Benthic diatom communities from two salt marshes of the St. Lawrence Estuary (Canada)

Microphytobenthic diatom communities were investigated in the high and low sections of two salt marshes of the Lower St. Lawrence Estuary (eastern Canada): one featuring a sandy low marsh zone (Pointe-aux-Épinettes; PE) and one with a muddy low marsh area (Pointe-au-Père; PP). Based on diatom composition and diversity, bacterial abundance, chlorophyll-a, phaeopigments and geochemical analyses (Corg, Ntot, granulometry, extracellular polymeric substances), the PP high marsh area appeared to be singular compared to the other sampling sites. Estimated surface biomass ranged from 11 to 71 g C•m-2 in the PE marsh and from 24 to 486 g C•m-2 in the PP marsh. A higher diversity of diatom species was observed in the PP high marsh area with a dominance of epipelic forms, in opposition to the dominant epipsammic forms at the other sites. Statistical analyses showed that diatom density was mainly affected by nutrient availability while the relative abundance of epipelic and epipsammic species was related to sediment grain size. This study provides original data on the composition of benthic diatoms in surface sediments in St. Lawrence saltmarshes during summer time that represent the first step to the determination of the DBI (Diatom biological index) of these northern environments.La composition des communautés de diatomées benthiques a été étudiée dans les zones supérieures et inférieures de deux marais côtiers de l’estuaire maritime du Saint-Laurent (Québec, Canada), l’un possédant un estran sableux (marais de Pointe-aux-Épinette; PE) et l’autre possédant un estran vaseux (marais de Pointe-au-Père; PP). En nous penchant sur l’abondance et la diversité des diatomées benthiques ainsi que sur les caractéristiques biogéochimiques du sédiment (abondance bactérienne totale, granulométrie, composition élémentaire, concentration de pigments, de polysaccharides), nous avons observé que la zone supérieure du marais PP constituait un milieu singulier. Une plus grande diversité de diatomées a été observée dans cette zone avec une dominance des formes épipéliques alors qu’aux autres sites, nous avons observé une prédominance des formes épipsammiques. Nos analyses statistiques ont montré que l’abondance totale de diatomées est corrélée à la disponibilité des nutriments, alors que l’abondance relative de cellules de types épipélique et épisammique est corrélée à la taille des particules de sédiment. Selon nos estimations, la biomasse associée aux diatomées variait de 11 à 71 g C•m-2 dans le marais PE et de 24 à 486 g C•m-2 dans le marais PP. Cette étude décrit pour la première fois la composition détaillée des communautés de diatomées établies dans les sédiments des marais côtiers nordiques en saison estivale et constitue un premier pas vers la détermination de l’indice biologique diatomique de ces environnements nordiques

Regards croisés

En ces temps d’interrogation sur le réchauffement climatique est parue l’enquête d’Emmanuel Le Roy Ladurie : Histoire humaine et comparée du climat, qui fait suite à son premier livre sur la question publié en 1967. Guy Lemarchand (Université de Rouen), qui a associé Karine Rance (Université de Clermont-Ferrand) à son projet, a eu l’idée de demander à l’auteur des célèbres Paysans de Languedoc (1966) ce qui l’a amené à une démarche qui remet au premier plan, dans une synthèse large, l’orienta..

Toxicité des hydrocarbures et impacts des déversements sur les organismes marins et leur environnement

Les risques liés aux déversements opérationnels et accidentels d’hydrocarbures seront intensifiés par l’augmentation des besoins mondiaux en pétrole. Les accidents, bien que rares, se multiplient et causent d’innombrables effets sur l’environnement et sur les organismes qui s’y trouvent. Ce chapitre fait un survol de l’impact potentiel des hydrocarbures sur les organismes et sur les habitats ainsi que des conséquences sur le fonctionnement et les services écologiques que procurent les écosystèmes marins. La nature et le comportement des pétroles déversés ainsi que les risques associés aux méthodes d’intervention, par exemple l’utilisation de dispersants ou le nettoyage physique, y sont abordés. Les voies d’exposition des divers organismes (microorganismes, phytoplancton, zooplancton, invertébrés, oiseaux et mammifères marins) et les effets sur leur population sont illustrés en prenant exemple parmi les événements malheureux de l’échouage de l’Exxon Valdez en 1989 ou de l’explosion de la plateforme Deepwater Horizon en 2010. L’influence des conditions de déversement sur la résilience des écosystèmes touchés sera abordée

