Michel Ropert

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.

Comparative physiological energetics of two suspension feeders: polychaete annelid Lanice conchilega (Pallas 1766) and Pacific cupped oyster Crassostrea gigas (Thunberg 1795)

Abstract Feeding competition between the Pacific cupped oyster Crassostrea gigas and the polychaete Lanice conchilega was studied by assessing the polychaete suspension feeding activity. Retention efficiency was estimated by comparing particle size distributions at the output of experimental chambers containing the species and controls. Although particles ranging from 4 to 12 μm were collected by L. conchilega , no upper threshold or maximum retention rate was reached within this range. In contrast, C. gigas showed retention starting at 2 μm, and reaching an upper threshold at 6 to 8 μm. Based on our results, feeding competition is likely to occur between C. gigas and L. conchilega . Standardised filtration rates reached 0.225 l h −1 g dmw −1 (±0.08) for L. conchilega and 2.43 l h −1 g dmw −1 C. gigas for animals of 1 g dry meat weight (dmw). Assimilation rates, 0.44 for L. conchilega and 0.49 for C. gigas , were similar for the two species. Respiration rates were estimated at 0.113 and 0.68 ml O 2 h −1 for L. conchilega (Allometric coefficient=0.534) and C. gigas respectively. Therefore polychaete scope for growth (SFG) (4.01 J h −1 g dmw −1 ) was significantly lower when compared with C. gigas SFG (61.96 J h −1 g dmw −1 ). The impact of the L. conchilega population on that of cultivated oysters was evaluated from these results and field population assessment of both species. Based on field population estimates, L. conchilega was responsible for a 19% decrease in the carrying capacity and 30% of the oxygen depletion from the total activity of both species. However, L. conchilega SFG was only 16% of that of the C. gigas population. Several hypotheses regarding population interactions are discussed.

SPATIO-TEMPORAL CHANGES IN MORTALITY, GROWTH AND CONDITION OF THE PACIFIC OYSTER, CRASSOSTREA GIGAS, IN NORMANDY (FRANCE)

Abstract Summer mortalities have been observed in French shellfish areas (including Normandy) since 1994, but origin of this syndrome remains unclear and is suspected to be caused by a combination of several interacting extrinsic (biotic and abiotic) and intrinsic (genetic, physiological, immunological) factors. The French research program, MOREST aimed to identify the origin of oyster summer mortality along the French coast, focusing on the interactions between oysters, their pathogens, and the environment. The present study analyzed spatio-temporal variation in growth, condition and mortality in spat, and half-grown and market-sized oysters reared from February 2000 to October 2003 at six stations within two different areas in the Bay of Veys, Normandy: Grandcamp (GR), and Gefosse (GE) that is more estuarine. These biological parameters were compared between years, age groups, and areas. Results showed that shell growth was significantly lower in the station highest on the shore and similar in the four other sites, whereas tissue growth and condition index were higher in the Gefosse area. Results also showed large interannual, interage, seasonal and spatial variation in oyster mortality. In 2001, mortalities were markedly higher than in other years and all batches and sites were affected by high mortality rates. Moreover oysters suffered much higher mortalities in their second and third years than as spat, and the difference between age classes was accentuated when mortality was high. Increases in mortality occurred when the gonad was most extensively developed and the peak coincided with the spawning and postspawning periods when gonad volume began to decrease. Spatial variability showed that mortality was higher in Gefosse than Grandcamp. Chronology and spatial variations in mortality highlighted the importance of timing and confirmed that mass mortalities may be closely linked to reproduction. The risk seems to be associated with high reproductive effort, partial spawning, and/or slow gonad resorption. Spatial variation also suggests that the study sites experience varying degrees of stress caused by biological changes and probable differences in water quality reflecting the influence of freshwater input in Gefosse where mortality is higher.