Benthic flow environments affect recruitment of Crassostrea virginica larvae to an intertidal oyster reef

Restoration efforts to enhance Crassostrea virginica oyster populations along the Virginia, USA, coastline focus on creating benthic habitat suitable for larval recruitment, survival, and growth. To determine how benthic flow processes affect larval recruitment, velocity and turbulence we collected data over multiple intertidal benthic surfaces including a mud bed, a C. virginica oyster reef, and 2 restoration sites comprised of deposited C. virginica oyster shell or the relatively larger Busycotypus canaliculatus whelk shell. Mean estimates of the drag coefficient, CD, used as a measure of hydrodynamic roughness over the C. virginica reef were found to be 2 times greater than over the restoration sites and 5 times greater than over the mud bed. Enhanced fluid shear increased both peak Reynolds stresses and vertical momentum transport above the reef, but within the interstitial areas between individual oysters, velocities and turbulence were reduced. Larval settlement plates of varying triangular-shaped benthic roughness were used to mimic the natural topographic variability found along oyster reefs. The greatest larval recruitment occurred along interstitial regions between high-roughness topography, where shear stresses, which act to dislodge larvae, were found to be up to 20 times smaller than along exposed surfaces. Greater recruitment was also found on the more hydrodynamically rough whelk shell compared to the oyster shell restoration site. Results suggests that restoration efforts should consider creating 3-dimensional benthic topography similar to established oyster reefs to provide hydrodynamic conditions and settlement surfaces that promote larval recruitment, prevent burial by sediment, and provide refuge from predation.