Degree

Doctor of Philosophy (PhD)

Department

Renewable Natural Resources

Document Type

Dissertation

Abstract

Identifying distributions of submerged aquatic vegetation (SAV) across the northern Gulf of Mexico (NGOM) coastal landscape necessitates describing ecological processes in estuarine gradients. SAV assemblages are ecological indicators of aquatic ecosystem health; spatial and temporal distributions are strongly correlated to environmental conditions. Many wildlife species, including waterfowl, are dependent on SAV and seeds in NGOM coastal marshes for food and habitat. To understand SAV distributions at multiple spatial and temporal scales a multi-tiered project was designed to collect SAV presence, species assemblage, and cover data, and cores to describe seed food. The first tier sampled inter-annually in the growing seasons 2013-2015 from Mobile Bay, Alabama to San Antonio Bay, Texas. The second tier sampled seasonally, every 6-8 weeks in 2015, in Barataria Basin, Louisiana. These data were used to characterize SAV distributions and to drive a spatial species distribution model (SDM) in coastal Louisiana.

Across the NGOM landscape, SAV presence, percent cover, species assemblages, and seed resources varied across marsh zones and regions. There was no temporal effect at this spatial scale. The patterns of food seed and SAV distributions were almost entirely driven by regionally specific patterns in environmental conditions (i.e., salinity and depth). The SDM linked SAV occurrence to environmental conditions and identified winter mean salinity, turbidity, and exposure as significant predictors for SAV occurrence. Increases in these parameters were evident in saline marsh zones, which had a low likelihood of SAV occurrence. The seasonal study in Barataria Basin showed a significant interaction between SAV and invasive water hyacinth, as water hyacinth increased in cover during the summer season, SAV cover declined. Results indicate that SAV presence, cover, and species assemblages are seasonally mediated and spatially differentiated by environmental conditions in estuaries. These ecological patterns in turn affect the availability of potential food resources across estuarine gradients. Understanding region and estuary-specific gradients over time and space defines the fundamental and realized ecological niche space for SAV assemblages. The identification of this space illustrates how ecological patterns may influence associated species within the community, and provides a benchmark to assess future changes in these critical habitats.

Date

6-4-2018

Committee Chair

La Peyre, Megan

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