Temporal variation of delta C-13 in particulate organic matter and oyster Crassostrea gigas in Marennes-Oleron Bay (France): Effect of freshwater inflow

The temporal variability of delta(13)C in suspended particulate organic matter (POM) and oyster Crassostrea gigas along a salinity gradient was investigated from May 1992 to September 1993 within the estuarine bay of Marennes-Oleron (France). During this period the mean daily discharge of the Charente River exhibited large seasonal variation, with a high discharge from November 1992 to January 1993. Contrary to that at the river mouth and the marine littoral, delta(13)C in POM and in oysters at mid-estuary was affected by the high flood period. The delta(13)C values of POM decreased in mid-estuary and remained at low levels during the high discharge period, indicating an increasing contribution of terrestrial inputs to the estuarine POM pool. At the same site, a remarkable decrease of delta(13)C in oysters occurred between December 1992 and March 1993 (after a time lag compared to the ambient POM), indicating incorporation of terrestrial organic matter in oyster tissues during the high flood discharge. The lag between the delta(13)C decrease in POM and oysters is attributed to the time needed for oyster tissues to incorporate enough newly terrestrial light carbon to be recognized by the delta(13)C measure (about 1 to 2 mo). This time interval depends on tissue turnover time. The delta(13)C POM decrease (i.e. 1.3 parts per thousand) cannot explain entirely the decrease observed in oysters (i.e. 2.3 parts per thousand). In fact, the pattern exhibited by mid-estuarine oysters can be explained by the increasing contribution of terrestrial organic matter to their feeding, and the inability to preferentially utilize specific components of the estuarine POM that are C-13-enriched.

Ingestion of a bacterivorous ciliate by the oyster Crassostrea gigas: Protozoa as a trophic link between picoplankton and benthic suspension-feeders

The linked concepts of 'microbial loop' and 'protozoan trophic link' have been very well documented in filter-feeding microzooplankton such as copepods, but have not been applied to energy transfer to benthic suspension-feeding macrofauna, with the exception of the recent demonstration of heterotrophic flagellate assimilation by mussels. The oyster Crassostrea gigas obtains energy resources by filtering microalgae (similar to 5 to 100 mu m). However, in turbid estuaries, light-limited phytoplanktonic production cannot entirely account for oyster energy requirements. Conversely, picoplankters (<2 mu m), which are main effecters of coastal energy flow and matter cycling, are not efficiently retained by oyster filtration. Ciliate protozoal as both micro-sized cells (similar to 5 to 100 run) and bacteria grazers, may represent a major intermediary in trophic transfer between picoplankton and metazoa. The ciliate Uronema was intensely cultured and labelled, using the cyanobacteria Synechococcus as an auto-fluorescent biomarker. The labelled ciliates were offered as potential prey to oysters. We report here the first experimental evidence of a significant retention and ingestion of ciliates by oysters, supporting the role of protozoa as a realistic trophic link between picoplankters and filter-feeding bivalves and thus enhancing their potential importance in estuarine microbial food webs.

The Kinome of Pacific Oyster Crassostrea gigas, Its Expression during Development and in Response to Environmental Factors

Oysters play an important role in estuarine and coastal marine habitats, where the majority of humans live. In these ecosystems, environmental degradation is substantial, and oysters must cope with highly dynamic and stressful environmental constraints during their lives in the intertidal zone. The availability of the genome sequence of the Pacific oyster Crassostrea gigas represents a unique opportunity for a comprehensive assessment of the signal transduction pathways that the species has developed to deal with this unique habitat. We performed an in silico analysis to identify, annotate and classify protein kinases in C. gigas, according to their kinase domain taxonomy classification, and compared with kinome already described in other animal species. The C. gigas kinome consists of 371 protein kinases, making it closely related to the sea urchin kinome, which has 353 protein kinases. The absence of gene redundancy in some groups of the C. gigas kinome may simplify functional studies of protein kinases. Through data mining of transcriptomes in C. gigas, we identified part of the kinome which may be central during development and may play a role in response to various environmental factors. Overall, this work contributes to a better understanding of key sensing pathways that may be central for adaptation to a highly dynamic marine environment.

Characterization of 27 microsatellite loci in the European flat oyster Ostrea edulis

The flat oyster Ostrea edulis is native to Europe and populations have been severely depleted by the parasite Bonamia ostreae since the 1980s. Additional genetic markers are required to improve population genetics study and linkage map development for selection for B. ostrea-resistance in this species. Here, we characterized 27 novel microsatellite loci for O. edulis. Number of alleles per locus ranged from 6 to 25 and observed heterozygosity between 0.375 and 1. Null alleles were suggested at a few loci but most loci were in Hardy-Weinberg agreement enabling their reliable use in further population and mapping genetics approaches.

