A 30-YEAR STUDY OF CORAL ABUNDANCE, RECRUITMENT, AND DISTURBANCE AT SEVERAL SCALES IN SPACE AND TIME

Observations over a 30-yr period revealed a considerable degree of nat ural variation in the abundance of corals on Heron Island, Great Barri er Reef, Queensland, Australia. Cover ranged from <0.1% to >80%, with a similar large range in colony density, at several temporal and spati al scales. Much of this variation was due to the type, intensity, and spatial scale of disturbances that occurred. Coral assemblages usually recovered from acute disturbances, both on Heron Island and on other Indo-Pacific reefs. In contrast, corals did not recover from chronic d isturbances of either natural or human origins, or from gradual declin es. Recovery was slower after acute disturbances that altered the phys ical environment than after disturbances that simply killed or damaged corals. The space and time scales of declines and recoveries in abund ance were much smaller on the wave-exposed side of the reef than on th e side protected from storms. Recruitment rates were reduced by preemp tion of space by corals or macroalgae, and by storms that altered the substratum. Thus, the dynamics of abundance in this coral community ca n be largely understood through the variation in types and scales of d isturbances that occurred, and the processes that took place where dis turbances were rare.