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| Registros recuperados: 11 | |
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| Maguer, Jean-francois. |
| Des mesures de cuivre total dans les sédiments de quelques estuaires bretons ont été réalisées. Il a été trouvé une relation directe entre le cuivre et la granulométrie, les concentrations les plus élevées correspondant aux granulométries les plus fines. La relation entre le cuivre et la matière organique n'est pas évidente. Il semble que les concentrations en cuivre sont en relation avec le rapport : porcs (sauf petits en lactation) / surface cultivée, dans les cantons où ont été faits les prélèvements. |
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| Ano: 1990 |
URL: http://archimer.ifremer.fr/doc/00075/18635/16183.pdf |
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| Bednarz, Vanessa N.; Grover, Renaud; Maguer, Jean-francois; Fine, Maoz; Ferrier-pages, Christine. |
| Tropical corals are associated with a diverse community of dinitrogen (N-2)-fixing prokaryotes (diazotrophs) providing the coral an additional source of bioavailable nitrogen (N) in oligotrophic waters. The overall activity of these diazotrophs changes depending on the current environmental conditions, but to what extent it affects the assimilation of diazotroph-derived N (DDN) by corals is still unknown. Here, in a series of N-15(2) tracer experiments, we directly quantified DDN assimilation by scleractinian corals from the Red Sea exposed to different environmental conditions. We show that DDN assimilation strongly varied with the corals ' metabolic status or with phosphate availability in the water. The very autotrophic shallow-water (similar to 5 m)... |
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| Ano: 2017 |
URL: https://archimer.ifremer.fr/doc/00616/72832/72319.pdf |
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| Ezzat, Leila; Maguer, Jean-francois; Grover, Renaud; Ferrier-pages, Christine. |
| During the 20th century, seawater temperatures have significantly increased, leading to profound alterations in biogeochemical cycles and ecosystem processes. Elevated temperatures have also caused massive bleaching (symbiont/pigment loss) of autotrophic symbioses, such as in coral-dinoflagellate association. As symbionts provide most nutrients to the host, their expulsion during bleaching induces host starvation. However, with the exception of carbon, the nutritional impact of bleaching on corals is still unknown, due to the poorly understood requirements in inorganic nutrients during stress. We therefore assessed the uptake rates of nitrogen and phosphate by five coral species maintained under normal and thermal stress conditions. Our results showed that... |
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| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00616/72845/72920.pdf |
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| Llopis Monferrer, Natalia; Leynaert, Aude; Tréguer, Paul; Gutiérrez‐rodríguez, Andrés; Moriceau, Brivaela; Gallinari, Morgane; Latasa, Mikel; L'Helguen, Stéphane; Maguer, Jean-francois; Safi, Karl; Pinkerton, Matthew H.; Not, Fabrice. |
| We examined biogenic silica production and elementary composition (biogenic Si, particulate organic carbon and particulate organic nitrogen) of Rhizaria and diatoms in the upper 200 m along a transect in the Southwest Pacific sector of the Southern Ocean during austral summer (January–February 2019). From incubations using the 32Si radioisotope, silicic acid uptake rates were measured at 15 stations distributed in the Polar Front Zone, the Southern Antarctic Circumpolar Current and the Ross Sea Gyre. Rhizaria cells are heavily silicified (up to 7.6 nmol Si cell−1), displaying higher biogenic Si content than similar size specimens found in other areas of the global ocean, suggesting a higher degree of silicification of these organisms in the silicic acid... |
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| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00692/80407/83515.pdf |
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| Berthelot, Hugo; Duhamel, Solange; L’helguen, Stéphane; Maguer, Jean-francois; Wang, Seaver; Cetinić, Ivona; Cassar, Nicolas. |
