Life histories and abundance patterns of colonial corals on Jamaican reefs

Large-scale patchiness within the cervicornis zone at Discovery Bay, Jamaica, before the recent hurricane was due chiefly to variations in cover of Acropora cervicornis. Montastrea annularis and Agaricia agaricites, the 2 other important species in the zone, varied less among 3 sites surveyed, though M. annularis had slightly greater cover on the exposed east forereef. Relative species abundances of corals < 5 cm in diameter were very different from those in the total faunas. In all areas, A. agaricites predominated. A. cerv~cornis and M. annularis were rare. To examine processes producing the abundance patterns, life history observations were made on natural massive substrata surveyed in June 1977 and September 1978, and experimental substrata set out in April 1977 and examined from December 1977 to March 1978 and from October 1978 to January 1979. Agariciids were even more important as recruits than in the small-coral abundance data. Growth of small corals was variable, apparently somewhat greater In the branching A. cervicornis than in other species. Mortality on experimental substrata was > 90 %, as compared with < 60 % for natural substrata. The difference probably reflected the smaller size of corals on experimental substrata: size differences had a significant effect on mortality on natural substrata. Five-day laboratory experiments with the omnivorous echinoid Diadema antillarum showed that its grazing activities could cause strongly size-dependent early mortality. Extrapolation suggested that a coral remaining < 3 mm in diameter for 2 to 3 mo would have only a 20 % chance of surviving longer. With minor specific differences in early growth, the small-coral abundance patterns might thus develop from recruitment patterns. In feeding experiments, the common predators Hermodice carunculata and Coralliophila abbreviata both showed a strong preference for A. cerv~cornis. Corall~oph~la also ate M. annularis, but A. agaricites was untouched. Apparently the activities of these predators alone would simply increase the relative abundance of the predominant small coral. Known routine processes in this system are insufficient to account for the abundance patterns of corals in the zone These results emphasize the need to consider long-term processes and rare events in accounting for the abundance of long-lived colonial organisms.