Reproductive cycle of reef‑building scleractinians from a Mediterranean mesophotic coral reef

Coral reefs are typically widespread in shallow waters from tropical seas, while in the Mediterranean Sea they currently have a very reduced extension. Only recently, a true coral reef has been identified on mesophotic bottoms along the coasts of southeastern Italy. The reef was mainly built by the non-symbiotic Caryophylliidae Phyllangia americana mouchezii and Polycyathus muellerae. Investigating the reproductive cycle of a scleractinian is a useful tool for assessment and conservation purposes, especially in the case of engineering species that play a key role in biogenic habitats. In the Mediterranean Sea, reproductive biology has been studied only in a minority of the 33 species of scleractinians recorded so far. This contribution represents the first attempt of describing the sexual reproductive cycle of P. a. mouchezii and P. muellerae, taking into account its possible relationship with budding and water temperature. In general, the study revealed that both species are oviparous and hermaphroditic. They showed an irregularly cyclical trend of gametogenesis, with a greater energy investment during summer. There was a substantial stasis of oogenesis during winter and the concentration of spermatogenesis in spring/ summer. P. muellerae showed a slight advance in gametogenesis, with peak production one month before that of P. a. mouchezii. Budding did not appear to interfere with sexual reproduction, nor did an anomalous peak in water temperature recorded during one of the monthly samplings. Finally, the study allowed to intercept gametes’ spawning in some colonies of the target species reared in tanks under controlled conditions.