Histological observations in the sexual reproduction of the scleractinian coral, Porites cylindrica in the Bolinao-Anda Reef Complex, Northwestern Philippines

Abstract

Porites cylindrica in northwestern Philippines is a gonochoric brooder that follows a lunar schedule in its release of larvae. The study investigated the gametogenesis of this scleractinian coral within one lunar cycle. Ten colonies of Porites cylindrica collected from the Bolinao-Anda Reef Complex exhibited a sex ratio of 1:1. Colonies were maintained ex situ for one lunar month and two coral fragments were collected from each colony twice a week from November 9, 2014 to December 10, 2014. Fragments were histologically processed and gonads were measured and classified by gametogenic stage. Data show that the different stages of oogenesis and spermatogenesis demonstrated lunar periodicity in development except for stage I oocytes and spermaries which were infrequently observed. Stage II to stage IV spermaries predominated at distinct lunar days indicating that spermatogenesis occurs within one lunar period while the apparent overlap in the relative occurrence of stage II to stage IV oocytes suggests that oocyte maturation may take more than one lunar period. Nevertheless, data revealed that both male and female gametes were observed to mature simultaneously at around the first quarter moon. Decrease in the relative occurrence of larva was observed during the 25th lunar day as planulation occurred. At approximately 12th lunar day of the succeeding lunar cycle, an increase in the relative occurrence of larva and decrease in the relative occurrence of both male and female gametes indicates the release of mature sperm and subsequent fertilization of mature oocytes and embryogenesis.