Date Awarded

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Romauld N Lipcius

Committee Member

Rochelle D Seitz

Committee Member

Jian Shen

Committee Member

Kevin C Weng

Committee Member

Raymond Grizzle

Abstract

Native oyster populations have largely collapsed worldwide, with extensive losses of habitat and ecological function. Efforts to restore oysters have been initiated in Europe, Australia, China and North America. In 2004, the first large-scale oyster restoration project was constructed in Chesapeake Bay, employing novel methods including increasing reef height to mimic pre-exploitation reefs, enlarged reef area to address spatial scale, and augmenting recruitment. High-relief reefs (HRR) were built from 25-40 cm in height to better mimic pre-exploitation reefs, while low-relief reefs (LRR) were built at 6-8 cm off existing bottom, mimicking repletion methods by state fishery management agencies used for almost a century. Results documented in 2009 for the HRR were very promising but questions remained regarding longevity of these reefs, as no restoration construction at the time showed evidence of long-term persistence nor gain in function, declining significantly within five years post-construction. We document here the ongoing high performance and long-term persistence of this restored oyster reef network, located in the Great Wicomico River, Virginia. Chapter 1 is an introduction to the topic. Chapter 2 is a thorough description and analysis of the history of the oyster fishery in Virginia from colonial times to the present. To properly restore oysters, an understanding of what happened to them and their habitat since European colonization was deemed necessary to avoid the mistake of shifting the baseline. Such a shift would lead to a lowering of standards, necessary research, and development of restoration methods such that restoration failure would likely continue. Chapter 3 assesses the efficiency of the fishing gear, an oyster patent tong, to measure the number of oysters precisely and accurately in a given sample. As it is our chosen gear for monitoring throughout the study period, it was essential to ensure the monitoring gear chosen was sufficient to produce reliable results. Chapter 4 investigated the recruitment signal in the Great Wicomico River, compared it to pre-construction data and determined that the recruitment signal in the river was enhanced, beginning several years post-construction of the sanctuary reefs. The assessment also provided information that suggests the stock-recruitment signal for oysters is strongly influenced by regional weather patterns, with drought conditions significantly enhancing the recruitment signal, even when stock levels are too low to see any distinct pattern between stock and recruitment. Chapter 5 documents the results of all monitoring data from 2006-2019 and, due to this, also serves as my ending discussion. Oyster densities, biomass and shell volume were examined. Results suggest the restored reef network has successfully transitioned to a self-sustaining reef system, with high density and biomass/m2 on the HRR, along with a positive shell budget. LRR lags far behind regarding density and biomass/m2 and does not demonstrate a positive shell budget over time. The HRR is also demonstrating a positive rate of reef height gain relative to local sea level rise. Overall, our data suggest that native oyster restoration can be successful, though novel methods were required to do so.

DOI

https://dx.doi.org/10.25773/v5-w2xn-vj16

Rights

© The Author

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