Monitoring of French Polynesia coral reefs and their recent development

French Polynesia, consisting of 118 islands in the centre of the Pacific Ocean, has more than 15000 km2 of reefs and lagoons managed by the local government. Tourism and pearl culture are the two main economic resources of the country. Polynesian coral reefs are extremely diverse and are among those for which we have thorough knowledge. The exploitation of local resources has been recorded for multiple decades and includes : coral materials, fishing, harvest and export of mother-of-pearl molluscs, pearl production, and ornamental fish. All over the country, many monitoring programmes have been launched to measure the health of reefs and the natural and anthropogenic perturbations that they suffer : hurricanes and seismic events, water quality, health of benthic and fish communities, pearl oyster pathology and radiobiology. These data, collected over the last few decades, allowed to defi ne the relative importance of natural and anthropogenic degradation on reefs and lagoons, and to explain the present status of reefs at different spatial scales. Devastating hurricanes are rare (1903-1906, 1982-1983 and occasionally at other times), but they may annihilate outer slope coral communities on some islands. Bleaching events with considerable coral mortality at different geographical scales occurred mainly in 1991, 1994 and 2003. Outbreaks of Acanthaster destroyed numerous reefs (lagoons and outer slopes) from 1978-1982 and a new demographic wave began in 2006 at many Society islands. Eutrophication events only occurred occasionally and only in some lagoons. Whereas natural catastrophic events degrade the coral reef ecosystem across many islands, at the archipelago or even regional scale, anthropogenic degradation is limited to a few Society Islands, occurring rarely on atolls and not at all on those (one third) which are uninhabited. The main causes of reef degradation in some areas of Tahiti and Moorea include the embankment of fringing zones, coral mining, overfishing, absence of urban sewage treatment and the development of leisure and tourism activities. Because of its large geographical extent, one may conclude that major reef degradation in French Polynesia is caused by catastrophic natural events. On the other hand, anthropogenic degradation is more localized. Unfortunately, the synergistic effects of these causes of degradation prevent reefs from recovering. Optimum coral cover on French Polynesian outer reef slopes is between 50-60 %. After a major destructive impact (hurricane, bleaching, Acanthaster) a reef is reduced to less than 10 % coral cover, however if no more major disturbance events occur a reef will recover in about 12 years. Most of the 15000 km2 of reefs and lagoons in French Polynesia are in good health, and along with their neighbouring reefs in East and Central Pacific they are considered as the least degraded reefs worldwide and at a low risk of becoming degraded in the few next decades. However, we are more and more anxious about the future of reefs in the world particularly because present simulations predict that major impacts of climate change would include : elevation of sea surface temperatures, increase in the strength of hurricanes and acidification of seawater which will affect the formation of coral structuresLa Polynésie française, 118 îles au coeur du Pacifique, possède une surface de plus de 15000 km2 de récifs et lagons gérés par le gouvernement polynésien. Le tourisme et la perliculture représentent les deux ressources économiques majeures du Pays. Les formations récifales très diversifiées sont parmi les mieux connues. Plusieurs suivis d'exploitation des ressources sont opérationnels depuis des décennies : granulats coralliens, pêche pour l'alimentation, collecte et exportation de mollusques nacriers, production de perles, poissons d'ornement. À l'échelle du Pays de très nombreux programmes de surveillance de l'état des récifs et des perturbations qu'ils subissent, naturelles et anthropiques, ont été mis en place: perturbations cycloniques et sismiques, qualité des eaux, état de santé des peuplements benthiques et ichtyologiques, pathologie des nacres, radiobiologie. Toutes ces données recueillies au fil des décennies ont permis d'établir l'importance relative des dégradations naturelles et anthropiques sur les récifs et lagons polynésiens et d'expliquer leur état de santé actuel en considérant différentes échelles spatiales. Les périodes cycloniques dévastatrices pour les récifs sont rares (1903-1906, 1982-1983 et épisodiquement) mais les cyclones ont parfois anéanti les communautés coralliennes de pentes externes dans certaines îles. Les blanchissements suivis de mortalités importantes à des échelles spatiales diverses, ont été surtout ceux de 1991, 1994 et 2003. Les explosions démographiques d'Acanthaster ont détruit de nombreux récifs (lagons et pentes externes) en 1978-1982 et une nouvelle pullulation s'amplifie depuis 2006 dans plusieurs îles de la Société. Les crises dystrophiques n'ont perturbé qu'épisodiquement certains lagons. Si les événements naturels précédents dégradent les récifs à l'échelle de plusieurs îles, d'archipel ou du Pays, les dégradations anthropiques sont limitées à quelques îles peuplées de la Société, plus exceptionnellement dans les atolls et encore moins dans un tiers d'entre eux qui sont inhabités. Les remblais en zone frangeante, les extractions de matériaux coralliens, la surpêche, l'absence de réseaux d'assainissement des eaux usées urbaines et le développement d'activités de loisir et du tourisme sont les causes essentielles de la dégradation des communautés coralliennes du lagon dans certains secteurs de Tahiti et de Moorea. Ainsi apparaît-il clairement que les dégradations majeures des récifs en Polynésie sont occasionnées par des phénomènes naturels compte tenu de leur étendue géographique. En revanche les dégradations anthropiques sont géographiquement plus localisées. Malheureusement la synergie des deux causes de dégradation ne facilite pas la récupération des récifs. Il est établi qu'une pente externe avec un recouvrement corallien de 50-60 % est à son optimum. Une dégradation majeure (cyclone, blanchissement, Acanthaster) réduit ce recouvrement à moins de 10 %. La communauté met une douzaine d'années pour revenir au recouvrement optimum si aucune autre perturbation importante ne survient. La très large majorité des 15000 km2 de récifs et lagons de Polynésie française sont en bonne santé. Avec leurs voisins du Pacifique Est et Central, ces formations coralliennes sont considérées comme les moins dégradées au monde et à faible risque de dégradation dans les prochaines décennies

