Growth, Survival and Reproduction of the Giant Clam Tridacna maxima (Röding 1798, Bivalvia) in Two Contrasting Lagoons in French Polynesia

Abstract

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.

The Giant Marine Gastropod Campanile Giganteum (Lamarck, 1804) as a High‐Resolution Archive of Seasonality in the Eocene Greenhouse World

“…(a) Plots of growth curves of specimens of Campanile gastropods from this study with growth curves of other fast growing gastropods and bivalves showing how the growth of these giant gastropods compares to that in other mollusks. Data on the large extant gastropod L. gigas (Berg, 1976; Radermacher et al, 2009), the large extant bivalve Tridacna gigas (Van Wynsberge et al, 2017), the fastest‐growing extinct elevator rudist bivalve Vaccinites ultimus (Gili & Götz, 2018), and the smaller fast‐growing gastropods Trochus pyramis , Nerita albicilla , and Conus flavidus (Frank, 1969) from different families are included for comparison. (b) Maximum annual growth rates of Campanile shells (this study) and other mollusk taxa.…”

The Small Giant Clam, Tridacna maxima Exhibits Minimal Population Genetic Structure in the Red Sea and Genetic Differentiation From the Gulf of Aden

“…Information on the spawning frequency or natural spawning cues of T. maxima is important to understand the larval dispersal potential, and yet it is largely lacking. The natural spawning activity of giant clams in a semi-enclosed basin could be triggered by temperature changes corresponding to the periods of lagoon water renewal (Gilbert et al, 2006;van Wynsberge et al, 2017). During the summer months, the water in the southern Red Sea is refreshed by the intrusion of colder and nutrient-rich Gulf of Aden Intermediate Water (GAIW), which stretches nearly the entire length of the Red Sea (∼1500 km) (Bower and Abualnaja, 2012).…”

“…These large mollusks act as ecosystem-engineers in coral reefs by supporting high calcification rates (Rossbach et al, 2019) and helping to maintain the overall reef biodiversity and functionality (Neo et al, 2015). Giant clams are generally found on shallow reefs, where light is essential for the survival, growth, and reproduction (van Wynsberge et al, 2017) because the mantle tissue is packed with extracellular single-celled algae of the Symbiodiniaceae family (Taylor, 1969;Yonge, 1975). These algal symbionts within the clams are vulnerable to prolonged thermal stress that can result in giant clam bleaching (Junchompoo et al, 2012).…”

Drivers of the Abundance of Tridacna spp. Giant Clams in the Red Sea

“…densities on a global scale and across regions, it is important to consider the latest revisions of the Tridacninae taxonomy, including the recent evidence for high cryptic diversity (Kubo and Iwai, 2007;Huelsken et al, 2013;Fauvelot et al, 2020). Especially for regions that are inhabited by a number of different giant clam species (e.g., the Coral Triangle, Western Pacific and the Eastern Indian Ocean), previous density estimates for T. maxima, the species with the broadest geographical distribution (bin Othman et al, 2010), may thus be under-or over-estimated (Johnson et al, 2016;Van Wynsberge et al, 2017). This could be particularly true where reefs are also inhabited by the recently resurrected Tridacna noae (Su et al, 2014), as this species has been reported to be frequently misidentified as T. maxima (Su et al, 2014;Borsa et al, 2015;Neo and Low, 2017).…”