Exploring Multi-scale Variation of Fish Community Diversity in a Dynamic Coastal Estuary

Examining diversity over multiple spatial and temporal scales affords the opportunity to develop a mechanistic understanding of the factors influencing community diversity dynamics, and how these may shift in a changing world. This thesis first examines multi-decadal fish community diversity metrics across a coastal biogeographic transition zone to quantify changes in species assemblages, assess relationships between fish community diversity and the abiotic environment, and capture potential shifts in the location of a putative biogeographic break. Results of this chapter indicate not only a change in fish community composition, but also a shift in the location of the biogeographic transition zone. If these trends continue, a potential 16-62km shift northward by the year 2100 could occur. Understanding the novel species assemblages these shifts could result in is necessary for the future management of this area. Next this thesis examines diversity on a local scale, assessing the response of the fish community to restoration of oyster reefs and coastal wetlands which act as essential fish habitat. Results support the idea that fish community composition at restored oyster reefs is more similar to those of live reefs than dead reefs, however, results of abundance and diversity analyses were equivocal. Living shoreline analyses produced no differences between control and restored sites before or after restoration. Possible explanations for lack of clear trends in the fish community could be explained by the presence of other essential fish habitats in the area, scale of restoration, and length of monitoring. This thesis explores diversity on a multitude of spatial and temporal scales to better understand how fish communities respond to change and generates fundamental knowledge that can improve our ability to conserve and manage coastal communities and better inform the development of ecosystem-based management strategies