Influence of coastal Mediterranean rivers on the organic matter composition and reactivity of continental shelf sediments: The case of the Têt River (Gulf of Lions, France)

International audienceRiver-dominated ocean margins (RiOMars) are areas of high productivity, rapid sediment deposition, and in-tense recycling. The Gulf of Lions, located in the North occidental Mediterranean Sea, is no exception to thisgeneral rule and is under the prevalent influence of the Rhône River. One particularity of this continental shelf is that it is also fed by several small coastal rivers whose inputs actively contribute to the coastal dynamic and export to the deep-sea. Our objective was to gauge the influence of coastal rivers on the quality and reactivity of the organic matter delivered to the continental shelf as these properties control two important functions of coastal areas: benthic productivity and carbon sequestration. We chose for this study, the Têt River, which is typical of coastal Mediterranean rivers with a torrential regime. Sediment cores were sampled five times over a one-year period on four stations located along the dominant trajectory of the Têt River plume. The biogeochemical characteristics of the surface sediments were analysed to highlight spatio-temporal trends in the sedimentary organic matter composition and to identify the major environmental factors controlling its reactivity. Nutrient and dissolved oxygen fluxes at the water-sediment interface were furthermore measured at two stations using ex-situ whole core incubations.Results from this study highlight the seasonal influence of riverine versus autochthonous productions on thequality of sedimentary organic matter in the vicinity of the river mouth. Farther on the mid shelf, a terrestrial imprint is still visible, but the temporal signal is blurred as a consequence of strong mixing during frequent episodes of resuspension/deposition. Organic matter is efficiently remineralised in this system with total oxygen uptake (TOU) rates comparable to those measured off the Rhône River. Finally, organic matter quality and reactivity are also constrained in this system by physical forcings, which promote remineralisation and advection of sediments

Origine, qualité et réactivité de la matière organique d'origine continentale dans les sédiments du prodelta du Rhône et sur le plateau adjacent

Le Rhône est la principale source d'eau douce et de matériels terrigènes vers le bassin méditerranéen. Une question est soulevée sur le devenir de ces grandes quantités de carbone organique délivrées par le fleuve vers le milieu marin et en particulier leur impact sur les communautés microbiennes benthiques et l'intensité du recyclage de la matière organique. Lors de quatre campagnes de terrain réalisées en avril 2007, mai 2008, décembre 2008 et juin 2009 dans le cadre de l ARN CHACCRA, des carottes de sédiments ont été prélevées à l embouchure du fleuve et sur le plateau adjacent. La contribution des apports continentaux et leur distribution ont été étudiées à l aide de paramètres globaux (granulométrie, azote total et carbone organique), tandis que les descripteurs moléculaires (pigments, acides gras, acides aminés totaux et biodisponibles) ont permis de déterminer l'origine, et d évaluer la qualité ainsi que l'état de dégradation de la matière organique dans les sédiments. La structure de la communauté bactérienne a été caractérisée par la technique de polymorphisme de conformation des simples brins par électrophorèse capillaire. Ces travaux mettent en évidence des gradients d origine et de qualité depuis l embouchure vers le large. De plus, l influence des événements de crue est clairement visible dans les sédiments, et les signatures biochimiques des dépôts sont différentes selon le type de crue. Enfin, l incubation des sédiments a permis d évaluer la dégradabilité en condition oxique de la matière organique sédimentaire à l embouchure et de montrer que la fraction labile était très réactive à la dégradation.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocBANYULS/MER-Observ.Océanol. (660162201) / SudocSudocFranceF

Stimulatory effect of sulphide on thiotaurine synthesis in three hydrothermal-vent species from the East Pacific Rise

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Effects of cadmium on nuclear integrity and DNA repair efficiency in the gill cells of Mytilus edulis L

Although the effects of heavy metals on marine invertebrate species are well studied in term of their toxicity and bioaccumulation, less is known about their genotoxicity. The aim of this investigation was to assess the DNA damaging potential of cadmium (Cd) in an important pollution sentinel organism, the mussel Mytilus edulis. Cadmium is one of the most toxic and widespread heavy metals found in the marine environment, and is a recognised carcinogen in mammals. Based on the results of the comet assay (alkaline single cell gel electrophoresis), Cd was found not to be genotoxic in mussel gill cells under acute and chronic exposure conditions, whereas pre-exposure to low concentrations of Cd was found to enhance the genotoxicity of another mutagen, hydrogen peroxide (H2O2). The effects of H2O2 were normally reversible when cells were transferred to clean saline buffer. However, in cells that had been pre-treated with Cd, in vivo or in vitro, we observed a decrease in this post-treatment DNA repair. The effects of Cd were reversed by zinc which suggests that the inhibitory effect of Cd on DNA repair was due to the displacement of zinc ions from active sites on proteins involved in the repair process (a property already described for mammals). Moreover, since Cd inhibits or delays the onset of apoptosis (programmed cell death), this removes one of the main defence mechanisms responsible for protecting the organism against neoplasia. There appears to be a close similarity between the effects of Cd on marine molluscs and mammals

