Models to Predict Potential Occurrence and Density of the Zebra Mussel, Dreissena polymorpha

Limnological features of different lakes may limit the density of, or even completely restrict, populations of the European zebra mussel, Dreissena polymorpha. We developed statistical models to predict the occurrence (presence or absence) and density (number per square metre) of Dreissena in lakes, based on multivariate correlations between the density of Dreissena populations and the limnological characteristics of the lakes they inhabit. We found that both occurrence and average density of Dreissena populations were highly correlated with water chemistry. Dreissena was not found in lakes with average pH values below 7.3 and concentrations of calcium ion below 28.3 mgŽL. Above these thresholds, Dreissena density was negatively related to concentration of the algal nutrients PO4 and NO3.