Western Lake Erie Quagga Mussel growth estimates and evidence of barriers to local population growth

Invasive Quagga Mussels (Dreissena rostriformis bugensis) and Zebra Mussels (D. polymorpha) have been present in the Great Lakes for almost four decades and have caused substantial economic and environmental impacts. Factors that influence dreissenid mussel growth and population dynamics warrant more study, particularly for Quagga Mussels. We conducted a five-month field experiment in western Lake Erie to measure multiple growth metrics for Quagga Mussels at two sites with different conditions using mussels contained in cages on instrumented moorings. We also quantified dreissenid mussels that colonized into the cages and surveyed dreissenid mussels in the sediments at each site. By multiple measures of growth except for one, growth rates were similar between the two sites despite different chlorophyll a and turbidity levels as well as notable differences in the density and size distribution of mussels found in the sediments at these sites. The growth rates were approximately 0.03 mm d-1 for 12-mm Quagga Mussels and these rates declined with increasing initial shell length. Specific growth rate did not differ between shell and tissue measures or between sites, but both shell and tissue specific growth rates were much higher for smaller mussels. Site WE2, which is closer to Maumee River, had very few dreissenid mussels present in the sediments surrounding the mooring despite having a potential for growth comparable to that at WE4. The high level of colonization on the mooring at WE2 indicated that conditions at the sediment surface inhibit mussel settlement; adjacent benthic surveys indicated that very few mussels survive beyond the juvenile stage. Ultimately, the results from this study provide useful mussel growth parameters and indicate substrate or other limitations for dreissenid mussel populations in western Lake Erie.