A scientific framework for conservation aquaculture: A case study of oyster restoration in central California

Abstract

The emerging field of conservation aquaculture focuses on the potential for incorporating aquaculture techniques into restoration. Extensive loss of oyster reefs worldwide has led to restoration initiatives that sometimes incorporate aquaculture, but few scientific studies of this approach have been published. We developed a scientific framework to determine whether aquaculture is an appropriate conservation tool, and applied it to Olympia oysters (Ostrea lurida) in Elkhorn Slough, an estuary in central California, USA. Over 12 years of monitoring, we documented precipitous declines in density, highlighting the need for restoration. We tracked settled oysters and found that growth and survivorship is high, showing that hatchery-raised juveniles have the potential to survive to reproductive age. No natural recruitment has occurred in the estuary in seven years, suggesting that this population is recruitment limited. Thus, we determined a need for conservation aquaculture. We produced juvenile oysters from local broodstock in a hatchery and settled them on native clam shells, which we attached to stakes to form small clusters that mimic natural biogenic habitat created by this species. We deployed these near the upper limit of the intertidal range of oysters, where oyster cover dominates over non-native fouling species. The outplanted oysters grew to adult, reproductive size within months of outplanting, and survivorship was generally high, providing the first new generation of oysters in this estuary in seven years. The science-based approach we implemented and our incorporation of traditional restoration principles of natural habitat structure and dominance by native species can serve as a model for conservation aquaculture for oysters and other species.