Alain Bodoy

Gametogenic cycle and reproductive effort of the tropical blacklip pearl oyster, Pinctada margaritifera (Bivalvia: Pteriidae), cultivated in Takapoto atoll (French Polynesia)

The gametogenic cycle and the reproductive effort of the blacklip pearl oyster, Pinctada margaritifera, cultivated in Takapoto lagoon were studied for a 1-year period (March 1997-April 1998) by bimonthly observations of gonadal sections, dry tissue weights and gonadal index in a population of pearl oyster composed of three age-groups. Pearl oysters attained sexual maturity in the end of their first year (height ≈ 40 mm), implying that P. margaritiferais a late-maturing species in comparison with other Pteriidae. This species was also confirmed to be a marked protandrous successive hermaphrodite in culture, with 100 % of males at first maturity and 75 % in older pearl oyster (height > 120 mm). The general pattern of gametogenic activity, fairly synchronous in both sexes, was comparable with that of other tropical bivalves: reproduction occurs continuously throughout the year with a maximal activity during the warm season (November-May). No resting period was observed. Quantitative growth data showed that P. margaritifera exhibits an annual synchronised polymodal spawning pattern, with two spawning peaks in age-group I (height ≈ 70 mm) and five in age-groups II (height ≈ 100 mm) and III (height ≈ 120 mm). Spawning was sometimes incomplete, nevertheless a clear relationship between gamete production (PR, g) and size (height H, mm) was obtained: PR = 5.26 × 10 -7 H 2.91 (R_ = 0.99, P < 0.05). Estimation of PR was used to calculate the annual reproductive effort in P. margaritifera. Reproductive effort (%) was similar to those calculated for temperate species and showed a progressive increase with the age of pearl oyster, from 7 % in age-group I to 38 % in age-group III. This study showed that, in a fairly stable tropical environment such as the Takapoto lagoon, P. margaritifera is a multiple spawner, which uses an opportunistic reproductive strategy, allowing investment, all year around, of any surplus energy into gamete production. Surplus energy is ensured by the high pumping rates developed by this non-symbiotic bivalve to succeed in low seston conditions.

In situ suspension feeding behaviour of the pearl oyster, Pinctada margaritifera: combined effects of body size and weather-related seston composition

Abstract In situ clearance rate (CR) and biodeposition of the black pearl oyster, Pinctada margaritifera , were followed during several field experiments from 1996 to 1998 in the lagoon of Takapoto. Serial measurements of total particulate matter (TPM, mg l −1 ), particulate inorganic matter (PIM, mg l −1 ), and particulate organic matter (POM, mg l −1 ) were related to meteorological conditions, especially wind speed. As a general case, POM and PIM increased with wind speed. Nevertheless, PIM increased faster than POM so that the organic content (OC, %) of the TPM decreased progressively when wind speed increased. These TPM variations induced direct changes in feeding processes of P. margaritifera . CR (l h −1 ) averaged 22 l h −1 for a pearl oyster of 1 g dry tissue weight and varied with POM, PIM and dry tissue weight ( W , g) according to the following equation: CR=26.96 PIM −0.42 POM 0.96 W 0.61 . This clearance activity appeared to be the highest of those mentioned for bivalve species in their natural habitats. Pseudofaecal (PF, mg h −1 ) production started for very low PIM load (i.e., 0.17 mg l −1 ) and POM load (i.e., 0.28 mg l −1 ) in water and followed the equation: PF=32.6(POM−0.28)(PIM−0.17) W 0.77 . In other bivalve species, PF are generally observed for higher PIM or POM levels. These PF were mainly constituted of mineral matter (more than 80% in weight). Faecal production (F, mg h −1 ) increased with seston load and reached progressively a plateau (i.e., maximal intestinal transit time) as shown by the equation describing the faecal biodeposition F=20 W 0.49 (1−e −0.66 TPM ). The quantity and the composition of the faecal biodeposit were in a range commonly found in literature. This work confirms, by in situ experiments, previous results obtained in laboratory and especially that P. margaritifera has developed a trophic strategy which consists of processing large amounts of water to gain sufficient energy in poor waters. But this work also showed that meteorological conditions have indirect influences on feeding processes of pearl oyster by modifying significantly the concentration and the composition of seston.

