Document Type



Doctor of Philosophy (PhD)



First Advisor's Name

Michael Heithaus

First Advisor's Committee Title

Committee chair

Second Advisor's Name

William Anderson

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Heather Bracken-Grissom

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Kevin Boswell

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Maureen Donnelly

Fifth Advisor's Committee Title

Committee member


trophic ecology, deep-sea, stable isotope, elasmobranch, teleost, scavenger, food web, Gulf of Mexico

Date of Defense



The deep-sea is the largest habitat on earth, containing over 90 percent of the world’s oceans and home to over 20,000 species. Deep-sea ecosystems are increasingly impacted by human activities including fishing and oil extraction. To understand potential impacts on deep-sea food webs, it is crucial to gather baseline data in these systems. I quantified the trophic interactions of three groups of deep-water animals across a range of trophic levels living in the northern and eastern Gulf of Mexico using stable isotope analysis. First, I propose methods for correcting δ15N values for the presence of nitrogenous metabolic waste products (e.g., urea) in muscle tissue using chemical extractions and/or species-specific mathematical normalizations. Significant differences in δ15N, %N, and C:N values as a result of extractions were observed in eight of ten shark and all three hagfish species. The δ15N values increased, but shifts in %N and C:N values were not unidirectional. Mathematical normalizations for δ15N values were successfully created for four shark and two hagfish species. I then describe the trophic interactions of three consumer assemblages. Carbon isotopic values indicate a heavy reliance on allochthonous nutrient inputs from surface waters. Nitrogen isotopic values reveal somewhat atypical taxa as top predators in the deep sea. Shark, teleost, and invertebrate species across a wide range of body sizes are feeding at a similar trophic level. This apparent lack of size structuring could be the result of a high degree of opportunistic scavenging or perhaps feeding at many trophic levels simultaneously in an oligotrophic system. There was a high degree of isotopic niche overlap among species within each consumer assemblage, perhaps the result of limited nutrient resources in the deep-sea. In general, individuals from the northern sampling stations displayed higher δ13C and δ15N values than those from the eastern sites. With the exception of a few species, there were no strong relationships between body size and isotopic values. The present study is among the first characterizations of the trophic structure of deep-sea organisms in the Gulf of Mexico and establishes system baselines for future studies describing deep-water systems and investigating anthropogenic impacts.





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