Though the ocean is expected to become more acidic on average over the next several decades, it is not clear whether climate change will have the same effect on California’s estuaries, since these waterways are highly influenced by local freshwater in-flows and upwelling dynamics. In this project, Tomales Bay will be used as a test bed for studying the relative importance of pH, salinity, plants and mixing on oyster populations. This will be achieved through targeted water sampling of key environments in the bay and through outplanting and resampling of young oysters to document rates of shell calcification, growth and survival. Sampling will be conducted on daily cycles to document the effects of plants on water characteristics and on seasonal cycles to document the effects of the region’s Mediterranean climate. There will also be episodic sampling during major events such as large ocean storms or heavy rains. The data that will be collected during the project will allow scientists to explain whether pH or other factors are more important in explaining patterns observed in the field. Findings will be shared with native oyster restoration groups and local shellfish producers at annual stakeholder meetings to be convened by the researchers, and through outreach materials, to be produced through the cooperative extension program of UC Agriculture and Natural Resources.