Semester of Graduation

Summer 2023

Degree

Master of Science (MS)

Department

Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Southeastern Louisiana’s coastal wetlands are important habitat for aquatic species, yet the spatial heterogeneity in habitat types and abundance of many basal energy sources makes it challenging to elucidate patterns of energy flow across the landscape mosaic. This ecosystem is experiencing substantial changes, both through anthropogenically-accelerated climate change and anthropogenic landscape modifications. Therefore, the overall goal of this thesis was to trace patterns of energy flow across coastal wetland landscapes to determine which basal energy pathways support aquatic food webs and if patterns of energy pathway dependence are altered by changes to the landscape. In the first part of this thesis, the efficacy of two stable isotope analysis (SIA) techniques (bulk-tissue SIA and compound-specific SIA of amino acids; CSIA-AA) was compared in assessing the effect of black mangrove (Avicennia germinans) expansion on the basal energy pathways supporting two marsh resident species with different foraging strategies. The results of this study showed that foraging strategy dictated trophic responses to black mangrove expansion; the nektonic grazer depended on algal energy pathways regardless of macrophyte dominance, while the epibenthic deposit-feeder shifted from terrestrial plant reliance to algal reliance with a transition from marsh to mangrove habitat. Additionally, CSIA-AA improved basal energy source distinctions and provided more constrained estimates of energy source contributions to wetland consumers than bulk-tissue SIA. In the second part of this thesis, bulk-tissue SIA was used to identify the patterns of food web connectivity across a brackish marsh landscape and determine if marsh creation reestablishes trophic linkages between nekton communities. The results of this study showed that nekton communities were highly linked across sub-habitats and that trophic relay does occur, as evidenced by consistent terrestrial energy pathway contributions across the landscape. Additionally, marsh creation generally restored food web connectivity. Understanding coastal wetland food web dynamics will help with planning and evaluating the most effective coastal restoration techniques (e.g., prioritizing marsh or mangrove habitat, knowing which marsh creation practices are effective in reestablishing food web structure) in southeastern Louisiana.

Date

6-28-2023

Committee Chair

Polito, Michael J.

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