Reproduction of reef-building scleractinians (Cnidaria, Anthozoa) from the Apulian coral reef: preliminary data and relationship with temperature

This contribution supplies the first description of the reproductive cycle of Phyllangia americana mouchezii and Polycyathus muellerae (Cnidaria, Anthozoa), the main builders of the Mediterranean coral reef recently described for the first time along the Apulian coasts, focusing on both the sexual and asexual reproductive activity and trying to assess the relationship between gametogenesis and seawater temperature. Sample collection was performed monthly, from December 2020 to January 2022, at depths between 35 and 45 m, and at the same time seawater temperature was measured at 1 m and 40 m of depth. At the laboratory, samples were subjected to histological procedures aimed at highlighting the presence of reproductive elements in the polyp tissues. A multiple regression analysis was then performed to test the relationship between gametogenesis in the two species, depth, and surface and deep-water temperature. On the whole, both species resulted oviparous and gonochoric, with a sex ratio between male and female colonies of 1:2.3 in P. a. mouchezii and 1:1.6 in P. muellerae. However, hermaphrodite colonies were sometimes found during the investigation, accounting for about 7% of the total reproductive colonies in the former species and 11% in the latter. In P. a. mouchezii about 32% of the colonies resulted in gametogenesis, in P. muellerae about 37%. Both species showed an irregularly cyclical trend of gametogenesis, with a greater energy investment during Summer. In general, the oogenesis was less intense during Winter and the spermatogenesis was concentrated in Spring/Summer. Statistical analysis revealed that in both species surface water temperature was a predictor for spermatogenesis, while oogenesis seemed to be less linked to water temperature fluctuations. No significant regression was observed for the other variables considered. The data provided may in the future contribute to the conservation of the Mediterranean coral reef, a peculiar and still poorly known habitat recently proposed as belonging to a real mesophotic system present along the Apulian coasts.