Submarine carbon dioxide (CO2) seeps as natural laboratories to study coral reef acclimatization to ocean acidification

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Ocean acidification (OA) due to the oceanic uptake of anthropogenic CO2 could have far reaching ramifications for coral reefs due to a fundamental alteration in seawater carbonate chemistry. Thus far, the majority of research to assess the impact of OA on coral reefs was conducted in simplified systems, maintained under laboratory conditions. While crucial and informative, these studies had limitations with respect to natural variability, duration, age distribution, genetic diversity and multispecies interaction. A possible solution to those limitations is the study of coral reefs in the vicinity of submarine CO2 seeps, which naturally experience elevated CO2, mimicking pH and temperature conditions predicted to occur with OA by 2100. Three such coral reefs were studied and interestingly at each site the results of OA were different; resulting in depauperate coral reefs, octocoral communities, and macro algae dominated rocks, at sites in Papua New Guinea, Japan and the Northern Mariana Islands, respectively. A possible explanation for this discrepancy is the fact that those studies were flawed in the sense that not all parameters detrimental to coral reef health were accounted for. Generally, submarine CO2 seeps are accompanied by submarine hot springs with temperatures up to 100 °C. This discharge further alters ambient seawater conditions by exerting steep temperature gradients and introducing a suite of heavy metals into the study area. These are two effects, which have to be considered when using CO2 seeps as natural environments for the study of OA. With this in mind, the purpose of the planned international collaboration is to bring together a team with expertise in aqueous chemistry and coral physiology to carry out detailed chemical and biological characterizations of CO2 seeps in coral reefs to better understand the implications of OA.