Reproductive traits and Microstructure of Acropora digitifera and Acropora gemmifera (Scleractinia, Anthozoa) inhabiting the Northern Red Sea (Hurghada, Egypt).

Reef-building scleractinian corals proliferate and maintain their populations, in part, through sexual reproduction. They typically reproduce sexually as either gonochoric (separate male and female) or hermaphroditic (producing both eggs and sperm) colonies. Both types of sexual reproduction achieved as spawning processes that take place once a year and this process affected by environmental conditions such as temperature, photoperiod and pH level. In relation, the current study was designed to explore the reproduction patterns of two Acroporoid coral species; Acropora digitifera and Acropora gemmifera which inhabiting the northern Red Sea (Hurghada, Egypt). A scanning electron microscope (SEM) was used to identify both coral species and to obtain their microstructure details. For reproduction study purpose, gonads maturity status and spawning timing of both studied species were noticed, either by direct field observations, during the study period including two consecutive spawning seasons, or observed in aquaria, by taking live coral colony samples for watching their specific spawning release.
Results indicated that both investigated species are hermaphroditic broadcasting spawner (release buoyant egg-sperm bundles) and showed gradual gonads maturity development begin from October until their spawning time in late April. All polyps became empty from egg sperm bundles in early May. There was a clear relationship between the spawning time of the two coral species and the lunar cycle, temperature, and photoperiod. Spawning of study species occurred on nights (nearly 3-4 hours after sunset) during the new moon and full moon phases. The present study concluded that A. digitifera and A. gemmifera both spawned before April full moon within two days.