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Histo-blood group antigens (HBGAs) comprise a family of cell-surface carbohydrates that are considered norovirus-specific binding receptors or ligands. HBGA-like molecules have also been detected in oysters as common norovirus carriers, although the pathway involved in the synthesis of these molecules in oysters has yet to be elucidated. We isolated and identified a key gene involved in the synthesis of HBGA-like molecules, FUT1, from Crassostrea gigas, named CgFUT1. Real-time quantitative polymerase chain reaction analysis showed that CgFUT1 mRNA was expressed in the mantle, gill, muscle, labellum, and hepatopancreatic tissues of C. gigas, with the hepatopancreas exhibiting the highest expression level. A recombinant CgFUT1 protein with a molecular mass of 38.0 kDa was expressed in Escherichia coli using a prokaryotic expression vector. A eukaryotic expression plasmid was constructed and transfected into Chinese hamster ovary (CHO) cells. The expression of CgFUT1 and membrane localization of type H-2 HBGA-like molecules in CHO cells were detected using Western blotting and cellular immunofluorescence, respectively. This study indicated that CgFUT1, expressed in C. gigas tissues, can synthesize type H-2 HBGA-like molecules. This finding provides a new perspective for analyzing the source and synthetic pathway of HBGA-like molecules in oysters.

Bivalves are regulators of coastal lagoons and provide a wide range of ecosystem services. However, coastal lagoons are sensitive to climate change. Our objective was to describe the drivers of the cascade of ecological events that occurred during a summer heatwave and which resulted in recruitment failure of the Pacific oyster Crassostrea gigas. Results show that elevated temperatures and salinity caused a shift in planktonic food availability toward smaller taxa. These trophic changes did not affect food accumulation by oyster larvae or their fatty acid composition but did affect post-metamorphosis success, with up to 24% fewer young metamorphosed postlarvae at some sites and no development of juveniles at all sites. This resulted in the failure of oyster recruitment and in the development of tubeworms, a trophic and spatial competitor that can better ingest small particles. This knowledge suggests that, in the context of marine heatwaves, the ecological limits of oyster larvae are narrower than their physiological limits.

In this study, GC-IMS was used to analyze the volatile component and flavor profiles of Crassostrea gigas individuals of different ploidy and gender. Principal component analysis was used to explore overall differences in flavor profiles, and a total of 54 volatile compounds were identified. The total volatile flavor contents in the edible parts of tetraploid oysters were significantly higher than in diploid and triploid oysters. The concentrations of ethyl (E)-2-butenoate and 1-penten-3-ol were significantly higher in triploid oysters than in diploid and tetraploid oysters. In addition, the volatile compounds propanoic acid, ethyl propanoate, 1-butanol, butanal, and 2-ethyl furan were significantly higher in females than in males. The volatile compounds p-methyl anisole, 3-octanone, 3-octanone, and (E)-2-heptenal were present in higher levels in male than in female oysters. Overall, different ploidy and gender of oysters are connected with different sensory characteristics, providing new insights for understanding the flavor characteristics of oysters.

The Pacific Oyster has adapted well to the southern Brazilian environmental conditions, where the combination of factors allows harvest in less than eight months. Although convenient for most of the year, it is during summer that water temperature can exceed 30 ºC, a summer condition that leads to high mortality rates. According to the literature, if spawning is not triggered, a substantial reduction in mortality can be achieved. Studies previously presented at CYTEF 2020 showed that confining oysters at temperatures close to those of basal metabolism can inhibit the effects of gametogenesis. Further research was conducted in order to verify the possible outcomes of long term confinement of late autumn harvested oysters, presenting high glycogen reserves. This article reports the experimental results of those tests, regarding the preservation of quality attributes and the reduction of mortality rates, when confining oysters under temperatures similar to those of basal metabolism regime.

付着生物にとっての着定基質構造の評価を行う一環として，産業重要種であるマガキCrassostrea gigas 幼生採苗器（カキ幼生コレクター）の表面粗さの定量化を，光沢度を用いて試みた。その結果，カキ幼生コレクターの表面では光沢度が3.6以下で幼生は24個体/cm2以上，裏面中心部では光沢度が8.6以上で幼生は10個体/cm2以下となり，カキ幼生コレクターの部位毎の光沢度及びマガキ幼生の付着数には有意な相関が認められた。次に，紙やすりを用いて光沢度の値を凹凸の粗さに対応させることを試みた。 その結果，紙やすりの粒径と光沢度は，決定係数が低いものの有意な相関が認められた。また，0.25 mm以上の凹凸では光沢度が測定出来ないことも明らかとなった。表面粗さの定量化については今後もさらなる詳細且つ多様な解析が必要であるが，本研究結果からは，カキ稚貝の密度が最も高くなる基質表面の粗さとそれを示す光沢度を解明できる可能性が示された。これらの成果を応用することで，将来的にカキ幼生の採苗密度の向上が期待できる。, To quantify the effect of surface roughness of epiphytic substrates on sessile organisms, the density of oyster larva and gloss unit were measured at three sites of five collectors for spat collection of scallop shells. As a result, higher oyster larva densities were observed at lower gloss units with statistically significant differences. In this study, the surface roughness of greater than 0.25 mm on the grain size of sandpaper was not measured by the gloss unit. The f indings demonstrate that it is possible to determine the roughness of the substrate surface where the density of oyster larva is maximum and the gloss unit that indicates it. Through the application of these results, it is expected that oyster larva densities will improve in the future.

In the framework of the Sustainable Development Goals (SDGs) led by the United Nations, coastal management methods are required to achieve both sustainable food production and environmental conservation as a climate change countermeasure. Oyster farming is an important food production method now being developed in coastal areas around the world. Recently, climate change has caused several negative effects on oyster aquaculture such as poor spat collection due to oligotrophication, ocean acidification, and poor spat growth and survival due to frequent anoxic events derived from high seawater temperature. The oysters cultivated in many regions of the world are intertidal species inhabiting intertidal zones such as sandy/muddy tidal flats and estuaries, where seagrass beds are often distributed in adjacent lower intertidal and subtidal areas. Seagrass vegetation is one of the most important ecosystems functioning as a countermeasure for global climate change. Not only does it mitigate greenhouse gas emissions by sequestration and storage of blue carbon derived from atmospheric CO2, but it also functions as an adaptation measure providing a buffering function against ocean acidification and water quality mprovement. Based on the concept of aquaculture supported by natural ecosystem interactions between oysters and seagrass beds, our project examined whether aquaculture techniques that take into account both mitigation and adaptation to climate change are effective for both sustainable use of coastal areas and environmental conservation. We conducted field experiments in both the French Mediterranean Sea and the Seto Inland Sea of Japan to clarify the effect of eelgrass beds on (1) natural oyster spat collection and (2) growth and survival of oyster spat. The results of our experiments revealed that spat recruitment was significantly higher in areas without eelgrass distribution, while spat growth and survival rate after the settlement were significantly higher in eelgrass beds even when anoxic events occurred in the study areas. Therefore, our results indicate a possibility that seagrass vegetation contributes to sustainability of oyster aquaculture by mitigating environmental degradation during cultivation

Prosjektleder: Gunhild Borgersen NIVA har gjennomført en kartlegging av sjøarealer i Moss kommune. Kartleggingen omfattet statussjekk på kartlagte grunne bløtbunnsområder av «viktig» verd og på ålegrasenger av «svært viktig» og «viktig» verdi. Kartlegging av fastsittende alger og dyr på hardbunn og bløtbunn ble gjennomført med videotransekter, i tillegg til kvantitativ prøvetaking av dyr som lever på bløtbunn (bløtbunnsfauna). Økologisk tilstand for bløtbunnsfauna ble klassifisert til «god». Det ble også gjenomført en kartlegging av forekomst av stillehavsøsters rundt verneområdene Rambergbukta, Eldøya og Taralden, i tillegg til at potensialet for hummerfredning rundt Gullholmsundet og effekten av hummerfredningsområdet i Mossesundet er vurdert. Moss kommune

