Biodiversity of the Indian Ocean from the perspective of staghorn corals (Acropora spp)

The Indian Ocean represents a vital link in the knowledge of where modern reef-building corals began existence, how they survived changes in the configuration of world oceans and how they will survive into the future. To address the central questions of the Census of Marine Life (CoML) for the Indian Ocean, we use the dominant modern reef-building coral genus Acropora as an exemplar, working from a large database of world-wide distributions. Previous biodiversity and biogeographic studies of this genus indicated a demarcation between Indian and Pacific Ocean faunas, despite predominantly widespread distribution ranges. From the distribution of modern and fossil Acropora assemblages, it is evident that the genus Acropora evolved in either the western Indian Ocean or Mediterranean regions of the late Tethys Sea, rather than the central Indo-Pacific as is often assumed from “centre of origin” models. In this paper, additional data on Acropora biodiversity from regions of the Indian Ocean is examined to give a preliminary indication of the nature and origin of their biogeographic relationships. The Indian Ocean has unique faunas particularly in the region of the Red Sea and Arabian Gulf. While it is open to influx of Pacific Ocean species via the Indonesian Throughflow current, there is little likelihood of migration of Indian Ocean species into the Pacific. In the event of continuation of global warming, southerly migration of coral species ranges may also take place. Monitoring for such changes could be built into a further detailed compilation of Acropora species composition from sites within the Indian Ocean, which will also lead to finer-scale resolution of the distribution patterns shown here.