The effects of increasing CO2 concentrations (180, 380, and 780 ppm, representing past, present-day, and future atmospheric pCO2, respectively) on marine production, bacterial growth and activity as well as degradation of organic matter was studied during a joint bipartite laboratory experiment (Part I: Production, Part II: Degradation) of BIOACID subprojects 1.2.1, 1.2.2, 1.23 and 1.2.4 in April/May 2010. Here we report on the effect of pCO2 on the turn-over of dissolved organic matter (DOM) and transparent exopolymer particles (TEP) as well as activity rates of extracellular enzymes. The latter play an important role in the turn-over of DOM as they process organic matter degradation as well as nutrient regeneration. Ocean acidification (OA) is expected to affect the enzymatic hydrolysis, resulting in changes of the microbial decomposition of exopolymers. During Part I, growth and total TEP production of Nodularia was significantly enhanced at 780 ppm. TEP production normalized to chlorophyll a was highest at 180 ppm, suggesting that cell growth was more stimulated by CO2 than TEP production. During Part II, degradation of TEP was low in all treatments with highest decline at 780 ppm. Throughout the Part I, aminopeptidase activity increased over time in all CO2 treatments, whereas alpha- and beta-glucosidase activity remained very low. Inorganic phosphate was rapidly depleted in all treatments. Activity rates of extracellular phosphatase were highest at 780ppm, which is confirmed by strongest decline of dissolved organic phosphorus (DOP) in these treatments. No phosphatase activity was measured after removing Nodularia cells in Part II. These results suggest that ocean acidification may increase the rates of organic phosphorus recycling and therewith indirectly support algal growth.