Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
Oyster shell for native oyster reef restoration is scarce in Chesapeake Bay and other estuaries (Chapter 1). Consequently, alternative substrates merit consideration in oyster restoration. This dissertation examines the suitability of shell alternatives, including granite, concrete, limestone marl, concrete modules and reefballs with reef surveys and experiments in the Rappahannock and Lynnhaven Rivers of Chesapeake Bay. Oyster recruitment, growth, survival, density, biomass, condition, and disease stress, as well as reef accretion and persistence, were measured. In the Lynnhaven River, intertidal riprap had a mean density of 978 oysters m-2 (165 g AFDM m-2) and peak densities > 2000 oysters m-2 (Chapter 2), which are among the highest abundances on alternative reefs, shell or otherwise. Riprap reefs supported a robust population size structure, signifying consistent annual recruitment and reef sustainability. Riprap age (older > younger) and location influenced reef performance; granite and concrete both supported dense oyster-mussel assemblages. In 2005 and 2007, oyster and mussel population structure, density and biomass were quantified on a novel, subtidal concrete modular reef deployed in 2000 in the Rappahannock River (Chapter 3). The reef was not seeded or harvested. Densities (m-2 river bottom) were very high for oysters (2005: 991 m-2; 2007: 2191 m-2) and mussels (2005: 8433 m-2; 2007: 6984 m-2) and comparable to the highest densities on shell reefs. An adjoining 0.44 ha array of concrete reefs (Steamer Rock) was deployed in 1994 and sampled in 2006. These reefs contained > 4 million oysters and > 30 million mussels. Oysters from both reef systems had low disease prevalence and intensity. In a field experiment (Chapter 4), treatments simulating oyster habitat were placed at three intertidal sites in Long Creek of the Lynnhaven River. Granite had highest oyster recruitment and abundance (density > 1500 m-2 and biomass > 200 g AFDM m-2). Many reefs reached a mature state after two years. By Year 3, some reefs had accreted 15-20 L of shell m-2 river bottom, and contained three year classes; some treatments had > 30 % of live oysters growing on other oysters. Large oysters (> 95 mm shell height) had lower intensities of Dermo infection than smaller (60-90 mm) oysters. These patterns indicate that oyster disease tolerance has developed in these high-salinity waters, and highlight the importance of substrate type and reef location in ecological oyster reef restoration. In summer 2006, nine reefs were constructed at two shoreline sites in the Lynnhaven River (Chapter 5), three each of oyster shell (OS), riprap (RR), and concrete modules (CM). Six reefballs were placed at each site, half pre-seeded with hatchery-reared oysters. Finally, in situ setting of triploid oyster larvae on OS, RR and CM reefs was attempted. After 2.5 yrs, all reefs had high oyster density and biomass (unseeded: 150-1200 m -2, 150-600 g AFDM m-2; seeded: 30-1800 oysters m -2), and sustainable accretion rates (8-15 L m-2 yr -1); diploid and triploid oysters had light Dermo infections. Consequently, alternative substrates can serve as effective oyster reefs under diverse conditions in subtidal and intertidal environments of Chesapeake Bay.
© The Author
Burke, Russell Paul, "Alternative substrates as a native oyster (Crassostrea virginica) reef restoration strategy in Chesapeake Bay" (2010). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1539616589.