Date Published: January 24, 2017
Publisher: Public Library of Science
Author(s): Simon Van Wynsberge, Serge Andréfouët, Nabila Gaertner-Mazouni, Colette C. C. Wabnitz, Mathilde Menoud, Gilles Le Moullac, Peva Levy, Antoine Gilbert, Georges Remoissenet, Jodie L. Rummer.
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 Tatakoto 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.
Among the 12 species of giant clams (Family Cardiidae, Subfamily Tridacninae), Tridacna maxima and T. squamosa, are widespread throughout the Indo-Pacific and can be found from the Red Sea and southeast Africa in the west to the Central Pacific in the east . Depth range is also species-dependent, but individuals are usually restricted to shallow areas (< 7–10 m for T. maxima), where light provides them most of the energy necessary for survival, growth, and reproduction, owing to the ability of their symbiotic zooxanthellae to photosynthesize . The geographical ranges of these two widespread species also cover a variety of reef types, including continental islands, open and closed atoll and submerged reefs, all characterized by very different biophysical environments . In this study, we highlight notable differences in estimated growth rates and natural mortality for T. maxima between the lagoons of Tatakoto and Tubuai. These differences may be due to a number of biotic and abiotic factors, which we discuss below. Source: http://doi.org/10.1371/journal.pone.0170565