Joy McCullough

Major Professor

The quagga mussel, Dreissena rostriformis bugensis, is an invasive species that is spreading rapidly throughout the Colorado River Aqueduct (CRA) and the reservoirs of southern California. Currently, the upstream CRA reservoirs have well-established quagga populations, while downstream reservoirs are in an earlier colonization stage. Because quagga mussels filter out phytoplankton and possibly also dissolved organic carbon directly from the water column, high densities of quagga mussels affect aquatic ecosystems through changes in zooplankton population and composition, nutrient cycling and aquatic food web dynamics. We will evaluate changes in the trophic structure of four CRA reservoirs by characterizing the stable isotope composition of the pelagic food web. This approach is based upon the fact that consumers take on the carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope composition of their diet. The mussels may significantly alter phytoplankton and zooplankton levels in lakes, changing the prey available to planktivorous fish, thereby changing the stable isotope composition of the food web. We hypothesize that the isotope distributions in the pelagic food webs will vary along the invasion gradient. Improved understanding of the ecology of quagga mussels and their impacts on the food web will help us identify ecological impacts, as well as vulnerabilities in their life cycle, and aid in the development of management strategies.