SEXUAL REPRODUCTION OF A SOFT CORAL: SYNCHRONOUS AND BRIEF ANNUAL SPAWNING OF SARCOPHYTON GLAUCUM (QUOY & GAIMARD, 1833)

The sexual reproduction of the alcyonacean octocoral Sarcophyton glaucum (Quoy & Gaimard, 1833) was studied for a period of about four years on the coral reefs of the northern Red Sea. S. glaucum is a dioecious species with gonads borne in the autozooids. The smallest colonies bearing testes measure 11 cm3 (6-7 years old) while females attain maturity at a much larger colony size of at least 61 cm3 (> ten years old). Sex ratio of the population is 1:1. The annual development of the sperm sacs takes 10-12 months. Oogenesis occurs every year, however egg maturation requires 22-23 months, resulting in the presence of two cohorts of oocytes in each female. The mature eggs are large with a maximal diameter of 500-750 µm. S. glaucum has a brief annual spawning period which occurs in the majority of the population during a single night (in 1980, spawning was on 9 July). The large size of the eggs is not the ultimate cause for their prolonged period of oogenesis. Nevertheless, the synchronous maturation of numero...