Jean Prou

Effects of high natural seston concentrations on the feeding, selection, and absorption of the oyster Crassostrea gigas (Thunberg)

Feeding, selection and absorption were determined for the Pacific oyster Crassostrea gigas cultivated in the Bay of Marennes-Oleron, over a spring/neap tidal cycle. Physiological determinations were related to the highly variable food environment with continuous recordings of turbidity and fluorescence. In this bay, resuspension processes have a major influence on food availability and quality. Seston characteristics experienced by oysters can be summarized by high turbidity levels from 20 to 350 mg·l−1 and a predominance of the detritic fraction among the organic fraction (mean C/N ratio=16.57). Food is diluted by the fine resuspended sediment, and organic content of particulate matter in the water column decreases from 30% to 10% with increasing seston loads. Significant differences (Ancova, P<0.01), due to low retention efficiencies of the smaller particle size range, were recorded between the food quality (estimated by the organic content and the total pigment content) measured in the water column and the fraction retained by the oysters gill. Below seston concentrations of 90 mg·l−1 ingestion rate was regulated by pseudofaecal production. Above 90 mg·l−1, a sharp reduction of filtration and rejection rates suggests physical constraints limiting food acquisition. The oyster selectively rejects inorganic from organic particles, enriching the ingested fraction. Amongst the potentially nutritive particles, significantly fewer particles containing phytopigments were rejected relative to organic particles (non-linear regressions, P<0.001). The negative influence, through food dilution, of high seston loads on net absorption efficiency was determined. This efficiency decreases with decreasing organic ingested fraction. Scope for growth calculations confirm the negative influence of seston loads, but show, supported by field growth measurements, that resuspended organic particles play an important role in the oysters nutrition.

No influence of food quality, but ration-dependent retention efficiencies in the Japanese oyster Crassostrea gigas

Abstract Relative retention efficiency (Er) in Crassostrea gigas was estimated in the laboratory with seven artificial diets consisting of variable proportions of algae and silt, as well as in the natural environment at high seston concentrations up to 64.37 mg/1. Crassostrea gigas did not adjust retention efficiency according to the food quality, gill porosity being controlled by the concentration of paniculate matter. At low seston load (1.34 mg/1), the oyster showed no change in retention for particles larger than 3–4 μm (Equivalent Spherical Diameter, ESD). But at the highest concentration (64.37 mg/1), it could only retain particles larger than 12 μm (ESD) with maximum efficiencies. The Japanese oyster therefore has an active response to high particle concentration, and which was described by a model where retention efficiency (Er) varied with suspended particulate matter (Vol mm 3 /l) as follows: Er= − 12.537 Vol e (−0.304 ESD ) + 100

Pearl Formation: Persistence of the Graft During the Entire Process of Biomineralization

Most bivalves species of the genus Pinctada are well known throughout the world for production of white or black pearls of high commercial value. For cultured pearl production, a mantle allograft from a donor is implanted into the gonad of a recipient oyster, together with a small inorganic bead. Because of the dedifferentiation of cells during the first steps of the host oyster’s immunological reaction, so far the fate of the graft and its exact role in the process of pearl formation could not be determined via classical histological methods. Here we report the first molecular evidence of the resilience of the graft in the recipient organism by showing that cells containing genome from the donor are still present at the end of pearl formation. These results suggest the existence of a unique biological cooperation leading to the successful biomineralization process of nacreous secretion in pearl formation.

