• European Marine Science
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Estuaries are essential fish habitats because they provide nursery grounds for a number of marine species. Previous studies in the Bay of Vilaine (part of the Bay of Biscay, France) have underlined the estuarine dependence of juvenile common sole (Solea solea, L) and shown that the extent of sole nursery grounds was positively influenced by the variability of the river flow. In the present study, stable carbon and nitrogen isotopes were used to describe the trophic network until the young-of-the-year sole and to compare interannual variations in the dominant trophic pathways in the sole nursery areas in this bay. Particulate organic matter (POM), sediment organic matter (SOM), microphytobenthos, benthic invertebrate sole prey and young-of-the-year common sole were collected during the summer over 4 years characterised by contrasting river discharges. POM isotopic signatures were used to identify the origins of nutrient and organic matter assimilated into the estuarine food web through benthic organisms to juvenile common sole. Interannual spatial variations were found in the POM carbon stable isotope signatures, with the importance of these variations depending on the interannual fluctuations of the river flow. Moreover, the spatio-temporal variability of this POM isotopic signature was propagated along the food webs up to juvenile sole, confirming the central role of river discharge and terrigeneous subsidy input in the estuarine benthic food web in determining the size of the sole nursery habitat. (C) 2009 Elsevier B.V. All rights reserved.

Measurements of the partial pressure of CO, (pCO(2)) in surface waters, and other water properties were performed monthly during a 2-year period from February 1998 through February 2000, at a station in the open northwestern Mediterranean Sea (Dyfamed Station). On seasonal timescale, the pCO(2) minimum of 300 muatm in winter was followed by an increase of 120 muatm (pCO(2) reaching 420 muatm) related to warming of surface waters in summer. Estimates of the underlying processes (mixing, biological activity and air-sea gas exchange) governing the monthly variations of the upper layer PC02 were obtained from observed variations in total inorganic carbon content (TCO2) in the surface, and from the vertical distribution of physical parameters and TCO2, Monthly variations in TCO2 due to gas exchange were determined from wind speed and from the air-sea PC02 gradient. The impact of biological activity was estimated from the difference between the observed variations in TCO2 and the evaluations of air-sea exchange and carbon supply by physical processes. Mixing at the base of the mixed layer counteracts the late winter to summer TCO2 drawdown (about 80 mmol m(-3)) due to a net organic production of about 100 mmol m(-3). The carbon consumption continues until early summer despite the absence of nutrients in the upper layer from April or May. The net carbon production in the mixed layer during the warming period exceeds by a factor of 1.6 the carbon production deduced from nitrate fluxes and using the usual Redfield C:N ratio of 6.6:1. The TCO2 increase during the autumn is primarily associated with convective vertical mixing induced by upper layer cooling and deepening. On the other hand, the contribution of air-sea gas exchange to TCO2 variations remains relatively small aside from summer months, when the CO2 oversaturation is high and the mixed layer is only 15-20 m depth. (C) 2002 Elsevier Science Ltd. All rights reserved. International audience

Successful prevention and mitigation of biological invasions requires retracing the initial steps of introduction, as well as understanding key elements enhancing the adaptability of invasive species. We studied the genetic diversity of the green alga Caulerpa taxifolia and its associated bacterial communities in several areas around the world. The striking congruence of alpha and beta diversity of the algal genome and endophytic communities reveals a tight association, supporting the holobiont concept as best describing the unit of spreading and invasion. Both genomic compartments support the hypotheses of a unique accidental introduction in the Mediterranean and of multiple invasion events in southern Australia. In addition to helping with tracing the origin of invasion, bacterial communities exhibit metabolic functions that can potentially enhance adaptability and competitiveness of the consortium they form with their host. We thus hypothesize that low genetic diversities of both host and symbiont communities may contribute to the recent regression in the Mediterranean, in contrast with the persistence of highly diverse assemblages in southern Australia. This study supports the importance of scaling up from the host to the holobiont for a comprehensive understanding of invasions. project IBISA - Portuguese Foundation for Science and Technology (FCT) [PTDC/MAR/64749/2006] French ANR project CLONIX [ANR-11-BSV7-0007] info:eu-repo/semantics/publishedVersion FEDER FSE FCT

