Dreissenidae in Lake Ontario: Impact assessment at the whole lake and bay of Quinte spatial scales

The total abundance in Lake Ontario of Dreissena polymorpha (Dreissenidae), the zebra mussel, and D. bugensis (Dreissenidae), the quagga mussel, was calculated by aggregating data front several surveys carried out in 1991 to 94. In 1993, there were between 3.0 x 10 and 8.7 x 10(12) Dreissenidae mussels in Lake Ontario. A filtration model was contructed using depth-specific density estimates, a digital bathymetric map of the lake, and literature estimates of clearance rates for individual mussels. With reasonable estimates of both densities and filtration rates, the mean, area-weighted, turnover time of Lake Ontario water by dreissenid mussels was about I year. At the smaller spatial scale of the Bay of Quinte, the same model estimated turnover times of 0.05 0.2, and 10 days for the lower middle, and tipper areas of the bay, respectively. Depth-specific secondary production estimates for dreissenids, combined with literature estimates of net primary production and energy transfer efficiencies, were incorporated into a food demand model that indicated about 1.25 gC/y mussel of food in Lake Ontario and a consumption efficiency of 50%. At the smaller spatial scale of the Bay of Quinte, the same model estimated one to two orders of magnitude less food per mussel and 62%, 130% and 115% consumption efficiency for the lower, middle and upper areas of the bay, respectively. Dreissenidae mussels may not have a huge impact on the Lake Ontario food web when considered at a whole-lake scale, but their potentially striking impact at the smaller spatial scale of embayments like the Bay of Quinte indicate that they may be locally important. When these effects are aggregated across several sub-systems Dreissenidae mussels may have unpredictable, larger scale effects in the Lake Ontario ecosystem as a whole.