Growth and survival rates of juveniles of pacific oyster Crassostrea gigas are estimated for the first time in conditions of Peter the Great Bay (Japan Sea). The data were collected at artificial hatchery in the Aquaculture Center located on Popov Island in 2019. The juveniles were settled and reared on two types of substrate: 1) perforated plastic plates with the diameter of 30 cm (area 7.1 dm2), and 2) scallop shells with the height about 10 cm (average area 0.8 dm2) mounted in the western Peter the Great Bay (Voevoda Bay) in September 2019. Before placing in this site, the average height of the juveniles’ shells did not exceed 7 mm. In July 2020, after the 9-month exposure of the collectors with spat in the Voevoda Bay, the height increased in 12–18 times and reached 55–90 mm on the substrate 1 and 25–65 mm on the substrate 2. Then the oysters reared on the substrate 1 were replaced from the plastic plates to the cage shelves and the cages were moved to the Stark Strait. Difference in the growth rate became more apparent in September 2020, when the height of shells settled on the plastic plates reached 67 mm, on average (73 % in the range 50–85 mm) and for the shells settled on the scallops — 32 mm, on average (72 % in the range 20–45 mm). The shell height increased to 76.6 and 52.4 mm, respectively, to the end of October 2020. Finally, about 59 % of the oysters reared on the substrate 1 and cage shelves and 9 % of the oysters reared on the substrate 2 reached the commercial size (80–100 mm). Their survival in the period from mid-October 2019 to July 2020 is estimated as 46.9 % (28.8–98.2 %) for the substrate 1 and 33.5 % (4.0–78.3 %) for the substrate 2. On the substrate 1, survival of the mollusks attached to lower surface of the plates was twice higher. The survival had a tendency to decrease with increasing of the juveniles density. The experiment showed good viability for artificially hatched juveniles of pacific oyster in conditions of Peter the Great Bay. Their growth in the Voevoda Bay and the Stark Strait, with necessary technological measures, as replacing, thinning, and substrate cleaning from fouling, allows to produce oysters with the commercial size.

Ocean acidification and warming (OAW) are pressing contemporary issues affecting marine life and specifically calcifying organisms. Here, we investigated the direct effects of OAW on life-history traits of the Pacific oyster Crassostrea gigas, the most cultivated bivalve species worldwide. We also tested whether parental conditioning history shaped the phenotypic characters of their progenies (intergenerational carryover effects). Adult oysters and their offspring were exposed to two temperatures (18°C, +3°C) under ambient pH conditions or under an end-of-century acidification scenario (−0.33 pH unit). In adults, we monitored standard biometric and reproductive parameters, stress response by quantifying neuroendocrine metabolites and gamete quality. In larvae, we measured hatching rate, size, biochemical quality, and behavior. We found that reducing pH reduced growth rate and activated the serotonin system, but increasing temperature attenuated these effects. There was no effect of pH on reproduction at either temperature, and no intergenerational carryover effects. Larval characteristics were similar between treatments, regardless of parental conditioning history. Thus, the Pacific oyster seems robust to changes in pH, and increasing temperature is not an aggravating factor. We emphasize that the use of neuroendocrine indicators holds promise for revealing sublethal impacts of environmental changes.

Marine bivalves, organisms with a worldwide distribution, have an essential role in ecosystem structure and functioning. Some species consumed by humans are considered economically valuable. Nowadays, in order to meet the worldwide demand for seafood resources without putting the natural stocks at risk of overharvesting, marine bivalves are primarily obtained from aquaculture production. Marine bivalves are often produced in aquacultures located in transitional waters systems, which are considered ideal sites for their optimal development. However, these systems are impacted by a substantial number of pollutants, including microplastics, that may cause adverse effects in the marine bivalves produced for human consumption. In this study, a year-long monitorization was conducted in a bivalve aquaculture located in the Ria de Aveiro coastal lagoon, Portugal, to understand the occurrence of microplastic pollution in different environmental matrices: marine bivalves, water and sediment. Crassostrea gigas (diploids and triploids) and Ruditapes philippinarum were the bivalve species studied and were sampled once every three months, from September 2019 to July 2020. The occurrence of microplastics in these species was examined at the tissue level, with observation of separate tissues (muscle, digestive gland, gills, remaining visceral mass). Water and sediments were collected once a month from September 2019 to September 2020. Microplastics were found in every environmental matrix. Microplastics were detected in higher quantities in sediments, followed by water surface and marine bivalve species. Fragments, fibers and films were common types of microplastics found and their colours included blue, pink, white, and others. FTIR analysis revealed that the most prevalent polymers found in the aquaculture were polyethylene, polypropylene, and polystyrene. Further investigation will be conducted to assess the possible effects of the presence of these common microplastic polymers in the marine bivalves produced for human consumption. Also see: https://micro2022.sciencesconf.org/427052/document, In MICRO 2022, Online Atlas Edition: Plastic Pollution from MACRO to nano

Whole-genome sequencing is widely used to better understand the transmission dynamics, the evolution and the emergence of new variants of viral pathogens. This can bring crucial information to stakeholders for disease management. Unfortunately, aquatic virus genomes are usually difficult to characterize because most of these viruses cannot be easily propagated in vitro. Developing methodologies for routine genome sequencing of aquatic viruses is timely given the ongoing threat of disease emergence. This is particularly true for pathogenic viruses infecting species of commercial interest that are widely exchanged between production basins or countries. For example, the ostreid herpesvirus type 1 (OsHV-1) is a Herpesvirus widely associated with mass mortality events of juvenile Pacific oyster Crassostrea gigas. Genomes of Herpesviruses are large and complex with long direct and inverted terminal repeats. In addition, OsHV-1 is unculturable. It therefore accumulates several features that make its genome sequencing and assembly challenging. To overcome these difficulties, we developed a tangential flow filtration (TFF) method to enrich OsHV-1 infective particles from infected host tissues. This virus purification allowed us to extract high molecular weight and high-quality viral DNA that was subjected to Illumina short-read and Nanopore long-read sequencing. Dedicated bioinformatic pipelines were developed to assemble complete OsHV-1 genomes with reads from both sequencing technologies. Nanopore sequencing allowed characterization of new structural variations and major viral isomers while having 99,98 % of nucleotide identity with the Illumina assembled genome. Our study shows that TFF-based purification method, coupled with Nanopore sequencing, is a promising approach to enable in field sequencing of unculturable aquatic DNA virus.

Survival and growth of the native oyster Crassostrea gasar along the juvenile and adult phases were evaluated in three different stocking densities [low (D), medium (2D) and high (3D)] and in two grow-out systems (fixed and floating system). The fixed system consisted of a rack made with PVC, fixed from the bottom with wood sticks. The floating system consisted of floating bags suspended by a rack made with PVC and maintained submerged from the seawater surface by eight floats. Survival and shell height of oysters cultured after 30, 60 and 90 days were registered in each phase and in each grow-out system. Results showed that the grow-out system did not affect survival and growth of C. gasar in the juvenile and adult phases. The tested densities affected the survival of oysters cultured over time in both phases but did not affect oyster growth. At times analyzed, it was observed positive growth in juvenile oysters grow after 90 days of culture. However, in the adult phase, no growth was observed after 90 days of culture. Oyster yield was higher in the density 3D, in both juvenile and adult phases. These findings contributed to the development of the oyster C. gasar culture.

The Pacific cupped oyster Crassostrea gigas is one of the most 'globalized' marine invertebrates and its production is predominant in many parts of the world including Europe. However, it is threatened by mortality events associated with pathogenic microorganisms such as the virus OsHV-1 and the bacteria Vibrio aestuarianus. C. gigas is also a host for protozoan parasites including haplosporidians. In contrast with Haplosporidium nelsoni previously detected in Europe, H. costale was considered exotic although its presence in French oysters was suggested in the 1980s based on ultrastructural examination. Here, a combination of light and transmission electron microscopy, PCR and sequencing allowed characterizing the presence of the parasite in the context of low mortality events which occurred in 2019 in France. Histological observation revealed the presence of uninucleated, plasmodial and spore stages within the connective tissues of some oysters. Ultrastructural features were similar to H. costale ones in particular the presence of axe-shaped haplosporosomes in spore cytoplasms. Three fragments of the genome including partial small subunit rRNA gene, the ITS-1, 5.8S and ITS-2 array and part of the actin gene were successfully sequenced and grouped with H. costale homologous sequences. This is the first time that the presence of H. costale was confirmed in C. gigas in France. Furthermore, a TaqMan real-time PCR assay was developed and validated [DSe = 92.6% (78.2-99.8) and DSp = 95.5% (92.3-98.6)] to enable the rapid and specific detection of the parasite. The application of the PCR assay on archived samples revealed that the parasite has been present in French oyster populations at least since 2008. Considering the little information available on this parasite, the newly developed TaqMan assay will be very helpful to investigate the temporal and geographic distribution and the life cycle of the parasite in France and more generally in C. gigas geographic range.

