Relating variation in species composition to environmental variables: a multi-taxon study in an Indonesian coral reef complex

In order to manage and conserve coral reefs it is essential to understand the factors that structure reef communities. In Indonesia's Jakarta Bay - Pulau Seribu reef complex, pronounced on-to-offshore variation in a number of variables was observed. Live coral cover, and echinoderm and fish species richness were higher in midshore sites than either in- or offshore sites. Variation in habitat structure, the abiotic environment, distance between sample sites and covariation of these factors separately explained 9.6 to 15.1% of the spatial variation in the composition of corals, echinoderms and fishes. Together, all three components explained > 50% of the variation in composition. This indicates that spatial and environmental factors influence the distribution of species across the study area and have important implications for the large-scale management of this reef ecosystem. Large scalemanagement and protection of these reefs will probably be important because the majority or reefs were in poor to very poor condition as exemplified by low (< 25%) coral cover. The coral cover of some inshore reefs was particularly low (< 1%). Inshore coral assemblages tended to be composed of stress-tolerant or specialised pioneers of highly perturbed environments. There were also locally high densities of potentially destructive species such as the sea urchin Diadema setosum. Midshore sites had relatively high coral cover comprising Acropora and Montipora spp. that were rare or absent elsewhere, presumably due to their sensitivity to pollution and mechanical damage. Most of the offshore sites had relatively low live coral cover and were dominated by rapidly growing pioneers or by stress- or -sediment-tolerant species. Spatial variation in the composition of taxa is discussed in the context of past-and-ongoing disturbances, including land-based pollution, coral mining, sedimentation and destructive fishing practices.