Mono- and polychromatic inner shell phenotype diversity in Pinctada margaritifera donor pearl oysters and its relation with cultured pearl colour

The pearl oyster Pinctada margaritifera has the specific ability to produce pearls with the widest range of colours among all pearl oyster species. This pearl colour diversity originates from the mantle biomineralising tissue (graft) of the donor oyster, which is originally responsible for the variety of colours of the inner shell surface. This study aimed to: 1) assess the geographic distribution and establish a first stocklist of the colourful oyster phenotypes used as donors in French Polynesia, and 2) investigate the phenotypic relation between inner shell colouration and the corresponding colour of harvested pearls. With the support of a pearl farmers' network, we investigated the different donor phenotype frequencies among five collection sites (Ahe, Apataki, Takaroa, Takume and Mangareva). This donor evaluation was made during grafting of pearl oysters (N = 49,938) obtained from collector stations. Results showed that pearl production is mainly based on six common colourful donor phenotypes classified as monochromatic and polychromatic profiles, which shown different frequencies among the collection sites. Experimental grafts (N = 4640) were then realised and subsequent culture conducted at a single site in order to avoid pearl colour variation due to environmental influences. Traceability between donors (N = 232) and pearls (N = 2776), revealed that: 1) yellow (gold) and aubergine (reddish) pearls could be mostly obtained by using the monochromatic yellow and red donor phenotypes, respectively, and 2) one third to one quarter of grey pearls was inevitably harvested, whatever the polychromatic phenotype chosen as the donor, which leaves at least half the harvest composed of the attractive green and peacock colours. This preliminary stocklist of colour range together with analysis of the colour phenotype transmission between inner shell and pearl provide the basis for producing multiple pearl oyster “colour lines” through hatchery propagation and would be helpful for future selective breeding programs. Statement of relevance : Donor shell colour selection predict colours of pearl

Revisiting wild stocks of black lip oyster Pinctada margaritifera in the Tuamotu Archipelago: the case of Ahe and Takaroa atolls and implications for the cultured pearl industry

Spat collecting of the black lip oyster (Pinctada margaritifera) is the foundation of cultured black pearl production, the second source of income for French Polynesia. To understand spat collecting temporal and spatial variations, larval supply and its origin need to be characterized. To achieve this, it is necessary to account for the stock of oysters, its distribution and population characteristics (size distribution, sex-ratio). While the farmed stock in concessions can be easily characterized, the wild stock is elusive. Here, we investigate the distribution and population structure of the wild stock of Ahe and Takaroa atolls using fine-scale bathymetry and in situ census data. Stocks were surprisingly low (∼666,000 and ∼1,030,000 oysters for Ahe and Takaroa respectively) considering these two atolls have both been very successful spat collecting atolls in the past. Furthermore, in Ahe atoll, wild populations are aging with a dominant but small female population. Comparison with the cultured stock population (∼14 millions oysters) and its dominant young male population suggests that to maximize larval supply and spat collecting on the long term, it would be useful to increase the number of females in selected sanctuaries. We discuss the implication of our findings for the long-term management of stocks and for spat collection in pearl farming atolls, and for on-going numerical modelling studies on larval dispersal