Previously, we have reported that the intake of oyster extract (OE), prepared from Pacific oysters (Crassostrea gigas), can attenuate symptoms of dextran sulfate sodium (DSS)-induced acute experimental colitis in mice. Herein, we aimed to evaluate whether OE intake ameliorates chronic experimental colitis induced by repeated DSS administration in mice. Male C57BL/6J (4-week-old) mice were fed either the standard diet AIN93G (control diet) or the control diet containing 5.0% (w/w) OE (OE diet). After 21 days of diet feeding, chronic experimental colitis was induced by three cycles of 2.0% (w/w) DSS solution administration (5 days), followed by distilled water (5 days). Mice fed OE alleviated the shortened colonic length, increased the relative weight of the spleen, colonic histopathological score (regeneration), and blood in the stool score compared with mice fed control diet. A tendency to improve the α-diversity of fecal microbiota, which was exacerbated by colitis, was observed in mice fed OE. Correlation analysis suggested that the anti-colitis effect of OE intake could be related to the valeric acid content and relative abundances of Ruminococcus and Enterococcus in the feces. In conclusion, OE could ameliorate DSS-induced chronic experimental colitis by improving the gut environment, including the microbiota community and SCFA composition.

The application of zinc (Zn) isotope compositions in bivalve organisms to quantify anthropogenic Zn bioaccumulation in marine biota is of great interest to environmental marine management programs such as the “Mussel Watch Program”. Field studies, however, are urgently needed to test its practical value. To this end, we investigated Zn isotope variations in the oyster Crassostrea gigas collected over four decades near the Loire estuary (France), where previous geochemical studies provided evidence for a regionally uniform but temporally variable metal contamination. We show that the Zn temporal isotope profile of oysters matches that of the sedimentary records with an isotope offset of approximately +0.5–0.7‰, tentatively attributed to compromised estuarine processes and trophic transfer. A Zn isotope model for quantifying anthropogenic Zn bioaccumulation suggests an overall decrease in anthropogenic estuarine Zn levels over the past 40 years. This first successful application of Zn isotope ratios in a bivalve species to quantify anthropogenic Zn bioaccumulation confirms their utility for supporting environmental management strategies in marine biomonitoring programs.

Aquaculture activities are often established in the vicinity of highly populated, potentially contaminated areas. Animals cultured at such locations, namely bivalves, are frequently used as test organisms in ecotoxicological testing. In this case, a period of depuration is required to allow the normalization of physiological processes, which are likely to be altered after exposure to a multiplicity of waterborne contaminants occurring in the wild. One of the most important species in modern marine aquaculture is the oyster species Crassostrea gigas. The aim of this study was to assess if the current depuration time frame of 24 h (adopted by most aquaculture facilities), is long enough to permit oysters to revert potential toxic effects exerted by environmental contaminants, allowing their use in laboratory-based ecotoxicological studies. The selected approach involved the monitoring of biochemical (antioxidant defence, oxidative damage, phase II metabolism, and neurological homeostasis) and physiological (condition index) parameters, along a period of 42 days. The obtained results showed that a period of 24 h does not revert any of the potential toxic effects caused by environmental contaminants to which animals may have been previously subjected; even a period of 42 days was not long enough for the oysters to completely normalize the levels of their antioxidant defences, namely total GPx activity, which increased over time. Lipid peroxidation was also increased during the depuration period, and the activity of the metabolic isoenzymes GSTs was significantly decreased. Furthermore, AChE activity measured in the adductor muscle of oysters was increased over time. These assumptions suggest that a period of depuration longer than 24 h is mandatory to obtain adequate test organisms of this oyster species, to be used for ecotoxicological testing purposes. published

In the framework of the Sustainable Development Goals (SDGs) led by the United Nations, coastal management methods are required to achieve both sustainable food production and environmental conservation as a climate change countermeasure. Oyster farming is an important food production method now being developed in coastal areas around the world. Recently, climate change has caused several negative effects on oyster aquaculture such as poor spat collection due to oligotrophication, ocean acidification, and poor spat growth and survival due to frequent anoxic events derived from high seawater temperature. The oysters cultivated in many regions of the world are intertidal species inhabiting intertidal zones such as sandy/muddy tidal flats and estuaries, where seagrass beds are often distributed in adjacent lower intertidal and subtidal areas. Seagrass vegetation is one of the most important ecosystems functioning as a countermeasure for global climate change. Not only does it mitigate greenhouse gas emissions by sequestration and storage of blue carbon derived from atmospheric CO2, but it also functions as an adaptation measure providing a buffering function against ocean acidification and water quality improvement.Based on the concept of aquaculture supported by natural ecosystem interactions between oysters and seagrass beds, our project examined whether aquaculture techniques that take into account both mitigation and adaptation to climate change are effective for both sustainable use of coastal areas and environmental conservation. We conducted field experiments in both the French Mediterranean Sea and the Seto Inland Sea of Japan to clarify the effect of eelgrass beds on (1) natural oyster spat collection and (2) growth and survival of oyster spat. The results of our experiments revealed that spat recruitment was significantly higher in areas without eelgrass distribution, while spat growth and survival rate after the settlement were significantly higher in eelgrass beds even when anoxic events occurred in the study areas. Therefore, our results indicate a possibility that seagrass vegetation contributes to sustainability of oyster aquaculture by mitigating environmental degradation during cultivation.

Bivalve predation by seabream has been observed worldwide and is a major concern for bivalve farmers. Farmed bivalve-seabream interactions must be better understood to ensure the sustainability of bivalve aquaculture. The objectives of this study were to characterize gilthead seabream Sparus aurata presence in a bivalve farm in Prevost Lagoon (Mediterranean Sea) using acoustic telemetry and to evaluate monthly losses of mussels Mytilus galloprovincialis and oysters Crassostrea gigas due to seabream predation over an 18 mo period inside the farm and at an unprotected experimental platform. Large (281 to 499 mm TL) seabream were more commonly detected in the bivalve farm than were small (200 to 280 mm TL) seabream. In contrast to small seabream, 90% of large seabream returned to and spent extended periods in the study area the following year, suggesting inter-annual site fidelity for large fish that used the bivalve farm as a feeding site. Signs of predation were observed on mussels and oysters throughout the year at the unprotected experimental platform. Farmers noted losses in the farm from April to September. Maximal losses (90 to 100%) were observed post-oyster ‘sticking’ and mussel socking. Despite the deployment of nets as mechanical protection to reduce predation, oyster losses represented 28% of the annual value of oysters sold while mussel losses were estimated at ca. 1%. These results suggest that bivalves must be protected by nets throughout the year to avoid predation, particularly post-handling. A collaboration between shellfish farmers and fishermen could be a sustainable solution for bivalve farming, by regularly fishing for seabream in farms, between tables and inside protective nets.

International audience; Vibrio aestuarianus infection in oyster populations causes massive mortality, resulting in losses for oyster farmers. Such dynamics result from host-pathogen interactions and contagion through water-borne transmission. To assess the spatiotemporal spread of V. aestuarianus infection and associated oyster mortality at a bay scale, we built a mathematical model informed by experimental infection data at 2 temperatures and spatially dependent marine connectivity of oyster farms. We applied the model to a real system and tested the importance of each factor using a number of modelling scenarios. Results suggest that introducing V. aestuarianus in a fully susceptible adult oyster population in the bay would lead to the mortality of all farmed oysters over 6 to 12 mo, depending on the location in which infection was initiated. The effect of temperature was captured by the basic reproduction number (R0), which was >1 at high seawater temperatures, as opposed to values

The Pacific oyster (Crassostrea gigas) has a very important economic potential for aquaculture, but on the other hand, is among the highly invasive species in the world and within the Mediterranean ecosystem. In the 1960s, C. gigas was brought to Europe for aquaculture in the Mediterranean and Black Sea regions from Japan and Canada. The Turkish waters are the part of the Mediterranean Sea, which is the world’s most invaded sea. The invasion of alien species results from marine transportation and aquaculture activities of non-native species. A heavy maritime traffic is also present in the Marmara Sea, which connects the Black Sea and Mediterranean Sea. The identification of the invasive species and their distributions is very prominent in terms of protecting natural habitat and monitoring the effects of invasive species. In this study, 30 individuals, morphologically identified as C. gigas, were collected from Bandırma bay. The genomic DNAs were extracted from each sample’s muscle tissue using universal salt extraction method. Partial sequences of COI and 16S Mitochondrial DNA loci of the sample DNAs were obtained for species identification. The sequences were searched against the database and results were retrieved from BLAST. All the sequences obtained in this study showed significant similarity with the C. gigas sequences present in the database (E=0). The sample sequences resulted in 9 different haplotypes for the COI locus (hd: 0.5296 and variance: 0.01256±0.112) and 5 different haplotypes for the 16S rDNA locus (hd: 0.2529, Variance: 0.01076±0.104). The results of this study provided the first molecular evidence for the presence of non-native Pacific oyster individuals in the Marmara Sea.

