Nature and origins of unique high diversity reef faunas in the Bay of Tomini, Central Sulawesi: the ultimate "centre of diversity"?

The species diversity of staghorn corals (Acropora app.) in the Togian Islands in the Bay of Tomini, Central Sulawesi, suggests that this bay may typify the maximal marine biodiversity associated with the idea of a "centre of diversity" in the central Indo-Pacific. In order to examine the broader application of this finding, faunal assemblages from several phyla in the Togian Islands were assessed against existing phylogenetic, biogeographic and genetic data. It was found that the Togian Islands support a fauna with strong affinities to sites in the western equatorial Pacific, in all the studied groups except gonodactyloid stomatopods. Both species composition and, for labrid and scarid fishes, the distribution of ecological functional groups appear to be influenced by unusually calm and high water clarity conditions in the islands. Populations within the islands have various levels of genetic connectivity to populations in other parts of Sulawesi, including complete isolation of some populations. It is proposed that these islands represent lagoonal refugia from Pleistocene lowstands, with affinities to similar refugia in the western Pacific. Additionally, it is proposed that the faunal composition of the bay has been influenced by post-Pleistocene invasion of Pacific species via the Pacific through-flow current with little or no influence from the Indian Ocean. a Keywords Biogeography, Diversity, Wallace's Line, Coral reefs, Centre of diversity. Introduction The concept of a "centre of diversity" for Indo-Pacific marine animals focuses on the region between the Pacific and Indian Oceans, within a triangle comprising Indonesia and various other island groups, particularly the Philippines (e.g. Stehli and Wells 1971, Piccoli et al. 1987, Briggs 1992, 1999 and the review of Wilson and Rosen 1998). Most frequently, it is assumed that a decrease of diversity away from this centre is synonymous with decreasing opportunities for dispersal eastwards into the Pacific Ocean and westwards into the Indian Ocean (Caley and Schluter 1997). With a view to providing alternative testable hypotheses about the source of central high diversity, this paper examines the components of species diversity within a species-rich bay located close to the perceived "epicentre " of Indo-Pacific biodiversity, the Bay of Tomini in Central Sulawesi (Umbgrove 1939, Wallace 1999a), here regarded as an exemplar of high diversity tropical marine fauna. The study area is within the so-called Wallacea region (Hall and Holloway 1998) which is bounded by Lydekker's line in the east and Wallace's line in the west. This has traditionally