MARINE ECOLOGY PROGRESS SERIES Vol. 126: 145-152,1995 Published October 5 Mar Ecol Prog Ser l Slow population turnover in the soft coral genera Sinularia and Sarcophyton on mid- and outer-shelf reefs of the Great Barrier Reef Katharina E. Fabricius* Australian Institute of Marine Science, PMB 3, Townsville, Queensland 4810, Australia ABSTRACT: Aspects of the life history of the 2 common soft coral genera Sinularja and Sarcophyton were investigated on 360 individually tagged colonies over 3.5 yr. Measurements included rates of growth, colony fission, mortality, sublethal predation and algae infection, and were carried out at 18 sites on 6 mid- and outer-shelf reefs of the Australian Great Barrier Reef. In both Sinularia and Sarco- phyton, average radial growth was around 0.5 cm yr.', and relative growth rates were size-dependent. In Sinularia, populations changed very slowly over time. Their per capita mortality was low (0.014 yr.') and size-independent, and indicated longevity of the colonies. Colonies with extensions of up to 10 X 10 m potentially could be several hundreds of years old. Mortality was more than compensated for by asexual reproduction through colony fission (0.035 yr.'). In Sarcophyton, mortality was low in colonies larger than 5 cm disk diameter (0.064 yr-l), and significantly higher in newly recruited small colonies (0.88 yr-'). Photographic monitoring of about 500 additional colonies from 16 soft coral genera showed that rates of mortality and recruitment In the family Alcyoniidae differed fundamentally from those of the commonly more 'fugitive' families Xeniidae and Nephtheidae. Rates of recruitment by larval set- tlement were very low in a majority of the soft coral taxa. The general assumption that soft corals are fast-growing pioneers does not apply to the Alcyoniidae on the central Great Barrier Reef, where their life history traits indicate great persistence. KEY WORDS: Octocorallia . Alcyoniidae . Sinularia . Sarcophyton - Life history traits . Growth . Mor- tality . Recruitment INTRODUCTION colonies, and asexual propagation by runner formation (Tursch & Tursch 1982). High potential for asexual The octocoral fauna of Indo-Pacific reefs is domi- propagation, fast growth and high predation rates nated by the 3 soft coral families Xeniidae, Nephthei- characterize the nephtheid Dendronephthya hemp- dae and Alcyoniidae (Bayer 1957). Previous demo- richi from the Red Sea (Fabricius et al. 1995). X. graphic investigations of reef-inhabiting xeniid and macrospiculata and the arborescent Nephthea brassica nephtheid taxa led to the generalization that soft corals can move very slowly over the substrate, by means of are ephemeral pioneer organisms, with rapid growth directional growth at the leading edge of the colony rates, high rates of vegetative reproduction, the ability stem and tissue resorption from the trailing edge to form runners, and whole-colony movement. For (Benayahu & Loya 1981, La Barre & Col1 1982). example, high rates of asexual reproduction were No studies so far have quantified life history traits of found in the xeniid Efflatounaria (Dinesen 1985) and tropical members in the third family, the Alcyoniidae, the Red Sea xeniid Xenia macrospiculata (Benayahu & in spite of the family's high abundances in a wide Loya 1984). The nephtheid Litophyton viridis shows range of reef types (Dinesen 1983). Habitats of Alcy- high growth rates, the ability to re-attach dislodged oniidae include wave-exposed areas of reef crests on the windward sides, flow-protected regions in lagoons, and zones of low irradiance on steep slopes, overhangs O Inter-Research 1995 Resale of full article not permitted 146 Mar Ecol Prog Ser 126: 145-1512. 1995 and below 30 m depth (K. Fabricius unpubl.). In the METHODS present study, life history parameters of the 2 most common alcyoniid genera, Sinularja and Sarcophyton, Study sites. Three monitoring sites were established were investigated on clear-water reefs 60 to 80 km off at 10 m depth on the windward sides of each of 6 mid- the east Australian coast. To date, 110 Sinularia and 36 and outer-shelf reefs. The reefs represented a range of Sarcophyton species have been described from the different habitat types within the region, with varying Indo-Pacific (reviews by Verseveldt 1980, 1982). How- degrees of hard and soft coral cover, current and wave ever, a great number of species are as yet undescribed, exposure, and slope angle (Table 1). Bowl, Dip and and field identification of most species is impossible. Coil Reef are located on the outer edge of the conti- An investigation of genera, rather than species, is jus- nental shelf and are exposed to strong currents and tifiable given the current taxonomic uncertainties. wave action, whereas the positions of Grub, Centipede