Addition of juvenile oysters fails to enhance oyster reef development in Pamlico Sound

Oyster reefs are one of the most depleted and degraded marine habitats worldwide. To reverse the current oyster reef declines, governmental and private organizations have invested substantial resources into oyster restoration. Restoration primarily consists of deploying hard substrate. If oyster recruitment is thought to be limited, hatchery-raised juvenile oysters are set on the hard substrate. These costly setting efforts are carried out despite limited information on whether seed oysters accelerate reef development and, if so, how oyster size and time of deployment maximize oyster survival. North Carolina, USA, has established subtidal oyster sanctuaries in Pamlico Sound using marl mounds and hatchery-raised juvenile oysters set on recycled shell. We experimentally manipulated marl mounds at 3 sanctuaries differing abiotically and biotically during summer 2010 and varied recycled shell and seed presence, seed size, and shell and seed deployment date. Although oyster settlement varied spatially, natural recruitment swamped any measurable effect of seeding. Our findings, in combination with information from 3 additional sanctuaries seeded in 2006 and 2008, indicate that seeding does not enhance oyster reef restoration efforts in Pamlico Sound. Financial resources used for oyster seed would be better used to increase the amount of substrate for oyster settlement. Although our results may not apply to areas with less natural oyster recruitment, our study highlights the need to quantify basic ecological processes on appropriate spatiotemporal scales to optimize restoration actions. Analogous information should underlie restoration planning for other biogenic habitats like seagrass meadows and coral reefs.