Background/Question/Methods Understanding community formation involves grappling with the relative importance of processes that act at different spatial scales. At local scales, species interactions and physiology can influence species inclusion within communities. This interpretation must be tempered with recent research in marine communities showing that regional or meta-ecosystem scale processes such as recruitment, subsidy inputs, and coastal oceanography can explain considerable variation in structure among communities. In this study, we manipulated species interactions of newly settled marine organisms (both algae and invertebrates) across a meta-ecosystem scale to separate local from regional effects on community formation. At 13 sites that span a meta-ecosystem oceanographic scale (450 km from central Oregon to northern California coast), we surveyed communities, quantified recruitment of sessile invertebrates, and quantified oceanographic conditions including temperature, phytoplankton concentration, nutrients and light. Results/Conclusions We found algal-dominated communities at persistent coastal upwelling locations and invertebrate-dominated communities at intermediate intermittent coastal upwelling locations. Experiments involving the manipulation of local interactions between invertebrate and macroalgal assemblages, and their consumers, showed that regional effects of oceanography and recruitment played an overwhelming role at most sites, resulting in either algal or invertebrate domination irrespective of local interactions. However, at some sites, both community types could “coexist” suggesting that local interactions can modify oceanographic influences and thus community formation results from an interplay of processes operating at different spatial scales. This research helps confirm our notion that communities connected at large regional scales vary in their response to both local and regional processes.