Background The impact of the microbiota on host fitness has so far mainly been demonstrated for the bacterial microbiome. We know much less about host-associated protist and viral communities, largely due to technical issues. However, all microorganisms within a microbiome potentially interact with each other as well as with the host and the environment, therefore likely affecting the host health. Results We set out to explore how environmental and host factors shape the composition and diversity of bacterial, protist and viral microbial communities in the Pacific oyster hemolymph, both in health and disease. To do so, five oyster families differing in susceptibility to the Pacific oyster mortality syndrome were reared in hatchery and transplanted into a natural environment either before or during a disease outbreak. Using metabarcoding and shotgun metagenomics, we demonstrate that hemolymph can be considered as an ecological niche hosting bacterial, protist and viral communities, each of them shaped by different factors and distinct from the corresponding communities in the surrounding seawater. Overall, we found that hemolymph microbiota is more strongly shaped by the environment than by host genetic background. Co-occurrence network analyses suggest a disruption of the microbial network after transplantation into natural environment during both non-infectious and infectious periods. Whereas we could not identify a common microbial community signature for healthy animals, OsHV-1 μVar virus dominated the hemolymph virome during the disease outbreak, without significant modifications of other microbiota components. Conclusion Our study shows that oyster hemolymph is a complex ecosystem containing diverse bacteria, protists and viruses, whose composition and dynamics are primarily determined by the environment. However, all of these are also shaped by oyster genetic backgrounds, indicating they indeed interact with the oyster host and are therefore not only of transient character. Although it seems that the three microbiome components respond independently to environmental conditions, better characterization of hemolymph-associated viruses could change this picture.

The combined use of satellite-derived environmental data and a dynamic energy budget (DEB) model to determine Pacific oyster growth potential was adapted for the South African marine environment. Study areas consisted of the West Coast (high-chlorophyll, low temperature) and the South Coast (variable chlorophyll, higher temperature) ecoregions. Chlorophyll-a and sea surface temperature products from the Moderate Resolution Imaging Spectroradiometer (MODIS) were used to simulate yearly growth for 18 years. Average growth performance at the end of the culture period was mapped and compared for prominent sectors. Industry-relevant growth indicators, "days to reach commercial weight" and "optimal culture period length" were also established. High growth potential was found in eastern nearshore sectors of the South Coast, particularly Plettenberg Bay, where oysters reached a median total weight (TW) of 271 g within 9 months. Other sectors in the region yielded Large commercial size within 150 days. However, South Coast growth hotspots were found to be highly variable, with transient unfavourable growth conditions leading to low flesh mass relative to TW. Growth potential was favourable in northern sectors of the West Coast, where oysters reached a median TW of up to 148 g in 9 months, Large commercial size within 200 days, and contained high flesh mass relative to TW. Current oyster production sites were not found to be optimal for growth. Higher-growth sites coincide with areas in economic decline or with high levels of poverty. However, due to constraints of applying DEB models over large spatial scales, these results are considered preliminary and await in situ verification, as well as a spatial multi-criteria analysis, before investment and development.

Lipid droplet accumulation (LDA) in hepatocytes is the initial stage of nonalcoholic fatty liver disease (NAFLD). In the search for natural compounds for the prevention of NAFLD, a series of β-carboline alkaloid derivatives, inspired by flazin and its derivative, newly identified in Crassostrea gigas Thunberg. extracts, were examined for LDA inhibition (LDAI) activity in oleic acid–loaded hepatocytes (HepG2). Eight compounds with a piperidine or pyridine C-ring were chemically synthesized (1–8). Among them, compounds 2 and 4 (flazin) with a carboxy group at C-3 and furfuryl alcohol moiety at C-1 showed low cytotoxicity and they exhibited significant LDAI activity. Compound 2 with piperidine C-ring was identified for the first time in C. gigas extract, and ameliorated the lipid accumulation with the LDAI value of 25.4%. Active compounds 2 and 4 significantly inhibited triacylglycerol species accumulation in cells. These compounds upregulated ATGL and downregulated SREBP1, FASN, and SCD1 genes, suggesting that they activated lipolysis and suppressed lipogenesis, respectively. These results suggest that β-carboline alkaloids, especially compounds 2 and 4, might be potentially useful for preventing NAFLD.

Context: Intertidal estuarine environments expose oysters to wide temperature variations. This can shift their microbiome composition towards pathogen-dominated communities. Understanding the impact of temperature on the microbiome will facilitate oyster health management. Aims: The present study was conducted to (1) assess the Pacific oyster microbiome at different temperatures (21°C, 22°C, 26°C and diurnal fluctuation between 22°C and 26°C) and (2) investigate microbiome changes in response to exposure to the pathogen Ostreid herpesvirus-1 (OsHV-1) at different temperatures. Methods: Pacific oysters (15 months of age; n = 480) were acclimated to different temperatures in laboratory aquaria. Samples were obtained before and after acclimation and after OsHV-1 exposure for quantification of OsHV-1, total bacteria and Vibrio, by quantitative PCR. Bacterial 16S rRNA gene (V1–V3) sequences were used to characterise the gill bacterial community. Key results: The alpha diversity (number of observed amplicon sequence variants) and total number of bacteria associated with the gills of oysters did not change with acclimation to different water temperature profiles, but there was variation in beta diversity. The highest mortality after OsHV-1 exposure occurred at 26°C and these, together with oysters at 22/26°C, had a higher concentration of OsHV-1 DNA compared with to the ones at the lower constant temperatures (P < 0.05). The total bacterial quantity increased after the OsHV-1 challenge in oysters at 22/26°C. The alpha diversity of microbiota increased after the OsHV-1 challenge in oysters at 21°C and 22/26°C. The beta diversity changed both after acclimation and OsHV-1 challenge. The highest abundance of Vibrio and higher OsHV-1 loads were seen in OsHV-1-challenged oysters at 26°C (P < 0.05). Conclusions: The gill microbiome altered with seawater temperature and OsHV-1 challenge. Higher mortality following OsHV-1 exposure was associated with a higher water temperature and greater abundance of Vibrio spp. arising from the microbiome. Implications: Higher seawater temperature can be considered a key risk factor influencing oyster health by altering the microbiome, increasing susceptibility to OsHV-1 and increasing the Vibrio fraction in the oyster microbiome.

En el mar ecuatoriano, la presencia del cultivo de la ostra japonesa o del Pacifico, ha permitido contar con una nueva especie de ostra de alto valor nutricional, con lo que se planea poner fin a la escasez del mercado nacional de este producto, que generalmente se comercializa al filo costero o en mercados y muy poco en ciudades. In the Ecuadorian sea, the presence of the cultivation of the Japanese or Pacific oyster, has allowed to have a new species of oyster of high nutritional value, with which it is planned to put an end to the shortage of the national market of this product, which is generally marketed at the coastal edge or in markets and very little in cities.

The physiological response of two species of mussels (Mytilus edulis and M. galloprovincialis) and two species of oysters (Crassostrea gigas and Ostrea edulis) to temperature, oxygen levels and food concentration, factors likely to vary as a result of climate change, was determined experimentally. Bivalves of similar size from different origins were exposed to six temperatures (3, 8, 15, 20, 25 and 30 °C) at two food regimes (2 and 10 μg Chl a L−1) for 6 weeks. In a parallel running experiment M. edulis from the same batches were exposed to three different temperatures (15, 20 and 25 °C) and three different oxygen levels (30, 50 and 100%) at two food regimes (2 and >8 μg Chl a L−1) for 3–4 weeks. Survival during the experiment ranged from 93% to 100% except for the mussels exposed to 30 °C which showed 100% mortality after three to 32 days. Higher food conditions showed higher optimal temperatures for growth of mussels and oysters. In addition, at the high food treatment, reduced O2 saturation resulted in lower growth of mussels. At the low food treatment there were no differences in growth among the different O2 levels at the same temperature. At high food concentration treatment, M. edulis growth was higher with low temperature and high oxygen level. Condition index was higher at higher food concentrations and decreased with increasing temperature. In addition, condition was lower at low oxygen saturation. Lower clearance rates were observed at high food concentrations. At 100% saturation of oxygen, mussel clearance rate increased with temperature at High food regime, but not at Low food regime. Mussel clearance rates were significantly reduced with low oxygen concentrations together with high temperature. Oxygen consumption significantly increased with temperature. Oxygen saturation was the main factor affecting mussel clearance rate. High temperature and low oxygen concentration combined significantly reduced clearance rate and increased oxygen consumption. These response curves can be used to improve parameterisation of individual shellfish growth models taking into consideration factors in the context of climate change: temperature, food concentration, oxygen concentration and their interactions. The observation that abiotic factors interact in affecting mussels and oysters is an important result to take into account.

