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Biogeosciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/bg-2017-303
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
06 Sep 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Biogeosciences (BG).
Overcalcified forms of the coccolithophore Emiliania huxleyi in high CO2 waters are not pre-adapted to ocean acidification
Peter von Dassow1,2,3, Francisco Díaz-Rosas1,2, El Mahdi Bendif4, Juan-Diego Gaitán-Espitia5, Daniella Mella-Flores1, Sebastian Rokitta6, Uwe John6, and Rodrigo Torres7,8 1Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
2Instituto Milenio de Oceanografía de Chile
3UMI 3614, Evolutionary Biology and Ecology of Algae, CNRS-UPMC Sorbonne Universités, PUCCh, UACH
4Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, UK
5CSIRO Oceans and Atmosphere, GPO Box 1538, Hobart 7001, TAS, Australia
6Marine Biogeosciences | PhytoChange Alfred Wegener Institute – Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
7Centro de Investigación en Ecosistemas de la Patagonia (CIEP), Coyhaique, Chile
8Centro de Investigación: Dinámica de Ecosistemas marinos de Altas Latitudes (IDEAL), Punta Arenas, Chile
Abstract. Marine multicellular organisms inhabiting waters with natural high fluctuations in pH appear more tolerant to acidification than conspecifics occurring in nearby stable waters, suggesting that environments of fluctuating pH hold genetic reservoirs for adaptation of key groups to ocean acidification (OA). The abundant and cosmopolitan calcifying phytoplankton Emiliania huxleyi exhibits a range of morphotypes with varying degrees of coccolith mineralization. We show that E. huxleyi populations in the naturally acidified upwelling waters of the Eastern South Pacific, where pH drops below 7.8 as is predicted for the global surface ocean by the year 2100, are dominated by exceptionally overcalcified morphotypes whose distal coccolith shield can be almost solid calcite. Shifts in morphotype composition of E. huxleyi populations correlate with changes in carbonate system parameters. We tested if these correlations indicate that the hypercalcified morphotype is adapted to OA. In experimental exposures to present-day vs. future pCO2 (400 µatm vs. 1200 µatm), the overcalcified morphotypes showed the same growth inhibition (−29.1 ± 6.3 %) as moderately calcified morphotypes isolated from non-acidified water (−30.7 ± 8.8 %). Under OA conditions, production rates of particulate organic carbon (POC) increased, while production rates of particulate inorganic carbon (PIC) were maintained or decreased slightly (but not significantly), leading to lowered PIC/POC ratios in all strains. There were no consistent correlations of response intensity with strain origin. OA affected coccolith morphology equally or more strongly in overcalcified strains compared to moderately calcified strains. OA conditions appear not to directly select for exceptionally overcalcified morphotypes over other morphotypes directly, but perhaps indirectly by ecologically correlated factors. More generally, these results suggest that oceanic planktonic microorganisms, despite their rapid turn-over and large population sizes, do not necessarily exhibit adaptations to naturally high CO2 upwellings, and this ubiquitous coccolithophore may be near a limit of its capacity to adapt to ongoing ocean acidification.

Citation: von Dassow, P., Díaz-Rosas, F., Bendif, E. M., Gaitán-Espitia, J.-D., Mella-Flores, D., Rokitta, S., John, U., and Torres, R.: Overcalcified forms of the coccolithophore Emiliania huxleyi in high CO2 waters are not pre-adapted to ocean acidification, Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-303, in review, 2017.
Peter von Dassow et al.
Peter von Dassow et al.
Peter von Dassow et al.

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Short summary
Coccolithophores are microalgae which produce much of the calcium carbonate in the ocean, important to making organic carbon sink to great depths, and they may be negatively affected by the decline in ocean pH as CO2 rises. Can these important microbes adapt? This study found that coccolithophores inhabiting waters naturally low in pH may have already reached the limit of their ability to adapt. This suggests that how the ocean's biota sequester carbon will be strongly affected in the future.
Coccolithophores are microalgae which produce much of the calcium carbonate in the ocean,...
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