Marine bacteria thrive when the ocean acidifies

Extracellular enzymes process organic matter degradation as well as nutrient regeneration and hence play an important role in the turnover of dissolved organic matter (DOM). Ocean acidification is expected to affect enzymatic hydrolysis, resulting in changes in microbial decomposition of organic matter.The effects of increasing CO2 concentrations on the natural planktonic community, bacterial exopolymer degradation, and particle export were studied during a joint SOPRAN/BIOACID mesocosm experiment in the Raunefjord in southern Norway. Here, we report on the effect of pCO2 on production of transparent exopolymer particles (TEP) and exo-enzymatic degradation. Nine 25m-long Kiel Off-Shore Mesocosms for Future Ocean Simulations (KOSMOS) were adjusted to different pCO2 levels ranging from ca. 280 to 3000 μatm by stepwise addition of CO2 saturated seawater. After CO2 addition, samples were taken every second day for 34 days. The first phytoplankton bloom developed around day 5. On day 14, inorganic nutrients (5 μmol L-1 nitrate and 0.1 μmol L-1 phosphate) were added to the enclosed, nutrient-poor waters to stimulate a second phytoplankton bloom, which occurred around day 20. We determined bacterial cell counts, rates of extracellular enzyme activities using fluorescent-labelled substrate analogues, as well as concentration and composition of organic matter. We observed increasing bacterial cell numbers and TEP concentrations over time with highest increase in the high pCO2 treatments. Preliminary results show higher extracellular enzyme activities at higher CO2 concentrations. Positive effects of ocean acidification on the bacterial community and especially on extracellular enzymes may potentially increase bacterial degradation activity and consequently the release of CO2 to the atmosphere in the future ocean