Sinularia colonies form mats several centimeters thick and Yankee Reefs provide more protection from these whose surfaces are structured by protruding lobes or physical forces. High numbers of crown-of-thorns ridges. Large sclerites are densely packed in the colony, starfish (Acanthasterplanci)removed most of the hard and only 1 polyp type exists. Sarcophyton colonies are coral cover on 3 of the reefs 5 to 8 yr prior to the com- distinctly mushroom-shaped, with a thick fleshy stem mencement of the study (Grub, Yankee and Dip). The elevating the polyp-bearing marginally folded colony other 3 reefs (Centipede, Bowl and Coil) were affected disk (capitulum)off the substratum. The colonies are di- very little, if at all, by these coral-eating starfish (Bass morpbic, i.e. they possess 2 polyp types: the autozooids et al. 1988) and hard coral cover was significantly or feeding polyps, and embedded between those, the higher than on the disturbed reefs in 1991 (K. Fabricius tentacle-free and sterile siphonozooids. Both taxa are unpubl.). A direct comparison of life history traits light-dependent due to their symbiotic zooxanthellae. between sites was not attempted, slnce each site may Sinularia and Sarcophyton are both abu.ndant on the have h.ad a unique species compos~tion.The distance central Great Barrier Reef. A survey on 14 mid- and between the 3 sites on each reef was 500 to 2000 m. outer-shelf reefs showed that Sinularia contributed on Because of their wave exposure, 4 of the sites were average 20 to 42 % to the total soft coral cover (1.7% * inaccessible at later resurvey attempts (2 at Bowl, 1 at 2.4 SD cover of hard substratum) at 5 to 30 m depth. Yankee, 1 at Centipede Reef), and were excluded from Sarcophyton accounted for 7.0 % + 6.5 SD of soft coral the data set. Some colonies were lost due to over- cover (0.4% + 0.7 SD of hard substratum) in the upper growth of tags used for labeling. 15 m of water. Its proportion in total soft coral cover Field measurements. The first 10 Sinularia and 10 increased to 55 % at 30 m depth (K. Fabricius unpubl.). Sarcophyton colonies encountered, regardless of size, The present study investigates life history characteris- were at each site permanently marked, with small, tics which allow these genera to achieve such promi- numbered PVC tags which were nailed or tied onto nence. An understanding of their demographic traits is the adjacent substrate. The distance between closest also relevant to the assessment of the effects of anthro- neighbours of tagged colonies ranged from 0.5 to 10 m. pogenic influences and natural forces in coral reefs, The initial 360 colonies were surveyed 7 times over and to refine mechanistic models of succession after 41 mo between February 1991 and July 1994. reef disturbances (Pearson 1981). The present study Colony size was determined as longest and shortest demonstrates life history traits in 2 common alcyoniid colony disk diameter, and stem or colony circumfer- genera which contrast strongly to those described for ence, using calipers and measurement tapes. Repeated any other reef-inhabiting soft coral taxon. size determinations on 30 colonies in expanded and Table 1. Characteristics of the 6 study reefs (3 sites per reef). Wave exposure according to the location on the continental shelf, average cover on the w~ndwardside at 10 m depth of hard and soft corals (based on two 25 m long line transects at each site); COT: records of recent crown-of-thorns starfish outbreaks; slope angle on the 3 study sites Reef Wave exposure Hard coral cover Soft coral cover COT outbreaks Slope ("4. k SD) (''78 + SDI - Bowl High (outer-shelf] 44.4 + 12.8 10.6 i 4.4 No Gradual (15") c011 High (outer-shelf) 43.9 t 16.5 8.6 i 2.4 No Steep (60-80') Dip High (outer-shelf) 19.2 * 8.4 14.1 * 5.7 Yes (1983-1985) Steep (50-80") Yankee Medium (mid-/outer-shelf) 23.3 + 8.1 12.2 i 4.7 Yes (1984-1987) Various (20°, 80') Centipede hloderdte (mid-shelf) 44.1 + 8.0 5.6 i 3.0 No/low Various (40°, 40°, 70') Grub Sloderate (mid-shelf) 27.8 20 9 7.5 i 3.1 Yes (1985-1986) Various (40°,40°, 80') Fabricius: Slow population turnover in soft corals contracted state (5 min after firmly touching the Sinularia and Sarcophyton could not be assessed with colony), plus an interval between the first and second the photographs, because the extent of size reduction survey of only 6 wk, were used to estimate the error during colony contraction was not known. due to colony contraction. This indicated that contrac- In a pilot study on relative recruitment success in soft tion reduced the colony diameter on average by 9% * coral taxa, 180 settlement plates (10 X 15 cm, 2 cm 1.3 SE in healthy Sinularia colonies, and 12% * 1.9 SE thick) cut out of Porites skeleton were tied in lots of in Sarcophyton.