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Marine Ecology Progress Series

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MEPS 682:51-64 (2022)  -  DOI:

Ocean acidification reduces the growth of two Southern Ocean phytoplankton

Sarah M. Andrew1,3,*, Robert F. Strzepek2, Oscar Branson1,4, Michael J. Ellwood1

1Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
2Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS 7004, Australia
3Present address: Department of Marine Science, University of North Carolina at Chapel Hill, NC 27514, USA
4Present address: Department of Earth Sciences, University of Cambridge, CB2 1TN, UK
*Corresponding author:

ABSTRACT: Model projections for the Southern Ocean indicate that light, iron (Fe) availability, temperature and carbon dioxide (CO2) will change concurrently in the future. We investigated the physiological responses of Southern Ocean phytoplankton to multiple variables by culturing the haptophyte Phaeocystis antarctica and the diatom Chaetoceros flexuosus under various combinations of light, Fe, temperature and CO2. Using statistical models, the influence of each environmental variable was analysed for each physiological response, ultimately predicting how ‘future’ conditions (high temperature and high CO2) would influence the 2 phytoplankton species. Under future conditions, cellular chlorophyll a and carbon to nitrogen molar ratios were modelled to increase for both species in all light and Fe treatments, but at times were inconsistent with measured values. Measured and modelled values of the photochemical efficiency of photosystem II (Fv/Fm) declined in cultures of P. antarctica due to concurrent increases in temperature and CO2, under all light and Fe treatments. The trends in Fv/Fm for C. flexuosus were less clear. Our model and observations suggest that when temperature and CO2 are concurrently increased, the growth of both species remains largely unchanged. This modelling analysis reveals that high CO2 exerts a strong negative influence on the growth of both phytoplankton, and any ‘future’ increase in growth can be attributed to the positive effect of warming rather than a CO2 fertilisation effect.

KEY WORDS: Iron · Light · Temperature · Photosynthesis · Climate change

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Cite this article as: Andrew SM, Strzepek RF, Branson O, Ellwood MJ (2022) Ocean acidification reduces the growth of two Southern Ocean phytoplankton. Mar Ecol Prog Ser 682:51-64.

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