Acidification increases microbial polysaccharide degradation in the ocean

Abstract. With the accumulation of anthropogenic carbon dioxide (CO₂), a proceeding decline in seawater pH has been induced that is referred to as ocean acidification. The ocean's capacity for CO₂ storage is strongly affected by biological processes, whose feedback potential is difficult to evaluate. The main source of CO₂ in the ocean is the decomposition and subsequent respiration of organic molecules by heterotrophic bacteria. However, very little is known about potential effects of ocean acidification on bacterial degradation activity. This study reveals that the degradation of polysaccharides, a major component of marine organic matter, by bacterial extracellular enzymes was significantly accelerated during experimental simulation of ocean acidification. Results were obtained from pH perturbation experiments, where rates of extracellular α- and β-glucosidase were measured and the loss of neutral and acidic sugars from phytoplankton-derived polysaccharides was determined. Our study suggests that a faster bacterial turnover of polysaccharides at lowered ocean pH has the potential to reduce carbon export and to enhance the respiratory CO₂ production in the future ocean.