Date Approved
8-8-2025
Graduate Degree Type
Thesis
Degree Name
Biology (M.S.)
Degree Program
Biology
First Advisor
Matthew Cooper
Second Advisor
Ryan Otter
Third Advisor
Eric Snyder
Academic Year
2024/2025
Abstract
Coastal wetlands of the Great Lakes support abundant populations of fish, invertebrates, and vegetation, though the trophic linkages connecting primary production and lower consumers is not well understood in these systems. We implemented a multiple-tracer approach, pairing traditional food web isotope tracers like carbon (δ13C) and nitrogen (δ15N) with total mercury concentrations (THg). We predicted that filamentous algae would be the dominant energy resource in the diet of lower trophic-level invertebrates in the Grand River Estuary, a network of riverine coastal wetlands adjacent to lake Michigan. In addition, we predicted that adding THg as a tracer would improve the resolution of our food web models. Three basal energy sources were sampled (filamentous algae, emergent macrophytes, submersed macrophytes) along with organic detritus. Aquatic invertebrates were sampled across three functional guilds to represent primary and secondary consumers (amphipods, gastropods, odonates). Our findings suggest that organic detritus is the dominant resource responsible for energetically supporting lower trophic levels in the Grand River estuary, although algae and submersed macrophytes are important secondary resources for primary and secondary consumers, respectively. THg concentrations enhanced the resolution of dietary contribution estimates in MixSIAR models applied to consumer and source data. Isotope biplots revealed that THg concentrations were a more reliable predictor of trophic position than δ15N in GRE sites. This methodology has significant implications for future food web studies in complex ecosystems such as coastal wetlands and demonstrates the novel use of mercury as an ecological tracer.
ScholarWorks Citation
Smith, Alyssa M., "Investigating Food Web Dynamics of Great Lakes Coastal Wetlands Using a Novel Stable Isotope Approach" (2025). Masters Theses. 1167.
https://scholarworks.gvsu.edu/theses/1167
