Demographic aspects of the soft coral Sinularia flexibilis leading to local dominance on coral reefs C. Bastidas 1,2, *, K. E. Fabricius 1 & B. L. Willis 2 1 Australian Institute of Marine Science, PMB No. 3, QLD 4810, Australia 2 School of Marine Biology and Aquaculture, James Cook University, Townsville QLD 4811, Australia (*Author for correspondence: Tel.: +58-212-9063415/+58-416-6279224, Fax: +58-212-9063046, E-mail: cbastidas@usb.ve) Key words: GBR, population dynamics, Sinularia, soft corals Abstract We evaluated the role that demography may play in the formation of local aggregations of Sinularia flexibilis (Quoy & Gaimard, 1833), a soft coral that commonly dominates inshore coral reefs of the Great Barrier Reef (GBR), Australia. Two populations on inshore reefs of the Palm Islands were censused once a year for 3 years, starting 10 mo after the extensive bleaching mortality in early 1998. Larger colonies became more prevalent over time; mean colony size increasing by 35%, from 276 cm 2 in 1998 to 373 cm 2 in 2000. Growth rates were size dependent, with smaller colonies growing proportionally faster than larger colonies. Change in size relative to initial size indicated an expected mean annual growth of 128 cm 2 for a 50-cm 2 colony. Zero growth was predicted at 532 ± 21 cm 2 , with colonies larger than this likely to undergo fission or shrink. Forty-three percent of colonies were undergoing fission at any time at both localities. Most new colonies were produced by fission (70%, n ¼ 285), with the remainder produced by the recruitment of sexually produced larvae (19%) or by colony translocation (11%). The sexual and asexual recruitment rates were 0.24 and 1.0 recruits m )2 year )1 , respectively. Opportunistic recruitment and rapid growth following disturbances are commonly assumed to be the mechanisms leading soft corals to dominate locally. In this study, these mechanisms operated more slowly than expected, with no net change in population size. Introduction Despite comprising a large group of species that are represented in most phyla, clonal animals have received little attention compared to aclonal ani- mals or clonal plants (Hughes & Cancino, 1985; Tanner, 2001). Clonal species are morphologically flexible and often have the potential to grow rap- idly and attain large sizes. In sessile clonal species, these characteristics may result in the formation of large aggregations. The great capacity of clonal species to survive and recover from partial mor- tality, and a long life-span confer on them many advantages over aclonal organisms (Hughes & Cancino, 1985; Jackson, 1985). Life history dif- ferences between clonal and aclonal organisms lead to major differences in their demographies (Hughes & Jackson, 1980; Hughes, 1984; Tanner, 2001), differences that have not been fully explored in marine organisms. Soft corals are representative of clonal life histories but relatively few studies have examined demographic aspects of their populations world- wide. On the Great Barrier Reef (GBR), Australia, previous studies were conducted on offshore reefs, and revealed a large variability in the life histories (Dinesen, 1985; Lasker, 1988; Fabricius, 1995; Karlson et al., 1996). Studies of soft corals are lacking from inshore reefs where members of the Alcyoniina and Stolonifera form large Hydrobiologia 530/531: 433–441, 2004. D.G. Fautin, J.A. Westfall, P. Cartwright, M. Daly & C.R. Wyttenbach (eds), Coelenterate Biology 2003: Trends in Research on Cnidaria and Ctenophora. Ó 2004 Kluwer Academic Publishers. Printed in the Netherlands. 433