Toxic vents and DNA damage: first evidence from a naturally contaminated deep-sea environment

Levels of DNA strand breakage were measured, using the comet assay, in cells from vent mussels, Bathymodiolus azoricus, from three contrasting vent fields on the mid Atlantic Ridge. Different levels of DNA damage were recorded in untreated mussels, shortly after collection, and it was animals from the shallowest, and less active, Menez Gwen vent field (840-m depth), which showed the greatest amount of damage. In contrast to animals from two deeper and putatively more toxic sites, Menez Gwen animals went on to repair this damage and were able to survive under laboratory conditions at 1 bar pressure for several months. Animals from the two deeper sites showed both higher levels of initial mortality and a much reduced capacity for survival at 1 bar. The differences in DNA damage levels at the time of collection were interpreted as an expression of differences in cell viability/enzyme activity rather than a reflection of any differences in their natural environmental conditions. Small B. azoricus showed a capacity to repair DNA damage, whereas this ability appeared to be lacking in large individuals. By reproducing at a relatively early age, the deep-sea vent fauna may be able to resist the toxic effects of its environment by exploiting this natural, stage specific capacity to repair damaged DNA.<br/

Improved Comet assay for the assessment of UV genotoxicity in Mediterranean sea urchin eggs.

International audienceGametes and embryos of broadcast spawners are exposed to a wide range of chemical and physical stressors which may alone, or in conjunction, have serious consequences on reproductive outcomes. In this study, two Mediterranean echinoid species, Paracentrotus lividus and Sphaerechinus granularis, were chosen as models to study the genotoxicity of UV radiation (UVR) on the eggs of broadcast-spawning marine invertebrates. The single cell gel electrophoresis, or Comet assay, was successfully adapted to assess DNA strand breakage in sea urchin eggs. The results demonstrated that the genetic material of sea urchin eggs is susceptible to environmentally realistic UV exposure. The induction of DNA damage in the irradiated unfertilized eggs suggests that the previously described defense mechanisms in sea urchin eggs do not completely protect the egg's DNA against UV toxicity. Taken together, our results suggest that UV-impairment of the genetic integrity of the eggs might have a role in postfertilization failures and abnormal embryonic development. Although both species were vulnerable to UVR, embryonic development was less dramatically impaired in P.Lividus. This observation supports the postulation that species inhabiting shallower environments possess more efficient mechanisms to overcome UV-induced DNA alterations. The present demonstration of the utility and sensitivity of the Comet assay to evaluate DNA integrity in eggs from marine invertebrates opens new perspectives for monitoring the long-term effects of environmental exposure on populations and for the routine screening of substances for genotoxicity in marine systems

High amounts of sulphur-amino acids in three symbiotic mytilid bivalves from deep benthic communities

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Palynofacies reveal fresh terrestrial organic matter inputs in the terminal lobes of the Congo deep-sea fan

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Sulphur-amino acids in symbiotic species from hydrothermal vents and cold seeps

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Ultraviolet radiation induces structural and chromatin damage in Mediterranean sea-urchin spermatozoa.

International audienceThere is growing concern about the effects of enhanced levels of solar ultraviolet radiation on the living components of the biosphere (i.e. cancer, loss of biodiversity and productivity, etc.). In shallow coastal environments, many benthic species release their gametes directly in the water column where fertilisation occurs and the planktonic larvae remain for several weeks. Any effects on these early life stages could significantly impair reproductive input or alter the fitness of the community. The purpose of this paper is to provide new insights into the mechanisms of UV toxicity on sea-urchin spermatozoa in a cytological context, and to address the question of the potential ecological consequences of the damage. The Mediterranean sea-urchin Sphaerechinus granularis (Lamarck) was chosen as a model to study the effects of ecologically relevant doses of UV-R on the spermatozoa of marine invertebrates. Structural damage was visualised by use of transmission electron microscopy and the single-cell gel electrophoresis (Comet) assay was used to assess chromatin integrity in spermatozoa. The present results provide experimental evidence that irradiation with UV induces structural and chromatin damage in sea-urchin sperm. Almost 90% of spermatozoa exhibited morphological alterations and DNA strand breakage increased 2-fold. The observed alterations of the acrosome, plasma membrane and mitochondria can explain the concomitant impairment of fertilisation (23% decrease of fertilisation rate), which in turn may affect reproductive success. On the other hand, how DNA damage and fertilisation rate correlate remains unclear; however, when not repaired genetic lesions can lead to abnormal development and/or the transmission of heritable damage. The 3-fold decrease of the frequency of 2-celled embryos indicates a delay or inhibition of the first cell division, which may be ascribed to impairment of nuclear chromatin and/or other cellular targets