Mechanisms driving Antarctic microbial community responses to ocean acidification: a network modelling approach
Rising atmospheric CO2 concentrations and the subsequent changes to ocean chemistry may have pronounced effects on marine microbial communities, particularly for the cold Southern Ocean. Changes to the microbial community in this region could affect the way nutrients are cycled, impact the efficiency of carbon drawdown, and cause shifts in food supply to higher trophic levels. Increased CO2 could affect the bioavailability of iron to phytoplankton. Fertilisation experiments show that iron can influence phytoplankton community composition, favouring large phytoplankton species in iron-replete conditions. The potential interactive effects of CO2 and iron bioavailability are currently poorly understood but are likely to be important in determining CO2-induced changes to the microbial community. We employ a qualitative network modelling approach to evaluate alternative hypotheses regarding the effects of elevated CO2 on Antarctic microbial communities in incubation experiments. We used a sequential approach to model development and testing, where we first formulated a base model for microbial community interactions, and then sequentially added direct and indirect effects of elevated CO2 on particular groups. We found that model simulations were most consistent with observations from incubation experiments when we assumed an indirect effect of CO2 on phytoplankton. In particular, when we assumed a negative effect of elevated CO2 on the uptake of iron by large phytoplankton, as a result of a decrease in iron bioavailability. Our findings show that qualitative network models can be used to test hypotheses relating to results from experimental studies, and help identify key processes to target in future studies.
KeywordsModel CO2 Iron Antarctic microbial community
The authors would like to thank the two anonymous reviewers for providing valuable comments and suggestions. This study was supported by the Australian Government’s Cooperative Research Centres Programme through the Antarctic Climate and Ecosystems Cooperative Research Centre.
- Boyd PW, Watson AJ, Law CS, Abraham ER, Trull T, Murdoch R, Bakker DCE, Bowie AR, Buesseler KO, Chang H, Charette M, Croot P, Downing K, Frew R, Gall M, Hadfield M, Hall J, Harvey M, Jameson G, LaRoche J, Liddicoat M, Ling R, Maldonado MT, McKay RM, Nodder S, Pickmere S, Pridmore R, Rintoul S, Safi K, Sutton P, Strzepek R, Tanneberger K, Turner S, Waite A, Zeldis J (2000) A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization. Nature 407:695–702. doi: 10.1038/35037500 CrossRefPubMedGoogle Scholar
- Davidson AT, McKinlay J, Westwood K, Thompson PG, van den Enden R, de Salas M, Wright S, Johnson R, Berry K (2016) Enhanced CO2 concentrations change the structure of Antarctic marine microbial communities. Mar Ecol Prog Ser. doi: 10.3354/meps11742
- IPCC (2014) Climate change 2014. Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core writing team Pachauri R.K, Meyer L.A. (eds)]. IPCC, Geneva, Switzerland, p 151Google Scholar
- Laws RM (1985) The Ecology of the Southern Ocean: The Antarctic ecosystem, based on krill, appears to be moving toward a new balance of species in its recovery from the inroads of whaling. Am Sci 73:26-40. http://www.jstor.org/stable/27853059
- Midorikawa T, Inoue HY, Ishii M, Sasano D, Kosugi N, Hashida G, S-i Nakaoka, Suzuki T (2012) Decreasing pH trend estimated from 35-year time series of carbonate parameters in the Pacific sector of the Southern Ocean in summer. Deep-Sea Res Part I 61:131–139. doi: 10.1016/j.dsr.2011.12.003 CrossRefGoogle Scholar
- Orr JC, Fabry VJ, Aumont O, Bopp L, Doney SC, Feely RA, Gnanadesikan A, Gruber N, Ishida A, Joos F, Key RM, Lindsay K, Maier-Reimer E, Matear R, Monfray P, Mouchet A, Najjar RG, Plattner G-K, Rodgers KB, Sabine CL, Sarmiento JL, Schlitzer R, Slater RD, Totterdell IJ, Weirig M-F, Yamanaka Y, Yool A (2005) Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437:681–686. doi: 10.1038/nature04095 CrossRefPubMedGoogle Scholar
- Schulz KG, Bellerby R, Brussaard CP, Büdenbender J, Czerny J, Engel A, Fischer M, Koch-Klavsen S, Krug SA, Lischka S (2013) Temporal biomass dynamics of an Arctic plankton bloom in response to increasing levels of atmospheric carbon dioxide. Biogeosciences 10:161–180. doi: 10.5194/bg-10-161-2013 CrossRefGoogle Scholar