Use of predator cues to bolster oyster resilience for aquaculture and reef restoration

Abstract

Many mollusks alter their shell morphology in response to predator exudates or injured conspecifics to lower their predation risk. However, studies have yet to examine whether this predator-avoidance response can be applied to bolster reef restoration, fisheries enhancement, or aquaculture. We tested whether exposure to predator cues under hatchery conditions can increase the survival of oysters, Crassostrea virginica, planted in the field on the substrate. Juvenile oysters, set on shells and grown in a flow-through system, were exposed to either caged blue crabs, Callinectes sapidus, or controls of empty cages for either four or eight weeks then placed in the field for 30 days. We compared oyster shell strength and morphology as well as oyster survival among predator exposure time treatments. Oysters grown in the hatchery for eight weeks were 46% larger and almost 2× stronger than oysters grown for four weeks. However, predator exposure also caused a 50% increase in shell strength for both time periods. In the field, oysters suffered relatively little mortality when protected from predators using cages, and virtually all mortality was attributed to predation. Predator cue treatments significantly increased the survival probability of uncaged oysters (as would be done in reef restoration or stock enhancement) compared to unexposed treatments. Early cue exposure yielded substantially greater gains in survivorship over time as predator induced oysters nursed for four weeks exhibited 53% higher survival in the field than unexposed oysters while this survivorship gain jumped to 300% for eight weeks of cue exposure. Our findings demonstrate that predator cues can be an effective means for the industry to increase the operational efficiency of aquaculture and restoration efforts, and may potentially be applied to other bivalve fisheries.