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  • Publication . Article . Other literature type . 2020
    Open Access English
    Authors: 
    Delphine Destoumieux-Garzón; Laura Canesi; Daniel Oyanedel; Marie-Agnes Travers; Guillaume M. Charrière; Carla Pruzzo; Luigi Vezzulli;
    Publisher: HAL CCSD
    Country: France
    Project: EC | VIVALDI (678589)

    International audience; In the marine environment, bivalve mollusks constitute habitats for bacteria of the Vibrionaceae family. Vibrios belong to the microbiota of healthy oysters and mussels, which have the ability to concentrate bacteria in their tissues and body fluids, including the hemolymph. Remarkably, these important aquaculture species respond differently to infectious diseases. While oysters are the subject of recurrent mass mortalities at different life stages, mussels appear rather resistant to infections. Thus, Vibrio species are associated with the main diseases affecting the worldwide oyster production. Here, we review the current knowledge on Vibrio-bivalve interaction in oysters (Crassostrea sp.) and mussels (Mytilus sp.). We discuss the transient versus stable associations of vibrios with their bivalve hosts as well as technical issues limiting the monitoring of these bacteria in bivalve health and disease. Based on the current knowledge of oyster/mussel immunity and their interactions with Vibrio species pathogenic for oyster , we discuss how differences in immune effectors could contribute to the higher resistance of mussels to infections. Finally, we review the multiple strategies evolved by pathogenic vibrios to circumvent the potent immune defences of bivalves and how key vir-ulence mechanisms could have been positively or negatively selected in the marine environment through interactions with predators.

  • Publication . Article . Other literature type . 2010
    Open Access English
    Authors: 
    Laurent Brodeau; Bernard Barnier; Anne-Marie Tréguier; Thierry Penduff; Sergei K. Gulev;
    Publisher: HAL CCSD
    Country: France

    We develop, calibrate and test a dataset intended to drive global ocean hindcasts simulations of the last five decades. This dataset provides surface meteorological variables needed to estimate air-sea fluxes and is built from 6-hourly surface atmospheric state variables of ERA40. We first compare the raw fields of ERA40 to the CORE.v1 clataset of Large and Yeager (2004). used here as a reference, and discuss our choice to use daily radiative fluxes and monthly precipitation products extracted from satellite data rather than their ERA40 counterparts. Both datasets lead to excessively high global imbalances of heat and freshwater fluxes when tested with a prescribed climatological sea surface temperature. After identifying unrealistic time discontinuities (induced by changes in the nature of assimilated observations) and obvious global and regional biases in ERA40 fields (by comparison to high quality observations), we propose a set of corrections. Tropical surface air humidity is decreased from 1979 onward, representation of Arctic surface air temperature is improved using recent observations and the wind is globally increased. These corrections lead to a significant decrease of the excessive positive global imbalance of heat. Radiation and precipitation fields are then submitted to a small adjustment (in zonal mean) that yields a near-zero global imbalance of heat and freshwater. A set of 47-year-long simulations is carried out with the coarse-resolution (2 degrees x 2 degrees) version of the NEMO OGCM to assess the sensitivity of the model to the proposed corrections. Model results show that each of the proposed correction contributes to improve the representation of central features of the global ocean circulation. (c) 2009 Elsevier Ltd. All rights reserved.

  • Open Access English
    Authors: 
    D. Van Rooij; Dominique Blamart; Thomas G. Richter; Andrew J. Wheeler; M. Kozachenko; Jean-Pierre Henriet;
    Publisher: HAL CCSD
    Countries: Belgium, France, France, France

    The Belgica cold-water coral banks on the eastern slope of the Porcupine Seabight are closely associated with bottom currents. In order to better understand the local temporal and spatial characteristics, as well as the palaeoclimatologic influences, a 26 m long core, taken on a small contourite drift, was studied. This sediment record of approximately 100 ka BP reveals new insights into the regional glacial and sedimentary processes, which are intrinsically linked to several geological, climatological, biological and hydrodynamic variables. The glacial sequences in the core contain six ice-rafting events (IRE). They are comparable with the North Atlantic Heinrich Events, although their characteristics show dominant influences from the proximal British-Irish Ice Sheet (BIIS). These IRE have a low magnetic susceptibility and are deposited during two or three ice-rafting pulses. The record of ice-rafting suggests a millennial-scaled BIIS destabilisation and confirms the start of a final retreat about 25 ka ago. Additionally, the glacial sequence corresponds to a muddy contourite, influenced by bottom-current strength variations during interstadials, possibly triggered by sporadic reintroductions of Mediterranean Outflow Water in a glacial North Atlantic Ocean. The interglacial sequence features an 11-m thick deep-water massive sand unit, probably deposited under a high-energy bottom-current regime.

