The Wandering Mussels: Analyzing the Ecological Impact of Dreissenid Mollusks Across Spatial and Temporal Scales in Eastern Ontario Using Environmental DNA
Biological invasions profoundly disrupt aquatic ecosystems, yet predicting their long-term trajectories remains challenging. To address this, I propose the Alien Succession Hypothesis (ASH), a novel theoretical framework conceptualizing biological invasions as a form of ecological succession arrested by continued ecosystem disturbance, and the dynamics of invasive species interactions as phase and density dependent. I apply ASH to investigate the ecological consequences of dreissenid mussel invasions using environmental DNA (eDNA). Temporally, I tracked quantitative dynamics via qPCR and ddPCR on bloom forming cyanobacterial species and toxin producing genes using high-resolution sedimentary eDNA chronologies. Reinforced by spatial and temporal comparisons, these analyses revealed a correlation inversion between cyanobacterial concentrations and toxigenic potential from eutrophication to dreissenid invasion in the Bay of Quinte. During early eutrophication, low herbivory pressure drove a negative correlation between general Microcystis abundance (16S rRNA) and the toxigenic mcyE gene. Following the dreissenid invasion, intense selective grazing exerted high herbivory pressure, shifting this dynamic to a positive correlation toward toxigenic dominance. Expanding from these targeted analyses, my broader sedimentary community sequencing revealed successive failures of native biotic resistance in the Bay of Quinte. Pre-invasion eutrophication depleted obligate aerobic nutrient-cyclers, establishing a deep-anaerobic fermentative network. The subsequent dreissenid invasion circa 1990 catalyzed a compounding meltdown; mussels restructured the benthic microbiome by depleting historical taxa and uniquely enriching complex-polysaccharide fermenters that exploit nutrient-dense biodeposits. Spatially, I mapped the terminal, saturated stage of the hypothesis using Integrated Species Distribution Models (ISDMs) coupled with contemporary eDNA sampling across Eastern Ontario. These models demonstrated a biogeographical landscape with high dreissenid saturation, limited broadly by calcium but driven divergently by bathymetry for zebra mussels and temperature for quagga mussels. They captured spatial segregation between established populations, highlighting the transition into a novel alien consortium. Synthesizing these empirical findings, I suggest the danger of late-stage reactive mitigation and conclude that effective biosecurity demands hyper-sensitive lag-phase detection via next-generation analytical models (JSDMs) and rigorous, decentralized monitoring approaches.
eDNA, sedaDNA, Environmental DNA, Sedimentary DNA, SDM, Niche Modelling, Zebra Mussel, Quagga Mussel, Algal Bloom, Microcystis, Cyanobacterial Algal Bloom, Sediment Microbiome, Bay of Quinte, Eastern Ontario, Metabarcoding, ddPCR, qPCR
Networked Digital Library of Theses and Dissertations