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The Pacific oyster, Crassostrea gigas, is an osmoconforming bivalve exposed to wide salinity fluctuations. The physiological mechanisms used by oysters to cope with salinity stress are energy demanding and may impair other processes, such as defense against pathogens. This oyster species has been experiencing recurrent mortality events caused by the Ostreid herpesvirus 1 (OsHV-1). The objectives of this study were to investigate the effect of salinity (10, 15, 25 and 35‰) on energetic reserves, key enzyme activities and membrane fatty acids, and to identify the metabolic risk factors related to OsHV-1-induced mortality of oysters. Acclimation to low salinity led to increased water content, protein level, and energetic reserves (carbohydrates and triglycerides) of oysters. The latter was consistent with lower activity of hexokinase, the first enzyme involved in glycolysis, up-regulation of AMP-activated protein kinase, a major regulator of cellular energy metabolism, and lower activity of catalase, an antioxidant enzyme involved in management of reactive oxygen species. Acclimation to salinity also involved a major remodeling of membrane fatty acids. Particularly, 20:4n-6 decreased linearly with decreasing salinity, likely reflecting its mobilization for prostaglandin synthesis in oysters. The survival of oysters exposed to OsHV-1 varied from 43% to 96% according to salinity ( Fuhrmann et al., 2016). Risk analyses showed that activity of superoxide dismutase and levels of proteins, carbohydrates, and triglycerides were associated with a reduced risk of death. Therefore, animals with a higher antioxidant activity and a better physiological condition seemed less susceptible to OsHV-1.

Le naissain d’huître creuse Crassostrea gigas est touché chaque année depuis 2008 par des mortalités causées par un microvariant de l’ostreid herpesvirus 1 (OsHV-1 μVar). Plusieurs études montrent que ces évènements de mortalité se produisent préférentiellement lorsque la température de l’eau est comprise entre 16°C et 24°C. Par conséquent, une exposition rapide des huîtres infectées par OsHV-1 à des températures supérieures à 24°C pourrait limiter les mortalités causées par le virus. Il est proposé de (1) vérifier l’hypothèse selon laquelle l’exposition à haute température réduit la mortalité des huîtres infectées par OsHV-1, et (2) déterminer si les animaux qui ont survécu suite à l’infection par OsHV-1 et au traitement thermique sont sensibles/résistants à l’infection par OsHV-1et sains/porteurs lorsque la température est à nouveau favorable au développement d’une infection exprimée. La survie des huîtres infectées par OsHV-1 à 29°C est nettement supérieure (81%) à celle des huîtres à 21°C (49%) et à 26°C (41%). Par ailleurs, les huîtres survivantes à une infection par OsHV-1 à 29°C ne semblent pas infectieuses, même lorsque la température devient permissive pour le virus (21°C). Enfin, lors d’une seconde exposition au virus en milieu naturel, les huîtres survivantes à une infection par OsHV-1 à 29°C présentent un risque de mortalité 2 fois supérieur à celui des huîtres infectées aux autres températures. Néanmoins, considérée sur l’ensemble de l’expérience, la survie des huîtres exposées à OsHV-1 à 29°C est 1.5 fois supérieures (57%) à celles des huîtres exposées à OsHV-1 à 21°C et à 26°C (37%). Par conséquent, il y a un bénéfice à exposer les huîtres à OsHV-1 à 29°C plutôt qu’à 21°C ou à 26°C. Il restera à comprendre les fondements de cette interaction hôte-agent pathogène- température. La diminution du risque de mortalité à 29°C reste à élucider.

Acclimation and adaptation, which are key to species survival in a changing climate, can be observed in terms of membrane lipid composition. Remodelling membrane lipids, via homeoviscous adaptation (HVA), counteracts membrane dysfunction due to temperature in poikilotherms. In order to assess the potential for acclimation and adaptation in the honeycomb worm, Sabellaria alveolata, a reef-building polychaete that supports high biodiversity, we carried out common-garden experiments using individuals from along its latitudinal range. Individuals were exposed to a stepwise temperature increase from 15 °C to 25 °C and membrane lipid composition assessed. Our results suggest that S. alveolata was able to acclimate to higher temperatures, as observed by a decrease in unsaturation index and 20:5n-3. However, over the long-term at 25 °C, lipid composition patterns are not consistent with HVA expectations and suggest a stress response. Furthermore, unsaturation index of individuals from the two coldest sites were higher than those from the two warmest sites, with individuals from the thermally intermediate site being in-between, likely reflecting local adaptation to temperature. Therefore, lipid remodelling appears limited at the highest temperatures in S. alveolata, suggesting that individuals inhabiting warm environments may be close to their upper thermal tolerance limits and at risk in a changing climate.

