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

Disturbances have played major roles in shaping community structurein Great Barrier Reef coral communities in the period 1980–90.Major causes of coral death have been a coral bleaching episodein 1982, predation by crown of thorn starfish Acanthaster planci,and cyclone damage. A series of 30 permanent photo-transectswas established on six reefs on the Great Barrier Reef in 1979–80.This is a very small sample, but nearly all transects were affectedby one or other of these disturbances early in the decade. Thechanges are summarised as transitions among five stages identifiedin a model incorporating "normal" and "abnormal" patch dynamicsof coral communities. The major disturbances of bleaching, crownof thorns and cyclones tend to cause high coral mortality overlarge areas, but nevertheless it was surprising that such alarge proportion of photo-transects was affected. By the endof 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 than3 m had particularly poor recovery. Hydrodynamic models predictconsiderable patchiness in larval availability, an essentialprecursor for coral recolonization.