Assessing the Role of Invasive Asian Clams (Corbicula Fluminea) in Native Mussel Declines

We propose to evaluate the potential for food competition between native mussels and Corbicula in a research project with three components, described as follows. 1. We will build on our previous research on juvenile mussel growth in streams and the relationship of growth to ambient water chemistry and other factors. Briefly, this approach involves measuring growth of juvenile mussels during 3-month field deployments in silos, and measuring water chemistry during the exposures. Similar to most mussel research in the past, this research did not consider potential effects of Corbicula. We will extend this work by estimating Corbicula abundance and biomass at study sites in conjunction with measurements of juvenile mussel growth and water chemistry factors related to food availability (e.g., total organic carbon). Study sites will encompass a range of stream types in Kentucky representing different river drainages and physiography (e.g., Green, Kentucky, Licking, Cumberland; Appalachian Plateaus, Bluegrass, Highland Rim). 2. We will directly assess the potential for competitive effects of Corbicula in laboratory experiments. These experiments will involve measuring juvenile mussel growth in response to manipulation of Corbicula abundance and food availability. In addition to measuring growth, we will assess biochemical markers of nutritional status including glycogen, pyruvate, and metabolomics markers. This component also will evaluate differences in growth responses among species including species that remain widespread (e.g., Lampsilis cardium) and those that have declined across their range. Study species will be identified later based on availability and feasibility of existing culture methods. 3. We will build a bioenergetics model with which to assess the potential effect of food competition with Corbicula on juvenile mussel growth. This model will incorporate stream productivity and abundance of Corbicula to allow contextual, case-by-case evaluation of the potential for competition. This model will be based in large part on the information gleaned from components 1 and 2. Additional required information such as filtering and clearance rates of native mussels and Corbicula, and phytoplankton growth rates and turnover time, will be obtained from the literature or separate laboratory experiments as necessary. These three components will interrelate to provide a much clearer picture of the potential for competition with Corbicula than currently exists. Evaluating this factor is important to mussel conservation for at least two reasons. First, knowledge of causes of mussel declines is vital to avoid wasting scarce resources on conservation strategies that may not address the underlying causes of declines. Identification of Corbicula as a cause of mussel declines will provide the impetus for addressing this problem. Conversely, a lack of evidence for effects of Corbicula will provide support increased focus on other factors and conservation strategies. Second, Corbicula abundance varies widely over time and is often highest in the early phases of colonization. Declines in Corbicula abundance in some streams may mean that they now are capable of supporting native mussels, but remaining populations are too small to rebound quickly; these streams could be identified using our model and would be excellent candidates for restoration via captive propagation.