ABSTRACT
Guam 15 species, Fiji 13 species, and French Polynesia four species. Th e most distant site, Hawaii, harbors only one species of associated goby. Patterns of species richness appear to be similar for obligately associated shrimps. Because there are few published, comprehensive site-specific surveys for alpheid shrimps in the Indo-Pacifi c, we present unpublished data from our own research on Papua New Guinea, Taiwan, Fiji, and the Society Islands (Th ompson and Th acker, unpublished data) and published reports from the Red Sea (summarized in Karplus 1987). In addition, we include information on shrimp species from Hawaii where the list is likely complete. We collected and/or surveyed ten associated shrimps in Papua New Guinea, three in Taiwan, three in Fiji, and three in French Polynesia. In Hawaii, two species of associated shrimps are reported (Nelson, 2005). While these surveys were not necessarily comprehensive across all habitat types in these locations, the pattern of decreasing diversity away from Indonesia is similar to that shown by associated gobies (Fig. 4.4.1B, Table 4.4.3B). As mentioned in the Systematics section of this review, better elucidation of shrimp taxonomy may further clarify how species richness varies across coral reefs worldwide. Our fi nding that goby and shrimp diversity peaks near Indonesia and declines eastward and westward parallels studies of other coral reef taxa (Bellwood et al., 2005). A number of hypothesis exist to explain the notably high species diversity of marine organisms in the Indo-West Pacifi c (IWP) (reviewed in Palumbi, 1996, 1997). Th e center of origin model postulates that species arose in the IWP region in the west, and dispersed eastward. The center of accumulation model holds that speciation took place in outlying archipelagos such as Hawaii, the Marquesas Islands or the Society Islands, followed by dispersal westward into the IWP. Th e center of overlap model would indicate no consistent pattern for speciation or dispersal, because IWP diversity would simply be an artifact of overlapping biogeographic provinces in which speciation and dispersal occurred throughout. Although it is diffi cult to defi nitively state that one or more of these hypothesis explains the gradient in associated goby and shrimp species richness, Th ompson et al. (2005) showed that decreasing withinsite genetic diversity for Ctenogobiops feroculus and Alpheus djeddensis in an eastward direction is consistent with dispersal away from the center of diversity (see goby-shrimp phylogeography chapter in this review). Further molecular work on more goby-shrimp taxa could further elucidate causal patterns of the biogeographic gradient in the species richness of associated gobies and shrimps.
