Semester of Graduation

Spring 2021

Degree

Master of Science (MS)

Department

Entomology

Document Type

Thesis

Abstract

Marshes in Louisiana are under threat from numerous natural and anthropogenic sources. A consequence of these threats are sheared marsh margins, which result from the impact of storm surge on previously oiled, weakened marsh. These conditions occurred in Louisiana marshes after Hurricane Isaac in 2012 followed the Deepwater Horizon oil spill in 2010, particularly in the shorelines surrounding Bay Jimmy. The second and third chapters of this thesis focus on the differences in biodiversity between the sheared and intact marsh margins in impacted sites in Bay Jimmy. Metabarcoding methods were used to determine community composition of the sediment within marsh margins to test the hypothesis that the sheared and intact margins contained different communities. In the second chapter, DNA was extracted directly from sediments, while in the third chapter, the organic portion of the sediment was extracted before DNA extraction to focus on meiofauna. Meiofauna are near-microscopic animals which are a key component of marsh health. There was a significant difference in community composition between the sheared and intact margin samples in both chapters, but the commonly detected taxa were shared between both types of margin, leaving rare unique taxa in each margin type. An advanced rate of marsh loss has been reported for Louisiana estuaries primarily due to the construction of flood control structures. Freshwater diversions of the Mississippi have been proposed to combat marsh loss by delivering sediment into marshes. However, the potential significance of changes in the salinity regime on commercially important salt marshes are unknown. The final chapter of this thesis describes a survey of meiofauna present in fresh, brackish, and salt marsh zones within Caillou and Barataria Bays in Louisiana to create an inventory of taxa which could be used as baseline for changes in salinity. Metabarcoding methods were used to determine community composition within samples from these sites. The communities from the freshwater and salt marshes separated distinctly while the brackish marsh community overlapped both of the other zones. The results suggest that the communities detected in the freshwater and salt marsh samples are potentially useful as indicators for detecting salinity regime changes.

Committee Chair

Lane Foil

DOI

10.31390/gradschool_theses.5287

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