International audience; Since 2010, mass mortality events known as Pacific oyster mortality syndrome (POMS) have occurred in Crassostrea gigas in Australia associated with Ostreid herpesvirus 1. The virus was thought to be an OsHV-1 µVar or "microvariant", i.e. one of the dominant variants associated with POMS in Europe, but there are few data to characterize the genotype in Australia. Consequently, the genetic identity and diversity of the virus was determined to understand the epidemiology of the disease in Australia. Samples were analysed from diseased C. gigas over five summer seasons between 2011 and 2016 in POMS-affected estuaries: Georges River in New South Wales (NSW), Hawkesbury River (NSW) and Pitt Water in Tasmania. Sequencing was attempted for six genomic regions. Numerous variants were identified among these regions (n = 100 isolates) while twelve variants were identified from concatenated nucleotide sequences (n = 61 isolates). Nucleotide diversity of the seven genotypes of C region among Australian isolates (Pi 0.99 × 10 − 3) was the lowest globally. All Australian isolates grouped in a cluster distinct from other OsHV-1 isolates worldwide. This is the first report that Australian outbreaks of POMS were associated with OsHV-1 distinct from OsHV-1 reference genotype, µVar and other microvariants from other countries. The findings illustrate that microvariants are not the only variants of OsHV-1 associated with mass mortality events in C. gigas. In addition, there was mutually exclusive spatial clustering of viral genomic and amino acid sequence variants between estuaries, and a possible association between genotype/amino acid sequence and the prevalence and severity of POMS, as this differed between these estuaries. The sequencing findings supported prior epidemiological evidence for environmental reservoirs of OsHV-1 for POMS outbreaks in Australia.

International audience; The Pacific oyster, Crassostrea gigas is a successive irregular hermaphrodite mollusc which has an annual breeding cycle. Oysters are naturally diploid organisms, but triploid oysters have been developed for use in shellfish aquaculture, with the aim of obtaining sterile animals with commercial value. However, studies have shown that some triploid oysters are partially able to undergo gametogenesis, with numerous proliferating cells closed to diploids (3n alpha) or a partial one with an accumulation of locked germ cells (3n beta). The aim of our study therefore was to understand the regulation of spermatogenesis in both groups of triploid oysters (alpha and beta) from the beginning of spermatogenesis, during mitosis and meiosis events. Our results demonstrate that the reduced spermatogenesis in triploids results from a deregulation of the development of the germinal lineage and the establishment of the gonadal tract led by a lower number of tubules. Morphological cellular investigation also revealed an abnormal condensation of germ cell nuclei and the presence of clear patches in the nucleoplasm of triploid cells, which were more pronounced in beta oysters. Furthermore, studies of molecular and cellular regulation showed a downregulation of mitotic spindle checkpoint in beta oysters, resulting in disturbance of chromosomal segregation, notably on Spindle Assembly Checkpoint involved in the binding of microtubules to chromosomes. Taken together, our results suggest that the lower reproductive ability of triploid oysters may be due to cellular and molecular events such as impairment of spermatogenesis and disruptions of mitosis and meiosis, occurring early and at various stages of the gametogenetic cycle.

A contaminação microbiológica de moluscos bivalves representa uma das maiores preocupações, inerentes à segurança alimentar, desta importante fonte de receitas para a economia portuguesa. Por isso, existem zonas de captura com diferentes classificações, onde, dependendo da carga microbiológica e do conteúdo em outros contaminantes, os animais aí capturados serão ou não destinados a um processo de depuração, de modo a diminuir a concentração dessas substâncias. A depuração de moluscos bivalves, processo durante o qual os bivalves são mantidos em água limpa, em circuito fechado ou aberto, contribui de uma forma decisiva para o aumento dos níveis de segurança alimentar associados ao consumo destes organismos frescos. No entanto, durante este processo, os bivalves permanecem em água limpa, sem qualquer tipo de alimento, o que pode contribuir para a diminuição das suas características bioquímicas e respetivo valor nutricional. Por outro lado, a adaptação das condições de depuração, tendo em conta os requerimentos de cada espécie, poderá melhorar a própria capacidade de depuração e aumentar a qualidade do produto para o consumidor. O objetivo deste estudo passou por avaliar os efeitos de 3 regimes alimentares diferentes (sem adição de dietas, adição de uma dieta á base de Nannochloropsis sp., microencapsulada, e a adição de uma dieta á base de Nannochloropsis sp. microencapsulada e enriquecida com vitamina C e E) durante o processo de depuração, assim como na qualidade e tempo de prateleira de ostra (C. gigas) e de lingueirão (S. marginatus). Para tal, procedeu-se a 2 ensaios de 24 horas de depuração, seguidos de um período de armazenamento a 5 ± 1 ºC durante 6 dias. Analisaram-se os parâmetros bioquímicos, indicadores de stresse oxidativo, no início e fim da depuração, bem como a meio e no fim do período de prateleira (3º e 6º dias). Os resultados das análises nas ostras apontam a que a exitam diferenças no efeito dos diferentes regimes nas ostras, evidenciando-se os efeitos benéficos da dieta de Nannochloropsis sp. microencapsulada e enriquecida com vitaminas C e E em relação às demais. Já as analises dos lingueirões apenas apresentaram diferenças em 2 dos parâmetros testados, ainda assim os resultados indicam para maiores efeitos benéficos da dieta enriquecida com vitaminas C e E em comparação com os restantes 2 tratamentos. Microbiological contamination of bivalve molluscs represents one of the greatest concerns, inherent to food security, of this important source of income for the Portuguese economy. Therefore, there are capture zones with different classifications, where, depending on the microbiological load and the content of other contaminants, the captured animals will or will not be destined for a purification process, to reduce the concentration of these substances. The purification of bivalve molluscs, a process during which h the bivalves are kept in clean water, in a closed or open circuit, decisively contributes to increasing food safety levels associated with the consumption of these fresh h organisms. However, during this process, the bivalves remain in clean water, without any type of food, which h can contribute to the reduction of their biochemical characteristics and their nutritional value. On the other hand, adapting the purification conditions, considering the requirements of each h species, can improve the purification capacity itself and increase the quality of the product for the consumer. The aim of this study was to evaluate the effects of 3 different diets (no diet added, addition of a microencapsulated Nannochloropsis sp.-based diet, and the addition of a microencapsulated Nannochloropsis sp. based and vitamin C and E enriched diet) during the purification process, as well as the quality and shelf life of oysters (C. gigas) and razor clams (S. marginatus). To this end, 2 tests of 24-hour clearance were carried out, followed by a storage period at 5 ± 1 ºC for 6 days. Biochemical parameters, indicators of oxidative stress, at the beginning and end of depuration, as well as at the middle and end of the shelf period (3rd and 6t h days) were analysed. The results of the analyses in the oysters show that there are differences in the effect of the different diets in the oysters, showing the beneficial effects of the diet of Nannochloropsis sp. microencapsulated and enriched with vitamins C and E in relation to the others. The razor clams only showed differences in 2 of the tested parameters, yet the results indicate greater beneficial effects of the diet enriched with vitamins C and E compared to the other 2 treatments. Mestrado em Biologia Marinha Aplicada

Elevated carbon dioxide levels in ocean waters, an anthropogenic stressor, can alter the chemical equilibrium of seawater through a process called ocean acidification (OA). The resultant reduction of pH can be detrimental during the early developmental stages of the commercially important edible Pacific oyster Crassostrea gigas; the ability of larvae to join a population is likely to be compromised by declining ocean pH. Given this threat, it is important to study the molecular mechanisms that these organisms use to overcome OA stress at the gene expression level. Here, we performed transcriptome profiling in oyster larvae following exposure to ambient (8.1) and reduced (7.4) pH during the pre-settlement growth period (i.e., 18 d post fertilization) using RNA-seq with Illumina sequencing technology. In total, 1,808 differentially expressed genes (DEGs) were identified, 1,410 of which were matched by BLAST against the Swiss-Prot database. Gene ontology classification showed that most of these DEGs were related to ribosomal, calcium ion binding, cell adhesion and apoptotic processes. Pathway enrichment analysis revealed that low pH (7.4) enhanced energy production and organelle biogenesis but prominently suppressed several immune response pathways. Moreover, activation of the MAPK signaling pathway was observed along with inhibition of the Wnt, VEGF, and ErbB pathways, highlighting the fact that the initiation of stress responses is given priority over larval development or shell growth when the larvae cope with low pH. In conclusion, our study demonstrated a unique gene expression profiling approach in studying oyster larval responses to OA, which not only provides comprehensive insights into the mechanisms underlying oyster tolerance to CO2-driven decreases in ocean pH but also supplies a valuable genomic resource for further studies in this species.

