Black-lip Pearl Oyster Pinctada Research Articles

Assessing regional connectivity patterns of bivalvia in fragmented archipelagos: Insights from biophysical modeling in French Polynesia

Larval dispersal and connectivity are key processes that drive marine metapopulation dynamics, and therefore should be well characterized when designing effective management strategies. While temperature and food availability can structure marine species connectivity patterns, their contribution has not been thoroughly investigated in highly fragmented archipelagos. We used biophysical modeling of larval dispersal to explore the connectivity patterns of species with complex life-cycles across French Polynesia (FP), a territory formed by more than a hundred small, geographically isolated islands covering an area as large as Europe. We first simulated ten years of larval dispersal to investigate the spatial and temporal (seasonal and interannual) variability in larval dispersal pathways for different hypothetical species exhibiting a range of Larval Precompetency Period (LPP) values. Then, using the black-lip pearl oyster (Pinctada margaritifera) as a model species, we accounted for variability in the LPP induced by temperature and food availability, as derived from a Dynamic Energy Budget (DEB) model. The model showed that food availability and mesoscale turbulence (eddies) in the Marquesas jointly constrained larval dispersal, reducing its potential connectivity with other archipelagos in FP. The DEB simulations also revealed seasonal and interannual variability in connectivity driven by environmental conditions. However, accounting for food and temperature effects on larval development, barely changed the connectivity pattern at regional scale due to the remoteness of this archipelago. Our study thus provides appropriate management units definition at regional scale for the species across FP.

Pearl shape classification using deep convolutional neural networks from Tahitian pearl rotation in Pinctada margaritifera

Tahitian pearls, artificially cultivated from the black-lipped pearl oyster Pinctada margaritifera, are renowned for their unique color and large size, making the pearl industry vital for the French Polynesian economy. Understanding the mechanisms of pearl formation is essential for enabling quality and sustainable production. In this paper, we explore the process of pearl formation by studying pearl rotation. Here we show, using a deep convolutional neural network, a direct link between the rotation of the pearl during its formation in the oyster and its final shape. We propose a new method for non-invasive pearl monitoring and a model for predicting the final shape of the pearl from rotation data with 81.9% accuracy. These novel resources provide a fresh perspective to study and enhance our comprehension of the overall mechanism of pearl formation, with potential long-term applications for improving pearl production and quality control in the industry.

Improved ocean-based nursery culture of blacklip pearl oyster (Pinctada margaritifera) juveniles in mesh baskets using cyanoacrylate adhesive

The blacklip pearl oyster, Pinctada margaritifera, supports well-established cultured pearl industries throughout the Pacific with various nursery culture methods used to on-grow juvenile oysters to a size suitable for pearl production. Locally-available plastic baskets are commonly used to rear juvenile oysters, but they do not prevent oysters from aggregating, which negatively impacts production. To develop an understanding of how basket-based nursery culture might best be adapted for rearing juvenile P. margaritifera, this study examined growth and survival of juveniles of varying sizes and stocked at varying densities in mesh baskets when using a cyanoacrylate adhesive to prevent aggregation. During a 3.5-month ocean-based nursery culture period, stocking density was shown to have a significant effect on growth (F = 11.53, p < 0.001), yet a minimal influence on oyster survival (χ2 = 5.05, p = 0.28). By contrast, stocking size influenced survival (χ2 = 7.17, p = 0.03), but had minimal impact on growth (F = 3.24, p = 0.08). Given that mean ( ± SD) survival of juveniles ranged from 65.0 ± 14.4% to 94.0 ± 8.2% and dorsoventral shell growth ranged from 13.9 ± 6.2 mm to 19.7 ± 6.3 mm, depending on stocking density and stocking size, these factors clearly merit consideration before fixing juvenile oysters to baskets with an adhesive. Such results broaden our knowledge of nursery culture methods for P. margaritifera and improve options for small-scale pearl farmers in the Pacific.

Natural stocks of Pinctada margaritifera pearl oysters in Tuamotu and Gambier lagoons: New assessments, temporal evolutions, and consequences for the French Polynesia pearl farming industry.

