Cuing oyster recruitment with shell and rock: implications for timing reef restoration

Reducing uncertainty surrounding the biological responses of degraded habitat is key to providing confidence and efficiency in its restoration. Many coastal habitats are so extensively degraded that organismal responses to restoration interventions are entirely unknown. Among the most degraded coastal ecosystems are oyster reefs, whose restoration typically occurs where oysters are degraded to the point of functional extinction. This loss creates uncertainty on the fundamental processes for reef recovery; the timing of oyster recruitment and their preferred substratum for settlement. Such knowledge can inform restoration strategies to accelerate habitat recovery. Near the site of Australia's largest restoration of native oyster reef, we quantified temporal variability in recruitment of the native flat oyster ( Ostrea angasi ) and assessed their preference between the settlement substrata deployed for the reef restoration. Combining half a decade of environmental data with oyster recruitment data, we provide a model that identified distinct peaks in oyster recruitment which correlate with food availability and seawater temperature. In addition, oysters preferentially settled on oyster shell relative to other materials used in local restoration. In combination, these results suggest that there are opportunities to augment recruitment through addition of shell substratum synced with recruitment peaks. Our recruitment model likely represents a minor investment with large returns, providing opportunities to capture peak recruitment and greater confidence in utilizing natural recruitment as a restoration resource.