International audience; Ommochromes are one of the least studied groups of natural pigments, frequently confused with melanin and, so far, exclusively found in invertebrates such as cephalopods and butterflies. In this study focused on the purple color of the shells of a mollusk, Crassostrea gigas, the first evidence of a metabolite of ommochromes, xanthurenic acid (XA), was obtained by liquid chromatography combined with mass spectrometry (UPLC-MS). In addition to XA and various porphyrins previously identified, a second group of high molecular weight acid-soluble pigments (HMASP) has been identified with physicochemical and structural characteristics similar to those of ommochromes. In addition, fragmentation of HMASP by tandem mass spectrometry (MS/MS) has revealed a substructure common to XA and ommochromes of the ommatin type. Furthermore, the presence of melanins was excluded by the absence of characteristic by-products among the oxidation residues of HMASP. Altogether, these results show that the purple color of the shells of Crassostrea gigas is a complex association of porphyrins and ommochromes of potentially ommatin or ommin type.

International audience; Shellfish farming, a key sector of French aquaculture activity, allows the production of oyster spat in a controlled environment. Their production in commercial hatcheries requires control over the quality of the seawater used to sustain crossbreeding, breeding, and the production of fodder microalgae. Therefore, improving the filtration conditions of incoming water is crucial in ensuring the sustainability of production. An ultrafiltration pilot plant was therefore installed at Vendee Naissain. This ultrafiltration pilot plant allows filtration at 0.02 mu m; it is used upstream of hatcheries to eliminate pathogens and parasites that can influence the development of cultivated species and downstream to remove oyster gametes in hatchery effluents. The objectives of this work were: (i) to use ultrafiltered seawater for the culture of the microalga Isochrysis lutea (T-Iso) to determine whether better growth than that observed with borehole water, historically used by the producer, can be achieved; and (ii) to determine whether the use of ultrafiltered water results in better fertilization rates of the cupped oyster Crassostrea gigas compared to filtered and UV-treated seawater. Ultrafiltered water has shown definite efficiency for culturing T-Iso with rapid growth and significant reduction in contamination compared to cultivation in well water. The contribution of ultrafiltered water in hatching is more nuanced; ultrafiltered water does not stabilize hatch rates, and its quality is highly dependent on the quality of the seawater used.

Glycogen content is a quantitative trait, its phenotype differences are found between individual oysters due to genetic effects and environmental factors which were including food, water temperature, salinity, and so on. In this study, a full sibling family of Pacific oyster Crassostrea gigas showed different phenotypes with high and low glycogen content between South Huanghai Sea (Rizhao offshore area, RZ) and North Huanghai Sea (Kongtong Dao area, KTD), respectively. At the same time, the content of 11 glucogenic amino acids and 13 fatty acids were also significant differences between RZ and KTD. RNA-seq and small RNA-seq technologies were used for transcriptome sequencing and functional enrichment analysis of differentially expressed RNA were used by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. A total of 2,084 mRNAs, 1,080 long non-coding RNAs (lncRNAs), 34 circular RNAs (circRNAs), and 7 microRNAs (miRNAs) were differentially expressed. Based on these differentially expressed genes (DEGs), miRNA target interactions (lncRNA/circRNA–miRNA pairs and miRNA–mRNA pairs) were predicted using the miRanda software. The differentially expressed mRNAs in this network were mainly shown to be involved in calcium signaling pathway and insulin signaling pathway. These findings could help to speculate that environmental factors may be epigenetically regulated by non-coding RNA in C. gigas, thereby further affecting glycogen content.

Understanding the genetic basis of trait variations and their coordination between relative species or populations distributing in different environmental conditions is important in evolutionary biology. In marine ectotherms, growth-defense trade-offs are a common ecological and evolutionary phenomenon. However, the biochemical and molecular mechanisms that govern these trade-offs in marine ectotherms in the evolutionary perspective remain poorly investigated. Oysters are among the most important species in global aquaculture. Crassostrea gigas (C. gigas) and Crassostrea angulata (C. angulata) are two allopatric congeneric dominant oyster species that inhabit the northern and southern intertidal areas of China. Wild C. gigas and C. angulata were spawned, and their F1 progeny were cultured in the same sites to reduce the environmental effects. Untargeted metabolomics and transcriptomics, together with phenotypic parameters including morphological traits (growth performance), nutritional content (glycogen, crude fat, and fatty acid content), physiology (normalized oxygen consumption rate and total antioxidant capacity) were applied to assess metabolic and transcript divergences between C. gigas and C. angulata. Integrated analyses of metabolites and transcriptomes showed that C. gigas allocated more energy to storage and defense by suppressing glycolysis, fatty acid oxidation and by upregulating fatty acid synthesis, antioxidant gene expression, and related metabolites. The metabolic and transcript results were further confirmed by the phenotypic data that C. gigas has higher glycogen and crude fat content and fatty acid unsaturation and stronger antioxidant capacity than C. angulata. In contrast, C. angulata exhibited better growth performance and a higher oxygen consumption rate. These findings suggest that C. angulata allocates more energy to growth, which is embodied in its stronger aerobic capacity and higher levels of protein synthesis genes, metabolites, and growth-related biomarkers. This study will help to enlighten the evolutionary patterns and genetic basis of growth-defense trade-offs in marine ectotherms and the biochemical and molecular mechanisms underlying energy allocation. Also, the key genes and metabolites of glycogen and fatty acids pathway identified in this study will be applied for meat quality improvement in the oyster industry.

Asterias rubens is feeding at beds of Mytilus edulis and living on hard substrate between the mussels. The behaviour of Asterias rubens was studied in order to evaluate the choice of substrate without wave exposure, predators or prey available. In laboratory experiments, favoured selection of Fucus vesiculosus, Crassostrea gigas and covered stone was observed. Our observations showed preferential choice of shadowed substrate and revealed that presence of conspecifics did not affect the substrate choice of Asterias rubens juveniles. The experiments indicated that aggregation of individuals is not avoided, but no evidence is found for intended aggregation. The study demonstrated that the substrate choice behaviour of Asterias can’t be described as randomly., Asterias rubens frisst an Betten von Mytilus edulis und lebt auf hartem Substrat zwischen den Muscheln. Das Verhalten von Asterias rubens wurde untersucht, um die Wahl des Substrats ohne Wellenexposition, Räuber oder Beute zu bewerten. In Laborexperimenten wurde eine bevorzugte Selektion von Fucus vesiculosus, Crassostrea gigas und bedecktem Stein beobachtet. Unsere Beobachtungen zeigten eine bevorzugte Wahl des beschatteten Substrats und zeigten, dass die Anwesenheit von Artgenossen die Substratwahl von Asterias rubens (juvenil) nicht beeinflusste. Die Experimente zeigten, dass eine Aggregation von Individuen nicht vermieden wird, aber es werden keine Hinweise auf eine beabsichtigte Aggregation gefunden. Die Studie zeigte, dass das Substratwahlverhalten von Asterias nicht als zufällig beschrieben werden kann.

Triploid oysters have poor gonadal development, which can not only bring higher economic benefits but also have a potential application in the genetic containment of aquaculture. However, the key factors that influence germ cell development in triploid oysters remain unclear. In this study, data-independent acquisition coupled to transcriptomics was applied to identify genes/proteins related to sterility in triploid Crassostrea gigas. Eighty-four genes were differentially expressed at both the protein and mRNA levels between fertile and sterile females. For male oysters, 207 genes were differentially expressed in the transcriptomic and proteomic analysis. A large proportion of downregulated genes were related to cell division, which may hinder germ cell proliferation and cause apoptosis. In sterile triploid females, a primary cause of sterility may be downregulation in the expression levels of certain mitotic cell cycle-related genes. In sterile triploid males, downregulation of genes related to cell cycle and sperm motility indicated that the disruption of mitosis or meiosis and flagella defects may be linked with the blocking of spermatogenesis. Additionally, the genes upregulated in sterile oysters were mainly associated with the biosynthesis of glycogen and fat, suggesting that sterility in triploids stimulates the synthesis of glycogen and energy conservation in gonad tissue.

