water temperature, low pH and calcium concentration, and phytoplankton limitations may also have contributed to the low weight of Asian clams in the Roanoke River. A more extensive sampling effort is warranted to further define the role of environmental stressors in the Asian clam population.
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