Comparative demography of three species of scleractinian corals using age- and size-dependent classifications

Abstract

Three species of massive reef-building coral, Goniastrea aspera, G. favulus, and Platygyra sinensis, were studied on two fringing reef flats in the central Great Barrier Reef from 1982 to 1984. Total population sizes ranged from 25 to 292 colonies, and remained relatively constant. Population structures and dynamics based on both age and size were described. Differences between these two classifications were primarily due to tissue fission or shrinkage of colonies. In populations dominated by small size classes, young corals were not necessarily the most abundant. Similarly, populations dominated by the largest size classes were not always dominated by the oldest corals. In several populations, mean colony size decreased slightly with increasing age, though variability in size also increased. Mortality patterns were similar in all three species, with the youngest genets and smallest ramets suffering the highest death rates. While mortality in older or larger corals was low, the incidence of partial mortality and fission was higher in these groups. Age-specific fecundity increased rapidly once reproductive age was reached at ≈5 yr, but fecundity decreased slightly in the older age classes due to the decrease in mean colony size. Estimated mean generation times ranged from 33 to 37 yr.