SLOW POPULATION TURNOVER IN THE SOFT CORAL GENERA SINULARIA AND SARCOPHYTON ON MID-SHELF AND OUTER-SHELF REEFS OF THE GREAT-BARRIER-REEF

Aspects of the life history of the 2 common soft coral genera Sinularia 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 Sarcophyton, average radial growth was around 0.5 cm yr(-1), and relative growth rates were size-dependent. In Sinularia, populations changed very slowly over time. Their per capita mortality was low (0.014 yr(-1)) 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(-1)). In Sarcophyton, mortality was low in colonies larger than 5 cm disk diameter (0.064 yr(-1)), and significantly higher in newly recruited small colonies (0.88 yr(-1)). 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 settlement 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.