How does rising atmospheric CO2 affect marine organisms?

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The Hawaiian Corals of Oahu's Kaneohe Bay
Shamberger, K.E.F., Feely, R.A., Sabine, C.L., Atkinson, M.J., DeCarlo, E.H. and Mackenzie, F.T. 2011. Calcification and organic production on a Hawaiian coral reef. Marine Chemistry 127: 64-75.

The authors write that "laboratory studies on individual coral species and coral reef mesocosms have demonstrated, in most cases, that the calcification rate of corals decreases with increasing seawater pCO2 and decreasing saturation state with respect to aragonite (Ωarag)," and in harmony with these observations, they additionally state that "data from coral laboratory experiments have been used to predict that coral reef calcification could decrease globally by 17-35% by 2100," as a result of anticipated increases in anthropogenic CO2 emissions to the atmosphere, a goodly portion of which is absorbed by the world's oceans.

What was done
In a study that sheds new light on this subject, Shamberger et al. deployed newly designed "autosamplers" to collect water samples from the barrier coral reef of Kaneohe Bay, Oahu, Hawaii, every two hours for six 48-hour periods, two each in June 2008, August 2009 and January/February 2010. And based on these seawater measurements, they calculated net ecosystem calcification (NEC) and net photosynthesis (NP) rates for these periods.

What was learned
As expected, the six scientists found that "daily NEC was strongly negatively correlated with average daily pCO2, which ranged from 421 to 622 ppm." Most interestingly, however, they report that "daily NEC of the Kaneohe Bay barrier reef is similar to or higher than daily NEC measured on other coral reefs, even though Ωarag levels (mean Ωarag = 2.85) are some of the lowest measured in coral reef ecosystems [italics added]."

What it means
Shamberger et al. conclude the report of their study by saying "it appears that while calcification rate and Ωarag are correlated within a single coral reef ecosystem," as in the case of the barrier reef of Kaneohe Bay, "this relationship does not necessarily hold between different coral reef systems," and they state that it can thus be expected that "ocean acidification will not affect coral reefs uniformly and that some may be more sensitive to increasing pCO2 levels than others," which also means (taking a more positive view of the subject) that some may be less sensitive to increasing pCO2 than others. And in light of what we know about the potential for rapid evolution in corals and their symbionts - see Evolution (Aquatic Life) in our Subject Index - we can validly maintain an even stronger positive view of the subject.

Reviewed 18 April 2012