Date of Award

2012

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Earth and Environmental Sciences

First Advisor

Aaron T Fisk

Rights

CC-BY-NC-ND 4.0

Abstract

Understanding how communities and species assemblages persist is among the most fundamental objectives in ecology, particularly as human modifications to the landscape increase. Through application of traditional community metrics with emerging biochemical tracers in combination with community/food web ecology theory, I provide an evaluation of the effects of anthropogenically-altered freshwater flow disturbance on estuarine nekton community structure and trophic interactions. These two parameters are central toward understanding the functioning of aquatic communities and ensuring their persistence. This dissertation provides data regarding the effects of human-altered freshwater flow on estuarine nekton communities in tidal rivers and, in doing so, has fostered valuable findings regarding the application of stable isotopes to estuarine fishes and large vertebrates. Specifically, this research demonstrates that losses of estuarine nekton community biodiversity (Chapter 2), the shift in resource availability to lower trophic level species (Chapter 5), and changes to energy flow pathways leading to higher trophic level consumers (Chapter 6), are all associated with high flow events. This dissertation further demonstrates that the application of stable isotopes requires consideration of a species life history characteristics, as interpretation of a species diet and trophic roles can be complex (Chapters 3 and 4). Collectively, these findings suggest that high flow events affect the structure and trophic interactions of estuarine nekton communities and provide a greater understanding of the impacts of such anthropogenic-mediated stressors on these complex ecosystems. Whether altered high-flow disturbance events result in adverse or beneficial effects on the persistence of estuaries remains to be established. However, in order to maintain and/or restore the integrity of an ecosystem requires that conservation and management actions be firmly grounded in scientific understanding. This becomes especially relevant as worldwide changes to hydrologic connectivity continue with increasing anthropogenic pressures. This research demonstrates the potential for the simplification of food webs and changes to dominant trophic assemblages that are associated with flow alteration. For the commercially, recreationally and ecologically valuable species that define estuarine nekton communities, these observations emphasize the necessity of research and management programs aimed at maintaining the integrity of these highly-valued ecosystems.

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