Evaluation of newly discovered CO2 seeps as potential natural laboratories to study coral reef acclimatization to ocean acidification

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Acidification of the oceans through the uptake of anthropogenic CO2 could have far-reaching effects on coral reefs, since the carbonate chemistry of seawater can undergo fundamental changes. Until now, much of the assessment of the impact of ocean acidification on coral reefs has been carried out in simplified systems under laboratory conditions. While these studies were crucial and informative, they have limitations in terms of natural variability, duration, age distribution, genetic diversity and the interaction of several coral species. One possible solution to these limitations is to study coral reefs in the vicinity of submarine CO2 seeps, which cause increased CO2 levels in seawater. Accordingly, the pH and temperature conditions should be similar to those expected by 2100. Three such coral reefs have now been investigated and, interestingly, the results were all different at the sites in Papua New Guinea, Japan and the Northern Mariana Islands. One possible explanation for this discrepancy is that these studies were flawed in that not all parameters important for the health of the coral reefs were considered, such as toxic metal content. In general, submarine CO2 discharges are accompanied by hydrothermal fluids with temperatures up to 100 °C, which release heavy metals into the study area. These are two effects that have to be considered when using CO2 discharges as natural laboratories for the study of ocean acidification. With this in mind, the aim of this project is to assess several such CO2-emissions in Indonesia and the Philippines, in order to evaluate whether they can be used as natural laboratories to better understand the effects of ocean acidification.