Degree

Doctor of Oceanography and Coastal Sciences (POCS)

Department

Department of Oceanography and Coastal Sciences

Document Type

Dissertation

Abstract

Sediment diversions designed to mitigate land loss in coastal Louisiana will likely cause ecosystem-wide shifts. The first diversion, planned for Barataria Bay, will divert fresh water and sediment from the Mississippi River into the surrounding wetlands to help them keep pace with high rates of relative sea-level rise (RSLR). Estuarine benthic communities were used in this study as tools to characterize ecological patterns in the context of anticipated salinity changes. I reviewed relevant literature, conducted a two-year survey of Barataria Bay benthos, executed a reciprocal transplant experiment to describe changes that might occur in both community composition and trophic dynamics, and tested environmental DNA (eDNA) metabarcoding as a non-invasive method to survey the benthic community. In addition, I compared the estuarine benthic community of Barataria Bay to those found in lagoons (Texas) and a river (New Zealand) across a gradient of flow extreme and with different stochastic/deterministic community structure drivers to construct a theoretical ecological model. Barataria Bay was characterized by functional equivalence of species, and dominance of stochastic processes driving community organization. The reciprocal transplant experiment revealed that benthic communities will restructure quickly and completely according to prevailing salinity. The treatment of a lower salinity decreased species richness, and the treatment of a higher salinity increased both species richness and abundance. Suspended particulate matter (SPM) was overwhelmingly the most important basal resource for consumers, constituting over 80% of the diet of all benthic primary consumers. Under lowered salinity conditions, there was an increase in deposit feeder biomass, a more generalist trophic niche occupied by suspension feeders, and an increase in trophic position of deposit feeders, zoobenthivores, and omnivores. eDNA metabarcoding unveiled a wider array of taxa than coring methods, but it only captured about 10% of the dominant phyla in the Louisiana estuary. Sediment diversions will alter the ecology of this disturbed but resilient estuary, and continued biomonitoring will allow scientists to learn the most from this ecosystem-wide experiment.

Date

4-22-2024

Committee Chair

Glaspie, Cassandra N.

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Available for download on Tuesday, April 22, 2025

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