Date of Award

Summer 8-2021

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Ocean Science and Engineering

Committee Chair

Dr. M. Zachary Darnell

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Dr. Kelly M. Darnell

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Dr. Kevin S. Dillon

Committee Member 3 School

Ocean Science and Engineering

Committee Member 4

Dr. Mark S. Peterson

Committee Member 4 School

Ocean Science and Engineering


Seagrass structural complexity is a primary driver of nekton recruitment and faunal community structure. Few studies, however, have quantified the role of seagrass complexity on habitat use and trophic structures over large spatial scales. A large-scale simultaneous survey was conducted to assess relationships of multiple seagrass morphological complexity metrics to nekton habitat use, trophic dynamics, and blue crab (Callinectes sapidus) growth and mortality across the Northern Gulf of Mexico. Seagrass morphological and nekton community characteristics depended on site and season, and regional variation in seagrass morphology was an important driver of juvenile nekton abundance, species richness, beta diversity, assemblage structure, and functional diversity across the Northern GOM. Results from a stable isotope survey indicate that food web structures across turtle grass (Thalassia testudinum)-dominated ecosystems are similar, although there was a clear trend of more depleted carbon isotopes in primary producers, fish, shrimp, and crabs at sites in the Eastern GOM and more enriched isotopes at sites in the Western GOM, which may be associated with site-specific differences in environmental conditions, such as freshwater inflow and nutrient inputs. Blue crab growth and mortality experiments revealed that growth and mortality rates varied across the six sites, but overall mortality rate declined with increasing seagrass leaf area index and crab size. Blue crab growth rates, however, had no measurable relationship with seagrass complexity metrics. Results from this work indicate that habitat complexity metrics such as shoot density, canopy height, and leaf area index are important factors that define the nursery functions of seagrass habitats and should be incorporated into monitoring programs, conservation initiatives, and fishery models. This study also demonstrates the utility of conducting large-scale comparative studies to reveal regional differences and similarities in trophic structures. Finally, this study highlights the need for additional regional and species-specific studies of environmental drivers of nekton community production throughout the GOM, and our results suggest that models of nekton production in seagrass habitats should be created at regional, as well as local, scales to identify broad patterns but also to account for site-specific differences in nekton responses to environmental and habitat characteristics.