Mortality of young Pacific oysters Crassostrea gigas associated with the ostreid herpesvirus 1 (OsHV-1) is occurring worldwide. Here, we examined for the first time the effect of salinity on OsHV-1 transmission and disease-related mortality of C. gigas, as well as salinity-related effects on the pathogen itself. To obtain donors for OsHV-1 transmission, we transferred laboratory-raised oysters to an estuary during a disease outbreak and then back to the laboratory. Oysters that tested OsHV-1 positive were placed in seawater tanks (35‰, 21°C). Water from these tanks was used to infect naïve oysters in 2 experimental setups: (1) oysters acclimated or non-acclimated to a salinity of 10, 15, 25 and 35‰ and (2) oysters acclimated to a salinity of 25‰; the latter were exposed to OsHV-1 water diluted to a salinity of 10 or 25‰. The survival of oysters exposed to OsHV-1 water and acclimated to a salinity of 10‰ was >95%, compared to only 43 to 73% survival in oysters acclimated to higher salinities (Expt 1), reflecting differences in the levels of OsHV-1 DNA and viral gene expression (Expts 1 and 2). However, the survival of their non-acclimated counterparts was only 23% (Expt 2), and the levels of OsHV-1 DNA and the expression of 4 viral genes were low (Expt 1). Thus, OsHV-1 may not have been the ultimate cause of mortality in non-acclimated oysters weakened by a salinity shock. It appears that reducing disease risk by means of low salinity is unlikely in the field.

Mass mortality outbreaks (90-100%) in both juvenile and adult blue mussels were reported in 2014 along the Pertuis Charentais area of the French Atlantic coast. A series of studies were carried out to learn more about the phenomenon through detecting pathogens, describing environmental conditions and establishing the physiological status of the animals. Bacteria identif ied as belonging to the V. splendidus species were detected in dying mussels and seem able to cause mortality in blue mussels in the laboratory. Unusual environmental conditions (large amounts of fresh water, re-suspension of sediments during a series of storms, and a high renewal rate of specific water masses in Brittany’s Pertuis area) may be partially responsible for sparking the phenomen, Des épisodes de mortalité massive (90-100 %) ont été observés au sein des élevages de moules touchant à la fois les animaux adultes et les juvéniles au printemps 2014, dans les Pertuis charentais. Un ensemble de travaux a été réalisé afin d’analyser et de mieux comprendre ce phénomène en recherchant la présence d’agents infectieux, en décrivant les fluctuations environnementales associées et en étudiant l’état physiologique des animaux. Des bactéries identifiées comme appartenant à l’espèce V. splendidus ont été détectées chez les animaux moribonds et apparaissent capables d’induire des mortalités en laboratoire chez les moules bleues. De plus, des conditions environnementales particulières (apports importants d’eau douce, remise en suspension de sédiments au travers de tempêtes successives et temps de renouvellement des masses d’eau spécifiques du Pertuis breton élevé) ont été associées au déclenchement du phénomène

Here, we assess the physiological effects induced by environmental concentrations of pesticides in Pacific oyster Crassostrea gigas. Oysters were exposed for 14 d to trace levels of metconazole (0.2 and 2 mu g/L), isoproturon (0.1 and 1 mu g/L), or both in a mixture (0.2 and 0.1 mu g/L, respectively). Exposure to trace levels of pesticides had no effect on the filtration rate, growth, and energy reserves of oysters. However, oysters exposed to metconazole and isoproturon showed an overactivation of the sensing-kinase AMP-activated protein kinase alpha (AMPK alpha), a key enzyme involved in energy metabolism and more particularly glycolysis. In the meantime, these exposed oysters showed a decrease in hexokinase and pyruvate kinase activities, whereas 2-DE proteomic revealed that fructose-1,6-bisphosphatase (F-1,6-BP), a key enzyme of gluconeogenesis, was upregulated. Activities of antioxidant enzymes were higher in oysters exposed to the highest pesticide concentrations. Both pesticides enhanced the superoxide dismutase activity of oysters. Isoproturon enhanced catalase activity, and metconazole enhanced peroxiredoxin activity. Overall, our results show that environmental concentrations of metconazole or isoproturon induced subtle changes in the energy and antioxidant metabolisms of oysters.

