Corbin Hite

Biological invasions by non-native species into novel environments can induce ecological changes that negatively impact local communities and ecosystems. Elodea canadensis is a freshwater submerged macrophyte that was introduced to Alaska in 1982. Elodea has been shown to reduce the growth and trophic position of juvenile Coho salmon (Oncorhynchus kisutch) but effects on more pelagic-feeding sockeye salmon (O. nerka) are unknown. In both 2021 and 2022, we investigated potential effects of Elodea on juvenile sockeye salmon by placing full water-column permeable mesocosms in a freshwater lake near Cordova, Alaska, supporting an economically important sockeye salmon population. Across three replicates, one mesocosm was placed over a bed of native vegetation and one over a bed of Elodea. We stocked mesocosms with juvenile sockeye salmon (N=33-40 depending on year) and collected water chemistry samples (water-column nutrients, dissolved organic carbon, chlorophyll-a, and dissolved oxygen) biweekly. After 6 weeks, community members (fish, invertebrates, zooplankton, and macrophytes) were harvested from the mesocosms. We analyzed carbon and nitrogen stable isotopes of the community members to infer resource use pathways between treatments. Elodea did not produce detectable effects on water chemistry likely because of the permeable nature of the mesocosms. However, we observed a shift in the carbon isotope ratios of sockeye salmon towards Elodea isotope signatures. These findings indicate that water chemistry may not be a mechanism by which Elodea induces ecological change in this Alaskan lake, and that Elodea is partially incorporated into sockeye salmon food chains.