In the framework of the project CARiOCA, financed by ANR, during the first and second cruises onboard the R/V Alis (September 2016 and Mai 2017) we investigated coral reefs living at the CO₂ vents of Ambitle Island (New Ireland Province; 4°03'54'' S, 153°34'46'' E) where corals live at pH values expected for 2100. This unique vents system emits hot fluids and pure CO₂, offering the timely opportunity to study coral reef responses to climate change in a natural setting. The project proposes to use these unique sites, which has seawater conditions similar to those expected at the end of this century, to identify the phenotypic traits that allow certain coral species to survive and reproduce in seawater naturally enriched in CO₂. This will give new insights into the mechanisms that underlie acclimatization and adaptation to climate change.

During these first cruises all the objectives were acquired: i) perform accurate measurements of the main environmental parameters and seawater chemistry (e.g. temperature, salinity, oxygen dissolved, pH, total alkalinity, DIC, nutrients, metals); ii) assess general surveys of the coral reef composition around the vents (video transects); iii) collect coral samples, in and outside the vents area, and along a gradient of pH for bacterial and genetic analyses; iv) assess physiological and genetic responses of corals living in and outside the vents and on transplanted corals (8-month transplantation). In addition to these objectives and in agreement with the experimental design of the project PNG-Vents, which has been financed also by ANR, during the last cruise we build a pipeline to drive hot and acid fluids close to transplanted species of corals. This new experiment is a test to verify the feasibility of using the hot CO₂ vents also to study the combined effects of warming and acidification. The main goal of this third cruise will be to replicate this test and start a new large-scale innovative experiment.