Reference: Bil. Bull. 17ft: 32-42. (February, 1986) SEXUAL ACTION OF A SOFT CORAL: SYNCHRONOUS AND NNUAL SPAWNING OF SARCOPHYTON GLAUCUM (QUOY & GAIMARD, 1833) Y. BENAYAHU AND Y. LOYA The George S. Wise Faculty of Life Sciences, Department of Zoology, Tel Aviv University, Tel Aviv 69978, Israel ABSTRACT 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 1 1 cm 3 (6-7 years old) while females attain maturity at a much larger colony size of at least 61 cm 3 (> 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 ^m. 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 numerous eggs produced by a colony during a brief spawning period demands high energy expenditure which is allocated during two years. Fertilization is external and fully developed planulae are obtained 36 h after spawning. The larvae swim actively for 14 days, hence, promoting wide dispersal of the species. Life history features of S. glaucum include large body size, late age at the onset of reproduction, prolonged oogenic cycle, slow growth of the colony, and long life span. INTRODUCTION Anthozoans are capable of reproducing sexually in a variety of ways (Campbell, 1974; Chia, 1976; Fadlallah, 1983). Little attention has been paid to the sexual biology of soft corals (Octocorallia: Alcyonacea). Some studies have focused on planulating species of the family Xeniidae (Gohar, 1940; Benayahu and Loya, 1984a, b). Among members of the family Alcyoniidae several modes of sexual reproduction have been recorded. The temperate species Alcyonium digitatum releases gametes, and A. hib-ernicum has internal parthenogenesis of planular development (Hartnoll, 1977). Al-though ak jniids are very common on coral reefs, little is known about their sexual reproduction and gonadal development. Yamazato et al. ( 198 1 ) present circumstantial evidence for gamete spawning in Lobophytum crassum, and an external mode of planular brooding was described in the alcyoniid Parerythropodium fulvum fulvum (Benayahu and Loya, 1983). Moreover, recently spawned eggs were collected from several alcyoniids in the Great Barrier Reef, Australia (Bowden et al. 1985). Among the Sea soft corals, the alcyoniids are very abundant and constitute 52% of the total n i mber of soft coral species (Benayahu, in prep.). Sarcophyton glaucum (Fig. 1 ) is one of the most conspicuous alcyoniids on the Red Sea reefs and at numerous Received 28 August 1985; accepted 25 November 1985. 32
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