Theses and Dissertations

Date of Award

12-2023

Document Type

Dissertation

Degree Name

Ph.D.

Department

Marine Sciences

Committee Chair

Kelly M. Dorgan, Ph.D.

Advisor(s)

Dr. Brian Dzwonkowski, Dr. Davin Wallace, Dr. John Lehrter, Dr. Nils Volkenborn

Abstract

Shallow, river-influenced coastal sediments are important for global carbon storage and nutrient cycling and provide a habitat for diverse communities of invertebrates (infauna). Elevated bed shear stress from extreme storms can resuspend, transport, and deposit sediments, disrupting the cohesive structure of muds, and sorting and depositing sand eroded from beaches. These physical disruptions can also resuspend or smother infauna, decreasing abundances and changing community structure. Infaunal activities such as burrowing, tube construction, and feeding can impact sediment structure and stability. However, little is known about how physical disturbance impacts short and long-term sediment habitat suitability and whether disturbance-tolerant infauna influence sediment restabilization and community recovery. This dissertation investigated how infaunal communities recover following physical disturbance. Temporal changes to the geological and geotechnical structure of muds following manipulated resuspension were assessed in a laboratory experiment. Growth of small-bodied infauna delayed sediment restabilization by increasing erosion and reducing sediment bulk density but increasing cohesion. The remainder of this dissertation investigated short and long-term changes to infaunal community and sediment structure at 5-20 m depths in the northern Gulf of Mexico following Hurricanes Sally and Zeta (2020). A field survey was conducted to assess sediment structure and infaunal community structure before and after the storms. Substantial site-to-site variability in post-storm sediment property changes was consistent with flow interactions driven by local bathymetry leading to sand transport to some sites and near-surface fine sediment loss or little change at other sites. However, despite the variability in hurricane-induced sedimentary changes and persistence of post-storm impacts 8 months after Sally, there were few direct impacts on infaunal abundance, diversity, or community similarity that were consistent with the magnitude of sedimentary change. The lack of direct storm impacts to infauna may have resulted from a combination of pre-Sally disturbances, seasonal infaunal dynamics, and most taxa being tolerant of dynamic river-influenced coastal sediments. Linking infaunal community structure and sediment structure changes over time after extreme storms is important for understanding sediment stability and transport dynamics in frequently disturbed coastal sediments, especially because storm intensity is expected to increase with climate change.

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