Economically devastating mortality events of farmed and wild shellfish due to infectious disease have been reported globally. Currently, one of the most significant disease threats to Pacific oyster Crassostrea gigas culture is the ostreid herpesvirus 1 (OsHV-1), in particular the emerging OsHV-1 microvariant genotypes. OsHV-1 microvariants (OsHV-1 µvars) are spreading globally, and concern is high among growers in areas unaffected by OsHV-1. No study to date has compared the relative virulence among variants. We provide the first challenge study comparing survival of naïve juvenile Pacific oysters exposed to OsHV-1 µvars from Australia (AUS µvar) and France (FRA µvar). Oysters challenged with OsHV-1 µvars had low survival (2.5% exposed to AUS µvar and 10% to FRA µvar), and high viral copy number as compared to control oysters (100% survival and no virus detected). As our study was conducted in a quarantine facility located ~320 km from the ocean, we also compared the virulence of OsHV-1 µvars using artificial seawater made from either facility tap water (3782 µmol kg-1 seawater total alkalinity) or purchased distilled water (2003 µmol kg-1). Although no differences in survival or viral copy number were detected in oysters exposed to seawater made using tap or distilled water, more OsHV-1 was detected in tanks containing the lower-alkalinity seawater, indicating that water quality may be important for virus transmission, as it may influence the duration of viral viability outside of the host.

WOS:000531794600001; Ostreid herpesvirus-1 (OsHV-1) is known to associate with particles in seawater, leading to infection and disease in the Pacific oyster Crassostrea gigas. The estuarine environment is highly complex and changeable, and this needs to be considered when collecting environmental samples for pathogen detection. The aims of this study were to (1) compare different aspects of collecting natural seawater and plankton samples for detection of OsHV-1 DNA and (2) determine whether detection of OsHV-1 DNA in such environmental samples has merit for disease risk prediction. The results of one experiment suggest that sampling on the outgoing tide may improve the detection of OsHV-1 DNA in seawater and plankton tow samples (odds ratio 2.71). This statistical comparison was not possible in 2 other experiments. The method (plankton tow or beta bottle) and depth of collection (range: 250-1250 mm) had no effect on the likelihood of detection of OsHV-1. OsHV-1 DNA was found at low concentrations in plankton tow and seawater samples, and only when outbreaks of mortality associated with OsHV-1 were observed in nearby experimental or farmed populations of C. gigas. This suggests that single point in time environmental samples of seawater or plankton are not sufficient to rule out the presence of OsHV-1 in an estuary. The association of OsHV-1 with particles in seawater needs to be better understood in order to determine whether more selective and sensitive methods can be devised to detect it, before environmental samples can be reliably used in disease risk prediction.

The effects of Gymnodynium catenatum and Prorocentrum lima, dinoflagellate species present in the Gulf of California, on marine bivalves, have demonstrated physiological alterations and changes in gene expression patterns; however, modification effects of the genes involved in immune defense are still poorly understood. This study analyzed the mRNA levels of five genes encoding for the immune defense of oyster Crassostrea gigas spat fed with a control diet (Isochrysis galbana alone) and a combination of the two toxic dinoflagellates. Expression levels of lipopolysaccharide (LPS)-binding protein 1,3-glucan and cavorting genes were higher in oysters exposed to the combined diets in all treatments compared to the non-toxic diet at day three, which was probably related with an activation of the oysters’ immediate immune response during the first 24 h. Protein 44 interferon-induced gene expression level was repressed in treatments with the highest dinoflagellate concentration and overexpressed in the diet with equal dinoflagellate concentration. Interaction protein-Toll and immunoglobulin gene transcript levels reached the highest values at day seven in oysters exposed to all combined diets. Then, the immune defense appeared to be activated in oyster spat as a response of toxins and/or extra-cellular compounds produced by the dinoflagellates.

Intertidal culture in meshed bags on trestles is worldwide the most established culture method for oysters. Culturists can affect oyster performance by adjusting stocking density and immersion time, and it can be expected that these factors are not independent. The combined effect of stocking density and immersion time on survival, growth and condition of oysters was investigated on a culture site, where oysters are usually stocked at 8 kg bag−1. Half-grown oysters were stocked in three biomass densities: 4, 8 and 12 kg bag−1, nested within three immersion times (87%, 76% and 73% of tidal cycle). Chlorophyll-a concentration peaked in summer (~ 3–10 μg l−1) and was low in autumn (~ 1 μg l−1), and high chlorophyll-a levels coincided with oyster spawning period. Survival was not affected by density or immersion time. Shell growth per oyster and biomass production per bag were density dependent—higher at 4 than at 12 kg bag−1—but neither were different from 8 kg bag−1. Growth rates were negativity related with immersion over the spawning period but showed a (non-significant) positive trend over other periods. At harvest, condition per oyster decreased with stocking density and increased with immersion. There was no interaction between density and immersion. Treatments had a more pronounced effect on meat content than on biomass production. Hence, oysters might be kept at higher stocking densities to increase biomass production during most of the growth cycle but restocked in lower densities, with longer immersion times prior to harvest to maximize meat content at harvest.

The Warburg effect is one of the hallmarks of cancer cells in humans. It is a true metabolic reprogramming to aerobic glycolysis, allowing cancer cells to meet their particular energy needs for growth, proliferation, and resistance to apoptosis, depending on the microenvironment they encounter within the tumor. We have recently discovered that the Crassostrea gigas oyster can naturally reprogram its metabolism to the Warburg effect. Thus, the oyster becomes a new invertebrate model useful for cancer research. Due to its lifestyle, the oyster C. gigas has special abilities to adapt its metabolism to the extreme changes in the environment in which it is located. The oyster C. gigas is therefore a model of interest to study how the environment can control the Warburg effect under conditions that could not be explored in vertebrate model species., L’effet Warburg est l’une des caractéristiques des cellules cancéreuses chez l’homme. C’est une véritable reprogrammation métabolique vers la glycolyse aérobie, permettant aux cellules cancéreuses de satisfaire leurs besoins énergétiques en fonction du microenvironnement qu’elles rencontrent au sein de la tumeur. De par son mode de vie, l’huître Crassostrea gigas possède des capacités particulières afin d’adapter son métabolisme aux changements extrêmes du milieu dans lequel elle se trouve. Elle est naturellement capable de reprogrammer son métabolisme vers l’effet Warburg. C. gigas représente ainsi un modèle d’intérêt pour étudier comment l’environnement peut contrôler l’effet Warburg dans des conditions qui ne pourraient être explorées chez des espèces modèles vertébrés.

International audience; Summer mortalities of the adult Pacific oysters Crassostrea gigas are an important economic concern. In 2015 and 2016, the mortality of hatchery origin spat comprising 4 diploid batches and 9 triploid batches as well as 12 batches of wild caught diploids was followed at 3 sites in Normandy. Abnormal mortalities (> 20%) were observed at one site only and were significantly higher in triploid animals (P < .05). Triploid oysters are believed to be partially sterile but a high level of gametogenesis was observed in all monitored triploid batches. In 2015, preliminary results revealed that triploid oysters underwent strong gametogenesis with mature gametes (stage 3) and 50% of them were non-perturbed (i.e. named alpha). In 2016, 42% of triploid oysters were alpha. This study revealed that triploid oyster maturation occurred in September, which corresponded to the time of high mortalities in Normandy.

After an exceptional hydroclimatic year, a “massive green algae bloom”, dominated by the autotrophic picoeukaryote Picochlorum sp, was observed in 2018–2019 in the Thau lagoon. Oyster farmers informed decision-makers and scientists about an alarming halt to growth, loss of flesh weight and abnormal mortality in commercial size oysters, whereas mussel farmers observed no adverse effects. Two hypotheses were tested. First, Mediterranean mussels are capable of filtering Picochlorum spp. whereas Pacific and flat oysters are not. Second, picophytoplankton filtration rates vary with the size of the oyster, spats having greater ability than juveniles and commercial size oysters. A series of experiments was conducted in February 2019 using a series of beakers containing (i) three different types of solutions (1 L): water from the Thau lagoon containing Picochlorum at a rate of 45.2 million cells.L−1 (P) or diluted to 20.7 million cells. L−1 (D) and a solution of Isochrysis galbana containing 9.4 million cells. L−1; (ii) in the absence or presence of five types of bivalves: Pacific oysters of three different sizes (spat, juvenile and commercial size), flat oysters, and Mediterranean mussels of commercial size. Four separate water samples were taken during a 40-min incubation period to measure fluctuations in picophytoplankton and nanophytoplankton abundances using flow cytometry. Retention efficiency (%) was compared according to species and size. In contrast to Pacific and flat oysters, mussels with an average weight of 21.4 g, were able to drastically reduce the abundances of Picochlorum and depleted nearly one million Picochlorum cells per minute at 11.4 °C. These results suggest that the 1228 t of mussels that died in 2018 before the Picochlorum bloom could have helped limit the Picochlorum bloom if they had survived the heat and anoxia.

