Newly discovered CO₂ (carbon dioxide) vent cave drives r-strategy shift in a Mediterranean aphotoendosymbiotic coral

Submarine CO₂ volcanic vents represent peculiar environments with varying seawater chemical-physical parameters that may affect the ecological traits of calcifying organisms, such as growth and demographic characteristics. The present study focused on exploring the growth and population dynamics of a temperate, solitary and aphotoendosymbiotic coral Caryophyllia inornata (Duncan, 1878) living in a CO₂ vent cave at 14 m depth. The volcanic emissions in and around the cave led high levels of pCO₂, resulting in lower calcium carbonate saturation state (Ω_a: 2.1–2.2) values compared to those observed in the ambient seawater of the Mediterranean Sea, not affected by venting activity. Prolonged acidified conditions (pH_T: 7.5) did not affect C. inornata growth rate but resulted in a population with higher percentage of juvenile individuals, lower average ages and a lower age at maximum biomass percentage, thus suggesting a transition in its population dynamics towards an r-demographic strategy. This study provides a detailed characterization of a previously unexplored CO₂ vent cave, highlighting the importance of these sites as natural laboratories to offer valuable insights into understanding the full ecological impact of aphotoendosymbiotic corals under ocean acidification.