Gametogenesis and reproductive pattern of the reef-building coral Acropora millepora in northwestern Philippines

Coral populations continue to decline in many regions because of natural and anthropogenic disturbances; and the persistence of coral populations mainly relies on natural recruitment through coral reproduction. However, studies on the reproduction of many important reef-building coral species in one of the most biodiverse region, the Coral Triangle, are very limited. Here, we investigated the reproductive biology of the coral Acropora millepora in Bolinao-Anda Reef Complex, northwestern Philippines from February 2014 to March 2015, through in situ assessment of gamete maturity, histological examination of gamete development and ex situ spawning observations. Results showed that A. millepora exhibited an annual gametogenic cycle. Formation of oocytes took place within 8 months, whereas spermatocytes developed in 3 months before the gamete release. Abundance and size of eggs in A. millepora were greatest during the months nearest to the spawning period, which coincides with the rapid increase in sea surface temperature. Ex situ broadcast spawning occurred around the months of February–March, which suggests an extended spawning pattern. Results provide additional information on coral reproduction in the region and reveal the potential of A. millepora in providing coral propagules for the replenishment and recovery of degraded coral populations.