Constancy and Change in some Great Barrier Reef Coral Communities: 1980–1991

Abstract

Disturbances have played major roles in shaping community structure in Great Barrier Reef coral communities in the period 1980–90. Major causes of coral death have been a coral bleaching episode in 1982, predation by crown of thorn starfish Acanthaster planci, and cyclone damage. A series of 30 permanent photo-transects was established on six reefs on the Great Barrier Reef in 1979–80. This is a very small sample, but nearly all transects were affected by one or other of these disturbances early in the decade. The changes are summarised as transitions among five stages identified in a model incorporating “normal” and “abnormal” patch dynamics of coral communities. The major disturbances of bleaching, crown of thorns and cyclones tend to cause high coral mortality over large areas, but nevertheless it was surprising that such a large proportion of photo-transects was affected. By the end of the decade, none of the damaged transects had “recovered,” in terms of percentage coral cover or numbers of new colonies. Photo-transects and visual surveys showed sites deeper than 3 m had particularly poor recovery. Hydrodynamic models predict considerable patchiness in larval availability, an essential precursor for coral recolonization.