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PLoS One
2011 Mar 10;63:e17516. doi: 10.1371/journal.pone.0017516.
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Disturbance and the dynamics of coral cover on the Great Barrier Reef (1995-2009).
Osborne K
,
Dolman AM
,
Burgess SC
,
Johns KA
.
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Coral reef ecosystems worldwide are under pressure from chronic and acute stressors that threaten their continued existence. Most obvious among changes to reefs is loss of hard coral cover, but a precise multi-scale estimate of coral cover dynamics for the Great Barrier Reef (GBR) is currently lacking. Monitoring data collected annually from fixed sites at 47 reefs across 1300 km of the GBR indicate that overall regional coral cover was stable (averaging 29% and ranging from 23% to 33% cover across years) with no net decline between 1995 and 2009. Subregional trends (10-100 km) in hard coral were diverse with some being very dynamic and others changing little. Coral cover increased in six subregions and decreased in seven subregions. Persistent decline of corals occurred in one subregion for hard coral and Acroporidae and in four subregions in non-Acroporidae families. Change in Acroporidae accounted for 68% of change in hard coral. Crown-of-thorns starfish (Acanthaster planci) outbreaks and storm damage were responsible for more coral loss during this period than either bleaching or disease despite two mass bleaching events and an increase in the incidence of coral disease. While the limited data for the GBR prior to the 1980''s suggests that coral cover was higher than in our survey, we found no evidence of consistent, system-wide decline in coral cover since 1995. Instead, fluctuations in coral cover at subregional scales (10-100 km), driven mostly by changes in fast-growing Acroporidae, occurred as a result of localized disturbance events and subsequent recovery.
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21423742
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Figure 1. Temporal trends in percent cover of hard coral on the Great Barrier Reef (1995–2009).(A) Average coral cover for the whole GBR; (B–P) Average coral cover in each subregion. Dots and dashed lines show the average subregion temporal profile with 95% confidence intervals. For the whole GBR there was a non-significant linear trend of −0.27%, (−0.68, 0.14 95%CI) as a result of asynchronous increases and decreases in each subregion. The grey shaded area indicates periods of coral decline associated with disturbance.
Figure 2. Linear trends in percent cover of hard coral, Acroporidae and non-Acroporidae families on the Great Barrier Reef (1995–2009).(A) Hard Coral, (B) Acroporidae coral, (C) Non-Acroporidae coral. Straight lines show the linear trend and confidence intervals (dashed lines). Individual reef profiles are in grey. Non-Acroporidae coral declined significantly (Table S1).
Figure 3. Temporal trends in percent cover of hard coral on the Great Barrier Reef (1995–2009).(B–P) Average annual coral cover in each subregion. Dashed lines show the subregion temporal profile and the straight lines show the average linear trend. Individual reef profiles are in grey. Disturbances associated with coral decline are represented by a dot for each reef where that type of disturbance occurred.
Figure 4. Prevalence and severity of disturbance events.
A.planci, storms and multiple disturbances were associated with the greatest coral decline and the largest distribution of coral loss. Despite bleaching being widespread in 1998 and 2002, coral mortality was relatively low. (A) the loss in live coral cover as a percentage of the pre-event cover. (B) Relative magnitude of loss of pre-event cover summed for all reefs and years.
Figure 5. Intrinsic growth rates following different disturbance types.The intrinsic growth rate r estimated by fitting a logistic growth model to periods of coral recovery following disturbance events. Growth rates were similar following all disturbance types with the exception of A. planci. Carrying capacity K was estimated at 80.1%.
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