One of the main problems in laboratories of oyster seed production occurs in the stage of settlement or fixation and metamorphosis of the larvae. The organisms develop drastic morphological and physiological changes at this stage, exposing them to attack by pathogenic microorganisms. Numerous studies indicate that before larval settlement to a substrate, they require bacteria to stimulate and induce the process. In this study, Japanese oyster ( Crassostrea gigas ) larvae were fed with combinations of microalgae and bacteria previously selected for their probiotic potential; their impact on survival, growth, and settlement was evaluated. Larvae D of 12 days old were provided by a private company and transported to the laboratory under controlled conditions. Probiotic bacteria Lactobacillus plantarum 69Cr, L. fermentum 101Cc, and L. casei 43Cg were reactivated on MRS and applied at a concentration of 1×10 4 CFU mL -1 . Microalgae Isochrysis galbana and Chaetoceros calcitrans were grown in F2 medium and supplied at a concentration of 3×10 4 cells mL -1 . Results showed, in all treatments, a survival range of 39-53%, growth of 300-310 μm, and 34-56.5% settlement. However, the best bacteria combined with I. galbana and C. calcitrans was L. plantarum 69Cr with a 54% survival, 310 μm growth, and 56.5% settlement. It is concluded that the combination of L. plantarum 69Cr with I. galbana and C. calcitrans has the potential to be used in the production of Japanese oyster larvae.

Mollusks are a prospective food for the world’s growing population, but the contents of toxic and essential trace elements in them have not been studied comprehensively. In this work, using inductively coupled plasma mass spectrometry, the contents of 72 elements in soft tissues of the edible mollusks Mytilus galloprovincialis, Rapana venosa, and Crassostrea gigas from the coastal area of the southwestern Crimea were estimated and compared with the maximum permissible levels. Element accumulation similarities were observed in the two bivalve species. Cluster analysis applied to the non-normalized contents allowed finding an optimal number of non-overlapping element clusters: 1 group of macroelements, 1–2 groups of trace elements, and 1–2 groups of ultratrace elements. As an outcome of this analysis, the element accumulation universality index was introduced, which demonstrated the accumulation universality decrease in the order: mussel &gt, sea snail &gt, oyster. An original approach to estimating the mollusk consumption rate was proposed to assess human health risks. Two possible consumption scenarios were identified for Crimean residents. From the expected consumption of all species in both scenarios, there are no health risks, but they are not excluded, within the 95% probability, from high consumption of mussels and sea snails in the pessimistic scenario.

The Pacific oyster Crassostrea gigas is the world’s most cultivated oyster and seed supply is heavily reliant on hatchery production where recurring mass mortality events are a major constraint. Outbreaks of bacterial infection via microalgal feed are frequently implicated in these mortalities. This study assessed the effects of feeding compromised microalgae to developing oyster larvae. Intentionally ‘stressed’ (high pH) or non-stressed microalgae were fed to 11 day-old oyster larvae at two feeding rations for 96 h, followed by a recovery period. Biological endpoints of larval performance were measured following the 96 h exposure and subsequent recovery. Bacterial communities associated with the microalgae feed, rearing seawater, and the oyster larvae, were characterized and correlated with effects on oyster fitness parameters. Feeding stressed algae to oyster larvae for 96 h increased the occurrence of deformities (>70% vs. 20% in control), reduced feeding and swimming ability, and slowed development. Following the recovery period, fewer larvae reached pediveliger stage (2.7% vs. 36% in control) and became spat (1.5% vs. 6.6% in control). The quantity of stressed algae supplied to oyster larvae also influenced overall larval performance, with high feeding rations generally causing greater impairment than low rations. Bacterial profiling using 16S rRNA showed that most bacterial families characterized in larval tissue were also present in larval rearing seawater and in the microalgae feed (98%). The rearing seawater showed the highest bacterial richness compared to the larval and the microalgal compartments, regardless of feeding regime. In larval tissue, bacterial richness was highest in stressed and high-feed treatments, and negatively correlated with larval fitness parameters. These results suggest significant dysbiosis induced by compromised feed and/or increased feed ration. Several bacterial genera (e.g., Halomonas, Marinomonas) were strongly associated with impaired larval performance while the presence of genera in larvae including Vibrio was closely associated with overfeeding. Our research demonstrated that metabarcoding can be effectively used to identify microbiota features associated with larval fitness.

International audience; Provenance determination of archaeological remains is a valuable tool for reconstruction of past exchange networks. Among these materials, oyster shells are ubiquitous in sites from all prehistorical and historical periods. Thus, they seem to be promising candidates for provenance identification as they include chemical elements from the environment in their shells, which implies that an elemental fingerprint of the region of origin can be recorded in the shell composition. In this study, we present elemental measurements from 15 groups of modern and archaeological shells from 13 continental localities in mainland France and the island of Corsica (western Mediterranean Sea). Two of these localities had two oyster species (Crassostrea gigas and Ostrea edulis). Results indicate that (i) a species-specific elemental fingerprint exists and (ii) the Atlantic Ocean and Mediterranean Sea provenances can be identified for O. edulis shells. Moreover, if the shell originated from a locality only partially connected to the ocean (e.g. an estuary or lagoon), a fingerprint specific to the watershed can also be observed, even between groups originating from the same bay. Using these measurements as reference fingerprints, we characterize the Mediterranean origin of two groups of shells unearthed at Lyons (central France, 200 km away from the nearest shoreline), dated from the 1st c. CE.

Among Pseudo-nitzschia species, some produce the neurotoxin domoic acid (DA), a source of serious health problems for marine organisms. Filter-feeding organisms—e.g., bivalves feeding on toxigenic Pseudo-nitzschia spp.—are the main vector of DA in humans. However, little is known about the interactions between bivalves and Pseudo-nitzschia. In this study, we examined the interactions between two juvenile bivalve species—oyster (Crassostrea gigas) and scallop (Pecten maximus)—and two toxic Pseudo-nitzschia species—P. australis and P. fraudulenta. We characterized the influence of (1) diet composition and the Pseudo-nitzschia DA content on the feeding rates of oysters and scallops, and (2) the presence of bivalves on Pseudo-nitzschia toxin production. Both bivalve species fed on P. australis and P. fraudulenta. However, they preferentially filtered the non-toxic Isochrysis galbana compared to Pseudo-nitzschia. The presence of the most toxic P. australis species resulted in a decreased clearance rate in C. gigas. The two bivalve species accumulated DA in their tissues (up to 0.35 × 10−3 and 5.1 × 10−3 µg g−1 for C. gigas and P. maximus, respectively). Most importantly, the presence of bivalves induced an increase in the cellular DA contents of both Pseudo-nitzschia species (up to 58-fold in P. fraudulenta in the presence of C. gigas). This is the first evidence of DA production by Pseudo-nitzschia species stimulated in the presence of filter-feeding bivalves. The results of this study highlight complex interactions that can influence toxin production by Pseudo-nitzschia and accumulation in bivalves. These results will help to better understand the biotic factors that drive DA production by Pseudo-nitzschia and bivalve contamination during Pseudo-nitzschia blooms.

Oysters are one of the main aquatic products sold in coastal areas worldwide and are popular among consumers because of their delicious taste and nutritional value. However, the microorganisms present in oysters may pose health risks to consumers. In this study, the microbial communities of Pacific oysters (Crassostrea gigas) collected from aquatic product markets in three cities (Guangzhou, Zhuhai, and Jiangmen) of Guangdong Province, China, where raw oysters are popular, were investigated. The plate counts of viable bacteria in oysters collected in the three cities were all approximately 2 log colony-forming units/g. High-throughput sequencing analysis of the V3–V4 region of the 16Sribosomal DNA gene showed a high level of microbial diversity in oysters, as evidenced by both alpha and beta diversity analysis. Proteobacteria, Bacteroidetes, and Firmicutes were the dominant phyla of the microorganisms present in these samples. A variety of pathogenic bacteria, including the fatal foodborne pathogen Vibrio vulnificus, were found, and Vibrio was the dominant genus. Additionally, the relationship between other microbial species and pathogenic microorganisms may be mostly symbiotic in oysters. These data provide insights into the microbial communities of retail oysters in the Guangdong region and indicate a considerable risk related to the consumption of raw oysters.