Biogeography of the Decapod and Stomatopod Crustacea of the Tropical Pacific: Issues and Prospects1

Biogeographic patterns of the Crustacea (Decapoda and Stomatopoda) are given for the tropical Pacific, based on recent taxonomic studies combined with emergence of regional databases. Conclusive results are still difficult to obtain due to incomplete regional inventories and existence of complexes of sibling species with unclear taxonomic status. A time-series graph of the number of new records plotted against time is computed for several central Pacific islands (French Polynesia, Pitcairn, Easter Island, and Clipperton). It demonstrates that the fauna is still insufficiently known in those places. A biodiversity gradient is calculated for several taxa between West and East Pacific. The traditional decrease between Australia and French Polynesia is confirmed for higher taxa (Brachyura, Anomura), but at lower taxonomic levels it is not always verified (e.g., hermit crabs, Calcinus; crabs, Trapezia). A map is presented illustrating the following provisional biogeographic results: (1) cryptic endemic species recognized in the Marquesas Islands; (2) presence of a distinct faunistic province in the South Pacific, along the 25° S parallel, including Rapa and Easter Islands; (3) theoretical position of the border between the Indo-West Pacific (IWP) and East Pacific (EP) faunistic provinces (84° W on the seamounts of Sala y Gόmez/Nazca and 110° W on Clipperton); (4) differences between Clipperton, with a mixed IWP-EP fauna (43% IWP versus 57% EP species), and the Galápagos, with obvious EP affinities (10% IWP versus 90% EP species).