Suite aux surmortalités observées au sein des élevages de moules touchant à la fois les animaux adultes et les juvéniles au mois de mars, dans les Pertuis Charentais, la Direction Générale de l’Alimentation (DGAl) a adressé une saisine à Ifremer le 04 avril 2014. Celle-ci fait état d’une demande d’appui scientifique et technique d’Ifremer pour tenter d’apporter des éléments de réponse par rapport à cette mortalité subite et importante. L’Ifremer a proposé un projet d’action permettant l’expertise du phénomène de surmortalité de la moule bleue, selon 3 axes : l’impact environnemental, la pathologie et les caractéristiques physiologiques des moules. Il s’agit de mettre en évidence la présence ou non d’agents infectieux connus ou émergents, d’apporter des éléments de compréhension au regard des fluctuations environnementales, de la réponse physiologique et biochimique des moules dans la mer des Pertuis Charentais et des interactions entre ces trois volets.

L’objectif de cette étude vise à déterminer l’effet de basses températures (10°C et 13°C) pendant des durées variables (0 et 80 jours) sur la survie du naissain d’huîtres creuses préalablement infecté suite à une exposition en rade de Brest pendant 5 ou 8 jours. Le naissain d’huître creuse préalablement infecté par OsHV-1 µvar par exposition en milieu naturel pendant 5 d ou 8 d, puis transféré à basse température (10°C ou 13°C) pendant 5 à 80 d, présente des mortalités plus faibles et plus tardives que les animaux témoins en laboratoire. La réduction des mortalités observée dans le naissain exposé à basse température coïncide avec une diminution progressive des concentrations d’ADN appartenant à OsHV-1 dans les tissus, au point de devenir non-détecté ou non quantifiable après 6 à 41 d. En revanche, lorsque ces animaux sont exposés à une augmentation de température à 21°C en laboratoire, le virus est réactivé et d’importantes mortalités sont constatées. Bien que ces mortalités soient souvent inférieures à celles des animaux témoins, le gain de survie est généralement faible et semble indépendant de la température (10°C ou 13°C) et de la durée d’exposition à basse température (5 à 80 d). Enfin, lorsque les naissains sont réexposés en milieu naturel où la maladie sévit, des mortalités similaires à celles des groupes témoins sont constatées. Par conséquent, les huîtres naturellement exposées à OsHV-1, chez lesquelles le développement de la maladie est limité par une exposition plus ou moins longue à basses températures, demeurent sensibles à cet agent infectieux.

The aquaculture of the oyster Crassostrea gigas is largely based on natural recruitment of the species on spat collectors along the french Atlantic coast, the remaining spat being provided by hatcheries and nurseries. Due to an increase in the climate/meteorological variability, during the last twenty years, the natural spat collection has become variable, from null to overabundant depending on the year. Since 2008, the oyster spat mortalities worsen the situation, reducing the available spat and increasing the cost of the latter. However, the temporal variability of the natural recruitment modalities in the Mediterranean do not allow the aquaculture industry to rely on native spats, making the understanding of natural recruitment in the Mediterranean a challenge for the future in order to fit the professional needs.

Although spatial studies of diseases on land have a long history, far fewer have been made on aquatic diseases. Here, we present the first large-scale, high-resolution spatial and temporal representation of a mass mortality phenomenon cause by the Ostreid herpesvirus (OsHV-1) that has affected oysters (Crassostrea gigas) every year since 2008, in relation to their energetic reserves and the quality of their food. Disease mortality was investigated in healthy oysters deployed at 106 locations in the Thau Mediterranean lagoon before the start of the epizootic in spring 2011. We found that disease mortality of oysters showed strong spatial dependence clearly reflecting the epizootic process of local transmission. Disease initiated inside oyster farms spread rapidly beyond these areas. Local differences in energetic condition of oysters, partly driven by variation in food quality, played a significant role in the spatial and temporal dynamics of disease mortality. In particular, the relative contribution of diatoms to the diet of oysters was positively correlated with their energetic reserves, which in turn decreased the risk of disease mortality.

