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Ocean acidification, due to the increase of carbon dioxide (CO2) concentration in the atmosphere and its absorption by the oceans, affects many aspects of marine calcifying organisms' biology, including reproduction. Most of the available studies on low pH effects on coral reproduction have been conducted on tropical species under controlled conditions, while little information is reported for either tropical or temperate species in the field. This study describes the influence of decreasing pH on sexual reproduction of the temperate non‐zooxanthellate colonial scleractinian Astroides calycularis, transplanted in four sites along a natural pH gradient at the underwater volcanic crater of Panarea Island (Tyrrhenian Sea, Italy). The average pH values of each site (range: pHTS 8.07–7.40) match different scenarios of the Intergovernmental Panel on Climate Change (IPCC) for the end of the century. After 3 months under experimental conditions, the reproductive parameters of both oocytes and spermaries (abundance, gonadal index, and diameters) seem to be unaffected by low pH. However, a delay in spermary development in the pre‐fertilization period and a persistence of mature oocytes in the fertilization period were observed in the most acidic site. Furthermore, no embryos were found in colonies from the two most acidic sites, suggesting a delay or an interruption of the fertilization process due to acidified conditions. These findings suggest a negative effect of low pH on A. calycularis sexual reproduction. However, long‐term experiments, including the synergistic impact of pH and temperature, are needed to predict if this species will be able to adapt to climate change over the next century. [ABSTRACT FROM AUTHOR]

Atmospheric carbon dioxide enrichment alters seawater carbonate chemistry, thus threatening calcifying organisms such as corals. Coral populations at carbon dioxide vents are natural acidification experiments that mimic organism responses to seawater pH values projected for 2100. Even if demographic traits are paramount information to assess ecological relationships and habitat suitability, population dynamics studies on corals thriving under acidified conditions are lacking. Here, we investigate the demography and reproduction of populations of the solitary, symbiotic, temperate coral Balanophyllia europaea naturally living along a pH gradient at a Mediterranean CO2 vent. Gametogenesis and larval production were unaffected while recruitment efficiency collapsed at low and variable pH, contributing to coral abundance decline and suggesting that life stages between larval release and early polyp growth are hindered by acidification. Exploring these processes is crucial to assess coral fate in the forthcoming acidified oceans, to preserve coral ecosystems and the socioeconomic services they provide. [ABSTRACT FROM AUTHOR]

Coral age can be strictly related to size, but processes like fragmentation, fusion, and partial colony mortality can decouple this relationship. When these phenomena are negligible, such as in solitary corals, age-based growth and population dynamics models can be used. In this study, the population size, structure, and growth rates of the temperate solitary coral Caryophyllia inornata were assessed at Elba Island (north-western Mediterranean Sea). Growth rate of this species decreased exponentially with age. The two growth curves estimated by field measurements and by growth band analysis provided homogeneous relationships between size and age. The decreasing number of individuals with age indicated a steady state population, with a turnover time of 4 yr and a maximum life span of 22 yr. Maximum biomass yield and most reproductive output was by individuals of 8-15 yr age classes. The life strategy was characterized by high fecundity, continuous embryo production, high larval output, and high larval mortality. [ABSTRACT FROM AUTHOR]