Dreissena in large lakes: long-term population dynamics and population assessment using conventional methods and videography

Strong ecological and economic impacts of zebra and quagga mussels (Dreissena polymorpha and D. rostriformis bugensis) on the invaded waterbodies require timely and reliable estimates of their population densities. However, samples collected with conventional methods take years for processing. In this study, we analyzed video recorded using a Benthic Imaging System to assess quagga mussels distribution and density in near-real time (during a typical 2 week cruise aboard EPA research vessel Lake Guardian) in Lake Michigan in 2021 and in Lake Huron in 2022 and compared that data with the Ponar grab samples collected at the same sites. We found that videography could be a reliable and useful addition for dreissenid monitoring, especially on hard substrates where bottom grabs are not efficient. Analysis of dreissenid dynamics since the late 1990s revealed a strong increase in mussel density in the shallowest polymictic zones of both lakes, suggesting local boom and bust dynamics. In the deepest zone of Lake Michigan there was a further increase in quagga mussel density coincided with the ninefold decline in Diporeia density. Declines in Diporeia were also recorded in the main basin and in Georgian Bay of Lake Huron.