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The effect of carbonate chemistry on calcification and photosynthesis in the hermatypic coral Acropora eurystoma
Author(s) -
Schneider Kenneth,
Erez Jonathan
Publication year - 2006
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2006.51.3.1284
Subject(s) - hermatypic coral , seawater , ocean acidification , photosynthesis , carbonate , coral , chemistry , stylophora pistillata , zooxanthellae , calcification , alkalinity , carbon dioxide , total inorganic carbon , environmental chemistry , oceanography , biology , geology , symbiosis , biochemistry , paleontology , bacteria , medicine , organic chemistry , pathology
The rise in atmospheric CO 2 has caused significant decrease in sea surface pH and carbonate ion (CO 3 ‐2 ) concentration. This decrease has a negative effect on calcification in hermatypic corals and other calcifying organisms. We report the results of three laboratory experiments designed specifically to separate the effects of the different carbonate chemistry parameters (pH, CO 3 ‐2 , CO 2 [aq], total alkalinity [AT], and total inorganic carbon [CT]) on the calcification, photosynthesis, and respiration of the hermatypic coral Acropora eurystoma. The carbonate system was varied to change pH (7.9‐8.5), without changing CT; CT was changed keeping the pH constant, and CT was changed keeping the pCO 2 constant. In all of these experiments, calcification (both light and dark) was positively correlated with CO 3 ‐2 concentration, suggesting that the corals are not sensitive to pH or CT but to the CO 3 ‐2 concentration. A decrease of ~30% in the CO 3 ‐2 concentration (which is equivalent to a decrease of about 0.2 pH units in seawater) caused a calcification decrease of about 50%. These results suggest that calcification in today's ocean (pCO 2 = 370 ppm) is lower by ~20% compared with preindustrial time (pCO 2 = 280 ppm). An additional decrease of ~35% is expected if atmospheric CO 2 concentration doubles (pCO 2 = 560 ppm). In all of these experiments, photosynthesis and respiration did not show any significant response to changes in the carbonate chemistry of seawater. Based on this observation, we propose a mechanism by which the photosynthesis of symbionts is enhanced by coral calcification at high pH when CO 2 (aq) is low. Overall it seems that photosynthesis and calcification support each other mainly through internal pH regulation, which provides CO 3 ‐2 ions for calcification and CO 2 (aq) for photosynthesis.