New paper finds corals not affected by life-long exposure to high CO2 levels

Note: Corals evolved over 500 million years ago when CO2 levels were ~15 times higher than the present.

From the latest edition of the NIPCC Report:

Lifelong exposure of Scleractinian Corals to Elevated CO2

Reference: Noonan, S.H.C., Fabricius, K.E. and Humphrey, C. 2013. Symbiodinium community composition in Scleractinian corals is not affected by life-long exposure to elevated carbon dioxide. PLOS ONE 8: e63985.

In the words of Noonan et al. (2013), "ocean acidification (OA) is expected to negatively affect coral reefs," but they say that "little is known about how OA will change the coral-algal symbiosis on which reefs ultimately depend." In fact, they indicate that "to date it remains unknown if corals are able to respond to rising CO2 concentrations by changing to better adapted dominant Symbiodinium types after long-term exposure to elevated pCO2 in the field," where field, of course, to them means ocean.

Against this backdrop Noonan et al., as they describe it, "used denaturing gradient gel electrophoresis (DGGE) of the internal transcribed spacer 2 (ITS2) region of ribosomal DNA to investigate the dominant types of Symbiodinium associating with six species of scleractinian coral that were exposed to elevated partial pressures of carbon dioxide (pCO2) in situ from settlement and throughout their lives." This was done "at three naturally occurring volcanic CO2 seeps (pCO2 ~500 to 900 ppm, pHTotal 7.8-7.9) and adjacent control areas (pCO2 ~390 ppm, pHTotal ~8.0-8.05) in Papua New Guinea," while "Symbiodinium associated with corals living in an extreme seep site (pCO2 >1000 ppm) were also examined."

The three Australian researchers report that within five of the six species studied, "85-95% of samples exhibited the same Symbiodinium type across all sites, with remaining rare types having no patterns attributable to CO2 exposure." The sixth species of coral, however, did display "site specific differences in Symbiodinium types," but these were "unrelated to CO2 exposure." Last of all, they found that "Symbiodinium types from the coral inhabiting the extreme CO2 seep site were [also] found commonly throughout the moderate seeps and control areas."

The findings of Noonan et al. suggest that the six species of coral they studied, plus the various Symbiodinium types they encountered, were all able to not only survive, but to function well throughout the full range of CO2-induced pH values to which they had been exposed throughout their entire life spans.

Prior posts on why ocean acidification claims are overblown