Zebra and quagga mussels, the invasive dreissenid bivalves, are considered the most aggressive invaders in freshwaters. They have become major drivers of ecosystem processes and one of the primary regulators of phosphorus cycling in the Laurentian Great Lakes since the early 1990s. To predict the ecosystem effects of invasive species and to develop the best management strategies, we need to understand their current and future population dynamics and factors regulating their population growth. For the first time, we combined all lake-wide studies of Dreissena since their initial invasion to the Great Lakes and found that invasion dynamics are largely governed by lake morphometry, or the shape and structure of a lake. Where both species are present, quagga mussels generally become dominant in 8–13 years. Thereafter, zebra mussels remain common in shallow lakes, where lake-wide Dreissena density may stabilize. In contrast, in deep lakes, the invasion of quagga mussels leads to a near-complete displacement of zebra mussels, followed by a dramatic increase in overall dreissenid density.
In shallow lakes and in nearshore zones of deep lakes, dreissenids reach maximum density soon after their initial colonization, then decline. In the intermediate zones of deep lakes (30–50 m), Dreissena densities increase more slowly, peak later, and subsequently decline from their maximum levels to a lesser extent. In the deepest zone (>90 m), quagga mussel density and biomass continue to increase, and the lake-wide population shifts toward deeper areas, revealing a potentially strong offshore carbon and phosphorus sink.
The resulting research paper “Lake morphometry determines Dreissena invasion dynamics” is published online with @SpringerNature in Biological Invasions.
Image caption: A dense patch of dreissenid mussels on the lake bottom in a still image taken from video footage.
