The Hawaiian Corals of Oahu's Kaneohe Bay

According to Shamberger et al. (2011), "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 (Ω_arag)," 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.

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.

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 Ω_arag levels (mean Ω_arag = 2.85) are some of the lowest measured in coral reef ecosystems [italics added]."

Shamberger et al. conclude the report of their study by saying "it appears that while calcification rate and Ω_arag 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 is known about the potential for rapid evolution in corals and their symbionts - see Evolution (Aquatic Life) in our Topical Archive - an even stronger positive view of the subject may be obtained.