Age-dependence of cultured pearl grade and colour in the black-lipped pearl oyster Pinctada margaritifera

Pinctada margaritifera is an economically important marine bivalve species for cultured pearl production in French Polynesian aquaculture. In order to evaluate the influence of donor oyster age on pearl quality traits, experiments were conducted over 6 years using both grafts and surgreffe operations. At harvest, 6 pearl quality traits were recorded and compared: surface defects, luster, grade, darkness level, and visual color. Analyzing the quality traits of pearls harvested in the initial graft process and those of pearls obtained from surgreffe experiments allowed a comparison of the influence of pearl sac cells originating from the initial mantle graft, which aged together with their recipient oysters. The results demonstrated a significant decrease between these successive grafts in luster, grade (A-B-C,) darkness level, and green color – traits that are of major importance in the pearl market. The duplicated graft experiment allowed the comparison of donor oyster families at 2 and 5 years old, where a mantle graft was inserted into recipient oysters aged 2.5 years old. The results showed the same tendencies to a lesser extent, with 1) an improved pearl grade, predominantly through a most important rate of 0 surface defect category, and 2) a green / grey ratio in favor of the younger donor. A comparison between the graft-surgreffe and the duplicated graft experiments also highlighted: 1) the indirect role played by the younger recipient oysters, which must be optimized for optimal pearl quality realization, and 2) the complex interplay between donor and recipient oysters

The pearl oyster (Pinctada margaritifera) aquaculture in French Polynesia and the indirect impact of long-distance transfers and collection-culture site combinations on pearl quality traits

In French Polynesia, the P. margaritifera pearl aquaculture industry is spread over a vast area, as large as Europe. All the oysters for this the highly economically important activity are supplied from just a few collection lagoons, but they are grown in numerous sites across three archipelagos (Gambier, Society and Tuamotu). Many oyster transfers thus indirectly bring about grafting combinations mixing different geographic origins and production sites. This study aims to examine the impact of such graft combinations on cultured pearl quality traits. For this, six homogeneous and standardised experimental graft combinations (N = 6197) were conducted at commercial scale in the two growing locations the most frequently used in French Polynesia: Arutua atoll (Tuamotu) and Mangareva island (Gambier), using oysters supplied from by the top three collection sites: Ahe, Takapoto and Mangareva lagoons. At harvest, four main pearl quality traits: nacre weight deposition speed, pearl colour components (darkness level and green overtone), grade and shape categories were recorded by a professional sorter from the Tahiti auction and compared. Results revealed effects of the combinations of oyster origin and grow-out location, with: 1) significant origin ´ site interaction for nacre weight deposition speed; 2) colour variation at intra- and inter-site scales, with Ahe origin producing the most dark pearls and Gambier highest rate of the attractive green coloured pearls; and 3) higher grade categories for the Gambier origin and rearing location. These oyster-site combination effects highlight the benefit for the Polynesian pearl industry of switching from a mono-site/ company production system to a new multi-site production strategy to maximize overall cultured pearl quality expressio

Growth Performance Comparison of Pinctada margaritifera Juveniles Produced by Thermal Shock or Gonad Scarification Spawning Procedures

The black-lipped pearl oyster Pinctada margaritifera is of high economic importance in French Polynesia. Arecent decline in pearl value led to the initiation of several genetic breeding programs aiming to improve production traits, including oyster shell growth, which dictates the time of grafting, size of the implanted nuclei, and biomineralization capacities. We assessed shell diameters on hatchery-produced spat to analyze juvenile growth performance of four half-sib families derived from polyandry (one dam crossed with two sires) and polygyny (two dams crossed with one sire) using gametes obtained by thermal shock or gonad scarification. Spat growth was monitored over 3 mo, with shell diameter measured weekly. Results revealed that the spawning method had no significant effect on juvenile growth; however, the half-sib families produced with the polygyny mating design showed significant differences in average shell diameter between dams throughout the experiment, whereas none were observed between sires with the polyandry mating design. Precocious larval size selection within each family was performed by separation into batches of small, medium, and large size, and their maintenance through juvenile stages, providing the possibility for early growth selection. These findings are important for genetic breeding programs (1) as breeding of sires and dams exhibiting the most colorful inner shell phenotypes would be possible with the gonad scarification spawning procedure without affecting overall growth performance and (2) because P. margaritifera is a protandrous hermaphrodite species, genetic selection strategies in the pearl industry must take into account the differential influence of polygyny and polyandry mating designs

