Ocean acidification may stimulate primary production through increased availability of inorganic carbon in the photic zone, which may in turn change the biogenic flux of dissolved organic carbon (DOC) and the growth potential of heterotrophic bacteria. In order to investigate the effects of ocean acidification on marine bacterial assemblages, a two-by-three factorial mescosom experiment was conducted using surface seawater from the East Greenland Current in Fram Strait. Pyrosequencing of the V1-V2 region of bacterial 16S ribosomal RNA genes was used to investigate differences in the endpoint (Day 9) composition of bacterial assemblages in mineral nutrient-replete mesocosms amended with glucose (0 μM, 5.3 μM and 15.9 μM) under ambient (250 μatm) or acidified (400 μatm) partial pressures of CO2 (pCO2). All mesocosms showed low richness and evenness by Chao1-estimator and Shannon-Wiener diversity index, respectively, with general dominance by Gammaproteobacteria and Flavobacteria. Non-metric multidimensional scaling analysis and two-way analysis of variance of the Jaccard dissimilarity matrix (97% similarity cut-off) demonstrated that the significant community shift between 0 μM to 15.9 μM glucose addition at 250 μatm pCO2 was eliminated at 400 μatm pCO2. These results suggest that the response potential of marine bacteria to DOC input may be altered under acidified conditions.
Ray J. L., Töpper B., An S., Silyakova A., Spindelböck J., Thyrhaug R., DuBow M. S., Thingstad T. F., Sandaa R.-A., in press. Effect of increased pCO2 on bacterial assemblage shifts in response to glucose addition in Fram Strait seawater mesocosms. FEMS Microbiology Ecology. doi: 10.1111/j.1574-6941.2012.01443.x. Article (subscription required).