  • Open Access English
    Authors: 
    Marine Remize; Frédéric Planchon; Ai Ning Loh; Fabienne Le Grand; Antoine Bideau; Nelly Le Goïc; Elodie Fleury; Philippe Miner; Rudolph Corvaisier; Aswani K. Volety; +1 more
    Publisher: Multidisciplinary Digital Publishing Institute
    Country: France

    : The present study sought to characterize the synthesis pathways producing the essential polyunsaturated fatty acid (PUFA) 20:5n-3 (EPA). For this, the incorporation of 13C was experimentally monitored into 10 fatty acids (FA) during the growth of the diatom Chaetoceros muelleri for 24 h. Chaetoceros muelleri preferentially and quickly incorporated 13C into C18 PUFAs such as 18:2n-6 and 18:3n-6 as well as 16:0 and 16:1n-7, which were thus highly 13C-enriched. During the experiment, 20:5n-3 and 16:3n-4 were among the least-enriched fatty acids. The calculation of the enrichment percentage ratio of a fatty acid B over its suspected precursor A allowed us to suggest that the diatom produced 20:5n-3 (EPA) by a combination between the n-3 (via 18:4n-3) and n-6 (via 18:3n-6 and 20:4n-6) synthesis pathways as well as the alternative &omega -3 desaturase pathway (via 20:4n-6). In addition, as FA from polar lipids were generally more enriched in 13C than FA from neutral lipids, particularly for 18:1n-9, 18:2n-6 and 18:3n-6, the existence of acyl-editing mechanisms and connectivity between polar and neutral lipid fatty acid pools were also hypothesized. Because 16:3n-4 and 20:5n-3 presented the same concentration and enrichment dynamics, a structural and metabolic link was proposed between these two PUFAs in C. muelleri.

  • Open Access English
    Authors: 
    Mathieu Woillez; Jacques Rivoirard; Pierre Petitgas;
    Publisher: HAL CCSD
    Country: France

    Fisheries research monitoring surveys provide an ensemble of measurements on fish stocks and their environment. Because the interannual variability in such survey-based indicators is high and because diagnostics on fish stocks cannot be based on noise, our concern is to make use of what is continuous in time to obtain a reliable diagnostic. In this paper, we show how min/max autocorrelation factors (MAFs) can be useful for assessing the status of a fish stock. Indeed, MAFs will allow us to (i) summarize the multivariate indicator signals into orthogonal factors that are continuous in time, (ii) select those indicators that carry the major signal in time, and (iii) forecast stock status by modelling the time continuity of the MAFs. These different potential uses of MAFs in an indicator-based approach to assessment were illustrated with North Sea cod, for which a suite of biological and spatial indicators are available over a 21-year survey series.

  • Open Access English
    Authors: 
    Maxime Georges des Aulnois; Damien Réveillon; Elise Robert; Amandine M.N. Caruana; Enora Briand; Arthur Guljamow; Elke Dittmann; Zouher Amzil; Myriam Bormans;
    Publisher: HAL CCSD
    Countries: France, Germany, France, France

    The transfer of Microcystis aeruginosa from freshwater to estuaries has been described worldwide and salinity is reported as the main factor controlling the expansion of M. aeruginosa to coastal environments. Analyzing the expression levels of targeted genes and employing both targeted and non-targeted metabolomic approaches, this study investigated the effect of a sudden salt increase on the physiological and metabolic responses of two toxic M. aeruginosa strains separately isolated from fresh and brackish waters, respectively, PCC 7820 and 7806. Supported by differences in gene expressions and metabolic profiles, salt tolerance was found to be strain specific. An increase in salinity decreased the growth of M. aeruginosa with a lesser impact on the brackish strain. The production of intracellular microcystin variants in response to salt stress correlated well to the growth rate for both strains. Furthermore, the release of microcystins into the surrounding medium only occurred at the highest salinity treatment when cell lysis occurred. This study suggests that the physiological responses of M. aeruginosa involve the accumulation of common metabolites but that the intraspecific salt tolerance is based on the accumulation of specific metabolites. While one of these was determined to be sucrose, many others remain to be identified. Taken together, these results provide evidence that M. aeruginosa is relatively salt tolerant in the mesohaline zone and microcystin (MC) release only occurs when the capacity of the cells to deal with salt increase is exceeded. Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe; 1130

