Coral populations naturally occur in high pCO2 environments on the coast of Ischia

Natural volcanic CO2 vents cause local acidification of seawater and are used as natural analogues of future ocean acidification (OA) conditions. Populations associated with these high pCO2 environments provide an unparalleled opportunity to assess the mechanisms of acclimatization and adaptation to climate variability and extremes. Here, we investigate two CO2 vent systems on the coast of Ischia (Italy) and how elevated seawater pCO2 exposure influences coral populations that naturally occur in these acidified environments. We studied two Mediterranean long-lived scleractinian corals of key relevance for conservation as habitat-forming species: the zooxanthellate Cladocora caespitosa and the azooxanthellate Astroides calycularis. We compare populations living near the vents (pHT = 7.6 -7.8) to reference areas with ambient pH (pHT = 8.0) hosting similar geomorphology but outside the influence of CO2 venting. Our research addresses questions related to the physiology, ecology, and adaptive responses of corals to ocean warming and acidification. To achieve this, we integrate environmental data (carbonate chemistry), ecological field surveys and laboratory experiments, encompassing population demographics, skeletal characteristics, gametogenesis, and transcriptomic approaches. Further, we witnessed the spawning of Astroides calycularis in the field, allowing us to run an experiment on the effects of acidification on early life stages and explore whether differences in gene expression between populations and treatments exist. Through the study of these high pCO2 environments and their populations, we gain new insight into how natural coral populations survive, as well as their adaptive strategies and resilience to high pCO2 environments