Proceedings 9th International Coral Reef Symposium, Bali, Indonesia 23-27 October 2000, Vol. 1 Nature and origins of unique high diversity reef faunas in the Bay of Tomini, Central Sulawesi: The ultimate “centre of diversity”? C.C. Wallace1, G. Paulay2, B.W. Hoeksema3, D.R. Bellwood4, P.A. Hutchings5, P.H. Barber6, M. Erdmann7 and J. Wolstenholme1,4 ABSTRACT The species diversity of staghorn corals (Acropora spp.) 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. Keywords Biogeography, Diversity, Wallace’s Line, attention paid to the marine organisms of the area. This is Coral reefs, Centre of diversity. despite the importance of the area for marine biogeo- graphy, as it represents the region where the Indian and Introduction Pacific oceans meet. While references to dual patterns of distribution of The concept of a “centre of diversity” for Indo-Pacific terrestrial fauna and flora across the Indonesian archi- marine animals focuses on the region between the Pacific pelago have been commonplace since the pioneering and Indian Oceans, within a triangle comprising Indonesia discovery of Alfred Wallace (1857) (e.g. Whitmore 1981, and various other island groups, particularly the Michaux 1991, Parenti 1991, Vane-Wright 1991, How Philippines (e.g. Stehli and Wells 1971, Piccoli et al. and Kitchener 1997) the possibility of a dual pattern of 1987, Briggs 1992, 1999 and the review of Wilson and distribution for marine organisms has been recognised Rosen 1998). Most frequently, it is assumed that a less frequently and only quite recently (e.g. Woodland decrease of diversity away from this centre is 1983, Wallace 1997, 2001, Hoeksema 1989, 1992, 1997, synonymous with decreasing opportunities for dispersal Parenti and Louie 1998, Woodruff et al. 1999, Barber et eastwards into the Pacific Ocean and westwards into the al. 2000). Species compositions of Acropora, the staghorn Indian Ocean (Caley and Schluter 1997). With a view to coral genus, show a pattern that is reminiscent of the providing alternative testable hypotheses about the source “Wallace’s Line” patterns (Wallace 1997, 2001) and the of central high diversity, this paper examines the Togian Islands in the Bay of Tomini appear to have an components of species diversity within a species-rich bay additional fauna that is unique in the archipelago (Wallace located close to the perceived “epicentre” of Indo-Pacific 1999a). biodiversity, the Bay of Tomini in Central Sulawesi Studies by the first and last authors reported several (Umbgrove 1939, Wallace 1999a), here regarded as an new species of Acropora in this area, some of which exemplar of high diversity tropical marine fauna. were seen to be endemic to the Bay of Tomini (Wallace The study area is within the so-called Wallacea region and Wolstenholme 1998). New data from the Acropora (Hall and Holloway 1998) which is bounded by Lydek- fauna of New Britain in NE Papua New Guinea revealed ker’s line in the east and Wallace’s line in the west. This an unusually close affinity with that of the Bay of Tomini has traditionally been an area of great biogeographic (Wallace 1999b). This suggested a possible explanation interest because it lies between the Asian and Australian similar to that found for amphidromous fish assemblages plates which have converged in relatively recent in lakes of Central Sulawesi, Borneo and Papua New geological history (Hamilton 1979, Hall 2000). However, Guinea by Parenti (1991), i.e that a Tethyan relictual the great majority of studies concern terrestrial and fauna was retained in those localities (Wallace 1999a). freshwater organisms and there has been very little 1 Museum of Tropical Queensland, Townsville, Qld. 4810, Australia. [email protected] 2 Florida Museum of Natural History, University of Florida, Gainsville, FL32611-7800, USA 3 Department of Invertebrates, National Museum of Natural History, P.O. Box 9517, 2300 RA Leiden, The Netherlands 2300RA 4 Department of Marine Biology, James Cook University, Townsville, Qld. 4811, Australia. 5 Australian Museum, P.O. Box A285, Sydney South, N.S.W. 2010, Australia. 