Effects of colony size and polyp position on polyp fecundity in the scleractinian coral genus Acropora

This study examined the effects of colony size and polyp position on six variables of polyp fecundity [egg number, egg size, total egg volume, total testis volume, total gonad volume, and gonad ratio (egg volume/testis volume)] in three tabular Acropora corals (Scleractinia), A. hyacinthus, A. japonica, and A. solitaryensis. Samples were collected from various colony sizes (n = 21–30 colonies species^?1), just before the predicted spawning at Kochi, Japan, in 2009. Five replicate polyps were sampled at three positions (center, middle, and outer) from the center to the marginal area in each tabular colony. Results indicated effects of colony size and polyp position on both male and female gonads polyp^?1. A positive effect of colony size was observed on variables of female gonads polyp^?1 (egg number, total egg volume) in A. hyacinthus only, while the positive effect on the variable of male gonads polyp^?1 (total testis volume) was common in all Acropora species, with total testis volume polyp^?1 increasing 2–4-fold from the small (200–400 cm²) to the large size class (5,000–9,000 cm²). Among the polyp positions, lower values were observed mostly in center polyps in A. hyacinthus, while lower values were observed only in outer polyps in the other Acropora species. The distinct patterns between A. hyacinthus and the other two Acropora species suggest different reproductive strategies at the species level. Further studies are needed to confirm the prevalence of these effects in scleractinian corals, which will broaden our understanding of reproductive life history strategies and improve the estimation of reproductive performance.