Transparent exopolymer particles (TEP) form from dissolved precursors and significantly contribute to the pool of particulate organic carbon in the ocean. In addition, TEP are an important structural component since they provide attachment sites for microbes on a nanometer to micrometer scale. To investigate the effect of ocean acidification on the concentration and dynamics of TEP, we conducted a series of experimental studies in the Baltic Sea in summer 2007 within the frame of the SOPRAN (Surface Ocean PRocesses in the ANthropocene) project. At this time diazotrophs were the main primary producers. Thus, the relation between autotrophic N2-fixation and heterotrophic activity (uptake of radiolabeld Leucine) was determined and compared with TEP concentration measurements to elucidate how production and fate of TEP may be altered due to short term responses to acidification.We observed that the amount of TEP as well as microbiological activities were sensitive to changes in pCO2. Our results indicate a decrease of TEP concentration with increasing pCO2 under net heterotrophic conditions. Furthermore, significant correlations between TEP concentration and bacterial abundance suggest a tight coupling between the dynamics of acidic carbohydrates and bacteria dynamics.Our results imply that ocean acidification could potentially affect microbial carbon turn-over and, hence, organic matter cycling in the ocean.