Temporal patterns in coral assemblages on the Great Barrier Reef from local to large spatial scales

From 1992 to 1997 changes in cover of hard and soft corals and macro-algae were monitored using annual video transect surveys on the northeast flank of up to 52 reefs along most of the Great Barrier Reef (GBR). Trends in cover of hard corals, algae and soft corals were usually consistent among clusters of adjacent or nearby reefs. This consistency probably reflected the spatial scales of the effect of episodic disturbances caused by cyclones or crown-of-thorns starfish Acanthaster planci. Hence, our comprehensive monitoring of a single habitat provided an effective indicator of the status and trends on adjacent reefs. Moreover, we observed broad-scale patterns of increase and decline in coral cover that suggest that a 'patchwork mosaic' null model is a useful concept at scales of whole reefs and regions. At a large spatial scale (up to 10 degrees of latitude), cover of hard corals within the NE slope habitat averaged 29% (+/-12.4 standard deviation) and increased by 1.7% (+/-6.5) over 5 yr of surveys. Cover of soft corals and algae remained constant and averaged 14% (+/-12.4) and 41% (+/-16.6) respectively. Inner shelf, mid-shelf and outer shelf reefs in a 'recovery' phase increased their cover of hard coral at average annual rates of 2.6% (+/-3.0), 3.9% (+/-4.1) and 4.3% (+/-4.5) respectively. Year-to-year changes in cover of soft corals were typically smaller and less variable than changes in cover of hard corals or algae. There was no evidence of any shift to alternative stable states of assemblage composition.