Photosynthetic eukaryotes have a critical role as the main producers in most ecosystems of the biosphere. The ongoing environmental metabarcoding revolution opens the perspective for holistic ecosystems biological studies of these organisms, in particular the unicellular microalgae that often lack distinctive morphological characters and have complex life cycles. To interpret environmental sequences, metabarcoding necessarily relies on taxonomically curated databases containing reference sequences of the targeted gene (or barcode) from identified organisms. To date, no such reference framework exists for photosynthetic eukaryotes. In this study, we built the PhytoREF database that contains 6490 plastidial 16S rDNA reference sequences that originate from a large diversity of eukaryotes representing all known major photosynthetic lineages. We compiled 3333 amplicon sequences available from public databases and 879 sequences extracted from plastidial genomes, and generated 411 novel sequences from cultured marine microalgal strains belonging to different eukaryotic lineages. A total of 1867 environmental Sanger 16S rDNA sequences were also included in the database. Stringent quality filtering and a phylogeny-based taxonomic classification were applied for each 16S rDNA sequence. The database mainly focuses on marine microalgae, but sequences from land plants (representing half of the PhytoREF sequences) and freshwater taxa were also included to broaden the applicability of PhytoREF to different aquatic and terrestrial habitats. PhytoREF, accessible via a web interface (http://phytoref.fr), is a new resource in molecular ecology to foster the discovery, assessment and monitoring of the diversity of photosynthetic eukaryotes using high-throughput sequencing. International audience

Le domaine des Approches occidentales de la Manche constitue une zone clé pour caractériser l'évolution post-rift des marges continentales NW européennes associées à la collision Afrique/Europe. Malgré les divers témoins des inversions cénozoïques jalonnant le pourtour de la Manche, la structuration et l'amplitude des mouvements demeurent néanmoins incertaines au sein de la partie méridionale française des Approches occidentales. Il en est de même sur le rôle de l'inversion de la mer du Nord dans la mise en place du Fleuve Manche qui drainait un bassin versant bien supérieur à la Manche actuelle durant les grandes régressions plio-quaternaires et alimentait les éventails sous-marins Celtique et Armoricain en bas de pente. La réalisation des campagnes de sismique-réflexion haute résolution GEOMOC et GEOBREST03 dont les résultats font l'objet de cet article permettent de répondre à ces questions en complétant la connaissance géologique de la Manche. Les nouvelles observations soulignent le diachronisme et le contraste de l'amplitude des mouvements du système de failles associées à l'inversion du bassin d'Iroise. Celle-ci se fait en deux épisodes: un épisode paroxysmal paléogène décomposé en deux phases, éocène (Yprésien probable) et oligocène, et un épisode néogène plus modéré réactivant partiellement les structures impliquées antérieurement. Les déformations se concentrent le long de l'accident nord Iroise (NIF) situé dans le prolongement de la faille Médio-Manche et entraîne localement des plissements de la couverture sédimentaire à l'aplomb des accidents profonds. L'inversion induit ainsi un soulèvement de près de 700 m du plateau médian situé au sud de l'accident nord Iroise. La cartographie isochrone des séquences sismiques identifiées démontre également le contrôle majeur des structures tectoniques sur la mise en place des dépôts néogènes. Le soulèvement de la partie orientale du bassin favorise ainsi la mise en place de vastes prismes progradants d'âge miocène supérieur, et contrôle le développement postérieur du réseau des paléo-vallées constituant l'extrémité occidentale du fleuve Manche. Ce réseau présente une géométrie en baïonnette marquée par de brutaux changements de directions variant de N040 à N070, cette dernière direction caractérisant la plus grande partie des failles néogènes associées au bassin d'Iroise. Les paléo-vallées se seraient développées lors d'une chute du niveau marin au-delà du rebord de plate-forme et la stratigraphie établie à travers cette étude amène à placer le début des incisions au Pliocène (Reurévien ou pré-Tiglien). La chute amplifiée par l'inversion du bassin d'Iroise serait suivie d'un basculement tardif de la plate-forme externe à l'instar des observations réalisées sur de nombreuses marges du pourtour nord atlantique. International audience

