Bioerosion of live massive corals and branching coral rubble on Indonesiancoral reefs

The degree of bioerosion of live massive corals and rubble from branching c orals mere measured on nine reefs from two regions of Indonesia: the Java S ea and Ambon. Bioerosion in massive corals was measured by collecting live corals, cutting and X-raying slabs, and measuring the cross-sectional area removed from each slab by the various bioeroding organisms. A technique ana lysing branching coral rubble was developed and similarly used to evaluate the degree of bioerosion on the reefs. This rubble technique has potential advantages over the massive coral technique since it does not require the e xpense and technical expertise of making and analysing X-rays, nor does it require the destruction of living coral heads. The effectiveness of this ru bble technique is evaluated here, Levels of bioerosion in massive coral hea ds and rubble from branching corals are each compared with environmental va riables and health parameters of the nine reefs. Overall, both techniques s howed that bioerosion levels mere positively correlated with environmental variables indicative of eutrophication. Bioerosion of live massive corals a nd of branching coral rubble mere positively correlated. At the Ambon sites , where the eutrophication levels differ only slightly compared to the Java sites, bioerosion in coral rubble was a more sensitive indicator of eutrop hication stress than bioerosion measured from massive coral heads. The rubb le technique we outline is a useful rapid reef assessment technique that co uld be a valuable contribution to the 'reef survey toolbox'. (C) 2000 Elsev ier Science Ltd. All rights reserved.