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Coral Calcification and Photosynthesis in a CO2-Enriched World of the Future
Volume 11, Number 21: 21 May 2008

Many are the people who have predicted that rates of coral calcification, as well as the photosynthetic rates of their symbiotic algae, will dramatically decline in response to what they typically refer to as an acidification of the world's oceans, as the atmosphere's CO2 concentration continues to rise in the years, decades and centuries to come (see Calcification (Corals) in our Subject Index). As ever more pertinent evidence accumulates, however, the true story appears to be just the opposite of what these climate alarmists continue to tell us.

A case in point is the recent study of Herfort et al. (2008), who note that an increase in atmospheric CO2 will cause an increase in the abundance of HCO3- (bicarbonate) ions and dissolved CO2, and who report that several studies on marine plants have observed "increased photosynthesis with higher than ambient DIC [dissolved inorganic carbon] concentrations," citing the works of Gao et al. (1993), Weis (1993), Beer and Rehnberg (1997), Marubini and Thake (1998), Mercado et al. (2001, 2003), Herfort et al. (2002) and Zou et al. (2003).

To further explore this subject, and to see what it might imply for coral calcification, the three researchers employed a wide range of bicarbonate concentrations "to monitor the kinetics of bicarbonate use in both photosynthesis and calcification in two reef-building corals, Porites porites and Acropora sp." This work revealed that additions of HCO3- to synthetic seawater continued to increase the calcification rate of Porites porites until the bicarbonate concentration exceeded three times that of seawater, while photosynthetic rates of the coral's symbiotic algae were stimulated by HCO3- addition until they became saturated at twice the normal HCO3- concentration of seawater.

Similar experiments conducted on Indo-Pacific Acropora sp. showed that calcification and photosynthetic rates in these corals were enhanced to an even greater extent, with calcification continuing to increase above a quadrupling of the HCO3- concentration and photosynthesis saturating at triple the concentration of seawater. In addition, they monitored calcification rates of the Acropora sp. in the dark, and, in their words, "although these were lower than in the light for a given HCO3- concentration, they still increased dramatically with HCO3- addition, showing that calcification in this coral is light stimulated but not light dependent."

In discussing the significance of their findings, Herfort et al. suggest, as we have long contended (Idso et al., 2000), that "hermatypic corals incubated in the light achieve high rates of calcification by the synergistic action of photosynthesis [our italics]," which, as they have shown, is enhanced by elevated concentrations of HCO3- ions that come courtesy of the ongoing rise in the air's CO2 content.

As for the real-world implications of their work, the three researchers note that over the next century the predicted increase in atmospheric CO2 concentration "will result in about a 15% increase in oceanic HCO3-," and they say that this development "could stimulate photosynthesis and calcification in a wide variety of hermatypic corals." This well-supported conclusion stands in stark contrast to the outworn contention of the world's climate alarmists that continued increases in the air's CO2 content will, as restated by Herfort et al., "cause a reduction in coral growth and planktonic calcification." This claim, as they and many others have now demonstrated, is about as far from the truth as it could possibly be.

Sherwood, Keith and Craig Idso

Beer, S. and Rehnberg, J. 1997. The acquisition of inorganic carbon by the sea grass Zostera marina. Aquatic Botany 56: 277-283.

Gao, K., Aruga, Y., Asada, K., Ishihara, T., Akano, T. and Kiyohara, M. 1993. Calcification in the articulated coralline alga Corallina pilulifera, with special reference to the effect of elevated CO2 concentration. Marine Biology 117: 129-132.

Herfort, L., Thake, B. and Taubner, I. 2008. Bicarbonate stimulation of calcification and photosynthesis in two hermatypic corals. Journal of Phycology 44: 91-98.

Idso, S.B., Idso, C.D. and Idso, K.E. 2000. CO2, global warming and coral reefs: Prospects for the future. Technology 7S: 71-94.

Marubini, F. and Thake, B. 1998. Coral calcification and photosynthesis: evidence for carbon limitation. In: International Society for Reef Studies (ISRS), European Meeting, Perpignan, September 1-4, 1998, p. 119.

Mercado, J.M., Niell, F.X. and Gil-Rodriguez, M.C. 2001. Photosynthesis might be limited by light, not inorganic carbon availability, in three intertidal Gelidiales species. New Phytologist 149: 431-439.

Mercado, J.M., Niell, F.X., Silva, J. and Santos, R. 2003. Use of light and inorganic carbon acquisition by two morphotypes of Zostera noltii Hornem. Journal of Experimental Marine Biology and Ecology 297: 71-84.

Weis, V.M. 1993. Effect of dissolved inorganic carbon concentration on the photosynthesis of the symbiotic sea anemone Aiptasia pulchella Carlgren: role of carbonic anhydrase. Journal of Experimental Marine Biology and Ecology 174: 209-225.

Zou, D.H., Gao, K.S. and Xia, J.R. 2003. Photosynthetic utilization of inorganic carbon in the economic brown alga, Hizikia fusiforme (Sargassaceae) from the South China Sea. Journal of Phycology 39: 1095-1100.