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Poisot T.,CNRS Integrative Biology of Marine Organisms | Verneau O.,CNRS Training and Research Center on Mediterranean Environments | Desdevises Y.,CNRS Integrative Biology of Marine Organisms
PLoS ONE | Year: 2011

Lamellodiscus Johnston & Tiegs 1922 (Monogenea, Diplectanidae) is a genus of common parasites on the gills of sparid fishes. Here we show that this genus is probably undergoing a fast molecular diversification, as reflected by the important genetic variability observed within three molecular markers (partial nuclear 18S rDNA, Internal Transcribed Spacer 1, and mitonchondrial Cytochrome Oxidase I). Using an updated phylogeny of this genus, we show that molecular and morphological evolution are weakly correlated, and that most of the morphologically defined taxonomical units are not consistent with the molecular data. We suggest that Lamellodiscus morphology is probably constrained by strong environmental (host-induced) pressure, and discuss why this result can apply to other taxa. Genetic variability within nuclear 18S and mitochondrial COI genes are compared for several monogenean genera, as this measure may reflect the level of diversification within a genus. Overall our results suggest that cryptic speciation events may occur within Lamellodiscus, and discuss the links between morphological and molecular evolution. © 2011 Poisot et al.

Elguindi N.,CNRS Laboratory for Aerology | Somot S.,Meteo - France | Deque M.,Meteo - France | Ludwig W.,CNRS Training and Research Center on Mediterranean Environments
Climate Dynamics | Year: 2011

In this study we have evaluated the ability of the CNRM-ARPEGE CLIMATE V4 general circulation model (GCM) to estimate the present-day hydrological budget components [precipitation minus evaporation over the sea (P - E) and fresh water runoff (R)] over the Mediterranean, Black and Caspian sea basins. Three simulations were performed which were exactly identical except for horizontal resolution, allowing for a unique opportunity to isolate and study the effects of resolution on simulating the hydrological components. Model calculated values of runoff and P - E were compared to a variety of data sources and show that the model's performance improves significantly with increased resolution, especially in regions with mountainous terrain. Corresponding future climate simulations (following the IPCC A2 scenario) were also performed and indicate that while resolution does not seem to have a significant effect on the qualitative impacts of future climate change on the hydrologic balance, quantitatively the results vary significantly among the models. These results suggests that high resolution global models, or downscaling models such as RCMs, are necessary in order to assess the magnitude of future changes in the hydrological components of these basins. © 2009 Springer-Verlag.

Lavigne H.,University Pierre and Marie Curie | D'Ortenzio F.,University Pierre and Marie Curie | Migon C.,University Pierre and Marie Curie | Claustre H.,University Pierre and Marie Curie | And 5 more authors.
Journal of Geophysical Research: Oceans | Year: 2013

Phytoplankton phenology is primarily affected by physical forcing. However, its quantification is far from being completely understood. Among the physical forcing factors, the mixed layer depth (MLD) is considered to have the strongest impact on phytoplankton dynamics, and consequently, on their phenology. The role of MLD variations in shaping the phytoplankton phenology was explored in the Mediterranean Sea, a basin displaying contrasting phenological regimes. A database of MLD estimations was merged with ocean color chlorophyll concentrations ([Chl]SAT) to generate concomitant annual MLD and [Chl]SAT cycles. Several indices were calculated to quantitatively analyze these cycles. The relevance of indices summarizing the temporal difference between main characteristics of MLD and [Chl]SAT cycles was emphasized. As previously observed, two dominant phenological regimes coexist in the Mediterranean Sea. The first is marked by a typical spring bloom, as in temperate regions. The second displays a low seasonality and an absence of an intense [Chl]SAT peak as in subtropical areas. The MLD is shown to play a key role in determining the dominant phenological regime in a given area. Results also show that regions having low seasonality display concomitant MLD and [Chl]SAT maxima, whereas [Chl]SAT peaks are generally observed 30 days after MLD peaks in regions with strongest seasonality. Over the whole basin, [Chl]SAT increase starts 1 month after the initiation of MLD deepening. Finally, after examining the impact of MLD on light and nutrient availability for phytoplankton, mechanisms were proposed to explain the time lags between MLD and [Chl]SAT increase and MLD and [Chl]SAT maxima. ©2013. American Geophysical Union. All Rights Reserved.

