Growth, survival and reproduction of the giant clam Tridacna maxima (Röding 1798, Bivalvia) in two contrasting lagoons in French Polynesia

Simon van Wynsberge (1) , Serge Andrefouet (2, 1) , Nabila Gaertner-Mazouni (3) , Colette Wabnitz (4) , Mathilde Menoud (3) , Gilles Le Moullac (3) , Peva Levy (3) , Antoine Gilbert (5) , Georges Remoissenet (6)

1 ENTROPIE [Nouvelle-Calédonie] - Ecologie marine tropicale des océans Pacifique et Indien
2 IRD [Nouvelle-Calédonie] - Institut de Recherche pour le Développement
3 EIO - Ecosystèmes Insulaires Océaniens (UMR 241)
4 Secretariat of the Pacific Community
5 CoReUS - Écosystémique des communautés récifales et de leurs usages dans le Pacifique insulaire
6 Direction des Ressources Marines et Minières

Shell growth, reproduction, and natural mortality of the giant clam Tridacna maxima were characterized over a two-year-period in the lagoon of the high island of Tubuai (Austral Archipelago) and in the semi-closed lagoon of Tatakoto (Tuamotu Archipelago) in French Polynesia. We also recorded temperature, water level, tidal slope, tidal range, and mean wave height in both lagoons. Lower lagoon aperture and exposure to oceanic swells at Tata-koto than at Tubuai was responsible for lower lagoon water renewal, as well as higher variability in temperature and water level at Tatakoto across the studied period. These different environmental conditions had an impact on giant clams. Firstly, spawning events in the lagoon of Tatakoto, detected by gonad maturity indices in June and July 2014, were timed with high oceanic water inflow and a decrease in lagoon water temperature. Secondly, temperature explained differences in shell growth rates between seasons and lagoons, generating different growth curves for the two sites. Thirdly, local mortality rates were also found to likely be related to water renewal patterns. In conclusion, our study suggests that reef aperture and lagoon water renewal rates play an integral role in giant clam life history, with significant differences in rates of shell growth, mortality and fertility found between open versus semi-closed atoll lagoons in coral reef ecosystems.

Mots clés: Population-size; Mass mortality; Archipelago; Islands; Invertebrates; Communities; Juvenile; Reproduction; Giant Clam; Atoll; Tridacna maxima; Lagoons; Eastern Tuamotu; French Polynesia

Domaines: Biologie animale

Simon van Wynsberge, Serge Andrefouet, Nabila Gaertner-Mazouni, Colette Wabnitz, Mathilde Menoud, et al.. Growth, survival and reproduction of the giant clam Tridacna maxima (Röding 1798, Bivalvia) in two contrasting lagoons in French Polynesia. PLoS ONE, 2017, 12 (1), ⟨10.1371/journal.pone.0170565⟩. ⟨hal-02155838⟩