Master of Science (MS)


Oceanography and Coastal Sciences

Document Type

Access to Thesis Restricted to LSU Campus


Salt marshes in the northern Gulf of Mexico provide critical habitat for many species, including those of economic and ecological interest. However, it remains both a critical and challenging task to quantify the carbon flow from various primary producers to higher trophic levels in such a complex system. Trophic biomarkers, which are measurable tracers of an organism’s diet, are used to study energy flow in food webs. In the first part of this thesis, three trophic biomarker techniques (bulk stable isotope analysis of C and N, compound-specific stable isotope analysis (CSIA) of amino acids, and fatty acid analysis) were compared in the characterization and quantification of different carbon sources that support the salt marsh consumer, the seaside sparrow (Ammodramus maritimus). The results of this study show that, while fatty acids can provide qualitative information about an organism’s carbon sources, only the stable isotope methods can quantitatively estimate them. Further, CSIA provides more precise estimates than bulk SIA. However, all three trophic biomarker techniques indicated that both terrestrial and aquatic carbon was important to the seaside sparrow. In the second part of this thesis, CSIA of amino acids was used to quantify carbon sources for a variety of terrestrial and aquatic salt marsh taxa in order to determine how terrestrial primary production may support aquatic consumers and vice versa in the salt marshes of Barataria Bay, Louisiana. The results of this study indicate that terrestrial and aquatic consumers rely on different carbon source profiles, with plant carbon found almost exclusively in terrestrial taxa and phytoplankton carbon found almost exclusively in aquatic taxa. Carbon from detritus and from benthic microalgae was found in both terrestrial and aquatic consumers, suggesting that these sources provide important links between the terrestrial an aquatic sectors of the marsh food web. Quantifying the carbon source pools of marsh consumers will help constrain models of energy flow which aim to predict how changes in primary production or food web structure will affect populations of interest.



Document Availability at the Time of Submission

Student has submitted appropriate documentation to restrict access to LSU for 365 days after which the document will be released for worldwide access.

Committee Chair

Polito, Michael