| Nitrogen (N) is a limiting nutrient in vast regions of the world’s oceans, yet the sources of N available to various phytoplankton groups remain poorly understood. In this study, we investigated inorganic carbon (C) fixation rates and nitrate (NO3−), ammonium (NH4+) and urea uptake rates at the single cell level in photosynthetic pico-eukaryotes (PPE) and the cyanobacteria Prochlorococcus and Synechococcus. To that end, we used dual 15N and 13C-labeled incubation assays coupled to flow cytometry cell sorting and nanoSIMS analysis on samples collected in the North Pacific Subtropical Gyre (NPSG) and in the California Current System (CCS). Based on these analyses, we found that photosynthetic growth rates (based on C fixation) of PPE were higher in the CCS... |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00462/57383/64185.pdf |
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| Tremblay, Pascale; Gori, Andrea; Maguer, Jean-francois; Hoogenboom, Mia; Ferrier-pages, Christine. |
| Symbiotic scleractinian corals are particularly affected by climate change stress and respond by bleaching (losing their symbiotic dinoflagellate partners). Recently, the energetic status of corals is emerging as a particularly important factor that determines the corals' vulnerability to heat stress. However, detailed studies of coral energetic that trace the flow of carbon from symbionts to host are still sparse. The present study thus investigates the impact of heat stress on the nutritional interactions between dinoflagellates and coral Stylophora pistillata maintained under auto-and heterotrophy. First, we demonstrated that the percentage of autotrophic carbon retained in the symbionts was significantly higher during heat stress than under... |
| Tipo: Text |
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| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00616/72835/72989.pdf |
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| Pupier, Chloe A.; Bednarz, Vanessa N.; Grover, Renaud; Fine, Maoz; Maguer, Jean-francois; Ferrier-pages, Christine. |
| Corals are associated with dinitrogen (N-2)-fixing bacteria that potentially represent an additional nitrogen (N) source for the coral holobiont in oligotrophic reef environments. Nevertheless, the few studies investigating the assimilation of diazotrophically derived nitrogen (DDN) by tropical corals are limited to a single scleractinian species (i.e., Stylophora pistillata). The present study quantified DDN assimilation rates in four scleractinian and three soft coral species from the shallow waters of the oligotrophic Northern Red Sea using the N-15(2) tracer technique. All scleractinian species significantly stimulated N, fixation in the coral-surrounding seawater (and mucus) and assimilated DDN into their tissue. Interestingly, N-2 fixation was not... |
| Tipo: Text |
Palavras-chave: Dinitrogen fixation; Diazotrophs; Scleractinian corals; Soft corals; Red Sea. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00512/62370/66644.pdf |
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| Maguer, Jean-francois; Madec, C.; Caradec, J.; Mage, C.. |
| Différentes espèces phytoplanctoniques ont été impliquées dans des efflorescences toxiques sur l'ensemble du littoral français ces dernières années. Parmi celles recencées, les efflorescences du dinoflagellé Alexandrium minutum s'avèrent comme particulièrement dangereuses en raison des toxines qu'elles produisent et qui sont responsables chez l'homme du syndrome PSP (Paralitic Shelfish Poisoning). A. minutum a été signalé pour la première fois en France il y a une vingtaine d'années dans les abers bretons puis dans la baie de Morlaix (Erard Le Denn, 1999). Depuis, des efflorescences récurrentes y sont observées, occasionnant régulièrement des interdictions préfectorales de commercialisation de mollusques bivalves. Les études menées dans l'estuaire de Penzé... |
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| Ano: 2005 |
URL: http://archimer.ifremer.fr/doc/00105/21597/19177.pdf |
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| Maguer, Jean-francois. |
| La production primaire dans l'océan est généralement limitée par l'azote. Ceci a été mis en évidence dans le domaine océanique (Thomas, 1966 ; 1969 ; Eppley et al., 1973) et dans les eaux côtières (Ryther et Dunstan, 1971 ; McCarthy et al., 1977). Par ailleurs, dans l'eau de mer, les cycles biogéochimiques des principaux éléments (C, N, P) sont étroitement liés (Redfield et al., 1963) et l'azote, en contrôlant la production primaire, règle pour une large part les flux des différents composés. Il régule en particulier les flux de carbone dans la zone euphotique et vers les couches profondes, déterminant ainsi la capacité des écosystèmes à exporter la matière organique. |
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| Ano: 1995 |
URL: http://archimer.ifremer.fr/doc/00103/21453/19034.pdf |
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| Registros recuperados: 11 | |
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