Normal Coral Growth Rates on Dying Reefs: Are Coral Growth Rates Good Indicators of Reef Health?

Massive coral growth rates may be poor indicators of coral reef health where coral reefs are subject to combined eutrophication and sedimentation. Massive coral growth (vertical extension) rates on polluted reefs were not different from extension rates on unpolluted reefs, while live coral cover was low and bioerosion intensity high, leading to net reef erosion and death of the polluted reefs. These combined patterns of coral growth rates, coral cover and bioerosion were documented on reefs affected by land-based pollution in the Java Sea, South Sulawesi and Ambon, Indonesia. Acid-insoluble content in coral skeletons reflected land-based pollution stress on reefs more reliably than did coral extension rates. Coral skeletal density was lower on polluted Java Sea reefs than on unpolluted reefs used as reference sites, but coral calcification rates were not significantly different. The most eutrophied Java Sea reefs had net carbonate loss, indicating net reef erosion, while a fringing reef adjacent to mangroves and two unpolluted coral cays both had positive net carbonate production. Coral growth and reef growth were decoupled, in that coral growth rates did not reliably predict rates of reef accretion. The apparently paradoxical combination of normal to rapid coral growth and net reef erosion on polluted reefs illustrates the need for a whole-reef perspective on coral reef health.