Joel Haure

Plasticity in resource allocation based life history traits in the Pacific oyster, Crassostrea gigas. I. Spatial variation in food abundance.

We investigated the quantitative genetics of plasticity in resource allocation between survival, growth and reproductive effort in Crassostrea gigas when food abundance varies spatially. Resource allocation shifted from survival to growth and reproductive effort as food abundance increased. An optimality model suggests that this plastic shift may be adaptive. Reproductive effort plasticity and mean survival were highly heritable, whereas for growth, both mean and plasticity had low heritability. The genetic correlations between reproductive effort and both survival and growth were negative in poor treatments, suggesting trade‐offs, but positive in rich ones. These sign reversals may reflect genetic variability in resource acquisition, which would only be expressed when food is abundant. Finally, we found positive genetic correlations between reproductive effort plasticity and both growth and survival means. The latter may reflect adaptation of C. gigas to differential sensitivity of fitness to survival, such that genetic variability in survival mean might support genetic variability in reproductive effort plasticity.

Influence of temperature on clearance and oxygen consumption rates of the flat oyster Ostrea edulis: determination of allometric coefficients

Abstract Clearance and oxygen consumption rates of Ostrea edulis were measured at different temperatures (10–30°C) in individual animals of a total weight ranging from 5 to 120 g (0.1 to 2.7 g dry tissue weight), outside the period of gametogenesis. For each temperature, the allometric relationship between the physiological response and dry tissue weight of the animal (DW) was estimated using the formula: Y = a ∗DW b . A statistical model is proposed for the variation in clearance rate or oxygen consumption rate ( Y ) with temperature ( T ) and DW: Y =[ a +( b ∗ c T )]∗DW d . The calculated value for d was 0.62 for clearance rate and 0.74 for oxygen consumption rate. The rates of both physiological functions increased as the temperature increased and reached maximum levels at 30°C (clearance rate:2.83±0.32 l h −l g −l ; oxygen consumption rate: 1.78±0.23 mg O 2 h −l g −l ) when the flat oysters were fed a Skeletonema costatum microalgal grown in underground seawater.

Rising water temperatures, reproduction and recruitment of an invasive oyster, Crassostrea gigas, on the French Atlantic coast.

The recent appearance and invasion of feral oysters (Crassostrea gigas) along the northern European Atlantic coast, underscores the necessity to investigate the relationship between environmental variables, reproductive physiology, larval development and recruitment. We studied these relationships at both high (HT) and intermediate (IT) - turbidity sites, through historical data on water temperatures, multi-parameter environmental probes, histological analyses, and field collections of planktonic larvae and settled post-larvae in 2005 and 2006. A progressive warming trend was observed, especially since 1995, when oyster proliferation first became severe. Threshold temperatures for oocyte growth, larval development and settlement were achieved in both 2005 and 2006. The HT site showed greater numbers of larvae and post-larvae than the IT site for both years, with the highest numbers of post-larvae observed at both sites during the warmer summer of 2006. These results suggest that increased temperatures in northern European waters allow successful reproduction, larval development, and recruitment of C. gigas. High turbidity conditions further enhance this success.

Feeding and respiratory time activities in the cupped oysters Crassostrea gigas, Crassostrea angulata and their hybrids

Abstract A comparative study of the ecophysiology of the cupped oysters Crassostrea gigas , Crassostrea angulata and their hybrids was carried out in January 2000. Progenies were obtained by crossing parental oysters that had been previously identified using a diagnostic mitochondrial genome marker. Thus, two pure progenies were obtained by crossing within C. angulata parents (AA) or C. gigas parents (GG). Two other progenies were produced by hybrid crossing of C. gigas females with C. angulata males (GA), or C. angulata females with C. gigas males (AG). Individual measurements of the ecophysiology of 35 animals from each progeny were carried out at 19±1 °C. The oysters were fed Skeletonema costatum . The means of clearance and oxygen consumption rates obtained from continuous data recording over 3 h did not reveal differences between the four lines. However, the feeding time activity (FTA) results showed significant differences: for AA, GG, GA and AG animals FTA were 73±10%, 89±6%, 89±7% and 85±8%, respectively. The FTA of the AA progeny was significantly lower than the three other lines. This study shows that FTA is an ecophysiological parameter that can account for observed differences in growth. The ecophysiological measures should now be completed by a study to determine the optimum temperature for each oyster taxon.