Knowledge of the status of the black-lipped pearl oyster Pinctada margaritifera populations is critical for the sustainability of the French Polynesia black pearl farming industry. Indeed, this activity relies on collection of spat settling out of the water column, which is inherently related to the abundance of in situ benthic stocks and their reproductive capacities. From surveys performed between 2016 and 2021, we present new stock assessments of natural wild oyster populations from four contrasted pearl farming lagoons (Gambier, Takapoto, Raroia, Takume). Also using Ahe atoll historical data, we first highlight how results vary with the methods (Direct, Zonal and Cokriging) used to scale in situ density measurements to lagoon-scale stocks. Takapoto and Gambier populations were also previously surveyed at least twice since the 1980s, allowing to demonstrate with field data clear changes in stock distributions and population structures. The consequences of our findings are discussed to provide recommendations for stock monitoring and management in the future.

Growth and Survival of Black-lip Pearl Oyster Pinctada margaritifera (Linnaeus, 1758) in Bamboo and Metal-framed Pocket Net Baskets Subjected to Cleaning and Without Cleaning Conditions

The farming of black-lip pearl oyster Pinctada margaritifera (Linnaeus, 1758) has been a viable industry for small and large-scale farmers in the South Pacific, but not in the Philippines, where it is monopolized by large-scale farms primarily based on the gold-lip pearl oyster Pinctada maxima. To promote the industry among small-scale players, we simplified the culture method by using bamboo slats as frame materials and compared them to the common material used in pearl oyster culture, metal rods. A total of 400 individuals seven-month-old hatchery-produced P. margaritifera were used as experimental animals, distributed in the following treatments with five replications: T1 (metal-framed pocket net basket with monthly cleaning), T2 (metal-framed pocket net basket without monthly cleaning), T3 (bamboo-framed pocket net basket with monthly cleaning), and T4 (bamboo-framed pocket net basket without monthly cleaning). Growth was fast in the first four months and slowed down after that. Two-way analysis of variance found no significant differences between the average anteroposterior shell (APS) length increments of pearl oysters between two types of frame, and between two cleaning conditions. Survival rates did not significantly differ between types of basket frame, and between cleaning conditions. Parameters of the “Typical” von Bertalanffy growth model (L∞ = 118.41 mm, K = 1.03 year-1, and t0 = 0.12) suggested that oyster would take about 23.16 months to reach 100 mm APS length, a size suitable for nucleus implantation. The life span of bamboo slats as basket frame was half of the metal frame, and the absence of cleaning has reduced the operational cost by up to 82.08%.

Assessment of an alternative Pinctada margaritifera spat collector in French Polynesia

Plastic waste in the oceans is a growing concern due to its size diversity, its ubiquitous nature and its impact on both marine organisms and ecosystems. While threatened by this marine plastic litter, the aquaculture industries also represent one of its major sources. In French Polynesia, black-lip pearl oyster (Pinctada margaritifera) farming is no exception. Wild spat collection has been described as a source of pollution because of the numerous particularly fragile and brittle shade-mesh plastic collectors used locally and often mismanaged when no longer usable. Thus, with the aim of helping to reduce this pollution, the present study is focused on the assessment of reusable plate collector as a potential alternative. We tested, using an in situ approach, the influence of the collecting surface position (i.e. horizontal vs vertical), plate color (i.e. black vs orange) and density (i.e. 25 plates vs 50 plates) on Pinctada margaritifera and Pinctada maculata spat settlement. Our results showed that 50-plates collectors, whatever their color and position, were more efficient to collect both kinds of spat than shade-mesh collectors (P < 0.0001). They also induced a higher number of Pinctada margaritifera spat than on the 25-plates collection device although there was no significant difference in numbers of Pinctada maculata spat (P < 0.0001). However, every type of plate collector presented a decreased mean length of the spat collected (P < 0.0001) compared to the shade-mesh collector. Furthermore, horizontal positioning of the collecting surface greatly improved the spat numbers on plate collectors (P < 0.0001) although there was no effect on shade-mesh collectors (P > 0.05). Finally, our results indicated that, among all the devices tested, the black horizontal 50-plates collector was the most efficient to collect spat and particularly Pinctada margaritifera. These first findings thus tend to suggest that these black re-usable plate collectors could be an efficient alternative to the currently used shade-mesh collectors.

