How much coral cover remained on surveyed Indo-Pacific reefs in 2003?

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Several factors have recently caused mass coral mortality throughout the world's tropical oceans. Yet little was known about when reef-building corals were lost, how quickly, or how the loss varied across locations, especially in the Indo-Pacific, which contains 75% of the world's coral reefs.

Researchers compiled and analyzed a coral cover database containing 6,001 quantitative surveys of 2,667 Indo-Pacific reefs conducted between 1968 and 2004. Surveys in 2003 showed an average coral cover of 22.1% (95% CI: 20.7–23.4); only 7 of the 390 reefs surveyed that year had coral cover above 60%.

Using survey data pooled by year, the researchers estimated annual coral cover loss at approximately 1% over the last twenty years and 2% between 1997 and 2003, or 3,168 km² per year. A repeated-measures regression analysis of a subset of reefs monitored for multiple years from 1997 to 2004 estimated annual loss at 0.72% (n = 476 reefs; 95% CI: 0.36–1.08).

The researchers concluded that the rate and extent of coral loss in the Indo-Pacific were greater than expected. Coral cover was surprisingly uniform across subregions and had declined decades earlier than previously assumed, even on some of the Pacific's most intensely managed reefs. They said the findings have significant implications for policymakers and resource managers seeking successful models to reverse coral loss.