  • Open Access English
    Authors: 
    Augustin Lafond; Karine Leblanc; Justine Legras; Véronique Cornet; Bernard Quéguiner;
    Publisher: HAL CCSD
    Country: France

    International audience; In the context of climate change, understanding the ecological processes controlling the functioning and the efficiency of the biological pump is of primary importance. Plankton community structure and species-specific properties are often invoked as likely to affect biogeochemistry and the export of organic and biogenic mate- rial to the ocean interior. Although a major player in this respect, diatoms are still viewed as a single functional type whose diversity is generally overlooked. Here we examine that question, building on the results achieved during the MOBYDICK expedition, which occurred in the vicinity of the Kerguelen Islands (Southern Ocean) in late summer, a time window corresponding to the demise of the annually recurrent phytoplankton blooms already known to be controlled by iron availability. The Si/C/N stoichiometry of the particulate matter was studied in conjunction with the different diatom community structures, their physiological states, as well as their species-specific carbon contents and silicification degrees. Our results show that diatoms outside the iron- fertilized plateau were more heavily silicified, due to the combined effects of both taxonomic composition of the resident community and a direct physiological response to iron stress, resulting in higher Si:C elemental ratios in diatoms as well as in the bulk particulate matter. Despite low silicic acid concentrations, large chains of weakly silicified Corethron inerme were able to grow in the upper mixed layer above the plateau, while in adjacent high nutrient low chlorophyll (HNLC) waters, communities were dominated by Fragilariopsis spp., Cylindrotheca closterium and the centric genera Actinocyclus/Thalassiosira spp. Depth was also an important factor shaping diatom communities, with the presence of a deep and inactive assemblage located within the pycnocline gradient, both on- and off-plateau, which likely resulted from the differential sinking and accumulation of species previously grown at the surface. In HNLC waters, below the mixed layer, detrital frustules of the heavily silicified species Fragilariopsis kerguelensis carried mostly Si, while above the plateau, Eucampia antarctica and Chaetoceros spp. (resting spores and vegetative stages) were efficient vectors of both Si and C to the deeper layers. Our study shows that the stoichiometry of the biological pump cannot be considered solely as a simple response to a single limiting factor (here iron) highlighting the importance of a species-centered approach in order to finely resolve biogeochemical fluxes and improve our understanding of the biological pump.

  • Open Access English
    Authors: 
    Pierre Josso; Ewan Pelleter; Olivier Pourret; Yves Fouquet; Joel Etoubleau; Sandrine Cheron; Claire Bollinger;
    Publisher: HAL CCSD
    Country: France

    Abstract Ferromanganese (Fe-Mn) deposits constitute a ubiquitous mineral type in oceanic settings, with metal (Cu, Ni, Zn, Co, Pt) and rare earth element (REE) enrichments of potential economic interest. Routine analysis of trace elements by ICP-MS has advanced our understanding of the impact of hydrogenetic, diagenetic and hydrothermal processes on the mobility and interaction of high field strength elements (HFSE: Zr and Ti) and REE and yttrium (REY) with Fe-Mn oxyhydroxides. Recent discoveries in the French exclusive economic zone (EEZ) of Wallis and Futuna (southwest Pacific Ocean) have brought new insight into the formation of low temperature (LT) hydrothermal Mn deposits and lead us to reconsider the classification and discrimination diagrams for Fe-Mn deposits and ore-forming processes. Using a suite of LT hydrothermal Fe-Mn crusts from Wallis and Futuna, we investigate how contrasting genetic processes influence the distribution of metals (Mn, Fe, Cu, Ni, and Co), HFSE and REY in hydrogenetic, diagenetic, hydrothermal and mixed-type deposits from different environments in the global ocean. The interaction of the different metal oxide-forming processes indicates that: (i) enrichment of Co, HFSE and REY is favored by hydrogenetic precipitation, (ii) diagenetic processes produce higher Mn, Cu, and Ni concentrations with oxic remobilization in the sedimentary column, while suboxic conditions promote greater Mn and Fe remobilization that competes with the incorporation of Cu and Ni ions in nodules. HFSE and REY derived from seawater are usually low in diagenetic precipitates, which discriminate between hydrogenetic and diagenetic inputs within nodules, (iii) hydrothermal Fe-Mn deposits show strong depletion in HFSE and REY due to rapid formation and high contents of either Fe or Mn oxides. We present a new discrimination scheme for the genetic types of Fe-Mn deposits using a 10 ∗ (Cu + Ni + Co) − 100 ∗ (Zr + Y + Ce) − (Fe + Mn) / 4 ternary diagram. The use of HFSE and REY in the classification allows for a more robust discrimination of: (i) each ore-forming process with well-delimited fields, without overlap of metal-rich hydrothermal samples and hydrogenetic samples, (ii) oxic and suboxic diagenesis within nodules, (iii) trends between hydrogenetic and diagenetic end-members forming a continuum, and (iv) mixed genetic types such as the presence of hydrothermal particles within hydrogenetic crust layers. Alternatives are also explored to adapt our discriminative diagram to elements measurable by on-board instruments to aid in exploration at sea.

