The shallow water hard corals of Pulau Weh, Aceh Province, Indonesia

The corals reefs of Aceh, Indonesia, are one of the few areas of the world where the fauna, in particular the scleractinian corals, have yet to be described. The area is likely to be of high biogeographical significance due to its position at the northern tip of Sumatra on the boundary of three major water bodies, the Indian Ocean, the Andaman Sea and the Straits of Malacca. Here, we present the quantitative description of the assemblage structure of the shallow water scleractinian corals of Pulau Weh. Carbonate reefs are rare on the island, the exception being some fringing reef development in shallow water in at least two locations. Most colonies are attached to granite boulders which make up the ocean floor at most sites on the north and west coast, or rest in the sandy substrates that dominate the ocean floor on the east coast. Coral cover in February 2009 was over 40% at most sites, ranging from 21% ± 3.0 SE to 80% ± 2.4. Coral assemblage structure varied widely around Pulau Weh with assemblages from the western and northern sites being dominated by Acropora spp. in particular, species with digitate, encrustingarborescent and tabular morphologies. In contrast, coral assemblages on the west coast were dominated by massive Porites spp. and Heliopora. The Acropora fauna is dominated by species with digitate and encrusting arborescent morphologies, very different from many other regions in Indonesia. This unusual species composition plus the presence of a high proportion of endemics indicates that the region should be a high priority for conservation efforts. Further taxonomic studies at depth and further afield are required to fully describe this unique fauna that supports a small diving industry and a number of fisheries.