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Front. Plant Sci. | doi: 10.3389/fpls.2018.01416

Arctic coralline algae elevate surface pH and carbonate in the dark

  • 1Max Planck Institute for Marine Microbiology (MPG), Germany
  • 2Department of Geographical and Earth Sciences, University of Glasgow, United Kingdom
  • 3Department of Botany, National University of Ireland Galway, Ireland

Red coralline algae are projected to be sensitive to ocean acidification, particularly in polar oceans. As important ecosystem engineers, their potential sensitivity has broad implications, and understanding their carbon acquisition mechanisms is necessary for making reliable predictions. Therefore we investigated the localized carbonate chemistry at the surface of Arctic coralline algae using microsensors. We report for the first time carbonate ion concentration and pH measurements ([CO32-]) at and above the algal surface in the microenvironment. We show that surface pH and [CO32-] are higher than the bulk seawater in the light, and even after hours of darkness. We further show that three species of Arctic coralline algae have efficient carbon concentrating mechanisms including direct bicarbonate uptake and indirect bicarbonate use via a carbonic anhydrase enzyme. Our results suggest that Arctic corallines have strong biological control over their surface chemistry, where active calcification occurs, and that net dissolution in the dark does not occur. We suggest that the elevated pH and [CO32-] in the dark could be explained by a high rate of light independent carbon fixation that reduces respiratory CO2 release. This mechanism could provide a potential adaptation to ocean acidification in Arctic coralline algae, which has important implications for future Arctic marine ecosystems.

Keywords: calcification, carbon concentrating mechanism, Carbonate chemistry, light independent carbon fixation, microenvironment, microsensor, Rhodolith

Received: 09 Feb 2018; Accepted: 06 Sep 2018.

Edited by:

Benoit Schoefs, University of Maine, France

Reviewed by:

Jonas Collén, Université Pierre et Marie Curie, France
Christopher E. Cornwall, Victoria University of Wellington, New Zealand
Fanny Noisette, Institute for Marine and Antarctic Studies (IMAS), Australia  

Copyright: © 2018 Hofmann, Schoenrock and De Beer. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Laurie C. Hofmann, Max Planck Institute for Marine Microbiology (MPG), Bremen, Germany, laurie.c.hofmann@awi.de