Sex change every year: A unique reproductive strategy of the stony coral, Fimbriaphyllia (Euphyllia) ancor

The present study documents a unique reproductive strategy of the colonial stony coral, Fimbriaphyllia ancora, during observations spanning 8 years. Of 26 colonies monitored at Nanwan Bay, southern Taiwan, about 70% changed their sexes every year, i.e., colonies that were males two years ago became females last year, and changed back to males this year. Apparently, the remaining 30% were permanently male or female. Sex-change and non-sex-change colonies were growing in close proximity or even side-by-side, suggesting that this sex change phenomenon is not driven by environmental factors. No significant differences were found in colony size between sex-change and non-sex-change colonies, suggesting that the sex change strategy may be related to intrinsic factors, e.g., age or genetics. Histological analysis showed that female-to-male sex change occurs 4-5 months after spawning, whereas male-to-female sex change occurs 0-3 months after sperm release. We propose that this unique strategy may increase success of sexual reproduction of sessile, colonial corals.