Successful eastern oyster (Crassostrea virginica) recruitment on intertidal artificial substrates in Virginia, USA

Declines of eastern oyster (Crassostrea virginica) populations and scarcity of natural oyster shell necessitate quantifying the effectiveness of artificial oyster reef substrates over varying environmental conditions. Oyster castles are often used in intertidal areas with moderate wave energy; however, new concrete, natural-looking substrates, GROW Reef Tiles, are now available. Eastern oyster recruitment and size on oyster castles (OC) and GROW Reef Tiles (GT), with 27% higher surface area on OC, were assessed three times over 25 months in locations with varying salinity. Four sites in the Chesapeake Bay region were examined: Cherrystone Inlet, Mockhorn Bay, Elizabeth River, and Lynnhaven Bay. At each site, 10 OC and 10 GT were randomly placed parallel to shore in the low-intertidal zone in May 2019. Sites were sampled non-destructively in October 2019, July 2020, and June 2021. A quadrat (0.30 m × 0.30 m) was placed on top of the structure, and one of four quadrants was randomly chosen to count and measure oysters for shell height and mortality status. Data from each year and combined data (2019–2021) were analyzed using the response variables oyster density and shell height along with combinations of year, site, and substrate type. Both substrate types had high oyster recruitment (>400 oysters m⁻²). At 25 months post-deployment, mean oyster densities differed significantly by substrate, with 553.3 oysters m⁻² on OC and 423.0 oysters m⁻² on GT (24% higher on OC). Oyster densities differed by site, with highest densities in Mockhorn Bay. Growth was ~60–70 mm over the 25 months, and oysters were smallest at the highest-salinity and highest-density site. Mean oyster shell height was greater on GT (61.7 ± 2.2 mm) than on OC (57.3 ± 2.1). Both substrates had high oyster recruitment (well above the Chesapeake Bay success metric: 50 oysters m⁻²), large oysters, and developed multiple cohorts, suggesting that both substrates could be used effectively for restoration. Given that GT is a natural-looking substrate, it may be preferable for nearshore restoration. This is important particularly for management agencies concerned with both appearance and functionality in large-scale restoration projects.