Rigual-Hernandez A.S.,University of Salamanca | Sierro F.J.,University of Salamanca | Barcena M.A.,University of Salamanca | Flores J.A.,University of Salamanca | Heussner S.,CNRS Training and Research Center on Mediterranean Environments
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2012

In order to investigate the seasonal and interannual variability of planktic foraminiferal fluxes in the NW Mediterranean, 266 samples from two 12-year-long sediment traps were analyzed. Two mooring lines were deployed at the east (Station Planier) and the west (Station Lacaze Duthiers) of the Gulf of Lions. The moorings were deployed at a water depth of around 1000m and were equipped with sediment traps at 500m above bottom (mab). In addition, an array of 13 core-tops recovered from different key areas of the Gulf of Lions is described. At Lacaze Duthiers, average foraminiferal fluxes were about double (411.8shellsm -2d -1) those found at the Planier sampling site (225.4shellsm -2d -1), probably due to the fertilizing effect of the Rhone river plume and the general oceanographic circulation. The annual total foraminiferal fluxes exhibited a unimodal trend, with maxima recorded during the winter-spring transition, i.e. the spring bloom, and minima during summer. Therefore, planktic foraminifers found in the sedimentary record in the Gulf of Lions may reflect the flux during the winter-spring period, rather than throughout the annual cycle. A total of eleven planktic foraminiferal species were identified in the sediment trap and core-top samples but only four species were dominant in the assemblages: Globigerina bulloides Neogloboquadrina pachyderma (dex.), Globorotalia inflata and Globorotalia truncatulinoides. The foraminiferal assemblages in the Gulf of Lions reflected the relatively cold conditions of the Northern Basin. No clear relationship between the NAO (North Atlantic Oscillation) and planktic foraminiferal fluxes was found in the sediment trap records. The low planktic foraminiferal fluxes recorded during the spring of 1998 were probably related to the anomalous environmental conditions triggered by the 1997-98 El Niño event. Furthermore, sediment trap samples were compared with surficial sediments recovered from different environmental and sedimentary settings of the Gulf of Lions and the application of these results in paleoceanographic reconstructions is discussed. © 2012 Elsevier Ltd.

Levoy F.,University of Caen Lower Normandy | Anthony E.J.,Aix - Marseille University | Monfort O.,University of Caen Lower Normandy | Robin N.,CNRS Training and Research Center on Mediterranean Environments | Bretel P.,University of Caen Lower Normandy
Marine Geology | Year: 2013

A field of long-crested transverse bars was monitored from a 2.5-year series of topographic Lidar surveys in the vicinity of a tidal inlet on the macrotidal (mean spring tidal range. = 7 to 12. m) west coast of Cotentin (Normandy, France). The bar field, the alongshore extent of which is about 1.8. km, is composed of a total of 8 bars with lengths varying from 320. m to 1300. m and mean heights comprised between 0.5. m and 2.5. m. Bar cross-sections are variable between bars and for a single bar, and also over time. The surveys show a consistent northward migration of the bars at a mean rate of about 2. m/month, but the rate is larger in winter than in summer. The Lidar observations show that the tidal inlet, located at the southern limit of the bar field where the bars start forming, comprises a large sediment platform that acts as a source of sand for the bars. The ebb jet debouching from the inlet is deflected northward by the ambient strong shore-parallel tidal currents in this large tide-range setting, and this may be the primary mechanism leading to the emplacement of the bars. Smaller wave-formed swash bars that further feed the development of these large transverse bars have also been observed. Monitoring of bar migration in the course of six consecutive spring tides with fair-weather conditions showed that strong spring tidal currents are sufficient to drive bar mobility in the absence of waves. Storm wave resuspension of sand is thus expected to enhance bar mobility rates, as shown by the higher rates of winter bar migration compared to the summer rates. The ebb jet explains the slower bar migration rates at the vicinity of the inlet, these rates increasing with distance northward of the inlet as the tidal currents become unimpeded. The main difference between these macrotidal transverse bars and their counterparts in microtidal settings resides in these strong tidal currents that are the essential driver of bar migration, unlike the wave-driven migration of microtidal bars. The large tidal range, in conjunction with storm wave activity, also induces longshore and seasonal variability in bar morphology. The transverse bars of Normandy appear to be inscribed in a sand circulation system involving the west Cotentin coast, the large ebb tidal delta from which they are formed, and the central Cotentin embayment where they are ultimately incorporated into the nearshore sand pool. Longer-term field hydrodynamic monitoring and modelling will be required in order to further elucidate the mode of formation of these transverse bars. © 2013 Elsevier B.V.

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