6 Department of Organismic and Evolutionary Biology, Harvard University, Ma. 02138, USA. 7 Department of Integrative Biology, University of California, Berkley, Ca. 94720, USA. Fig. 1 Location and detail of the Togian Islands (inset), within the Bay of Tomini, and stations used in the “Tethyana” expedition marked as stars. In light of these findings, we decided to investigate crustacea. Several of these groups were also sampled for whether similar patterns existed for other marine taxa in genetic and phylogenetic studies by the authors and by the Bay of Tomini. The “Tethyana Expedition” was associate researchers. Additionally, species of Acropora mounted to examine patterns of distribution and ende- were re-examined in line with the goals of this study. micity for other marine groups in the Bay, including During the expedition, the following hypotheses were bivalve mollusks, selected coral-associated gastropods, examined with respect to the composition of the marine labrid and scarid reef fishes, terebellid polychaetes, corals fauna of the Bay of Tomini: of the family Fungiidae and gonodactyloid stomatopod Table 1 Summary of the tests used to explore hypotheses regarding the biodiversity of the Bay of Tomini. Hypothesis Test 1. Tethyan relics Presence of endemics or narrowly distributed species, that are from basal phylogenetic lineages. 2. Specialisation Predominance of adaptive fauna (eg. deep, calm conditions). 3. Geographic isolation Presence of endemics and genetically isolated populations. 4. Pacific fauna Species composition in relation to biogeography. Presence of Pacific Ocean species not common in Indonesia. 5. Pleistocene refuge Presence of species shared with western Pacific refugia. 1. Endemics or narrowly distributed species that are 2. The Bay of Tomini offers opportunities for specia- Tethyan relics are retained around the islands lisation in unusual or protected habitats. (Parenti hypothesis, see above). The upper and 3. The bay is geographically isolated, leading to central arms of Sulawesi have different tectonic endemic fauna. Reports on the Pacific through-flow origins and were joined towards the end of the current to date indicate that this water body might Miocene (Surmont et al. 1994), so it is not difficult by-pass the Bay, or at least only exchange water to see the Bay as a remnant of the sea that origi- with the outer limits of the bay (Wyrtki 1961, nally lay between them (McKenzie 1991). Gordon and Fine 1996, Hall 2000). 4. A Pacific fauna is invading the bay. This is almost extinct in all but the deepest calm-water sites due the opposite of hypothesis 3, and follows the to reasoning that the Pacific through-flow current, even if only partially effective, would make it pos- Pleistocene low sea stands. sible for larvae to be transported westward from the This paper reports on preliminary findings from the Pacific at least since the last ice age (Hall 2000). expedition and tests for hypotheses that best fit the results 5. The bay includes a relictual Indo-West Pacific collected to date (Table 1). The taxonomy, biogeographic deepwater lagoonal fauna. This hypothesis was information, fossil record and genetic markers available previously developed to explain patterns of Pacific for these groups varied considerably, so that some hypo- molluscan distribution (Paulay 1990), and proposes theses could only be addressed from the perspective of that a previously more widespread fauna became some of the groups. Table 2 Summary of methods employed in collection and analysis of the different groups of organisms. Initials indicate researchers involved: CW Carden Wallace, GP Gustav Paulay, BH Bert Hoeksema, DB David Bellwood, PH Pat Hutchings, PB Paul Barber, ME Mark Erdmann, JW Jackie Wolstenholme. Group Sampling Methods / Researcher Analyses Terebellid Most specimens in-faunal: rock samples (approx 80 cm3) Species composition; phylogenetic studies, polychaetes collected, two each from deep slope (25 m), mid slope (10 biogeographic comparison with limited m) and reef top; polychaetes removed by breaking open available data. All other polychaete families rock above water. Limited genetics sampling. PH were collected and