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 characteristics, we describe patterns of zebra mussel (Dreissena polymorpha) distribution along the St. Lawrence and Hudson rivers and in Oneida Lake, New York, and develop empirical models for their abundance. Calcium-poor waters originating from rivers draining the Canadian Shield resulted in a complete lack of zebra mussel colonization along the north shore of the St. Lawrence River east of Montreal despite an abundance of suitable 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 wherever suitable substrate was found. Among the three systems, substrate size explained between 38 and 91 % of the variability in density. Other factors such as Secchi depth, calcium concentration in the water, the presence of crayfish, native unionid abundance, and the maximum width of the river at the site increased the amount of explained variance across the different systems. A model based on substrate size also successfully explained patterns of zebra mussel abundance from published sources.