Oral Presentation Freshwater Sciences 2023

Aquatic food web response to an invasive plant across the Copper River Delta of Alaska, USA (#130)

Amaryllis Adey 1 , Natalie Levesque 1 , Carmella Vizza 2 , Martin Berg 3 , Gordon Reeves 4 , Gary Lamberti 1
  1. Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana, United States
  2. Department of Natural Science, Hawaii Pacific University, Honolulu, Hawaii, United States
  3. Department of Biology, Loyola University Chicago, Chicago, Illinois, United States
  4. USDA Forest Service, Corvallis, Oregon, United States

The Copper River Delta (CRD) of southcentral Alaska (USA) is a remote and relatively pristine ecosystem; however, in 1982, Canadian waterweed Elodea canadensis was documented as the first known aquatic invasive plant to be introduced to the CRD. Elodea canadensis can grow quickly, reproduce vegetatively, and outcompete other aquatic vegetation, thereby creating monocultures in invaded water bodies. To assess whole food web responses to the presence of E. canadensis, we used stable isotopes of carbon and nitrogen of biota from ponds across the CRD. We analyzed niche space and niche overlap of consumers to evaluate the E. canadensis invasion affected the structure of the aquatic food web. We expected that E. canadensis would occupy a similar niche space to other primary producers, and that this might have bottom-up effects on the food web depending on E. canadensis consumption by primary consumers. Stable isotope samples from food web members (primary producers, invertebrates, fish, and waterfowl) were collected from 11 freshwater ponds across the CRD from 2006 to 2013 and again in 2019. We calculated a suite of isotope metrics and used generalized linear mixed effects models to determine which environmental factors had the greatest impact on these metrics. We found that E. canadensis occupied a similar isotopic niche space to native vegetation but had limited impacts on higher trophic levels. These results indicate that the vegetation of the CRD may be at risk of increased competition from and exclusion by E. canadensis from these freshwater pond habitats, but that threats to consumers within these systems may be limited. This study provides initial insights into the potential impacts of E. canadensis, but further exploration of bottom-up effects will further our understanding of these community responses.