Growth of the black-lip pearl oyster, Pinctada margaritifera, in suspended culture under hydrobiological conditions of Takapoto lagoon (French Polynesia)

Abstract Growth of the black-lip pearl oyster, Pinctada margaritifera var. cumingi, was studied for an annual cycle, from March 1997 to April 1998, in the lagoon of Takapoto atoll (Tuamotu archipelago, French Polynesia). Growth in shell and in tissue were measured every 15 days on three successive age groups of cultivated pearl oysters. At the same time, hydrobiological parameters (temperature, salinity, oxygen concentration, suspended particulate matter), known to have influence on bivalve growth, were followed each week during culture. No seasonal trend was observed in hydrobiological parameters, except for temperature which varied between 26°C and 31°C. The potential food for pearl oysters (particulate organic matter, POM, mg l−1) was slightly concentrated, but always available, so that, in this lagoon environment, no period seemed to be unfavourable to pearl oyster growth. Effectively, growth in shell was regular and shell did not exhibit any annual ring. Nevertheless, as it is often the case for bivalves, shell growth showed a progressive decrease with the age of pearl oyster and followed a classical Von Bertalanffy model: H=160.5 (1−e−0.038 (t−3.73)) with H the shell height (in mm) and t the age (in months). On the other side, growth in tissue did not follow the same pattern than for shell: P. margaritifera exhibited reduced growth rate in tissue during the warm season (November–April) so that a seasonal growth model was more appropriate: Wtissue=6.9/(1+e(5.58–0.208 t−0.435 sin (2π/12 (t−1.427)) with Wtissue, the dry tissue weight (in g) and t the age (in months). Several results concerning growth rates should be of interest for pearl farming. Firstly, the progressive decrease measured in shell growth rate implies, for pearl seeding operations, that the sooner the nucleus is implanted, the greater is the rate of nacreous deposition on this nucleus, and shorter is the time to obtain a marketable pearl for farmers. Secondly, exhaustive comparison, between growth rates obtained in our study and those obtained in other lagoons, tended to demonstrate that there is a small but significant variability in growth between lagoons of the Tuamotu archipelago. Further investigations need to be engaged in order to determine the most suitable sites for pearl farming in French Polynesia. Finally, comparison between growth of P. margaritifera var. cumingi and growth of other pearl oysters showed that P. maxima but also P. margaritifera var. erythraensis would also exhibit fast growth in Polynesian waters and then, would constitute potential candidates for further Polynesian diversification projects.

Triploidy induction in the black scallop (Chlamys varia L.) and its effect on larval growth and survival

Abstract Triploid scallops ( Chlamys varia L.) were produced by treating newly fertilized eggs with cytochalasin B. An exposure of 15 min was applied 10, 20 and 30 min after fertilization. The best results were obtained for a delay of 20 min, both in terms of triploid percentage (78.5%) and 24-h survival (87.5%). Triploidy was detected by karyological examinations of embryos. A karyotype is given for the species. Growth and mortality were compared during larval development for untreated diploid controls and for triploids. No significant difference was found for growth in length, whereas mortality was significantly higher for the triploids, before metamorphosis.

Nutrient fluxes between water column and sediments: potential influence of the pearl oyster culture.

This study quantifies benthic nutrient fluxes and sedimentation rates in the Ahe Atoll lagoon (French Polynesia), in two stations located under pearl oyster frames, and two control stations away from the pearl culture facility. Dissolved inorganic nitrogen fluxes ranged between 2 and 35 μmol N m(-2) h(-1) and Soluble Reactive Phosphorus varied between -3 and 8.2 μmol P m(-2) h(-1). Particulate sedimentation rates beneath the oysters were approximately five times higher than in the control zone and the percentage of small particles (≤63μm) were about the twice. In contrast, sediment composition was similar under and outside the direct influence of oyster frames. In this ecosystem, where primary production is dependent on the available nitrogen, our study revealed that, while highly variable, benthic fluxes could sometimes contribute up to 28% of the nitrogen demand for primary production.

Growth of the oyster, Ostrea puelchana (D'Orbigny), at two sites of potential cultivation in Argentina

Abstract Individual growth of the oyster, Ostrea puelchana , was monitored for 2 years, in two potential sites differing in their average temperature: an open bay, and a closed, coastal lagoon which, however, benefits from sea water exchange through a coastal sandhill. The hydrobiological parameters did not differ significantly between the two areas, except for the water temperatures for which extensive data were obtained and adjusted to sinusoidal models. The annual growth increments (shell height) varied between 10 and 45 mm. Marked seasonal variations in growth rate were observed, for two age groups. An off-bottom technique was used, as well as a suspended culture technique at two different depths. For every experimental condition, growth was faster in the coastal lagoon. Analysis of variance on the daily height-specific growth rates confirmed that these growth rates were significantly higher in the coastal lagoon for the off-bottom technique. For the two age groups, no differences were found between the different depths for the suspended culture technique. However, faster growth was observed in the coastal lagoon for the older individuals. Seasonal variations in growth during the experiments were described by a time-series approach, which included a linear trend and sinusoidal fluctuations. Since growth rates were correlated with the water temperature, this parameter was used to describe the seasonal fluctuations by means of a temperature model. The correlation coefficients between these mocels with two parameters and the original data varied from 0.862 to 0.929.