Finding new diatoms for intensive rearing of the pacific oyster (Crassostrea gigas): energy budget as a selective tool

Abstract Intensive shellfish rearing in the polders of Bourgneuf Bay on the French Atlantic coast (46–47°N, 1–2°W) relies on the diatom Skeletonema costatum (Grev.) Cleve produced in nutrient-rich saline ground water. An episodic reduction in biomass production caused by an unidentified protozoon stressed the need to find new microalgal species as substitutes for S. costatum and diversify the microalgae used by the bivalve industry. Three species met the requirements for year-round availability in Bourgneuf Bay coastal waters and growth potential in saline ground water: Nitzschia acicularis (Kutzing), Nitzschia closterium (Ehrenberg) Wm Smith and Nitzschia gandersheimiensis Krasske= Nitzschia tubicola Grunow. These microalgae were tested as food sources for adult Pacific oysters ( Crassostrea gigas ) by comparing short-term bivalve physiological responses with those obtained with S. costatum as reference. Suspended particulate matter concentrations in experimental diets ranged from 9.3 to 18.6 mg l −1 and particulate organic matter concentrations from 3.3 to 5.7 mg l −1 . Significant differences were observed, with clearance rates ranging from 4.0 l h −1 g −1 for N. acicularis to 7.3 l h −1 g −1 for N. gandersheimiensis . The filtration rate for organic matter was significantly higher for N. gandersheimiensis than the other species, but this algae was also significantly more rejected in pseudofaeces. No differences were found among the four mean faeces production rates. Net energy balance differed significantly among the four microalgae tested, ranging from 282 J h −1 g −1 for S. costatum to 27 J h −1 g −1 for N. closterium . However, no differences were found between S. costatum , N. acicularis and N. gandersheimiensis . These results suggest that N. acicularis and N. gandersheimiensis could be tested on a larger scale involving the production of microalgae in 50-m 3 outdoor tanks in association with Pacific oyster growth experiments.

Comparative growth of Bonamia ostreae resistant and wild flat oyster Ostrea edulis in an intensive system : II. Second year of the experiment

This paper reports the comparative growth and mortality of two crosses involving S85 and S89, two Ostrea edulis strains selected by IFREMER for their resistance to Bonamia ostreae. A first year of monitoring had revealed that the two crosses grew significantly better than two control populations from Quiberon Bay (Brittany) and Palavas (Mediterranean Sea). In a second and final year experiment which lasted from April to November 1995, the cross between the first generation of S89 and wild oysters (G0G1) performed better for most growth characteristics (whole weight, shell weight, length and width), than both the cross between the first generation of S89 and the second generation of S85 (G1G2) and the Quiberon control group, which were not significantly different from each other. Mortality was quite high during the experiment but was lower for the G0G1 cross (61%) than for both G1G2 (67%) and the Quiberon controls (76%). A low level of B. ostreae infection was detected during the experiments indicating early infections. These results are consistent with the previous one showing a direct or indirect effect of selection to B. ostreae resistance on growth.

Effects of low-dose exposure to pesticide mixture on physiological responses of the pacific oyster, Crassostrea gigas

This study investigated the effects on the physiology of Pacific oyster, Crassostrea gigas, of a mixture of pesticides containing 0.8 μg L−1 alachlor, 0.6 μg L−1 metolachlor, 0.7 μg L−1 atrazine, 0.6 μg L−1 terbuthylazine, 0.5 μg L−1 diuron, 0.6 μg L−1 fosetyl aluminum, 0.05 μg L−1 carbaryl, and 0.7 μg L−1 glyphosate for a total concentration of 4.55 μg L−1. The total nominal concentration of pesticides mixture corresponds to the pesticide concentrations in the shellfish culture area of the Marennes‐Oleron basin. Two varieties of C. gigas were selected on the foreshore, based on their characteristics in terms of resistance to summer mortality, to assess the effects of the pesticide mixture after 7 days of exposure under controlled conditions. The early effects of the mixture were assessed using enzyme biomarkers of nitrogen metabolism (GS, glutamine synthetase), detoxification metabolism (GST, glutathione S‐transferase), and oxidative stress (CAT, catalase). Sublethal effects on hemocyte parameters (phagocytosis and esterase activity) and DNA damages (DNA adducts) were also measured. Changes in metabolic activities were characterized by increases in GS, GST, and CAT levels on the first day of exposure for the “resistant” oysters and after 3–7 days of exposure for the “susceptible” oysters. The formation of DNA adducts was detected after 7 days of exposure. The percentage of hemocyte esterase‐positive cells was reduced in the resistant oysters, as was the hemocyte phagocytic capacity in both oyster varieties after 7 days of exposure to the pesticide mixture. This study highlights the need to consider the low doses and the mixture of pesticides to evaluate the effects of these molecules on organisms.

