Scared strong: using predator cues to bolster shellfish restoration

Oysters, Crassostrea virginica , are economically and ecologically valuable but have severely declined, and restoration is needed. As with the restoration and aquaculture of many shellfish species, restored oyster reefs are often impeded by predation losses, reducing restoration success and restricting locations where restored reefs are viable. Like many organisms, shellfish can modify their morphology to reduce predation risk by detecting and responding to chemical signals emanating from predators and injured prey. Oysters grow heavier, stronger shells in response to predation risk cues, which improves their survival. We tested if using predator cues to trigger shell hardening in oysters could be performed over a scale suitable for oyster reef restoration and improve oyster survival long‐term. We constructed an intertidal oyster reef using oysters grown in a nursery for 4 weeks while exposed to either exudates from Blue crab ( Callinectes sapidus ) predators or grown in controls without predator cues. Oysters grown with predators were 65% harder than those grown in controls, and after 1 year in the field, had a 60% increase in survival. Predation losses on the restored reef were significant, and the benefit of predator induction for survival was highest at intermediate tidal elevations, presumably due to intermediate levels of predation and abiotic stress. Our results suggest that manipulating the morphology of cultivated or restored species can be an effective tool to improve survival in habitats where consumers impede restoration success.