Understanding connectivity of pearl oyster populations within Tuamotu atoll semi-closed lagoons: Cumulative insight from genetics and biophysical modelling approaches

Connectivity affects species demography, (meta)population dynamics, evolution, phylogeny and biogeography. Various methodological approaches are applied to measure connectivity. Biophysical modelling can explore systematically the influence of atmospheric, oceanic and ecological forcing, while genetics measures connectivity patterns within the sampling strategy limit. In the Pacific Ocean pearl farming lagoons, the activity relies on spat collecting of the black lipped pearl oyster Pinctada margaritifera occurring after the larval dispersal phase, which follows spawning from wild or farmed populations. Biophysical 3D modelling and genomic studies have both separately brought insights on within-lagoon connectivity and on the origin of spats. Here, we combined previous genetics results with new realistic biophysical modelling scenarios to elucidate connectivity in Ahe Atoll lagoon. When combined, we identified the weather sequence likely explaining the realized connectivity observations. We discuss the strengths, weaknesses, opportunities and threats of combining these two approaches considering specific pearl farming demographic connectivity questions.

Tracing key genes associated with the Pinctada margaritifera albino phenotype from juvenile to cultured pearl harvest stages using multiple whole transcriptome sequencing

BackgroundAlbino mutations are commonly observed in the animal kingdom, including in bivalves. In the black-lipped pearl oyster Pinctada margaritifera, albino specimens are characterized by total or partial absence of colouration resulting in typical white shell phenotype expression. The relationship of shell colour with resulting cultured pearl colour is of great economic interest in P. margaritifera, on which a pearl industry is based. Hence, the albino phenotype provides a useful way to examine the molecular mechanisms underlying pigmentation.ResultsWhole transcriptome RNA-sequencing analysis comparing albino and black wild-type phenotypes at three stages over the culture cycle of P. margaritifera revealed a total of 1606, 798 and 187 differentially expressed genes in whole juvenile, adult mantle and pearl sac tissue, respectively. These genes were found to be involved in five main molecular pathways, tightly linked to known pigmentation pathways: melanogenesis, calcium signalling pathway, Notch signalling pathway, pigment transport and biomineralization. Additionally, significant phenotype-associated SNPs were selected (N = 159), including two located in the Pif biomineralization gene, which codes for nacre formation. Interestingly, significantly different transcript splicing was detected between juvenile (N = 1366) and adult mantle tissue (N = 313) in, e.g., the tyrosinase Tyr-1 gene, which showed more complex regulation in mantle, and the Notch1 encoding gene, which was upregulated in albino juveniles.ConclusionThis multiple RNA-seq approach provided new knowledge about genes associated with the P. margaritifera albino phenotype, highlighting: 1) new molecular pathways, such as the Notch signalling pathway in pigmentation, 2) associated SNP markers with biomineraliszation gene of interest like Pif for marker-assisted selection and prevention of inbreeding, and 3) alternative gene splicing for melanin biosynthesis implicating tyrosinase.

Understanding marine larval dispersal in a broadcast-spawning invertebrate: A dispersal modelling approach for optimising spat collection of the Fijian black-lip pearl oyster Pinctada margaritifera.

