Community structure and dynamics in estuarine seagrass systems across habitat configurations, environmental gradients, and spatial scales

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  • Yarnall, Amy H
    • Affiliation: College of Arts and Sciences, Curriculum in Environment and Ecology
Abstract
  • Determining the influence of habitat configuration and scale on faunal communities is a fundamental, yet difficult challenge that underpins landscape, movement, trophic, and conservation ecology. My dissertation examined multi-scale seagrass configuration effects on estuarine community structure and dynamics. I used a literature synthesis and multiple field-experiments to ask the overarching research question: How does habitat fragmentation (i.e., increasing patchiness with or without decreasing area) affect seagrass faunal community structure and predator-prey interactions? I also asked: How do patch-scale edge effects (i.e., ecological differences between patch edges and interiors) and fine-scale complexity influence seagrass communities, and are they underlying drivers of landscape-scale fragmentation effects? To address these questions, I first used quantitative meta-analysis to determine that edge effects help explain faunal responses (e.g., density, predation) within fragmented landscapes, yet variability in responses to landscape-scale configuration prevents edge effects from unilaterally “scaling up” to describe fragmentation effects (Ch 1). Next, I assayed predation rates across natural landscapes, and observed that initially higher blue crab (Callinectes sapidus) mortality in fragmented landscapes was later surpassed by mortality in continuous landscapes amidst increasing temperatures (Ch 2). This "flip" in relative mortality matched spatiotemporal trends in faunal densities indicating that faunal usage of habitat configurations can shift seasonally. To investigate the independent and interactive effects of habitat area and fragmentation per se (i.e., increasing patchiness without area loss), I constructed dozens of artificial landscapes in the field (120-m2 to 234-m2 each), mimicking eelgrass (Zostera marina) with consistent shoot densities. I found that total seagrass area more consistently influences faunal densities than patchiness, consumption rates along edges increased with area, and faunal diversity was elevated in both large-continuous and small-patchy habitats (Ch 3). Further, I found that small and patchy habitats support higher bay scallop (Argopecten irradians) survival and density, respectively (Ch 4). Overall, as natural drivers and anthropogenic disturbances shift seagrass meadows from large-continuous to small-patchy configurations, my dissertation suggests that faunal densities will decrease with meadow area. However, with some seasonal and taxon-specific variability, small and patchy meadows will continue to provide community-stabilizing functions, such as predation refugia and ecological-niche availability, which will maintain biodiversity.
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  • In Copyright - Educational Use Permitted
Advisor
  • Fodrie, Joel
  • Hurlbert, Allen H
  • Rosman, Johanna H
  • Byers, James E
  • Yeager, Lauren A
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2021
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