Gametogenic development and synchronous spawning of the acroporid corals Acropora cytherea and Acropora tenuis in the Red Sea

Sexual reproduction of corals is one of the essential processes for the stability and integrity of coral populations. Hence, this study was conducted to assess the reproductive and spawning patterns of two reef-building scleractinian corals belonging to genus Acropora, namely Acropora cytherea and Acropora tenuis inhabiting Hurghada, northern Red Sea. Histological and in situ examinations were carried out on 16 tagged colonies from the two coral species (8 for each species) in two selected shallow reef sites located in the north and south of Hurghada. Coral fragments were collected monthly from March 2018 to June 2018 and from October 2018 till May 2019 for dissection and histological analyses. The present results indicated that A. cytherea and A. tenuis were hermaphroditic broadcast spawners with a single annual gametogenic cycle (7 months) that began in October 2018 and terminated in April 2019, and both oogenesis and spermatogenesis were occurring for 7 and 6 months, respectively. Both species exhibited conspicuous spawning synchrony amongst colonies of the same species, and the time of spawning was mostly correlated with lunar cycle and photoperiod (day length). They spawned around the full moon in April 2018 and 2019. A. Cytherea spawned two days before the full moon (30 Apr) in April 2018 and one day before the full moon (19 Apr) in April 2019. A. tenuis spawned one day before the April full moon in 2018, while in 2019 it spawned in the full moon day (19 Apr) and one day after the full moon. This study provided information that will aid in future coral reef restoration and management. Further research on the reproduction of additional coral species is required in order to provide a better perspective of reproductive patterns in Red Sea scleractinian corals.