Fisheries and aquaculture industries worldwide remain reliant on seed supply from wild populations, with their success and sustainability dependent on consistent larval recruitment. Larval dispersal and recruitment in the marine environment are complex processes, influenced by a multitude of physical and biological factors. Biophysical modelling has increasingly been used to investigate dispersal and recruitment dynamics, for optimising management of fisheries and aquaculture resources. In the Fiji Islands, culture of the black-lip pearl oyster (Pinctada margaritifera) is almost exclusively reliant on wild-caught juvenile oysters (spat), through a national spat collection programme. This study used a simple Lagrangian particle dispersal model to investigate current-driven larval dispersal patterns, identify potential larval settlement areas and compare simulated with physical spat-fall, to inform targeted spat collection efforts. Simulations successfully identified country-wide patterns of potential larval dispersal and settlement from 2012–2015, with east-west variations between bi-annual spawning peaks and circulation associated with El Niño Southern Oscillation. Localised regions of larval aggregation were also identified and compared to physical spat-fall recorded at 28 spat collector deployment locations. Significant and positive correlations at these sites across three separate spawning seasons (r(26) = 0.435; r(26) = 0.438; r(26) = 0.428 respectively, p = 0.02), suggest high utility of the model despite its simplicity, for informing future spat collector deployment. Simulation results will further optimise black-lip pearl oyster spat collection activity in Fiji by informing targeted collector deployments, while the model provides a versatile and highly informative toolset for the fishery management and aquaculture of other marine taxa with similar life histories.

Population Connectivity and Genetic Assessment of Exploited and Natural Populations of Pearl Oysters within a French Polynesian Atoll Lagoon.

In French Polynesia, the production and exportation of black pearls through the aquaculture of the black-lip pearl oyster Pinctada margaritifera provide the second largest economic income for the country after tourism. This industry entirely relies on the collection of natural spats from few highly recruiting lagoons. In recent years, pearl oyster producers have experienced variable success rates in spat collection, with significant spatial and temporal variability in spat supply, driving uncertainty in the future of pearl production. This study combines, for the first time in a farmed lagoon, genetic (SNPs), demographic (sex ratio, age), and biophysical data (larval dispersal modelling) to shed new light on population dynamics, connectivity, and spat recruitment in Ahe Atoll, a well-studied pearl farming site. Our results indicate that the geographical structuring of the natural populations and the contribution of both natural and exploited stocks to the production of spats result from the interaction of hydrodynamic features, life history traits and demographic parameters: the northeastern natural populations are older, not well connected to the southwestern natural populations and are not replenished by larvae produced by adjacent exploited populations. Moreover, we observe that the exploited populations did not contribute to larval production during our experiment, despite a sampling period set during the most productive season for spat collection. This is likely the result of a strong male bias in the exploited populations, coupled with a sweepstakes reproductive strategy of the species. Our results warrant further investigations over the future of the northeastern older natural populations and a reflection on the current perliculture techniques.

Inside black pearls

The quality of natural and cultured pearls depends on the size, shape and properties of the surface. The inner structure of the pearl is not known, and not taken into account. Indeed, it is assumed that the cultured pearl is a nucleus covered by a thin organic layer, a thin prismatic layer and a thick nacreous layer. The examination of spherical and pear shape samples resulting from the grafting of the black lip pearl oyster (Pinctada margaritifera) shows that this assumption is, in most cases, erroneous. Optical, electron and atomic force microscopic observations, infrared and Raman analyses, as well as micro X-ray fluorescence and micro X-ray absorption near-edge spectroscopy data show that the inner structure of a pearl does not depend on its shape. Both circle or pear shape and spherical pearls show a large variability of the inner structures and composition. There are no two identical samples. Moreover, the arrangement is irregular within a single pearl, and some structures (aragonitic pseudo-prisms) do not exist in the shell.

Impact of environmental variability on Pinctada margaritifera life-history traits: A full life cycle deb modeling approach

The black-lipped pearl oyster (Pinctada margaritifera) is extensively farmed in French Polynesia to produce black pearls. For a sustainable management of marine resources, studying interactions between organisms and environment, and the associated factors and processes that will impact their life cycle and thus modulate population dynamics is a major research priority. Here, we describe black-lipped pearl oyster energy acquisition and use, and its control by temperature and food concentration within the Dynamic Energy Budget (DEB) theory framework. The model parametrization was based on literature data and a specific laboratory experiment. Model validation was carried out thanks to historical in-situ datasets and a dedicated field survey. Three theoretical environmental scenarios were built to investigate the response of the pearl oyster to environmental variations. We successfully modeled a wide range of life-stage-specific traits and processes, especially the delayed acceleration of growth after settlement. Applying the model on field data collected at three different culture sites required only one free-fitted parameter, the half saturation coefficient Xk, which controls how ingestion depends on food density. Xk integrates all variations linked to the trophic environment. Analysis of the kinetics of energy fluxes under theoretical environmental scenarios suggests that temperature variations induce seasonality of reproduction in a species thought to spawn opportunistically throughout the whole year. The major influence of food concentration fluctuations on growth rate and reproductive effort is highlighted. The model showed the lower performances associated with recovery time between food-rich and starvation periods. The implications of these findings in the context of black pearl farming in a changing environment are discussed.

