Rates of decline and recovery of coral cover on reefs impacted by, recovering from and unaffected by crown-of-thorns starfish Acanthaster planci: a regional perspective of the Great Barrier Reef

Manta tow surveys of the perimeters of reefs throughout the Great Barrier Reef (GBR) assessed broad-scale changes in hard coral cover on reefs impacted by, recovering from and unaffected by Acanthaster planci outbreaks. Mean coral cover was 16 to 40% on reefs with no history of A. planci outbreaks, depending on location on the GBR. Coral cover increased at approximately 2% yr(-1) on southern reefs, while there was no significant increase on such reefs in other regions. Hard coral cover on reefs with A. planci outbreaks declined at a mean annual rate of 6% to an average level of 9%. Coral cover on southern reefs that were recovering from sustained A. planci outbreaks increased at about 4% yr(-1) while such reefs showed an annual increase of 0.8% in the remaining regions. A total of 78% of recovering reefs showed a positive growth rate, assuming linear growth, the time for coral cover to increase by 30%, was estimated at between 5 yr and well over 1000 yr. In addition to providing regional estimates of the decline and recovery of reefs due to A. planci outbreaks, this study highlights the variability in rate of recovery between reefs and raises the possibility that not all reefs will recover from sustained outbreaks.