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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-224
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-224
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 26 Jun 2019

Submitted as: research article | 26 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Ocean acidification reduces growth and grazing of Antarctic heterotrophic nanoflagellates

Stacy Deppeler1,2, Kai G. Schulz3, Alyce Hancock1,4,5, Penelope Pascoe6, John McKinlay6, and Andrew Davidson5,6 Stacy Deppeler et al.
  • 1National Institute of Water and Atmospheric Research, Wellington, New Zealand
  • 2Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
  • 3Centre for Coastal Biogeochemistry, Southern Cross University, East Lismore, New South Wales, Australia
  • 4Antarctic Gateway Partnership, Hobart, Tasmania, Australia
  • 5Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tasmania, Australia
  • 6Australian Antarctic Division, Department of the Environment and Energy, Kingston, Tasmania, Australia

Abstract. High-latitude oceans have been identified as particularly vulnerable to ocean acidification if anthropogenic CO2 emissions continue. Marine microbes are an essential part of the marine food web and are a critical link in biogeochemical processes in the ocean, such as the cycling of nutrients and carbon. Despite this, the response of Antarctic marine microbial communities to ocean acidification is poorly understood. We investigated the effect of increasing fCO2 on the growth of heterotrophic nanoflagellates (HNF), nano- and picophytoplankton, and prokaryotes in a natural coastal Antarctic marine microbial community from Prydz Bay, East Antarctica. At CO2 levels ≥ 634 μatm, HNF abundance was reduced, coinciding with significantly increased abundance of picophytoplankton and prokaryotes. This increase in picophytoplankton and prokaryote abundance was likely due to a reduction in top-down control of grazing HNF. Nanophytoplankton abundance was significantly elevated in the 634 and 953 μatm treatments, suggesting that moderate increases in CO2 may stimulate growth. Changes in predator-prey interactions with ocean acidification could have a significant effect on the food web and biogeochemistry in the Southern Ocean. Based on these results, it is likely that the phytoplankton community composition in these waters will shift to communities dominated by prokaryotes, nano- and picophytoplankton. This may intensify organic matter recycling in surface waters, leading to a decline in carbon flux, as well as a reducing the quality and quantity of food available to higher trophic organisms.

Stacy Deppeler et al.
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Stacy Deppeler et al.
Data sets

Environmental data for Davis 14/15 ocean acidification minicosm experiment, Australian Antarctic Data Centre S. L. Deppeler, A. T. Davidson, and K. Schulz https://doi.org/10.4225/15/599a7dfe9470a

Data for manuscript "Ocean acidification reduces growth and grazing of Antarctic heterotrophic nanoflagellates", Australian Antarctic Data Centre S. L. Deppeler, K. G. Schulz, A. Hancock, P. Pascoe, J. Mckinlay, and A. T. Davidson https://doi.org/10.4225/15/5b234e4bb9313

Ocean acidification changes the structure of an Antarctic coastal protistan community, Australian Antarctic Data Centre A. M. Hancock, A. T. Davidson, J. Mckinlay, A. Mcminn, K. Schulz, and D. Van Den Enden https://doi.org/10.4225/15/592b83a5c7506

Stacy Deppeler et al.
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Our study showed how ocean acidification can exert both direct and indirect influences on the interactions among trophic levels within the microbial loop. Microbial grazer abundance was reduced at CO2 concentrations at and above 634 μatm, while microbial communities increased in abundance, likely due to a reduction in being grazed. Such changes in predator-prey interactions with ocean acidification could have significant effects on the food web and biogeochemistry in the Southern Ocean.
Our study showed how ocean acidification can exert both direct and indirect influences on the...
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