Coral Microbial Communities Along a Natural pH Gradient
Meron, D., Rodolfo-Metalpa, R., Cunning, R., Baker, A.C., Fine, M. and Banin, E. 2012. Changes in coral microbial communities in response to a natural pH gradient. ISME Journal 6: 1775-1785.
Against this backdrop, and departing from this common protocol, the six scientists took advantage of a natural pH gradient off the coast of Ischia (Gulf of Naples, Italy), which is created by an underwater CO2 flux from volcanic vents (Hall-Spencer et al., 2008). This they did for the purpose of examining potential impacts of a range of pH conditions (7.3 to 8.1) on coral microbial communities living under natural real-world conditions, focusing on two Mediterranean coral species: Balanophyllia europaea and Cladocora caespitosa. And what did they find?
"We found," as the research team writes in the abstract of their paper, that (1) "pH did not have a significant impact on the composition of associated microbial communities in both coral species," that (2) "corals present at the lower pH sites exhibited only minor physiological changes," and that (3) "no microbial pathogens were detected." Thus, they conclude that "at least for these two coral species, reduced pH does not seem to significantly reduce coral health," which further suggests that some of the contrary results obtained in laboratory studies could be due to the fact that "laboratory environments cannot mimic the dynamism and microbial diversity present in nature," as well as the possibility that "aquarium conditions themselves contribute to stress or disturbance in the microbial community," which view is supported in part by the finding of Kooperman et al. (2007) that "the same coral species has different associated microbial communities in the laboratory compared with field conditions."
Clearly, we need more studies of the potential effects - or non-effects - of declining seawater pH to be conducted in the real world of nature.
Hall-Spencer, J.M., Rodolfo-Metalpa, R., Martin, S., Ransome, E., Fine, M., Turner, S.M., Rowley, S.J., Tedesco, D. and Buia, M.-C. 2008. Volcanic carbon dioxide vents show ecosystem effects of ocean acidification. Nature 454: 96-99.
Kooperman, N., Ben-Dov, E., Kramarsky-Winter, E., Barak, Z. and Kushmaro, A. 2007. Coral mucus-associated bacterial communities from natural and aquarium environments. FEMS Microbiology Letters 276: 106-113.
Reshef, L, Koren, O., Loya, Y., Zilber-Rosenberg, I. and Rosenberg, E. 2006. The coral probiotic hypothesis. Applied Environmental Microbiology 8: 2067-2073.