Date Awarded

2023

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Virginia Institute of Marine Science

Advisor

Rochelle D Seitz

Committee Member

Romuald N Lipcius

Committee Member

Mark W Luckenbach

Committee Member

Lisa Kellogg

Abstract

Restoration of eastern oyster (Crassostrea virginica) reefs in the Chesapeake Bay and its tributaries is important, as oyster reefs provide habitat for temperate estuarine communities and shoreline protection. Oysters that settle in crevices, such as those found on natural shell substrates, suffer low mortality, but natural shell is becoming a limited resource in the Chesapeake Bay. Finding an alternative settlement substrate that is complex like natural shell and mimics the benefits of shell substrates with less expense could be the best way to encourage oyster recruitment and survival. The two main goals of this experiment were to (1) understand which artificial substrate type (granite stone, oyster castle, diamond, c-dome, and x-reef) promotes the highest oyster recruitment and survival compared to natural shell and (2) determine the effects of reef presence on macrofaunal community structure and productivity. It was hypothesized that a new settlement substrate, oyster diamonds, given the sloping surfaces with large surface area, will be best for oyster recruitment. Additionally, it was hypothesized that oyster reef presence will substantially enhance macrofaunal community abundance and increase macrofaunal productivity compared to unstructured sediment. To address these goals, infaunal macrofauna and sediment samples were taken at three experimental sites and two control sites along the York River in June 2021. Then, two replicates of each of six reef types were deployed in a randomized block design at each of three experimental sites. The reef types included loose oyster shell, granite, oyster castles, oyster diamonds, c-domes, and x-reefs. The fall after deployment, the structures were sampled for oyster density and shell height. One year after deployment, the structures were physically sampled, removing oysters to determine oyster density and biomass, and the macrofaunal community associated with the reefs. Control sites were sampled for benthic infauna and sediment analyses. Oyster densities and biomass were extremely high and were highest on the loose shell reef (9,852 oysters/m2 and 743 g AFDW/m2 based on model estimates), and the x-reefs had the second-highest recruitment and biomass (3,816 oysters/m2 and 531 g AFDW/m2 based on model estimates). Prior to deployment of reefs, control and impact sites had similar density, biomass, and diversity of macrofauna, but one year after reef deployment, the reef impact sites had higher densities, richness, diversity, biomass, and secondary productivity of macrofaunal organisms than the control sites with the impact sites having 145 times greater secondary productivity than the controls. The diversity among reef types did not vary but the granite reefs had the highest secondary productivity overall. All reef structures showed successful oyster and macrofaunal community recruitment based on Chesapeake Bay Fisheries Goal Implementation Team metrics and densities were among the highest for alternative substrates. Based on the results of this study, researchers and managers could choose from a variety of successful alternative reef types. Based on restoration goals, the use of different reef types could lead to differences in the achievement of goals.

DOI

https://dx.doi.org/10.25773/v5-gayz-s420

Rights

© The Author

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