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Link to original content: http://pubmed.ncbi.nlm.nih.gov/28118406/
Growth, Survival and Reproduction of the Giant Clam Tridacna maxima (Röding 1798, Bivalvia) in Two Contrasting Lagoons in French Polynesia - PubMed Skip to main page content
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Comparative Study
. 2017 Jan 24;12(1):e0170565.
doi: 10.1371/journal.pone.0170565. eCollection 2017.

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

Simon Van Wynsberge  1   2 , Serge Andréfouët  2 , Nabila Gaertner-Mazouni  1 , Colette C C Wabnitz  3 , Mathilde Menoud  1   4 , Gilles Le Moullac  4 , Peva Levy  4 , Antoine Gilbert  5 , Georges Remoissenet  6
Affiliations
Comparative Study

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

Simon Van Wynsberge et al. PLoS One. .

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.

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Conflict of interest statement

We declare no competing interests. The company “Ginger Soproner” did not fund this study. The fact that A. Gilbert is now employed by “Ginger Soproner” does not alter our adherence to PLOS ONE policies on sharing data and materials.

Figures

Fig 1
Fig 1. Location of studied sites.
(A) Map of French Polynesia highlighting the location of Tatakoto in the Tuamotu Archipelago and Tubuai in the Austral Archipelago. (B-C) Satellite images and monitoring stations (red dots) at Tubuai and Tatakoto. For comparison, white dots indicate tagging stations used in a previous study [18].
Fig 2
Fig 2. Temperature series recorded at Tatakoto and Tubuai over the timeframe of this study.
(A) Raw data; (B) Data centralized to their mean; (C) Data centralized to their mean and seasonality removed (i.e., residuals of models as estimated using Eq 4). Grey lines: sensor n°1 (Tatakoto); Yellow lines: sensor n°2 (Tatakoto); Red lines: sensor n°3 (Tatakoto); Black lines: sensor n°3 (Tubuai). See Table 1 and Fig 1 for location and depth of sensors. Predicted values of models defined by Eq 4 appear as smooth lines in the upper panel.
Fig 3
Fig 3. Physical characteristics of Tatakoto and Tubuai lagoons during the study period.
(A) Mean wave height, (B) water level (C) residuals of temperature (mean and seasonality removed) recorded by sensors n°3 (see Table 1 and Fig 1) at Tatakoto (black) and Tubuai (grey) during the 2013–2014 warm season. (D) Temperature series for the three sensors deployed at Tatakoto during a 10-day period of low wave height (< 10−3 m; indicated by dashed lines) (dashed line: sensor n°1, spaced dashed line: sensor n°2, solid line: sensor n°3).
Fig 4
Fig 4. Growth rate and growth curve of giant clams for the two studied sites.
(A) Predicted means (solid lines) and confidence intervals (dashed lines) for growth rate (G) as a function of mean shell length for Tridacna maxima at Tatakoto (red, n = 93) and Tubuai (black, n = 352). Shell growth rate G (cm.d-1) is the ratio between shell length increment and number of days between two measurements (see methods). (B) Growth curves obtained from data collected in this study (curve n°13 for Tatakoto and curve n°11 for Tubuai) and information gleaned from the literature. 1: Papua New-Guinea [28]; 2: Tonga [23]; 3: Solitary islands [29]; 4: Rose atoll [30]; 5: One Tree Island [21]; 6: Fangatau [18]; 7: Tatakoto [18]; 8: Tubuai [18]; 9: Aitutaki [25]; 10: Manihiki [25]; 12: Suwarrow [25]; 14: Takapoto [31]. (C) G (mean ± SD) estimated from sampling at each station. Stations are further subdivided into a deep site (P) and a shallow site (S) at Tatakoto.
Fig 5
Fig 5. Physical characteristics of the Tatakoto lagoon from August 2013 to July 2014.
Dashed vertical lines indicate when gonads were sampled. The lower panel displays values for the maturity indices SPZ (grey) and GSI (black), as well as the relative proportion of male and female tissues (GSR, black joined dots) obtained at each gonad sampling event. The water level line is greyed out before 15/10/2013 as the sensor was placed slightly deeper than usual on its pedestal (20 to 40 cm). Right panel is a zoom of water level (grey) and mean wave height (black) for the period 13–21 May.
Fig 6
Fig 6. Instantaneous rate of natural mortality (M) for the two studied sites over the course of the study period (2012–2014).
(A-B) Instantaneous rate of natural mortality (M) calculated per shell length class for Tatakoto (A) and Tubuai (B). Black dots display the number of samples used to calculate M. (C-D) Instantaneous rate of natural mortality (M) calculated for each station (mean ± SD over depth and survey time periods for Tatakoto (n = 4 for stations 11, 14 and 19; n = 8 for others) and over survey time periods for Tubuai (n = 3)).
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Publication types

Grants and funding

This work was supported by a PhD fellowship from the “Ministère de l’Enseignement Supérieur et de la Recherche” to Université de la Polynésie française and additional funding provided to Labex CORAIL under the TEKE-TEKE Project (www.labex-corail.fr). Sensors were sponsored by the SITADEL 2012 project, GOPS (www.observatoire-gops.org). The funders provided support in the form of salaries [SVW, MM], but did not have any role in study design, data collection or analyses performed, decision to publish, or preparation of the manuscript. The specific roles of individual authors are articulated in the ‘author contributions’ section.

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