Ecophysiologie et bilan énergétique de la palourde japonaise d'élevage Ruditapes philippinarum

Rates of filtration and respiration both follow a nonlinear model based on temperature of the form: Y = a × (T−T0)c × e −b(T−T0 with maximal values at 15 and 20°C, respectively. Quantities of seston varying from 0 to 30 mg · 1−1 have no effect in reducing the filtration rate. > 8 mg · 1−1, ingestion is regulated by the production of pseudofaeces. Maximal assimilation efficiency is ≈ 78%, but this is considerably reduced when the mineral content of the water increases. Assimilation efficiency for the Manila clam is reduced at both high (> 10 mm3· h−1) or low (< 2 mm3· h−1) values of ingested ration. The estimated value of growth efficiency (75%) and values of growth efficiency derived from the model k1 = 33%, K2 = 51% are optimized when ingested volumes are between 1 and 2 mm3. Standard metabolism is estimated as 0.11 ml O2 · h−1. Zero growth efficiency occurs at a ration level of 2 J · h−1 for an adult. The individual energy budget shows that production is dependent more on temperature than on the energy value of the food. Comparison of calculated and measured production reveals differences resulting from the higher levels of seston found in the field. In particular, during the winter when the mineral content of the seston is high (90 mg · 1−1), there is a continuous loss of weight. This results from a lower assimilation efficiency together with production of pseudofaeces. Excretion of organic nitrogen varies throughout the year, ammonia representing no more than a mean of 29.8% of the total nitrogen excretion.

History, status, and future of oyster culture in France.

ABSTRACT The history of French oyster culture consists of a succession of developmental phases using different species, followed by collapses caused by diseases. The indigenous species Ostrea edulis was replaced first with Crassostrea angulata, then C. gigas. France is now the top producer and consumer of oysters in Europe, producing around 120,000 t of the cupped oyster C. gigas annually, and an additional 15001 of the flat oyster O. edulis. Cupped oysters are produced all along the French coast from natural and hatchery spat. Various structures are used to collect spat from the wild. After a growing-on period, oysters are cultivated by three main methods: (1) on-bottom culture in the intertidal zone or in deep water, (2) off-bottom culture in plastic mesh bags in the intertidal zone, or (3) suspended culture on ropes in the open sea. The main recent development is the increasing use of hatchery oyster spat, especially triploids. Almost all oyster production is sold fresh and eaten raw straight from the shell. There is marked seasonality in sales, with the majority being made during Christmas and New Year. Abundant production and the lack of market organization induce strong competition among the production areas, causing prices to fall. Oyster farmers have developed strategies of sales promotion and regional quality labeling to overcome this difficulty. There are numerous production hazards, including environmental crises (microbiological pollution), unexplained mortality, and overstocking, and recent problems with toxic algae have disrupted oyster sales. However, oyster culture has many assets, including a coastal environment offering favorable sites for mollusc growth and reproduction. Oysters have been consumed in France since ancient times, and their culture is now well established with a concession system that favors small family firms. There is a young, well-educated farmer population, with technical expertise and savoir faire. Careful seawater quality monitoring ensures good consumer protection, and research is making innovative contributions (selection and polyploids). These points and opportunities for market expansion should bolster this industrys future, although the problem of toxic algae, probably linked to global warming and anthropogenic factors, and the threat of new diseases, pose vital questions for future research.

Spatio‐temporal variation in the genetic composition of wild populations of pearl oyster (Pinctada margaritifera cumingii) in French Polynesia following 10 years of juvenile translocation

The genetic impact of the cultural practice of spat collection and translocation between genetically distinct stocks of black‐lipped pearl oyster, Pinctada margaritifera cumingii, was studied by comparing samples collected in the 1980s and 2000s from seven atolls in French Polynesia. An amova revealed homogenization of the previously genetically distinct wild stocks of Tuamotu‐Gambier and Society archipelagos (the indices of genetic differentiation among archipelagos and among populations within archipelagos, respectively, ΦCT and ΦST, decreased from 0.032* and 0.025*, respectively, to 0.006NS and 0.007NS). These results suggest high success of spontaneous reproduction in farms, probably due to the very high density of cultivated pearl oysters, and underline the importance of genetic monitoring of future hatchery produced stocks.

