Local adaptation in an estuarine foundation species: Implications for restoration

Understanding the extent of local adaptation is critical for conservation and restoration planning in an era of environmental change. Adaptive differentiation among populations may mediate a species' response to environmental stress, yet these evolutionary processes are seldom studied in marine systems. We used native Olympia oysters (Ostrea lurida) as a model organism for studying local adaptation with applications to marine restoration. We tested whether populations of oysters in California estuaries are locally adapted to their home sites and to stressful low salinity events, which are predicted to increase in frequency with climate change. We spawned oysters from three sites in San Francisco Bay and raised their offspring under common laboratory conditions. These oysters were then reciprocally transplanted among the three field sites. At two of the three sites, oysters of local origin tended to survive better than those from other populations, suggesting that local adaptation may occur even within a single estuary. In a subsequent experiment, we raised oysters from two sites in San Francisco Bay and one site in Tomales Bay through two generations under common conditions and then subjected these oysters to a low salinity challenge in the laboratory. Oysters with the highest survival originated from the site with the lowest field salinity, suggesting that natural selection may favor stress tolerant phenotypes in certain regions. As interest grows in restoring heavily impacted native species, our results indicate that considering local adaptation may be essential to deciding how and where to conserve and restore species faced with changing conditions.