Graduate Theses and Dissertations (2019 - present)

Date of Award

5-2026

Document Type

Dissertation

Degree Name

Ph.D.

Department

Marine Sciences

Committee Chair

Ron Baker, Ph.D.

Advisor(s)

Havalend Steinmuller, Ph.D., Bret Webb, Ph.D., Sean Powers, Ph.D.

Abstract

Coastal built communities and natural coastal ecosystems face similar and interrelated hazards: shoreline sediment erosion, shoreline retreat, and worsening storms, each of which is exacerbated by relative sea level rise. Living shorelines are coastal defense projects that incorporate natural habitats to provide more sustainable shoreline defense and improve the coastal ecosystem. Living shorelines have been widely adopted, but their performance has been highly variable, and the mechanisms of project success and failure are unclear. The overarching goal of this dissertation was to better understand the ecosystem responses to coastal restoration, focusing on the primary habitats of coastal salt marsh and oyster reefs.

Salt marsh restoration and monitoring frequently involves characterizing marsh vulnerability by tracking interannual movement in marsh shoreline position. There are a variety of approaches to collect marsh shoreline data and estimate movement rates, but to date, there is no clear guidance on what approaches will provide reliable estimates of shoreline movement. Through simulations, I found that source data errors did not affect the precision of shoreline change estimates for marshes monitored with a sufficient number of cross-shore transects (>= 30), and shorelines moving faster than 0. 75 meters per year. Therefore, publicly available imagery will provide suitable data for reliable estimates of marsh shoreline movement for many marsh monitoring applications.

Living shorelines have variable efficacy at addressing ongoing marsh shoreline retreat. I estimated rates of marsh shoreline movement at restored and reference marshes prior to and following restoration to characterize the effectiveness of various projects in coastal Alabama. I found that incident wave energy and breakwater crest elevation were strong predictors of the marsh shoreline movement rates, but there was some evidence for site-specific marsh resilience that complicate this general relationship.

Oyster reefs can provide sustaining shoreline defense and enhance coastal ecosystems, but many living shoreline projects fail to develop sustaining oyster reefs. I investigated the factors that prevent intertidal oyster reef development in coastal Alabama using field experiments. I found that oyster survivorship was maximized at a thin intertidal band close to 50% inundation period, driven by predation in the lower and aerial exposure in the upper. Historic living shoreline breakwaters may have failed to maximize oyster reef development by building structures below the optimal tidal elevation.

In this dissertation, I provide methodology for effective monitoring of coastal marshes and oyster reefs relevant for their restoration. I show how some living shoreline designs may fail to maximize shoreline defense and oyster reef building due to insufficient breakwater crest heights. This research demonstrates the importance of considering local ecology to achieve specific restoration goals.

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