In the western U.S., the native Olympia oyster is a focal species for restoration and has been an important foundation species providing key ecosystem functions including increased benthic diversity. Among the threats to native oyster restoration are non-native predatory whelks that can decimate oyster populations. In central California, oysters have high survival where native crabs keep whelk populations in check as part of a well described trophic cascade. However, climate change has the potential to decouple predator-prey interactions with negative consequences for native oyster restoration. Current theory suggests that mobile predators may be more sensitive to climate change, due to metabolic constraints, whereas sessile prey may show greater tolerance of stressful conditions. We investigated this idea using field surveys and experimental mesocosm studies to examine two questions: 1) how will projected change in climate variables impact predation by non-native whelks on native Olympia oysters, and 2) how will these results influence the prospects for native oyster restoration in California bays. We used survey data of oyster populations linked with detailed measurements of environmental variables at several California locations. We also quantified the effects of climate change variables including temperature and salinity on both non-native whelk predators and native Olympia oysters in experimental mesocosms.
Results/Conclusions
Our field surveys showed that the most important stressors for native oysters in addition to whelk predation were low salinity, high air temperatures, and low dissolved oxygen. Other stressors were less important including competition with fouling species, sedimentation, contaminants, pathogens and disease, sea level rise and estuarine acidification. Experimental mesocosms results found that invasive whelks had a lower thermal optima and lower salinity tolerance than the native oysters. However, our results showed that warming in the near future will be within levels of thermal tolerance, thus warmer temperatures will exacerbate predatory impacts. We also found that impacts of low salinity events will depend on the magnitude and duration, which will vary among sites. We conclude that bays in which non-native whelks are abundant, which include bays lacking large salinity events that can also wipe out oysters, may be lower priority for native oyster restoration under climate change. This work also highlights the importance of linking physiological responses of predatory and prey with long-term environmental data in order to more accurately predict the impacts of climate change.