Article (refereed) -postprint Marine Bacterial Communities Are Resistant to Elevated Carbon Dioxide Levels 1 Running Title: Marine Bacterial Communities and Elevated Co 2 2 3

Marine bacterial communities are resistant to elevated carbon dioxide levels. Environmental Microbiology Reports, 6 (6). The NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. Summary 31 It is well established that the release of anthropogenic derived CO 2 into the atmosphere will be mainly 32 absorbed by the oceans, with a concomitant drop in pH; a process termed ocean acidification. As 33 such, there is considerable interest in how changes in increased CO 2 and lower pH will affect marine 34 biota, such as bacteria, which play central roles in oceanic biogeochemical processes. Set within an 35 ecological framework, we investigated the direct effects of elevated CO 2 , contrasted with ambient 36 conditions, on the resistance and resilience of marine bacterial communities in a replicated temporal 37 seawater mesocosm experiment. The results of the study strongly indicate that marine bacterial 38 communities are highly resistant to the elevated CO 2 and lower pH conditions imposed, as 39 demonstrated from measures of turnover using taxa-time relationships and distance-decay-40 relationships. In addition, no significant differences in community abundance, structure or composition 41 were observed. Our results suggest that there are no direct effects on marine bacterial communities 42 and that the bacterial fraction of microbial plankton holds enough flexibility and evolutionary capacity 43 to withstand predicted future changes from elevated CO 2 and subsequent ocean acidification.