OBJECTIVES AND BACKGROUND TO THE 1994 FRANCO-AUSTRALIAN EXPEDITION TOTAIARO ATOLL (TUAMOTU ARCHIPELAGO, FRENCH-POLYNESIA)

The 9 km(2) uplifted lagoon of Taiaro Atoll (15 degrees 45'S, 144 degr ees 38'W) is hypersaline due to its isolation from the ocean, yet it c ontains a high diversity of fish. The question unifying our expedition was to discover whether these assemblages could be self-sustaining de spite very limited contact with the ocean. Although we were constraine d by time, collections of fish larvae showed that some species can com plete their life-cycle within the lagoon, while others differed geneti cally between the lagoon and the ocean, consistent with restricted gen e flow. The lagoon contained few oceanic species of zooplankton, confi rming its general isolation, but nevertheless some fish species may de pend upon infrequent colonisation from the ocean (when large waves dri ve water over the normally dry reef crest). Isotopic signatures in fis h otoliths suggest the basis for a more definitive and inclusive test of the sources of the lagoonal assemblage.