Spat collection of the pearl oyster (Pinctada margaritifera cumingii) in French Polynesia: an evaluation of the potential impact on genetic variability of wild and farmed populations after 20 years of commercial exploitation

Pearl production, based on the aquaculture of the blacklipped pearl oyster Pinctada margaritifera, is an essential economic activity in French Polynesia. Production relies almost exclusively on the collection of wild spat, which makes the activity very dependent on natural resources. A good knowledge of these resources is thus essential for the rational management of farmed and wild populations. In this study, we analysed the structure of genetic variability, in wild and farmed populations distributed on four atolls from the Tuamotu–Gambier archipelago using four anonymous nuclear loci. No genetic difference was observed among samples from wild populations collected from Northern Tuamotu to Southern Gambier. This suggests that large-scale dispersal, either due to the absence of barriers to natural larval migration, or to the transport of collected spat for pearl production. No significant differences were found between wild and adjacent farmed populations for the number of alleles and observed heterozygosity, which supports the conclusion

Geomatics for the Management of Oyster Culture Leases and Production

The coastal zone of Charente-Maritime in France has a leading position in oyster culture production. Yet it is being jeopardized by a number of problems such as overstocking, inadequate distribution of culture types, wild stock in excess, and strong siltation processes. Some of these problems result from a lack of communication and realization within the professional community, others due to obsolete management tools. The introduction of geomatics is believed to help provide some answers, besides alleviating the classical task of lease management. This chapter shows how the system was built, the spatial data geo-referenced and linked to administrative data. Examples of queries on the spatial data base reveal some otherwise invisible facts and allow prioritization of management decisions. The system also acts as a communication tool between the actors, i.e. the professionals, the local authorities and the research sector. Perpectives on further uses are given.

A GIS‐BASED ASSESSMENT OF POTENTIAL AQUACULTURAL NONPOINT SOURCE LOADING IN AN ATLANTIC BAY (FRANCE)

Spatial-explicit quantitative dissolved inorganic nitrogen (DIN) and ortho- phosphorus (OP) loadings were developed from aquatic earthen ponds to the adjacent salt marshes. These loadings were based on water renewal, the concentration of constituents available for all land use, and the spatial positions of constituent sources. Potential loading was assessed at every sub-basin gauge station by adding the individual contribution of every land use polygon. Kriging was also used to spatialize loading from control stations to salt marshes. A grid of concentration values was established specific to the bay stream network using an eight-direction-point model. Analyses showed a more important concentration near intensive activities, from - 15 p,mol/L to 30 pmol/L of DIN and from 2 pmol/L to 7 pmol/L of OP. These values decreased rapidly near the ocean, where a dilution of about 75% was noticed for DIN and 87% for OP. Constituent concentrations were quite sensitive to parameter changes, and the system reacted more intensively to point source concentration changes than to water drain. The use of regional parameters to assess DIN and OP loadings from earthen ponds to salt marshes, based on land use and topography, may be useful when working on a regional scale. Modeling nonpoint sources of DIN and OP from aquacultural land to surface water can be both complex and data intensive. Our goal was to develop a simple model that would account for spatial pattern in topography and land use using Geographic Information System (GIS) databases.

Changes, Adaptations, and Resilience: The Case of French Oyster Farming

The history of French oyster farming is marked by threats and difficulties, thus subsequent adaptations. There have been some significant changes in the oyster practices, the economic operation of enterprises, and the place of oyster farming in coastal areas, whereas the persistence of the oyster farming sector facing significant threats has periodically been questioned. Environmental changes have played an important role in this activity closely related to the environment: pollution from various sources, increasing episodes of contamination by phycotoxins, extreme weather events, and climate change. Recently, the high-mortality syndrome questions the issue of the conditions for the sustainability of the activity. Taking into account the conflicting uses in the coastal zone and the importance of relationships with watershed activities, the development policies must also analyze the adaptation capacity of oyster farming socio-ecosystems in these environments highly dynamically, spatially, and temporally. Can we talk about the resilience of oyster culture? We introduce the concept of socio-ecosystem applied to oyster farming, as appropriate for the analysis of resilience. What are the questions lying behind the oyster farming resilience and which method can be used for its study? Using the case of French oyster farming, this communication proposes to discuss some answers to these questions, for different aspects.