Overview of the Development and Modern Landscape of Marine Pearl Culture in the South Pacific

Natural marine pearls were a rare and valuable by-product of a fishery targeting pearl oyster shells for their mother-of-pearl (MOP). This fishery developed around the world throughout the 18th century and increased significantly through the 19th century in Australia and the Pacific islands. Overfishing of the MOP resource led to the development of pearl oyster spat (juvenile) collection techniques to assist stock replenishment. Although the MOP industry eventually ceased in the 20th century, spat collection provided a basis for pearl culture industries in the Pacific, that used nucleated pearl culture techniques developed in Japan. Today, French Polynesia is the largest producer of cultured round pearls in the South Pacific using the endemic black-lip pearl oyster Pinctada margaritifera. The successful French Polynesian pearl industry was a catalyst for development of pearl culture in other Pacific island countries such as the Cook Islands and Fiji. As well as significant export income, pearl culture offers livelihood opportunities (upstream and downstream) to coastal communities at a number of levels, including collection of pearl oyster spat (juveniles) for on-selling to pearl farms, and jewelry and MOP shell craft production. Despite being compatible with local lifestyles, round pearl culture has significant barriers to entry, including high initial investment, high operational costs, and requirement for a high level of technical skills. Alternatively, significant opportunities for coastal communities exist from production of mabé pearls (half pearls) because although not as valuable as high-grade round pearls, they are cheaper to produce, demand fewer technical skills, and pearls can be produced by local people with minimum training. Diversification of round pearl farms into mabé pearl production, or the establishment of stand-alone mabé pearl farms, is increasingly prevalent in Pacific pearl-producing nations, motivated by risk minimization, a broader market base, and a much simpler and less costly industry entry pathway.

Macrozoobenthos in the intertidal zone of the Ly Son island

The surveys of macrozoobenthos fauna of Ly Son tidal area were carried out at 8 stations in September 2016. The 4 replicate samples were collected in high, middle and low tidal zones at each station. The results record 92 taxa of mollusc (accounting for 35% of total number of taxa), 76 taxa of crustacean (29%), 71 taxa of polychaete (27%) and 22 taxa of echinoderm (9%). Among them, there are 7 species of valuable resources that were exploited for food such as sea cucumber (Holothuria (Semperothuria) cinerascens), collector urchin (Tripneustes gratilla), diadema urchin (Echinothrix diadema), Diadema savignyi (belonging to Echinoderma), strawberry conch (Strombus luhuanus), goldmouth turban (Turbo chrysostomus) and bearded horse mussel (Modiolus barbatus). Some species with beautiful shapes and colors are used for handycraft such as black-lip pearl oyster (Pinctada margaritifera), small giant clam (Tridacna maxima), Chinese cowrie (Cypraea chinensis)... The densities of mactozoobenthos vary from 38 to 1,632 individuals/m2 between stations and tend to increase from high to low tide zones; from sandy bottom and shore rock to dead coral habitats covered by seaweed and seagrass bed.

