Restoration of the native eastern oyster (Crassostrea virginica) has been severely hindered by the dwindling supply and rising costs of fossil and new oyster shell for use in reef restoration. Consequently, emphasis has shifted to the use of alternative oyster reef materials, which need to be tested for their effectiveness as settlement substrate. Furthermore, low recruitment of wild larvae has also impeded restoration, indicating a need to assess the potential of field setting of cultured larvae. We experimentally examined oyster settlement, growth and survival on unconsolidated oyster shell, oyster shell embedded vertically in concrete, and concrete Oyster Castles® in field and mesocosm experiments. In addition, we examined settlement success of cultured larvae in the mesocosm experiment. In the field experiment, juvenile recruitment was 3x higher on castles and unconsolidated shell than on embedded shell. Castles retained 4x the number of oysters and hosted 5x the biomass than embedded shell, and retained 1.5x the oysters and hosted 3x the biomass than unconsolidated shell. The proportion of live oyster recruits on castles was 1.5x that on both embedded and unconsolidated shell. In the mesocosm experiment (90-d post-larval deployment), the castles recruited, retained, and hosted an oyster biomass 4x higher than that of unconsolidated and embedded shell. This study confirms that artificial reef materials such as Oyster Castles® are suitable alternative substrates for oyster restoration, and remote setting of larvae onto conditioned substrate can be effective under controlled environmental conditions. Future restoration efforts should consider use of alternative reef substrates and field setting of larvae to maximize oyster recruitment, while simultaneously minimizing the cost of reef restoration.
The potential effects of pre-settlement processes on post-settlement growth and survival of juvenile northern rock sole (Lepidopsetta polyxystra) in Gulf of Alaska nursery habitats