Antimicrobial Compounds from Eukaryotic Microalgae against Human Pathogens and Diseases in Aquaculture

The search for novel compounds of marine origin has increased in the last decades for their application in various areas such as pharmaceutical, human or animal nutrition, cosmetics or bioenergy. In this context of blue technology development, microalgae are of particular interest due to their immense biodiversity and their relatively simple growth needs. In this review, we discuss about the promising use of microalgae and microalgal compounds as sources of natural antibiotics against human pathogens but also about their potential to limit microbial infections in aquaculture. An alternative to conventional antibiotics is needed as the microbial resistance to these drugs is increasing in humans and animals. Furthermore, using natural antibiotics for livestock could meet the consumer demand to avoid chemicals in food, would support a sustainable aquaculture and present the advantage of being environmentally friendly. Using natural and renewable microalgal compounds is still in its early days, but considering the important research development and rapid improvement in culture, extraction and purification processes, the valorization of microalgae will surely extend in the future.

Spatial and temporal adjustments in gill and palp size in the oyster Crassostrea gigas

Spatial and temporal variations in gill and palp size were studied during 1 year in naturally-settled populations of the Pacific oyster Crassostrea gigas, reciprocally transplanted between two contrasting sites located along a marked gradient of turbidity conditions. The variability of suspended particulate matter (SPM) and food particles, estimated by the concentration of chlorophyll-a, was measured with in situ water-quality probes. Over a full seasonal cycle, oysters exposed to high-turbidity (HT) conditions exhibited a lower gill-to-palp (G:P) ratio, compared with those exposed to low-turbidity (LT) conditions. Seasonal variations in the G:P ratio were observed at the LT site in relation to the spring phytoplanktonic bloom, but differed from those that had been observed previously. In fact, palp enlargement and gill narrowing (lower seasonal G:P ratio) suggest that oysters improved their pre-ingestive selection efficiency as a priority, rather than their filtering capacity. This result indicates that suspension-feeding bivalves do not have independent plastic responses of their foraging structures to either SPM quality or quantity, and that the direction of variations in the G:P ratio depends on the combination of these two factors. At the HT site, no seasonal pattern was observed in the G:P ratio. This can be explained by the strong hourly variations in SPM and chlorophyll-a, associated with tidal cycles, with daily variations that can be similar to those observed over a year. Reciprocal transplantations showed that oysters originating from the same site can differ in their feeding apparatus morphology when they grow in different environments and that temporal variations in the G:P ratio of oysters transplanted to a new environment converge towards that of individuals that have spent their entire life in this environment. Variations in the relative gill and palp sizes of C. gigas appear therefore to be partly the consequence of reversible phenotypic plasticity in response to spatial and temporal variations in SPM quantity and quality. The results also suggest that the limits and dynamics of gill and palp plasticity are dependent on the origin of oyster populations. Considering its role in the exploitation of different trophic conditions, and consequently in the biological performances (growth and reproduction), plasticity in the feeding apparatus morphology of C. gigas could be a determinant in the establishment of invasive populations in new ecosystems or in the management of farmed oysters.

Storage and Detoxification of Bivalve Molluscs as a Tool in a Marketing Strategy

This study fostered partnership between scientists, shellfish growers, water treatment engineers, economists and regulators. The objective was to optimise land-based post-harvest treatments in such a way that oyster and mussel marketing could continue during toxic blooms of Dinophysis acuminata (DSP) and Alexandrium minutum (PSP). Among the different methods capable of eliminating toxic algae, sand filters reduced microalgae by 90–99 %, depending on sand grain size used, whereas immersed membranes (0.2 μm) retained 99 % of particles. However, equipment and operating costs were higher for immersed membranes. Experiments using disrupted algal cells showed that PSP and DSP toxins remained stable and soluble for 15 days following release from the cell. The soluble fractions were practically unavailable to mussels. The storage of oysters for 35 days required a re-circulating system at 16 °C, with a continuous algal food supply (Skeletonema costatum). These culture conditions provided a good balance between algal supply and sea water turnover, allowing for the conservation of mussel body condition and water quality, with regard to dissolved forms of nitrogen. The efficiency of detoxification was correlated with the ingestion of food particles. When oxidizing agents (H2O2) were used, detoxification kinetics followed a different course from those observed during natural decontamination processes. From an economic point of view, analysis of the type of shellfish farm provided a way to identify farms that were likely to purchase, either safe storage or detoxification equipment. Plant size was simulated as a function of the average quantity of shellfish processed.