Effects of water movement on the distribution of invasive dreissenid mussels in Lake Simcoe, Ontario

The effects of invasive organisms on an aquatic ecosystem will depend, in part, on the distribution and biomass of the invasive organisms in the system. Here we present the results of a lake-wide survey of the distribution of invasive dreissenid mussels (Dreissena spp.) in Lake Simcoe, Ontario and discuss some of the factors that shape their distribution pattern in the lake. Dreissenid biomass averaged 27.2 g shell-free dry mass (SFDM)/m2 in the main basin of Lake Simcoe and 12.4 g SFDM/m2 in macrophyte-dominated Cook's Bay. We argue that water movement is an important determinant of dreissenid distribution, both through catastrophic disturbance in shallow water and through non-catastrophic effects on substrate distribution and possibly food supply rates. In areas of dense macrophyte growth, mussel abundance was shown to be associated with that of preferred macrophyte taxa, in particular with that of Ceratophyllum demersum. We used the results of our survey and the relationships between environmental variables and dreissenid biomass to estimate the total biomass of dreissenids in Lake Simcoe: 11,897 tonnes SFDM. This study contributes to the understanding of dreissenid ecology and provides a baseline for future studies of dreissenid distribution and impacts in Lake Simcoe.