Phenotypic plasticity expands oyster survival and realized niche space across tidal elevations

Abstract

The realized niche of many sessile intertidal organisms is constrained by different stressors that set boundaries for their distribution based on tidal elevation. Higher tidal elevation increases desiccation risk but can provide a refuge from predation. Conversely, deeper water increases feeding time and growth but also increases vulnerability to benthic predators. Eastern oysters Crassostrea virginica harden their shells in response to predator cues, which reduces their mortality from predation. We performed a field study to investigate if this defense mechanism could be manipulated to expand their realized niche and increase space for oyster survival and growth. We raised oysters in the presence of predators (blue crabs Callinectes sapidus) or in no-predator controls, measured changes in shell morphology, and then monitored oyster survival at different tidal elevations across 7 locations with different predator and salinity regimes. Oyster survival was significantly higher at the highest tidal elevations tested. Exposure to predators before deployment also significantly increased shell hardness and survival, with intertidal oysters experiencing greater improvement in survival from cue exposure than subtidal oysters. Intertidal placement (>15% exposure time) had larger effects on survival than predator exposure, but predator exposure increased oyster survival at all tidal elevations, suggesting that predator induction could help oysters both deter predators and resist abiotic stressors like desiccation, and perhaps increase the spatial areas where oysters can be restored.