Originating from north-eastern Asia, the Pacific oyster Crassostrea gigas has been introduced, mainly for aquaculture purpose, into a large number of countries. Although highly variable, its invasive nature has been reported in an increasing number of coastal areas, notably. Northern Europe. We set up a common garden experiment based on the comparison of progenies of Pacific oysters sampled in France, where populations settled since the introduction of the species in the 70’s, and Denmark, where established populations were observed since the beginning of 90s. Pure and hybrid progenies, resulting from crosses within and between adults sampled in both populations, were studied for their sex-ratio, condition index, transcriptomics, and biochemical parameters

We bring new items in connection with the origins of the natural recruitment variability of the Pacific oyster Crassostrea gigas in Thau lagoon. A poor relationship between " number of larvae" and "number of spat" in 2012 shows a biological lock around oysterculture areas during the metamorphosis in spite of better success of recruitment outside shellfish farming zone. A comprehensive analysis of environmental factors effects and the development of prognosis tools are planned to assist oysterfarmers in rationalization of natural oyster recruitment around Mediterranean lagoon.

Background Dietary exposure to the cyanotoxin BMAA is suspected to be the cause of amyotrophic lateral sclerosis in the Western Pacific Islands. In Europe and North America, this toxin has been identified in the marine environment of amyotrophic lateral sclerosis clusters but, to date, only few dietary exposures have been described. Objectives We aimed at identifying cluster(s) of amyotrophic lateral sclerosis in the Hérault district, a coastal district from Southern France, and to search, in the identified area(s), for the existence of a potential dietary source of BMAA. Methods A spatio-temporal cluster analysis was performed in the district, considering all incident amyotrophic lateral sclerosis cases identified from 1994 to 2009 by our expert center. We investigated the cluster area with serial collections of oysters and mussels that were subsequently analyzed blind for BMAA concentrations. Results We found one significant amyotrophic lateral sclerosis cluster (p = 0.0024), surrounding the Thau lagoon, the most important area of shellfish production and consumption along the French Mediterranean coast. BMAA was identified in mussels (1.8 µg/g to 6.0 µg/g) and oysters (0.6 µg/g to 1.6 µg/g). The highest concentrations of BMAA were measured during summer when the highest picocyanobacteria abundances were recorded. Conclusions While it is not possible to ascertain a direct link between shellfish consumption and the existence of this ALS cluster, these results add new data to the potential association of BMAA with sporadic amyotrophic lateral sclerosis, one of the most severe neurodegenerative disorder.

Background: Bacterial infections are common in bivalve larvae and can lead to significant mortality, notably in hatcheries. Numerous studies have identified the pathogenic bacteria involved in such mortalities, but physiological changes associated with pathogen exposure at larval stage are still poorly understood. In the present study, we used an integrative approach including physiological, enzymatic, biochemical, and molecular analyses to investigate changes in energy metabolism, lipid remodelling, cellular stress, and immune status of Crassostrea gigas larvae subjected to experimental infection with the pathogenic bacteria Vibrio coralliilyticus. Findings: Our results showed that V. coralliilyticus exposure induced (1) limited but significant increase of larvae mortality compared with controls, (2) declined feeding activity, which resulted in energy status changes (i.e. reserve consumption, beta-oxidation, decline of metabolic rate), (3) fatty acid remodeling of polar lipids (changes in phosphatidylinositol and lysophosphatidylcholine composition,non-methylene-interrupted fatty acids accumulation, lower content of major C-20 polyunsaturated fatty acids as well as activation of desaturases, phospholipase and lipoxygenase), (4) activation of antioxidant defenses (catalase, superoxide dismutase, peroxiredoxin) and cytoprotective processes (heat shock protein 70, pernin), and (5) activation of the immune response (non-self recognition, NF-(kappa kappa) signaling pathway, haematopoiesis, eiconosoids and lysophosphatidyl acid synthesis, inhibitor of metalloproteinase and antimicrobial peptides). Conclusion: Overall, our results allowed us to propose an integrative view of changes induced by a bacterial infection in Pacific oyster larvae, opening new perspectives on the response of marine bivalve larvae to infections.

