Ed Ricketts Memorial Lecture
Research Professor of Biology,
University of California,
Long-Term Dynamics of Corals on Heron Island, Great Barrier Reef
At Heron Island, Great Barrier Reef, Australia, over a 30 year period, the abundance and recruitment of reef-building corals varied drastically, at several scales of space and time. At five of the six study areas, the abundance of corals declined nearly to zero at some time during the study period. Recurrent hurricanes were a major cause of coral mortality. Hurricane damage varied considerably among the different study areas. At different sites, both the degree of damage caused, and the rate and maximum extent of recovery thereafter, were influenced by the history of previous damage and recovery. Recruitment of corals also varied at different spatial and temporal scales. Recruitment varied substantially among years, but years of high rates were not consistent among the different study areas. Recruitment rate increased as free space increased, at 3 of the 4 shallow sites; free space was preempted by either corals or macroalgae. The spatial scales over which coral abundance varied gave evidence of the scales at which the underlying causal mechanisms operated. An individual hurricane usually caused about the same damage to all sites within a habitat, but its effects less often extended into another habitat. The temporal scales in which coral abundance varied also differed among habitats. The time scale between a trough and the next peak in abundance is at least 20 years, probably longer, in the shallower and deeper depths, while at intermediate depths, this time scale was about 10 years.