| Summary: | International audience Volcanic CO2 vents are ideal sites to study the long-term effects of ocean acidification on long- lived calcified species, such as corals. At the Island of Ischia (Italy), we investigated, both in situ and ex situ, whether past exposure to low pH confers physiological tolerance to ocean acidification in different life stages and affects sexual reproduction. Adult colonies of Astroides calycularis (azooxanthellate) and Cladocora caespitosa zooxanthellate), and larvae of A. calycularis were sampled at CO2 vent and ambient pH sites. They were then maintained under controlled conditionsin the laboratory, during two distinct 6-month experiments, under ambient (pHT 8.0), low (pHT 7.7) and extreme low pH (pHT 7.5, only for larvae from CO2 vents). Adult net calcification and respiration of both species, and net and gross photosynthesis of C. caespitosa were unaffected by the pH treatments regardless of their environmental history. Larvae of A. calycularis from the CO2 vents were smaller and had a lower survivorship and settlement success than larvae from the ambient pH site regardless of experimental pH treatment. Colonies of C. caespitosa were smaller and less abundant near CO2 vents. Histological sections of C. caespitosa from the vents demonstrated an asynchrony of spawning between male and female, which could have major effects on fertilization. Our results suggest that adult colonies of A. calycularis and C. caespitosa exhibit tolerance to acidification. However, long exposition to low pH appears to decrease sexual reproduction and early life stages development, which are both of particular relevance for the persistence of healthy populations.
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