Rotifers (Brachionus plicatilis), commonly used at first feeding in commercial fish hatcheries, carry a large bacteria load. Because they are relatively poor in essential fatty acids, it is common practice to enrich them with fatty acids, including arachidonic acid (AA). This study aims to determine whether prey enrichment with AA may act as a prebiotic and modify the microbial community composition either in AA-enriched rotifer cultures or in larval-rearing water using winter flounder (Pseudopleuronectes americanus) as a larval fish model. AA enrichment modified the bacterial community composition in both the rotifer culture tanks and the larval-rearing tanks. We observed an increase in the number of cultivable bacteria on TCBS (thiosulfate-citrate-bile salts-sucrose) agar, used as a proxy for the abundance of Vibrio sp. The results suggest that AA may also play an indirect role in larval health., Les rotifères (Brachionus plicatilis), fréquemment utilisés comme première source alimentaire dans les piscicultures commerciales, portent une charge bactérienne importante. Parce qu’ils sont relativement pauvres en acides gras essentiels, il est de pratique courante de les enrichir en acides gras, notamment en acide arachidonique (AA). Cette étude vise à déterminer si l’enrichissement des proies à l’AA peut agir comme prébiotique et modifier la composition de la communauté microbienne non seulement dans les cultures de rotifères enrichies à l’AA, mais aussi dans l’eau d’élevage des larves, en utilisant la plie rouge (Pseudopleuronectes americanus) comme modèle de larves de poisson. L’enrichissement en AA a modifié la composition de la communauté microbienne tant dans les bassins de culture de rotifères que dans les bassins d’élevage des larves. Un accroissement du nombre de bactéries cultivables sur la gélose TCBS (thiosulfate – citrate – sels biliaires – sucrose), utilisée pour estimer l’abondance de Vibrio sp., a également été observé. Les résultats suggèrent que l’AA peut aussi jouer un rôle indirect dans la santé des larves

INTRODUCTION - PRONAMED 2010-2011- Ce projet, initié le Comité Régional de Conchyliculture de Méditerranée (CRCM) et l’Ifremer a été mis en œuvre grâce à la collaboration du CRCM, du Cépralmar ainsi que du réseau VELYGER et du laboratoire environnement ressources du Languedoc Roussillon (LER-LR) de l’Ifremer. En outre, ce projet local a bénéficié de fonds d’état dans le cadre du programme de soutien à l’innovation dans la filière pêche et aquaculture proposé par FranceAgrimer, de fonds européens via le Fond d’Étude pour les Pêches, et de fonds publics locaux grâce aux subventions de la région Languedoc Roussillon et du conseil général de l’Hérault. PRÉAMBULE - La version initiale du projet PRONAMED comportait deux volets de recherche. Le premier, consacré au captage naturel, est exposé dans le présent rapport. Le second volet visait à produire des naissains issus de géniteurs locaux sélectionnés afin de produire des huîtres résistantes et adaptées aux conditions environnementales de la lagune de Thau. Le second volet a précocement avorté lors des essais de production de naissains en écloserie qui ont échoués tels que décrits dans l’Annexe 1. Le programme VELYGER, initié en 2008 par l’Ifremer dans le cadre de l’Observatoire National de la Conchyliculture, avait pour objectif d’observer, d’analyser et de gérer la variabilité du recrutement de l’huître creuse en France. Dans ce projet, quatre sites-ateliers répartis sur la façade Atlantique ont été l’objet de suivis de la reproduction, des abondances larvaires, du captage et des paramètres environnementaux. Dès 2010, l’étang de Thau a été désigné comme site atelier de seconde génération de ce programme. Dans le cadre du projet PRONAMED, le suivi des différents descripteurs s’est donc inscrit dans la continuité des protocoles mis en place pour VELYGER que ce soit en termes de matériel utilisé, d’approches méthodiques et d’analyse des résultats. Les données obtenues dans PRONAMED ont été mises à disposition du grand publ

Réponse à la saisine DPMA 12-2567: synthèse de quatre expérimentations qui ont été effectuées entre avril 2010 et avril 2012.

Quantification of mRNA of genes related to metabolism, immunity and cellular stress was examined in relation to a massive mortality event during the culture of American oyster larvae, Crassostrea virginica which was probably, in regard to previous microbiological analysis, induced by vibrio infection. To document molecular changes associated with the mortality event, mRNA levels were compared to biochemical and physiological data, previously described in a companion paper. Among the 18 genes studied, comparatively to the antibiotic control, 10 showed a lower relative gene expression when the massive mortality occurred. Six of them are presumed to be related to metabolism, corroborating the metabolic depression associated with the mortality event suggested by biochemical and physiological analyses. Relationships between the regulation of antioxidant enzyme activities, lipid peroxidation, and the mRNA abundance of genes linked to oxidative stress, cytoprotection, and immune response are also discussed. Finally, we observed an increase in the transcript abundance of two genes involved in apoptosis and cell regulation simultaneously with mortality, suggesting that these processes might be linked.