Indirect improvement of pearl grade and shape in farmed Pinctada margaritifera by donor "oyster" selection for green pearls

The top aquaculture species in French Polynesia is Pinctada margaritifera, a mollusc grown for the production of a unique gem: the black pearl. One of the challenges facing the pearl farming industry is to "produce less but better pearls" through genetic improvement. An experimental hatchery system was used to generate full-sib families to be tested for their potential as donor "oysters". A large-scale grafting experiments was done and seven cultured pearl quality traits: grade, surface defects, lustre, darkness level, visual colour categories, circles and shape categories were recorded. Our results revealed, for the first time, significant phenotypic relationships between these quality traits. The grade A cultured pearl class had the largest proportion of pearls with a green overtone (65%), the lowest number of circled pearls (15%) and the maximum of round-shaped pearls (45%). In contrast, the "reject" cultured pearl class had the largest proportion of pearls with grey bodycolor (65%), the greatest number of circled pearls (35%) and the maximum with a baroque shape (nearly 60%). When grade components were studied separately, cultured pearls in the zero surface defect class exhibited the same tendencies as grade A pearls, contrasting with the class where there were more than ten defects on the surface of each pearl. When cultured pearls were classified according to the presence or absence of lustre, pearls with lustre mostly had a green overtone colour, while pearls without lustre did not. These findings have major implications for cultured pearl quality improvement, as modern genetic breeding methods can increase the proportion of high quality cultured pearls though selected lines of donor oysters capable of producing pearls with a green overtone. Selection of appropriate donor phenotypes, incorporation of pigmentation traits into a pearl oyster breeding program and production of lines with desirable colours will be developed for oyster aquaculture in French Polynesia

A histological examination of grafting success in pearl oyster

Pearl oyster grafting is a complex surgical operation that should lead to pearl formation after approximately eighteen months. Although this technique has been used for many years in French Polynesia, the grafting process is still not standardised. While studies have been carried out in order to improve graft performance and yield, these remain highly variable due to post-grafting mortality, nucleus rejection and unreliable pearl quality, all of which constrain pearl farm profitability. The present study uses histological analysis to monitor oysters that either rejected or retained their nuclei. Both groups of oysters are compared in terms of evolution of the graft, which could influence retention, and the development of a pearl sac in cases where grafting was successful. Data show that rejection phenomena are linked to a number of causes, notably an inflammatory reaction in the “receiving” oyster, the presence of numerous tissue lesions and the quality of the grafted tissue. These results suggest that study is needed on the different concomitant elements of the grafting process: the graft “donor” oysters, the nucleus and the “receiving” oyster and their interactions

Macro-geographical differences influenced by family-based expression on cultured pearl grade, shape and colour in the black-lip "pearl oyster" Pinctada margaritifera: a preliminary bi-local case study in French Polynesia

In French Polynesia, the aquaculture of P. margaritifera is carried out in numerous grow-out sites, located over three archipelagos (Gambier, Society and Tuamotu). To evaluate the impact of macro-geographical effects of these growing sites on pearl quality traits, five hatcheries produced families were used as homogeneous donor oysters in an experimental graft. The molluscs were then reared in two commercial locations: Tahaa island (Society) and Rangiroa atoll (Tuamotu). At harvest, eight pearl quality traits were recorded and compared: surface defects, lustre, grade, circles, shape categories, darkness level, body and secondary colour and visual colour categories. Overall inter-site comparison revealed that: 1) all traits were affected by grow-out location except for lustre and round shape, and 2) a higher mean rate of valuable pearls was produced in Rangiroa. Indeed, for pearl grade, Rangiroa showed twice as many A-B and less reject samples than Tahaa. This was related to the number of surface defects (grade component): in Rangiroa, twice as many pearls had no defects and less pearls had up to 10 defects. Concerning pearl shape, more circled and baroque pearls were found in Tahaa (+10%). For colour variation, 10% more pearls have an attractive green overtone in Rangiroa than in Tahaa, where more grey bodycolor were harvested. Lustre does not seem to be affected by these two culture site (except at a family scale). This is the first time P. margaritifera donor family have been shown to vary in the quality of pearls they produce depending on their grow-out location