PATTERNS IN THE DISTRIBUTION AND ABUNDANCE OF ZEBRA MUSSEL (DREISSENA-POLYMORPHA) IN RIVERS AND LAKES IN RELATION TO SUBSTRATE AND OTHER PHYSICOCHEMICAL FACTORS

Using SCUBA and an in situ method of quantifying substrate characteris tics, we describe patterns of zebra mussel (Dreissena polymorpha) dist ribution along the St. Lawrence and Hudson rivers and in Oneida Lake, New York, and develop empirical models for their abundance. Calcium-po or waters originating from rivers draining the Canadian Shield resulte d in a complete lack of zebra mussel colonization along the north shor e of the St. Lawrence River east of Montreal despite an abundance of s uitable substrate. Calcium concentrations of 1 5 mg/L or less limited the distribution of zebra mussel. The entire south shore from Cornwall , Ontario, to ile d'Orleans, Quebec, was colonized by zebra mussel whe rever suitable substrate was found. Among the three systems, substrate size explained between 38 and 91 % of the variability in density. Oth er factors such as Secchi depth, calcium concentration in the water, t he presence of crayfish, native unionid abundance, and the maximum wid th of the river at the site increased the amount of explained variance across the different systems. A model based on substrate size also su ccessfully explained patterns of zebra mussel abundance from published sources.