Carbon stable isotopes and fatty acids were measured in the suspended particulate organic matter (POM) of the Thau lagoon to study its qualitative temporal changes in relation to environmental factors and to identify the food sources of bivalves over a one-yr-cycle in relation to their growth. Reciprocally, the impact of shellfish farming on POM was also studied. Oysters and mussels were sampled and measured for biometry, stable isotopes and fatty acid composition. Water samples were collected at two sites, both inside and outside of the shellfish farming area, to determine concentrations in POM, chlorophyll a (Chl a) and stable isotopes. Carbon isotopes and fatty acids in bivalves reflected seasonal changes in food sources, which varied consistently with the environment. Seasonal changes in delta C-13 and fatty acids in the bivalves suggested that dietary phytoplankton contribution varied according to season. Terrestrial organic matter and bacteria can contribute to the diet of bivalves during non-bloom periods. Mussels seemed to rely more on diatoms and less on terrestrial organic matter and bacteria than oysters did, particularly when phytoplankton biomass was low during the summer. Although one- and two-yr-old oysters showed similar delta C-13, their fatty acid dynamics differed slightly. Periods of high growth rate in bivalves were mainly fuelled by diatoms, thus highlighting the importance of seasonal blooms of microphytoplankton during the critical period of bivalve growth and gamete production. Although there was no significant effect of shellfish farms on Chl a and POM delta C-13, consistent differences indicate that stable isotopes could be used successfully to investigate the effects of bivalve aquaculture. (C) 2011 Elsevier B.V. All rights reserved.

Depuis 2009, l'Observatoire Conchylicole assure le suivi, sur des sites ateliers disposés sur l'ensemble du littoral français, de lots sentinelles d'huîtres creuses Crassostrea gigas représentatifs de la production française. Leur suivi permet d'acquérir des données nationales de croissance et de mortalité, de traduire la dynamique spatio-temporelle des performances d’élevage et ainsi de participer à la compréhension des phénomènes observés. Pour ce faire, des lots sentinelles d’huîtres correspondant à différentes origines (captage ou écloserie, diploïdes ou triploïdes) et à différents stades d’élevage (naissain ou adultes 18 mois) sont déployés simultanément sur 13 sites ateliers représentant les grandes régions conchylicoles du littoral français. En parallèle des suivis de croissance et de mortalité, des données associées à la présence d’agents infectieux dans ces huîtres, ainsi que des variables environnementales (température, salinité, flores sur certains sites) sont acquises. L’ensemble des données acquises par l’Observatoire Conchylicole est diffusé en temps quasiréel, par l’intermédiaire d’un site internet dédié affichant les courbes de mortalité, de croissance et de température sur chaque site (actualisé tous les 15 jours). Des bulletins résumant les évolutions des divers paramètres sont également téléchargeables sur le site. Enfin, les mesures haute fréquence de température, pression et salinité des différents sites sont accessibles en temps réel sur un serveur spécifique. Les résultats des suivis réalisés en 2011 mettent en évidence des différences significatives entre les taux de mortalité cumulée sur les lots de naissains diploïdes (moyenne nationale 73 % ± 11%), de naissain triploïde (moyenne nationale 44.4 % ± 20%) et d’huîtres de 18 mois (moyenne nationale 3.1 % ± 4%). Certains sites apparaissent fortement touchés quel que soit le lot de naissain (tels que l’étang de Thau ou Loix en Ré), en opposition à certains autres pour lesquels les taux de mortal

Ce rapport présente la comparaison des mortalités de deux lots de naissains de Crassostrea gigas dans plusieurs bassins conchylicoles et déterminer le gain de survie obtenu par la sélection pour des huîtres diploïdes

In this paper, biochemical and physiological analyses were used to characterize changes associated with mortality event occurred during veliger development of American oyster, Crassostrea virginica. Biochemical analyses included the evaluation of lipid classes, fatty acid composition and total protein content. Larval physiology was evaluated by studying feeding activity, enzymes related to energy metabolism, oxidative stress levels and enzymatic antioxidant defenses. These analyses were complemented by bacterial community analyses as well as by measuring larval oyster performance. We observed that mortality events coincided with (1) strong changes in the surrounding bacterial community; (2) a progressive decrease in feeding activity; (3) higher levels of some lipid classes (free fatty acids, diglycerides, and acetone mobile phospholipids); (4) lower levels of phospholipids and protein; (5) higher contents of non-methylene interrupted dienoic fatty acids (22:2 NMI); (6) a decrease in energy metabolism activity (citrate synthase and cytochrome oxidase activities); (7) a higher oxidative stress (lipid peroxidation level); and (8) an activation of antioxidant defences before mortality (glutathione peroxidase and superoxide dismutase). We hypothesized that mortality emergence was related to higher energy consumption coupled with the progressive decline in feeding activity, lowered energy reserves and a decrease in energy metabolism activity. Thus, the low energy availability limited the efficiency of antioxidant defenses, resulting in a higher oxidative stress.

