Significance of new records of Tridacna squamosa Lamarck, 1819, in the Tuamotu and Gambier Archipelagos (French Polynesia)

Abstract

The giant clam subfamily Tridacninae (family Cardiidae) is an important group of bivalve molluscs found throughout the Red Sea and Indo-Pacific, from East Africa to the Eastern Pacific biogeographic region. The Tridacna genus is currently revised with numerous cryptic species identified with molecular markers. New Tridacna records from the fringe of the known distribution areas are extremely useful to identify genetically unique species, geographic ranges, and to examine processes associated with species differentiation. While Tridacna maxima is abundant in French Polynesia (Central South Pacific Ocean) the larger fluted giant clam Tridacna squamosa was formerly reported only in the Austral Islands in the south. Following a recent survey that spanned 23 islands and atolls of the Society, Tuamotu and Gambier Archipelagos, the presence of T. squamosa between the Cook Islands and Pitcairn Islands is confirmed using both morphological and molecular information, suggesting a relic distribution across the Central Pacific Ocean. Tridacna squamosa is rare, but present throughout Tuamotu and Gambier. However, it remained undetected from the Society Islands, probably due to historical over-fishing. This species is valued by local inhabitants, and is sought after mainly as gifts and also for a limited local shell trade. The rarity of T. squamosa may call for conservation measures in the near future.

Keywords:

• Central Pacific
• Fakarava UNESCO Biosphere Reserve
• fishery management
• giant clam
• Society Islands
• Tridacna

Acknowledgements

We are grateful to a large number of individuals who helped by recording Tridacna squamosa data during the KSLOF expedition. This includes the entire crew of the R/V Golden Shadow; the divers at the Direction des Ressources Marines de Polynésie française Joseph Campanozzi-Tarahu, Gabriel Haumani and Fabien Tertre; the KSLOF scientific divers Laureline Chabran-Poète, Alexandra Dempsey and Marine Couraudon-Réale; and Jenna Moore from the Florida Museum of Natural History. We are also grateful to the inhabitants of Fakarava, Raraka and Hao for showing large shells, and for their kind hospitality. Finally, thanks to Bertrand Make and Valentina Piveteau from the Man and Biosphere Reserve and mandated by the Direction de l'Environnement de Polynésie for the KSLOF expedition, for carrying heavy giant clams shells, found in Fakarava atoll sediments, along 10 km of beach while searching for turtle tracks. M. P. Forster in Hao kindly authorised the use of his photograph (Fig. 6). Finally, we acknowledge two anonymous reviewers and the editors for their constructive comments and corrections.