Biogeochemical and diatom export fluxes are presented from two bathypelagic sediment trap deployments in the Antarctic Zone of the Southern Ocean. One of the sediment traps was deployed in very productive, naturally iron-fertilized waters downstream of South Georgia (P3, 2000m) and compared to a deployment in moderately productive waters upstream of the island system (P2, 1500m). At both sites significant diatom export events occurred in spring (November) and contained mostly empty cells that were associated with low particulate organic carbon (POC) fluxes. A summer export pulse occurred one month later at P2 (end February/March) compared to P3 (end January). Diatom fluxes at P3 were one order of magnitude higher than at P2, a difference mainly attributed to the short and intense export of resting spores from Chaetoceros Hyalochaete and Thalassiosira antarctica species. Aside from these resting spores, diatom export assemblages at both sites were dominated by empty Fragilariopsis kerguelensis frustules. The fraction of diatoms exported as empty frustules was considerably lower at P3 (52%) than P2 (91%). This differencewas related to the flux of intact diatom resting spores at P3 and may partially explain the lower Si:C export stoichiometry observed at P3 (1.1) compared to P2 (1.5). Through the enumeration of full diatom frustules and subsequent biomass calculations we estimate that diatom resting spores account for 42 % of annual POC flux in the productive waters downstream of South Georgia. At both sites the contribution of diatom vegetative stages to POC fluxes was considerably lower (<5 %). From these analyses we conclude that resting spore export contributes towards the slightly higher bathypelagic (POC) flux at P3 (40.6 mmol m-2 y-1) compared to P2 (26.4 mmol m-2 y-1). We compared our sediment trap records with previously published diatom assemblage data from the mixed layer and surface sediments (3760 m) around South Georgia. The relative proportion of diatom resting spores within diatom assemblages increases as a function of depth and is explained by selective preservation of their robust frustules. Our study highlights the significance of diatom resting spore export as a carbon vector out of the mixed layer. Furthermore, the contribution or resting spores to POC flux in the bathypelagic ocean and sediments suggests they play a particularly important role in sequestering biologically fixed CO2 over climatically relevant timescales. International audience

Les aptitudes de plusieurs des caractéristiques biochimiques de la matière organique particulaire sédimentée à décrire les changements quantitatifs de la faune benthique ont été comparées à partir des résultats de plusieurs campagnes de prélèvements ayant eu lieu dans le golfe du Lion au cours de ces dix dernières années. Ces travaux ont consisté en deux suivis haute fréquence conduits à une station littorale et à une station du large, en une évaluation de la variabilité saisonnière le long d’un gradient côte large, et, enfin, en une étude synoptique de la variabilité spatiale à mesoéchelle. Les paramètres biochimiques considérés sont la matière organique totale, le carbone organique, l’azote, les protéines totales, les protéines disponibles, les sucres, les lipides, les acides aminés totaux et les acides aminés disponibles. Les paramètres faunistiques considérés sont l’abondance et la biomasse de la meio- et de la macrofaune. Les résultats obtenus contribuent à délimiter l’importance relative de la digestibilité et de l’aptitude à satisfaire les besoins nutritionnels dans la définition de la valeur nutritive de la matière organique particulaire sédimentée. Ainsi, la constance des spectres en acides aminés totaux et disponibles quels que soient les environnements et les saisons étudiés, suggère-t-elle un plus grand rôle de la digestibilité de la matière organique particulaire que de son aptitude à satisfaire des besoins nutritionnels spécifiques dans le contrôle de la faune benthique. Par opposition aux sucres, les lipides et les acides aminés disponibles sont associés à la fraction la plus labile de la matière organique particulaire. Ceci rend inopérant l’usage de la somme des concentrations en protéines, sucres et lipides en tant qu’indice de la fraction labile de la matière organique, au moins dans les zones directement comparables au golfe du Lion. The abilities of several biochemical characteristics of sedimentary organic matter to describe quantitative changes in benthic fauna were assessed based on several surveys carried out within the Gulf of Lion during the last decade. Two sets of high frequency samplings were carried out both inshore and offshore, together with an assessment of seasonal variability along a depth gradient, and a synoptic assessment of mesoscale spatial variability. The considered biochemical parameters were: total organic matter, organic carbon, nitrogen, total proteins, available proteins, carbohydrates, lipids, total and available amino acids. The considered faunal parameters were the abundance and the biomass of both meio- and macrofauna. Our results contribute to unravel the relative importance of food digestibility and composition in controlling particulate organic matter nutritional value. Spectra of both total and available amino acids were almost constant irrespective of the seasons and/or the environments, which were studied during these surveys. This underlines the role of particulate organic matter digestibility relative to its ability to meet specific nutritional requirements in controlling benthic fauna. Multivariate analysis used to relate biochemical and faunal parameters suggest that available amino acids and lipids are the best descriptors of food nutritional value. In contrast with carbohydrates, these two parameters are both associated with the most labile fraction of particulate organic matter. This result suggests that the use of the sum of proteins, carbohydrates and lipids as a proxy for labile organic matter is precluded at least in areas similar to the Gulf of Lion.