Strong genetic isolation of the black-lipped pearl oyster (Pinctada margaritifera) in the Marquesas archipelago (French Polynesia)

The French Polynesian islands are internationally known for their black pearls, produced by culture of the black lipped pearl oyster Pinctada margaritifera. The ongoing development of hatcheries for P. margaritifera in French Polynesia poses new challenges for the industry, particularly regarding the maintenance of genetic diversity in the hatchery stocks. This emphasizes the necessity to characterize the genetic diversity and differentiation within natural and exploited populations, to carefully select putative parental populations. The present study aimed at validating the phylogenetic status and investigating genetic attributes of populations from the only two non-exploited archipelagos of French Polynesia, the Marquesas archipelago, and the Australes archipelago, never analysed before. We found that individuals from both archipelagos belonged to P. margaritifera species. However, while the Australes population was genetically similar to non-exploited populations of the Tuamotu, the Marquesas populations were highly differentiated from the rest of the populations. This differentiation cannot not be only attributed to geographic distance and aquaculture status, but likely to hydrodynamic barriers allowing vicariant events to take place. Our results add up to other studies describing the Marquesas archipelago as a hotspot for biodiversity and differentiation, with some of the highest levels of endemism and vicariance found among marine species worldwide and provide precious information on available genetic resources for the implementation of P. margaritifera selective breeding and its genetic conservation in French Polynesia.

Microbiome of the Black-Lipped Pearl Oyster Pinctada margaritifera, a Multi-Tissue Description With Functional Profiling.

Elucidating the role of prokaryotic symbionts in mediating host physiology has emerged as an important area of research. Since oysters are the world’s most heavily cultivated bivalve molluscs, numerous studies have applied molecular techniques to understand the taxonomic and functional diversity of their associated bacteria. Here, we expand on this research by assessing the composition and putative functional profiles of prokaryotic communities from different organs/compartments of the black-lipped pearl oyster Pinctada margaritifera, a commercially important shellfish valued for cultured pearl production in the Pacific region. Seven tissues, in addition to mucous secretions, were targeted from P. margaritifera individuals: the gill, gonad, byssus gland, haemolymph, mantle, adductor muscle, mucus, and gut. Richness of bacterial Operational Taxonomic Units (OTUs) and phylogenetic diversity differed between host tissues, with mucous layers displaying the highest richness and diversity. This multi-tissues approach permitted the identification of consistent microbial members, together constituting the core microbiome of P. margaritifera, including Alpha- and Gammaproteobacteria, Flavobacteriia, and Spirochaetes. We also found a high representation of Endozoicimonaceae symbionts, indicating that they may be of particular importance to oyster health, survival and homeostasis, as in many other coral reef animals. Our study demonstrates that the microbial communities and their associated predicted functional profiles are tissue specific. Inferred physiological functions were supported by current physiological data available for the associated bacterial taxa specific to each tissue. This work provides the first baseline of microbial community composition in P. margaritifera, providing a solid foundation for future research into this commercially important species and emphasises the important effects of tissue differentiation in structuring the oyster microbiome.

Variation in cultured pearl quality traits in relation to position of saibo cutting on the mantle of black-lipped pearl oyster Pinctada margaritifera

Cultured pearl production from Pinctada margaritifera uses the biomineralization capacities of the mantle graft, the saibo, which is usually obtained from only the middle mantle section of the donor oyster. To evaluate the potential for using other parts of the mantle, this study explores and describes the cultured pearl quality traits, pearl size, shape, surface defects and colour parameters obtained with saibo from the entire length of the mantle, comprising the four following sections: 1) posterior, 2) connection with the gills, 3) middle, (the section usually used commercially), and 4) anterior. Rates of nucleus retention and oyster mortality were also recorded and compared between sections. For this, two experimental grafts were designed and conducted in two contrasting culture sites, using 10 selected wild donor oysters in each to perform a total of 1536 grafts. Mantle section comparison revealed that the anterior section was different from the three other sections, showing: 1) the lowest nacre deposition rate in terms of weight and thickness, 2) the palest pearls, with lowest rate of the attractive overtone colour and the 3) a lower rate of pearls with lustre. For pearl circles and shape, no difference was recorded among the different mantle sections. Posterior, connection and middle sections showed similar pearl quality traits, revealing how the number of high quality saibo obtainable from the same batch of donors can easily be increased, thus benefitting the P. margaritifera pearl industry. This finding could provide significant benefits to pearl farmers and the further development of current pearl grafting practices.

