Evaluating the Role of Habitat Complexity in Structuring Seagrass Communities
Biogenic coastal habitats such as salt marshes, seagrasses, and oyster reefs, support diverse faunal communities and can serve as nursery areas by enhancing the abundance, growth, and survival of juvenile fish and crustaceans. The structure and complexity of these biogenic habitats can strongly influence the composition of marine faunal communities and contribute to their roles as nursery areas. It is imperative to understand how nursery areas are defined in the ecological literature as these definitions are applied to nursery area management across the United States. Further, the relative importance of how habitat structural attributes, which are influenced by abiotic and biotic factors, shape faunal communities within these nursery areas is critical to understand these important coastal ecosystems. My dissertation focuses on (1) how nursery frameworks in the ecological literature have evolved and how these frameworks are applied to state management of nursery areas; (2) how abiotic and biotic factors influence the restoration success and complexity of seagrass meadows; and (3) how, in turn, this habitat complexity influences faunal community composition and structure. For my first chapter, I found six overarching frameworks to define and delineate nursery areas in the ecological literature: measures of juvenile abundance and vital rates, habitat characteristics, seascape connectivity, populations fitness and contribution to adult biomass, and persistence. Of the 23 coastal states, only seven explicitly protect nursery areas and of these seven states, the aforementioned frameworks are not equally applied. Gathering and analyzing data necessary to integrate higher-order metrics (e.g., connectivity and biomass contribution) to designate nurseries will require significant research investment and greater collaboration between ecologists and fisheries scientists. My second chapter combines two years of observational seagrass and faunal surveys with a habitat preference experiment to investigate to which degree multiple seagrass complexity metrics influence the composition and abundance of faunal communities in North Carolina seagrass beds. Trawl surveys revealed that taller canopied seagrass beds support higher faunal abundances and species richness than shorter canopied beds, however this was not true across all species. There were species-specific relationships between complexity metrics and abundances, with these relationships shifting between the two years of our study, potentially due to the range of sampling months each year. Pinfish (Lagodon rhomboides), the most common fish found in North Carolina seagrass meadows demonstrated a preference for deep seagrass beds, but only preferred taller canopies when these areas also offered increased blade surface area. In Chapter 3, I conducted field surveys of natural seagrass beds to understand the spatio-temporal distribution and morphology of seagrasses in North Carolina coastal sounds and used these observations to inform a field transplantation experiment of the subtropical seagrass species, Halodule wrightii. Seagrass morphology differed across sampling months but only canopy height differed across depth. Depth was also influential in transplantation success with higher survival of intertidal seagrass transplants compared to subtidal. Considerations of both structural complexity and physical setting of the habitat are therefore imperative for a comprehensive approach in understanding how habitats as well as their faunal communities are responding to future changes across ecosystem settings.
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