In contrast to phytoplankton, ocean acidification's (OA's) effects on bacterioplankton are poorly understood. Microcosm experiments to assess bacterioplankton's response to organic matter obtained under current and future CO₂ levels were performed. An analysis of bacterial abundance, production, respiration, viability and changes in DOM concentration showed that OA affects bacterial metabolism through changes in the organic matter more than directly affecting future CO₂ concentration.