An Indian Ocean centre of origin revisited: Palaeogene and Neogene influences defining a biogeographic realm

Abstract

The biogeography and origins of the shallow marine fauna in the western and northern Indian Ocean are poorly known. Focusing on scleractinian corals, this study synthesizes evidence from extant biogeographical patterns, phylogenetics, plate tectonics and palaeoceanography to provide new support for a hypothesis on an Indian Ocean ‘centre of origin’ for shallow marine taxa. Location The western and northern Indian Ocean, from approximately 90°E westwards, including the Red Sea and Arabian Sea. Methods Synthesis of primary observations and published literature. Results Ten per cent of western and northern Indian Ocean coral species are endemic, with the genera Acropora, Anomastrea, Coscinaraea, Craterastrea, Ctenella, Gyrosmilia, Horastrea, Sclerophyllia, Siderastrea and Stylophora presenting evidence for deep and shallow evolutionary origins unique to the region. Evidence for origins in the Eocene Tethys Sea and Oligocene East Africa-Arabian Province, the global hotspots of shallow tropical marine biodiversity in their time, is derived from the fossil record, clade age, presence of relict species, intra- and inter-specific genetic diversity, Atlantic affinities and extant distributions. Evidence for Neogene origins in geologically active subregions of the Indian Ocean (Red Sea, Arabian Sea, Mascarene Islands) is derived from intraand inter-specific genetic diversity and endemism. The passive tectonic remnant margins of Gondwana (East Africa and Madagascar coasts), combined with prevailing ocean currents, are hypothesized to have provided a stable evolutionary refuge and region of species accumulation, perhaps since the Palaeogene. Main conclusions The evidence supports multiple ‘centres of origin’ for Indian Ocean corals, first in the Palaeogene Tethys Sea, then in the Neogene Red Sea, Arabian Sea and Mascarene Islands. The tectonically inactive East African and Madagascar coasts provide an evolutionary museum for old and new lineages, forming a second and phylogenetically distinct peak of global tropical scleractinian coral biodiversity in the Northern Mozambique Channel.