Starvation in the Depths: How Quagga Mussels Persist in the Most Challenging Habitat of the Laurentian Great Lakes

Abstract

The invasive quagga mussel (Dreissena rostriformis bugensis) can significantly alter the biogeochemical cycling of ecologically important nutrients, such as P and N, in lacustrine ecosystems. While D. rostriformis bugensis has invaded large portions of the Great Lakes, its distribution within waterbodies has fluctuated over time. Anticipating the effects of D. rostriformis bugensis on invaded ecosystems requires lake-wide monitoring because the effects of D. rostriformis bugensis are dependent on the size and distribution of mussel populations throughout a waterbody. During the summer of 2018 and 2019, I conducted a benthic survey consisting of ponar grabs and benthic imaging technology (BIS) to assess the distribution, areal density, and areal biomass of D. rostriformis bugensis populations in Lakes Huron and Michigan. I compared the results of my survey to other contemporary surveys of both lakes and found that, recently, D. rostriformis bugensis populations have expanded into deeper regions of Lake Michigan and contracted into more shallow regions of Lake Huron. In addition, ongoing recruitment by juvenile D. rostriformis bugensis has occurred in portions of both lakes that are deeper than other recent reports, which indicates the biomass of these populations will grow in the future. To better understand the ability of quagga mussels to invade profundal habitats and their response to food availability, I investigated the effects of starvation on quagga mussels under laboratory conditions. In an 8-month trial, I compared survival, growth, tissue elemental composition as well as respiration and nutrient transformation rates of starved mussels to mussels fed a high-quality diet. My results indicate that quagga mussels are highly starvation tolerant at temperatures characteristic of the hypolimnia in the Great Lakes, with greater than 95% survival rates after 231 days under starvation conditions. Starved mussels had lower respiration and excretion rates of P and N compared to well-fed mussels. I show that quagga mussels are highly resilient to disruptions in food supply, which helps explain their invasion success in the cold and food-limited profundal zone of the Great Lakes.