Physiological responses of three temperate coralline algae from contrasting habitats to near-future ocean acidification

Coralline algae are major calcifiers of significant ecological importance in marine habitats but are among the most sensitive calcifying organisms to ocean acidification. The elevated pCO(2) effects were examined in three coralline algal species living in contrasting habitats from intertidal to subtidal zones on the north-western coast of Brittany, France: (i) Corallina elongata, a branched alga found in tidal rock pools, (ii) Lithophyllum incrustans, a crustose coralline alga from the low intertidal zone, and (iii) Lithothamnion corallioides (maerl), a free-living form inhabiting the subtidal zone. Metabolic rates were assessed on specimens grown for one month at varying pCO(2): 380 (current pCO(2)), 550, 750 and 1000 mu atm (elevated pCO(2)). There was no pCO(2) effect on gross production in C. elongata and L. incrustans but L. incrustans respiration strongly increased with elevated pCO(2). L corallioides gross production slightly increased at 1000 mu atm, while respiration remained unaffected. Calcification rates decreased with pCO(2) in L. incrustans (both in the light and dark) and L. corallioides (only in the light), while C. elongata calcification was unaffected. This was consistent with the lower skeletal mMg/Ca ratio of C. elongata (0.17) relative to the two other species (0.20). L. incrustans had a higher occurrence of bleaching that increased with increasing pCO(2). pCO(2) could indirectly impact this coralline species physiology making them more sensitive to other stresses such as diseases or pathogens. These results underlined that the physiological response of coralline algae to near-future ocean acidification is species-specific and that species experiencing naturally strong pH variations were not necessarily more resistant to elevated pCO(2) than species from more stable environment. (C) 2013 Elsevier B.V. All rights reserved.