The bivalve's aquaculture industry is an important component of the economy in Eastern Canada. Seed collection is an initial and critical activity in most bivalve aquaculture industries including mussel farming in Prince Edward Island, production is entirely dependent on natural spat collection. Although seed supply is not a concern from a quantitative standpoint, there are growing concerns about the quality of natural seed. The general objective of this study was to identify and assess mussel seed quality criteria on the basis of physiological and biochemical status under laboratory and field conditions. The performance, as estimated by metabolic measurements, lipid class composition, multi-locus heterozygosity (MLH) and survival to stressful environment of seed from 6 different stocks sources was first compared under laboratory conditions at 12 degrees C and 25 degrees C. Results showed that MLH varied among the six sources of mussels in a way which is consistent with the physiological and biochemical indicators of seed quality. Mussels from Shippagan (New Brunswick) and Tracadie (Prince Edward Island) were found to have the highest quality scores and the best adaptive capacity to extreme water temperature under laboratory conditions. The results of the stock-site reciprocal field studies are in general agreement with those of the laboratory experiments with higher survival of mussels from Shippagan, Tracadie and St. Peters Bays in the various study sites. Our results suggest that the measure of MLH and survival curves at stressful temperature could be a good criteria combination to identify the improved survival potential of mussels stocks.

Several Vibrio species are known to be pathogenic to the Pacific oyster Crassostrea gigas. Survival varies according to pathogen exposure and high mortality events usually occur in summer during gametogenesis. In order to study the effects of gametogenetic status and ploidy (a factor known to affect reproduction allocation in oysters) on vibriosis survival, we conducted two successive experiments. Our results demonstrate that a common bath challenge with pathogenic Vibrio splendidus and Vibrio aestuarianus on a mixture of mature, spawning and non-mature oysters can lead to significant mortality. Previous bath challenges, which were done using only non-mature oysters, had not produced mortality. Immunohisto-chemical analyses showed the affinity of Vibrio for gonadic tissues, highlighting the importance of sexual maturity for vibriosis infection processes in oysters. Mortality rate results showed poor repeatability between tanks, however, in this bath challenge. We then tested a standardized and repeatable injection protocol using two different doses of the same combination of two Vibrio species on related diploid and triploid oysters at four different times over a year. Statistical analyses of mortality kinetics over a 6-day period after injection revealed that active gametogenesis periods correspond to higher susceptibility to vibriosis and that there is a significant interaction of this seasonal effect with ploidy. However, no significant advantage of triploidy was observed. Triploid oysters even showed lower survival than diploid counterparts in winter. Results are discussed in relation to differing energy allocation patterns between diploid and triploid Pacific oysters. (C) 2010 Elsevier Inc. All rights reserved.

The objective of this work is to understand why oysters Crassostrea gigas shows low settlement success in the Thau lagoon despite the fact that biomass of adults is elevated and that larvae show normal development in the water column. Our hypotheses are that oysters compete for food or space with other filter-feeders animals such as sponges, ascidians and other bivalves. To test the trophic hypothesis, we analysed the entire settler community harvested on four-month-old collectors deployed in the Thau lagoon during the summer 2009 for stable isotopes and fatty acids. Based on the isotopic, crustacean amphipods and barnacles can be rejected as a potential food competitor of juvenile oysters. However, other bivalves such as Mytilus sp., Anomia sp., and sponges seem to feed on the same diet. Our results also suggest that the ascidian Ascidiella sp. is the major food competitor of oysters followed by two other ascidian species and the bivalve Lima sp. To test the space hypothesis, sets of collectors were (1) maintained always underwater, which is normally the case in the Thau lagoon where tides are marginal, or (2) manually emerged every weeks to reduce the development of subtidal species. After few weeks, the collectors maintained underwater were dominated by sponges and ascidian whereas the regularly emerged collectors were successfully colonised by oysters and barnacles. This experiment clearly suggests that settlement of pacific oysters in the Thau lagoon is constrained by competition for space with other subtidal species. From a practical standpoint, it seems that it is possible to enhance spat collection of oysters until attaining commercial profitability by regularly emerging the collectors.

