Experiments in conservation aquaculture to optimize restoration for Olympia oysters Ostrea lurida in Elkhorn Slough, CA, USA Marine Ecology Progress Series

Foundation species are emerging as a focus in restoration to enhance long-term ecosystem recovery. Conservation aquaculture can support population recovery for depleted and low-density coastal foundation species, including oysters. Long-term restoration success may be constrained by conditions that reduce oyster survival and growth rates during the first months after transferring from the hatchery to the natural habitat. We conducted a series of experiments with aquaculture-raised, juvenile Olympia oysters Ostrea lurida in central California (USA) to inform adaptive management and develop best restoration practices. Oysters were outplanted to 2 tidal elevations. Low-elevation oysters initially had higher growth and survival, but after 1 yr, there was no difference in size or survival between elevations. The effect of age on survival in the estuary was tested by delaying outplanting for groups of oysters from the same cohort. Oysters that spent more time in the hatchery survived better than those outplanted earlier. In a separate experiment comparing 3 age groups outplanted at the same time, older juveniles had markedly higher survival rates than younger groups. Oysters settled on various substrate types had different survival rates. Juveniles on shell substrates generated cluster structures that are more typical in natural habitats. Cages did not inhibit growth and supported higher survival rates than uncaged substrates. This study demonstrates how conservation aquaculture provides an opportunity to conduct restoration experimentally for recovering foundation species.