Annual Reproductive Cycle and Unusual Embryogenesis of a Temperate Coral in the Mediterranean Sea

The stony coral Fimbriaphyllia (Euphyllia) ancora's reproductive strategy involves a sex change every year

A sex change phenomenon was reported in some free-living, non-sessile coral species of the Family Fungiidae. However, there are no reports describing sex change in sessile colonial species. Timing and cellular processes of sex change are also unclear in corals. Here, we report sex change of the colonial coral, Fimbriaphyllia ancora, and its cellular process. Of 26 colonies monitored at Nanwan Bay, southern Taiwan, about 70% changed their sex every year after annual spawning for least 3-4 consecutive years, i.e., colonies that were male two years ago became female last year, and male again this year. The remaining 30% were permanently male or female. Sex-change and non-sex-change colonies grew in close proximity or even side-by-side. No significant differences were found in colony size between sex-change and non-sex-change colonies. Histological analysis showed that, in female-to-male sex change, small oocytes were present up to 3 months in some gonads after spawning and disappeared by 5 months. This suggests that sex change occurred 4-5 months after spawning. In contrast, in male-to-female sex change, oocytes appeared weeks after sperm release and in most gonads by 3 months, suggesting that male-to-female sex change occurred 0-3 months after sperm release.

Decreasing pH impairs sexual reproduction in a Mediterranean coral transplanted at a CO2 vent

Ocean acidification, due to the increase of carbon dioxide (CO2) concentration in the atmosphere and its absorption by the oceans, affects many aspects of marine calcifying organisms' biology, including reproduction. Most of the available studies on low pH effects on coral reproduction have been conducted on tropical species under controlled conditions, while little information is reported for either tropical or temperate species in the field. This study describes the influence of decreasing pH on sexual reproduction of the temperate non-zooxanthellate colonial scleractinian Astroides calycularis, transplanted in four sites along a natural pH gradient at the underwater volcanic crater of Panarea Island (Tyrrhenian Sea, Italy). The average pH values of each site (range: pHTS 8.07-7.40) match different scenarios of the Intergovernmental Panel on Climate Change (IPCC) for the end of the century. After 3 months under experimental conditions, the reproductive parameters of both oocytes and spermaries (abundance, gonadal index, and diameters) seem to be unaffected by low pH. However, a delay in spermary development in the pre-fertilization period and a persistence of mature oocytes in the fertilization period were observed in the most acidic site. Furthermore, no embryos were found in colonies from the two most acidic sites, suggesting a delay or an interruption of the fertilization process due to acidified conditions. These findings suggest a negative effect of low pH on A. calycularis sexual reproduction. However, long-term experiments, including the synergistic impact of pH and temperature, are needed to predict if this species will be able to adapt to climate change over the next century.