Using bacterial extracellular enzymes to assess whether natural CO2 vents are robust analogues of the future ocean

Chair: Ulf Riebesell

Law, C. S. (1,2), Burrell, T.J. (3), Sander, S.G. (2), Maas, E.W. (1)
1 National Institute of Water and Atmospheric Research Ltd, Greta Point, Kilbirnie, Wellington, 6002, New Zealand.
2 Department of Chemistry, University of Otago, Dunedin, New Zealand
3 Victoria University of Wellington, School of Biological Sciences, Wellington, New Zealand

Background
Recent research indicates that bacterial extracellular activity is sensitive to ocean acidification with potential implications for the cycling and fate of organic matter. Natural CO 2 vent systems represent potential analogues of the future high CO2 ocean, and so offer a complimentary approach to small-scale perturbation experiments for examining potential future ecosystem impacts of ocean acidification.

Methods
We assessed the potential of CO2 vents in the Bay of Plenty (North Island, New Zealand), by comparing bacteria composition, productivity and extracellular enzyme activity over the vents with upstream control water and also control water adjusted to the same pH as the vent water. This allowed us to determine whether elevated CO2 was the primary driver of change in bacteria community, aminopeptidase and glucosidase activity, or whether other factors in vent water influenced the response.

Findings
Both the vent and acidified control water exhibited higher potential bulk and cell-specific glucosidase activity relative to control water; however, vent water glucosidase activity was double that of the acidified water, as was bacterial production in one experiment. There were also significant differences in bacterial community composition in the vent water after 84 hours incubation, including the presence of extremophiles.

Conclusions
The results suggest that pH was not the only factor influencing bacterial processes in water overlying the CO2 vent. This highlights the importance of characterizing vent water biogeochemical and microbial composition to confirm that natural CO2 vents are robust analogues for the future acidified ocean.