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Carbon-use strategies in macroalgea: differential responses to lowered pH and implications for ocean acidification

journal contribution
posted on 2023-05-18, 00:49 authored by Cornwall, CE, Hepburn, CD, Pritchard, D, Currie, KI, McGraw, CM, Hunter, KA, Catriona HurdCatriona Hurd
Ocean acidification (OA) is a reduction in oceanic pH due to increased absorption of anthropogenically produced CO2. This change alters the seawater concentrations of inorganic carbon species that are utilized by macroalgae for photosynthesis and calcification: CO2 and HCO3 increase; CO32– decreases. Two common methods of experimentally reducing seawater pH differentially alter other aspects of carbonate chemistry: the addition of CO2 gas mimics changes predicted due to OA, while the addition of HCl results in a comparatively lower [HCO3]. We measured the short-term photosynthetic responses of five macroalgal species with various carbon-use strategies in one of three seawater pH treatments: pH 7.5 lowered by bubbling CO2 gas, pH 7.5 lowered by HCl, and ambient pH 7.9. There was no difference in photosynthetic rates between the CO2, HCl, or pH 7.9 treatments for any of the species examined. However, the ability of macroalgae to raise the pH of the surrounding seawater through carbon uptake was greatest in the pH 7.5 treatments. Modeling of pH change due to carbon assimilation indicated that macroalgal species that could utilize HCO3 increased their use of CO2 in the pH 7.5 treatments compared to pH 7.9 treatments. Species only capable of using CO2 did so exclusively in all treatments. Although CO2 is not likely to be limiting for photosynthesis for the macroalgal species examined, the diffusive uptake of CO2 is less energetically expensive than active HCO3- uptake, and so HCO3--using macroalgae may benefit in future seawater with elevated CO2. Key index words: bicarbonate; carbon acquisition; carbon dioxide; climate change; dissolved inorganic carbon; HCl; macroalgae; ocean acidification; pH drift; photosynthesis Abbreviations: AT, total alkalinity; CCM, carbonconcentrating mechanism; DIC, dissolved inorganic carbon; OA, ocean acidification; PFD, photon flux density; PQ, photosynthetic quotient; PS, photosynthesis


Publication title

Journal of Phycology








Institute for Marine and Antarctic Studies


Blackwell Publishing Inc

Place of publication

350 Main St, Malden, USA, Ma, 02148

Rights statement

Copyright 2011 Phycological Society of America

Repository Status

  • Restricted

Socio-economic Objectives

Ecosystem adaptation to climate change

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    University Of Tasmania