Mixing processes at the pycnocline and vertical nitrate supply: Consequences for the microbial food web in San Jorge Gulf, Argentina

Little is known about the base of the food web that could support the high productivity and marine biodiversity found in San Jorge Gulf, Patagonia, Argentina. Here we examine the key components of the microbial food web, including the standing stock and physiological state of the phytoplankton in the context of key oceanographic variables in the gulf. Water samples were collected at 16 stations for biological and chemical analyses, together with measurements of vertical structure and currents. The dynamics of the water column and its impact on nutrient availability for primary producers was evaluated. Our results show that, in spite of the observed low surface nutrient concentrations and low biomass, phytoplankton cells were in good physiological state. This is possible because nutrients are replenished at the pycnocline depth, as estimated by means of Richardson’s dynamic stability. Turbulence created by tides and the shear between overlapping water masses favors the disruption of the pycnocline. We suggest that, during summer, San Jorge Gulf maintains not only high primary productivity but also high phytoplankton biomass turnover rate, which is supported by a high C:N ratio, consistent with strong zooplankton grazing and export of organic carbon to deep waters.Fil: Latorre, Maite Pilmayquen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Schloss, Irene Ruth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Almandoz, Gaston Osvaldo. Universidad Nacional de La Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lemarchand, Karine. Université du Québec à Rimouski; CanadáFil: Flores Melo, Elizabeth Ximena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Massé Beaulne, Valérie. Maurice Lamontagne Institute; CanadáFil: Ferreyra, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Université du Québec à Rimouski; Canad

Mixing processes at the pycnocline and vertical nitrate supply: consequences for the microbial food web in San Jorge Gulf, Argentina

Little is known about the base of the food web that could support the high productivity and marine biodiversity found in San Jorge Gulf, Patagonia, Argentina. Here we examine the key components of the microbial food web, including the standing stock and physiological state of the phytoplankton in the context of key oceanographic variables in the gulf. Water samples were collected at 16 stations for biological and chemical analyses, together with measurements of vertical structure and currents. The dynamics of the water column and its impact on nutrient availability for primary producers was evaluated. Our results show that, in spite of the observed low surface nutrient concentrations and low biomass, phytoplankton cells were in good physiological state. This is possible because nutrients are replenished at the pycnocline depth, as estimated by means of Richardson’s dynamic stability. Turbulence created by tides and the shear between overlapping water masses favors the disruption of the pycnocline. We suggest that, during summer, San Jorge Gulf maintains not only high primary productivity but also high phytoplankton biomass turnover rate, which is supported by a high C:N ratio, consistent with strong zooplankton grazing and export of organic carbon to deep waters.Facultad de Ciencias Naturales y Muse

Biofouling Growth in Cold Estuarine Waters and Evaluation of Some Chitosan and Copper Anti-Fouling Paints

Ecological concerns about antifouling paints containing non-green tin and copper compounds have highlighted the need for environmentally friendly alternatives. We report here a field test conducted in estuarine waters over two months designed to evaluate the efficiency of a number of active natural and man-made chemical ingredients added into a silicon-polyurethane marine paint. Early steps of biofouling in cold seawater of the St. Lawrence Estuary (Canada) were observed. Analyses, including dry biomass, flow cytometry and spectrofluorimetry, demonstrated a short-term antibacterial action of chitosan-based paints although no significant anti-algal action was observed. Cuprous oxide paints were efficient against bacteria and algae invasion in the first two weeks, especially those with added organic biocides such as isothiazolone and copper pyrithione. However, the overall dry biomass and chlorophyll a content were similar for all chitosan-and copper-based paints after 63 days. Microscopic observations revealed variation in the highly diverse benthic diatom population including species Navicula, Melosira, Cocconeis, Nitshzcia, Fragilaria and Amphora. Results suggest no real long-term efficiency for tested antifouling paints and highlight a particular need for green antifouling ingredients that are active under northern estuarine conditions