Bacterial community structure of the marine diatom Haslea ostrearia

The marine diatom Haslea ostrearia produces a water-soluble blue-pigment named marennine of economic interest (e.g. in aquaculture for the greening of oysters). Up to date the studies devoted to ecological conditions under which this microalga develops never took into account the bacterial-H. ostrearia relationships. In this study the bacterial community was analysed by PCR-TTGE before and after H. ostrearia isolation cells recovered from 4 localities, to distinguish the relative part of the biotope and the biocenose and eventually to describe the temporal dynamic of the structure of the bacterial community. The bacterial structure of the phycosphere differed strongly from that of the bulk sediment. The similarity between bacteria recovered from the biofilm and the suspended bacteria did not exceed 10% (vs. > 90% amongst biofilms). The differences in genetic fingerprints, more especially high between two H. ostrearia isolates showed also the highest differences in the bacterial structure as the result of specific metabolomics profiles. The non-targeted metabolomic investigation showed that these profiles were more distinct in case of bacteria-alga associations than for the H. ostrearia monoculture. At the scale of a culture cycle in laboratory conditions, the bacterial community was specific to the growth stage. When H. ostrearia was subcultured for 9 months, a shift in the bacterial structure was shown from 3-months subculturing and the bacterial structure stabilized afterwards (70-86% similarities). A first insight of the relationships between H. ostrearia and its surrounding bacteria was shown for a better understanding of the ecological feature of this diatom.

Premières observations sur la croissance des moules (Mytilus galloprovincialis Lmk) dans l'étang du Prévost

From 1972, oysters and mussels culture was introduced into a little lagoon of Languedoc, the lake of the Prévost. The principal geographic and hydrologic features of this lake are laid out . Then, the mussels growing (Mytilus galloprovincialis) from June 1973 to April 1974 is described.

Salinity influences disease-induced mortality of the oyster Crassostrea gigas and infectivity of the ostreid herpesvirus 1 (OsHV-1)

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.

VIVALDI, A H2020 European Project aiming at preventing and mitigating farmed bivalve diseases

The European shellfish industry enjoys a privileged position on the global scene. Its social dimension is essential, as it employs a high number of people in more than 8000 companies, mostly micro-companies. Shellfish production in Europe is little diversified and mainly relies on the industrially produced mussels, oysters and clams. Over the recent years, this sector has grown more slowly than other fish farming sectors, notably because it depends a great deal on the environmental quality and the emergence of diseases. Mortality events, linked to pathogen organisms such as viruses, bacteria and parasites (protozoa), tend to weaken the production’s sustainability. In this context, the European project VIVALDI (PreVenting and mItigating farmed biVALve DIseases) aims at increasing the sustainability and competitiveness of the shellfish industry in Europe, developing tools and approaches with a view to better preventing and controlling marine bivalve diseases. VIVALDI is a 4-years European Horizon 2020 project coordinated by Ifremer (2016-2020): 21 mostly European, public and private partners are involved, representing the diversity of the European shellfish industry landscape

Resposta metabólica da ostra Crassostrea gigas na presença do parasita Amyloodinium ocellatum

Dissertação de Mestrado, Aquacultura e Pescas, Especialização em Aquacultura, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2015

Biodiversidade e abundância da ictiofauna associada ao cultivo orgânico de Litopenaeus vannamei (Boone, 1931)

The expansion of shrimp farming has caused a series of environmental impacts, often as a result of lack of planning and adequate management. Organic aquaculture has emerged as an alternative to conventional shrimp farming, and differently, aims at the economical, ecological and farming potential of other organisms, such as fishes, oysters and seaweeds. The present study aimed at evaluating the biological diversity and abundance of the ichthyofauna associated to Litopenaeus vannamei organic culture at PRIMAR farm (Rio Grande do Norte, Brazil). The sampling period consisted of four culture cycles (1, 2, 3, and 4) accomplished in four grow-out ponds (V1, V7, V2, and V4) in 2005. The first two culture cycles were carried out during the rainy season, and the last two cycles, during the dry season. Environmental (temperature, salinity, transparency, and rainfall), biodiversity (diversity and uniformity and abundance indexes) of the ichthyofauna, and shrimp productivity data were collected throughout these four culture cycles. The results obtained for the environmental variables showed that both salinity and transparency oscillated in a significant way (p < 0.001) between culture cycles. In relation to the abundance of the ichthyofauna, fifty four species associated to the organic culture of Litopenaeus vannamei were collected and identified at PRIMAR. For the biodiversity criterion, larger species richness (S = 46) and uniformity (E = 0.59 ± 0.16) were observed during cycles 3 and 4 than in cycles 1 and 2 (S = 41 and E = 0.15 ± 0.12). A positive and significant correlation was obtained for the transparency with diversity and uniformity of fish species between cycles 1 and 2 (wet season) and cycles 3 and 4 (dry season) (p < 0.017 - Shannon Index; p < 0.008 - Pielou Index, respectively). A correlation could not be established between shrimp productivity and fish biomass. However, fish biomass decreased from cycles 1 and 2 to cycles 3 and 4, concomitant with an increase in shrimp productivity, most probably due to a higher (from 58.0% to 71.0%) shrimp survival. Regarding the culture potential of the ichthyofauna, three species (Mugil curema, Mugil liza and Chaetodipterus faber) were identified as potential farming alternatives, either singly or in consortium with Litopenaeus vannamei. A fourth species (Centropomus undecimalis) was indicated as an alternative for single culture or in consortium with other fish species. In conclusion, the large diversity of estuarine fishes associated to Litopenaeus vannamei farming observed at PRIMAR clearly indicated the ecological feasibility for organic aquaculture in northeastern Brazil