Soft-shell clam, Mya arenaria, culture on the east coast of Canada is characterized by high loss following seeding. To evaluate the importance of passive transport due to currents, an experimental flume study was designed. The purpose was to measure the effects of hydrodynamic conditions, substrate, and clam size on dispersal in controlled laboratory condition and to interpret these results in relation to field measurements. Unidirectional currents with gradual increasing velocities (0 to 60 cm s(-1)) were applied to three substrates (muddy sand, medium sand, and coarse sand) in which clams from one of three size classes (10, 15, and 20 mm) had burrowed. We also examined the resulting effects of turbulent kinetic energy on the erosion of medium-grain sand and clams from the three size classes. Turbulent energy was created with a homemade device acting on the unidirectional currents. Nearly 95% of buried clams (all substrates and size classes together) were unaffected by unidirectional currents of up to 60 cm s(-1), but only 10% withstood turbulent kinetic energy of 10.1 J m(-3), a level that is lower than that measured in the field during an autumnal storm. The transport of clams was found to be directly related to substrate erosion-levels. (C) 2010 Elsevier B.V. All rights reserved.

In a previous study, a major remodeling of lipids, consistent with the theory of homeoviscous adaptation, was observed in the juvenile hard clam Mercenaria mercenaria during a temperature reduction from 24 to -1 degrees C. In addition, the lipid remodeling varied between genetically distinct lines of hard clams. The present study examined whether adult hard clams originating from different locations and a selectively bred variety show differences related to their genetic characteristics in the remodeling of lipids that normally occur during decreasing temperatures. Wild hard clams from 4 locations in Atlantic Canada and the selectively bred M mercenaria var. notata were held at an aquaculture growout site located at the northern distribution limit of the species in the Gulf of St. Lawrence from August to December 2006. Gills were sampled monthly for lipid analyses. Hard clams from the 5 groups showed an increase in the unsaturation index, mainly attributable to 22:6n-3 and 20:5n-3 as temperature decreased during the fall, followed by an increase in the phospholipid to sterol ratio in December. Although hard clams from the wild showed a lower unsaturation index than the selectively bred clams, there was no effect of location on the lipid remodeling. This result coincided with low genetic differentiation among hard clams from the 5 groups. Interestingly, the levels of 20:5n-3, 20:4n-6 and 22:6n-3-3 fatty acids obtained from the diet-were generally lower in the environment compared to the levels in hard clams, thus suggesting some mechanisms for the selective incorporation of these fatty acids in hard clams.

This study examines the effects of varying dietary lipids on growth, survival, lipid composition and behaviour in lobster Homarus americanus (Milne Edwards, 1837) postlarvae. Lobsters were fed one of 3 diets during their early ontogeny: (1) Artemac, a widely used Artemia replacement; (2) a ternary mixture consisting of Artemac, frozen Artemia adults and Artemia flakes; or (3) a mixture of live A. salina nauplii and adults. We evaluated the olfactory capacity (response to predator odour plume) and cryptic behaviour (ability to hide during settlement) of lobster postlarvae as a function of these diets and the lipid and the fatty acid composition of lobsters. Growth and survival of lobster postlarvae were highest in those fed live Artemia, followed by the ternary mix, then Artemac. The low performance of lobster postlarvae fed Artemac may be attributable to dietary deficiencies in phospholipids (PLs) or 20:4n-6 and coincided with low levels of endogenous triacylglycerols (TAG). Those lobsters fed live Artemia showed low levels of 22:6n-3 and 20:5n-3 compared to levels occurring in wild animals. Here we report the selective incorporation of 20:4n-6, 20:5n-3 and 22:6n-3 to polar lipids and, to a lesser extent, to neutral lipids in lobsters. Finally, lobster postlarvae fed the 3 experimental diets responded to a predator odour plume by reducing their activity levels and increasing the time spent swimming downstream. However, lobster settlement behaviour varied as a function of the diet: low-performing lobsters fed Artemac were less active than those fed the other diets, presumably due to low levels of endogenous TAG or changes in dietary long-chain PUFA.