  • Open Access English
    Authors: 
    Caroline Vignet; Thibaut Larcher; Blandine Davail; Lucette Joassard; Karyn Le Menach; Tiphaine Guionnet; Laura Lyphout; Mireille Ledevin; Manon Goubeau; Hélène Budzinski; +2 more
    Publisher: HAL CCSD
    Country: France

    Supplementary Materials: Table S1: Detailed concentration of individual PAHs in produced diets (The following are available online at www.mdpi.com/2305-6304/4/4/26/s1.); Polycyclic aromatic hydrocarbons (PAHs) constitute a large family of organic pollutants emitted in the environment as complex mixtures, the compositions of which depend on origin. Among a wide range of physiological defects, PAHs are suspected to be involved in disruption of reproduction. In an aquatic environment, the trophic route is an important source of chronic exposure to PAHs. Here, we performed trophic exposure of zebrafish to three fractions of different origin, one pyrolytic and two petrogenic. Produced diets contained PAHs at environmental concentrations. Reproductive traits were analyzed at individual, tissue and molecular levels. Reproductive success and cumulative eggs number were disrupted after exposure to all three fractions, albeit to various extents depending on the fraction and concentrations. Histological analyses revealed ovary maturation defects after exposure to all three fractions as well as degeneration after exposure to a pyrolytic fraction. In testis, hypoplasia was observed after exposure to petrogenic fractions. Genes expression analysis in gonads has allowed us to establish common pathways such as endocrine disruption or differentiation/maturation defects. Taken altogether, these results indicate that PAHs can indeed disrupt fish reproduction and that different fractions trigger different pathways resulting in different effects.

  • Open Access English
    Authors: 
    R.V. Barbosa; Andrew J. Davies; Paulo Y. G. Sumida;
    Publisher: HAL CCSD
    Country: France

    WOS:000508749000008; International audience; In face of increasing anthropogenic disturbance in the deep sea, it is a priority to better understand the regional distribution of cold-water corals (CWC). These organisms create some of the most species-rich habitats in the deep sea and, for this reason, they must be properly protected and managed. In this study, we aimed to identify suitable habitat for multiple CWC taxa off the Brazilian continental margin and compare their environmental niches. Habitat suitability models were developed using the Maxent approach, which allowed for the prediction of species distribution and for the identification of potential 'hot spot' areas that may be important for biodiversity conservation. Ecological niches were determined by a PCA-env approach, and niche similarity and equivalence were evaluated based on niche overlap using the Schoener's D metric. Potentially suitable habitat for Octocorallia covered a broad latitudinal range encompassing nearly the entire Brazilian continental margin, whereas Scleractinia had greater potentially suitable habitat in the Central and Southern areas. Scleractinian species were observed to slightly differ in their environmental niche, with non-reef-forming species being more tolerant to a wider range of environmental conditions in comparison with reef-forming species, inhabiting a wider area of the South American continental margin. Due to the high potential suitability for several CWC species, the Central and Southern parts of the Brazilian continental margin should be considered as potential areas high CWC diversity. Considering the current state of the art and strategic assessment tools, these areas are important targets for conservation, management, and environmental impact assessment. Most reef-forming species had similar but not directly equivalent ecological niches, indicating that mapping efforts and management planning should consider CWCs at the species level.

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