Crossing Phenotype Heritability and Candidate Gene Expression in Grafted Black-Lipped Pearl Oyster Pinctada margaritifera, an Animal Chimera.

Grafting mantle tissue of a donor pearl oyster into the gonad of a recipient oyster results in the formation of a chimera, the pearl sac. The phenotypic variations of this chimera are hypothesized to be the result of interactions between the donor and recipient genomes. In this study, the heritability of phenotypic variation and its association with gene expression were investigated for the first time during Pinctada margaritifera pearl production. Genetic variance was evaluated at different levels, 1) before the graft operation (expression in graft tissue), 2) after grafting (pearl sac tissue expression in chimera), and 3) on the product of the graft (pearl phenotype traits) based on controlled biparental crosses and the F1 generation. Donor-related genetic parameter estimates clearly demonstrate heritability for nacre weight and thickness, darkness and color, and surface defects and grade, which signifies a genetic basis in the donor oyster. In graft relative gene expression, the value of heritability was superior to 0.20 in for almost all genes; whereas in pearl sac, heritability estimates were low (h2 < 0.10; except for CALC1 and Aspein). Pearl sac expression seems to be more influenced by residual variance than the graft, which can be explained by environmental effects that influence pearls sac gene expression and act as a recipient additive genetic component. The interactions between donor and recipient are very complex, and further research is required to understand the role of the recipient oysters on pearl phenotypic and gene expression variances.

Symbiotic relationship between the carapid fish &lt;em&gt;Onuxodon fowleri&lt;/em&gt; (Ophidiiformes: Carapidae) and the pearl oyster &lt;em&gt;Pinctada margaritifera&lt;/em&gt; (Mollusca: Bivalvia: Pteriidae)

At Makemo Atoll (French Polynesia), the carapid fish Onuxodon fowleri lives in symbiosis with the black-lip pearl oyster Pinctada margaritifera. Although the symbiont seems to live inside its host bivalve by using it as a shelter, additional data are still needed to better understand the exact nature of this association. For this purpose, we implemented an approach using stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N). The δ13C and δ15N values were measured in tissues of the pearl oyster (gonads, gills, mantle and muscles), white muscle tissue from the fish and other food sources. This stable isotope approach was also complemented by the analysis of stomach contents in the carapid fish. Overall, the isotopic compositions measured in the present study support a commensal relationship between O. fowleri and P. margaritifera. In addition, our isotopic data bring new information about another guest living inside P. margaritifera, namely the palaemonid shrimp Conchodytes meleagrinae. Based on the δ13C and δ15N values, it appears that the shrimp might feed on the bivalve gonads.

Influence of water temperature and food on the last stages of cultured pearl mineralization from the black-lip pearl oyster Pinctada margaritifera.

Environmental parameters, such as food level and water temperature, have been shown to be major factors influencing pearl oyster shell growth and molecular mechanisms involved in this biomineralization process. The present study investigates the effect of food level (i.e., microalgal concentration) and water temperature, in laboratory controlled conditions, on the last stages of pearl mineralization in order to assess their impact on pearl quality. To this end, grafted pearl oysters were fed at different levels of food and subjected to different water temperatures one month prior to harvest to evaluate the effect of these factors on 1) pearl and shell deposition rate, 2) expression of genes involved in biomineralization in pearl sacs, 3) nacre ultrastructure (tablet thickness and number of tablets deposited per day) and 4) pearl quality traits. Our results revealed that high water temperature stimulates both shell and pearl deposition rates. However, low water temperature led to thinner nacre tablets, a lower number of tablets deposited per day and impacted pearl quality with better luster and fewer defects. Conversely, the two tested food level had no significant effects on shell and pearl growth, pearl nacre ultrastructure or pearl quality. However, one gene, Aspein, was significantly downregulated in high food levels. These results will be helpful for the pearl industry. A wise strategy to increase pearl quality would be to rear pearl oysters at a high water temperature to increase pearl growth and consequently pearl size; and to harvest pearls after a period of low water temperature to enhance luster and to reduce the number of defects.