Origine, devenir et détection rapide de microorganismes entériques pathogènes à l'interface côtière (une application aux genres Salmonella et Cryptosporidium)

De nombreux microorganismes potentiellement pathogènes pour l'homme et les animaux sont présents à l'interface côtière, où ils peuvent avoir des implications importantes en terme de santé publique, comme en terme d'activité socio-économiques. Les difficultés inhérentes à la détection des pathogènes par les techniques classiques de mise en culture (i.e. temps, formes non cultivables) nécessitent le développement de méthodes alternatives permettant la quantification rapide de pathogène spécifiques en milieu naturel. Les travaux réalisés ont permis d'utiliser une méthode directe, couplée à une détection par cytométrie en phase solide, pour quantifier des oocystes de Cryptosporidium dans différents types d'eau, mais restent encore à être affinés dans le cas particulier des bactéries. L'analyse de la contamination du bassin versant du Tech (Pyrénées-Orientales, France) n'a pas permis d'établir une relation quantitative entre Salmonella, Cryptosporidium et deux indicateurs de pollution fécale (e.g. coliformes thermotolérants, streptocoques fécaux). Elle confirme la nécessité de rechercher les germes pathogènes de façon spécifique dans les eaux de surface. Les flux de pathogènes à l'interface côtière peuvent être direct ou diffus. Les apports diffus sont contrôlés par la fréquence de mobilisation des sources, animales ou humaines, de contamination et par la capacité de résistance des organismes face aux facteurs biotiques et abiotiques (e.g. salinité, rayonnement).L'analyse de la survie de sérotypes de "Salmonella enterica" provenant d'origines diverses démontre un comportement physiologique similaire pour l'ensemble des souches, conduisant à l'apparition de formes actives non cultivables. Une des hypothèses proposées afin de mieux comprendre les mécanismes à l'origine de la récurrence de certains sérotypes de "Salmonella enterica" en milieu fluvial, consiste en une sélection de cellules mutantes mieux adaptées aux conditions environnementales.LYON1-BU.Sciences (692662101) / SudocBANYULS/MER-Observ.Océanol. (660162201) / SudocSudocFranceF

Microbiota modification of Mytilus edulis larvae in response to the use of a new probiotic, the marennine, in aquaculture

In bivalve hatcheries, opportunistic pathogens have been associated with important mass mortality events of larvae and important economic lost for producers. New alternatives to the use of antibiotics, such as probiotics, have been proposed to limit the occurrence of such events in bivalve hatcheries and to stabilize bivalve production. Probiotics are microorganisms, or natural molecules, that are associated with beneficial effects for the host at different levels, especially to enhance their resistance to external stressors such as bacterial pathogens. It is know recognized that the composition of the host microbiota influences host health status and could be a target of probiotics. The aim of this study is to highlight the protective effect of a new probiotic, the marennine, on Mytilus edulis larvae during bacterial challenges in relation with a potential modification of the microbiota of the marennine-treated larvae. The main hypothesis is that the addition of marennine during larvae rearing processes could modify the conditions prevailing in the rearing medium and, as a consequence, the composition of the larvae microbiota, leading to a better resistance to bacterial infections. The marennine is a blue pigment originating from the diatom Haslea ostrearia, that have demonstrated a positive effect on larvae survival at a final concentration of 500 µg L-1. In this study, D-larvae (9 days old) and post-larvae (29 days old) were exposed for 96h to Vibrio splendidus with and without mareninne at a final concentration of 500 µg L-1. Our results demonstrated that at this concentration, the marennine have no direct antimicrobial effect on Vibrio splendidus growth kinetics. In addition, the presence of marennine did not modify the abundance of bacteria in the rearing medium, suggesting no direct antimicrobial effect of marennine on the bacterial load to which larvae were exposed during the experiments. Nevertheless, the presence of marennine increased the survival of D-larvae exposed to the pathogen but have no effect on post-larvae survival. The undergoing molecular analyses and the future metagenomics analyses of the larvae microbiota diversity will allow us to demonstrate if a modification in the larval microbiota’s richness might explain the increase of the survival rate during the production of blue mussels in aquaculture. Ultimately, our work will enable us to shed light on the importance of the larval microbiota in pathogen-resistance during bivalves rearing process