Semester of Graduation

Spring 2024

Degree

Master of Oceanography and Coastal Sciences (SOCS)

Department

Department of Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Benthic communities are vitally important for healthy aquatic ecosystems across Louisiana’s coast. Specifically in Lake Borgne, ecologically important species of fish like the Gulf Sturgeon (Acipenser oxyrinchus desotoi) rely on benthic macrofauna as their main food source. The purpose of this study was to determine the spatial landscape of biodiversity and abundance of the benthic macrofauna community in Lake Borgne. Environmental conditions played a key role in community structure during the study period (fall 2021 through summer 2023) with a major drought occurring in 2023. In 2023, the decline in the abundance of most benthic invertebrates and in benthic diversity as compared to pre-drought conditions showed the sensitivity of benthic macrofaunal communities to drought conditions in Lake Borgne. The relationship between the benthic community and environmental variables (temperature, salinity and sediment grain size) was examined for the pre-drought conditions that existed in 2022. In that year, the dominant clam Rangia cuneata was largely associated with low-temperature regions of Lake Borgne, while the common gastropods and Littoridinops palustris and Neverita sp. were associated with low salinity and coarser sediment. Dredging operations intended to supply sediment for marsh creation projects also occurred between the sampling periods. The foreknowledge of the dredging project allowed for an additional study looking at anthropogenic effects on the benthic macrofaunal community in Lake Borgne. A Before-After, Control-Impact (BACI) designed experiment revealed that a signature of dredging impact existed for R. cuneata abundance and overall species richness. This indicates that immediately after dredging in Lake Borgne, the biomass dominant species R. cuneata will likely be negatively impacted. This may result in consequences for species that feed on benthic organisms, such as Gulf sturgeon, and should be a consideration for future dredge site selection and environmental impact assessments. Ultimately more years of post-dredge monitoring are necessary to understand the long-term impacts on the benthic community.

Date

4-5-2024

Committee Chair

Glaspie, Cassandra

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