Diel and seasonal variations in abundance, activity, and structure of particle-attached vs free-living bacterial communities were investigated in offshore NW Mediterranean Sea (0-1000 m). Attached ...bacteria were always less abundant and less diverse but generally more active than free-living bacteria. The most important finding of this study was that the activity of attached bacteria showed pronounced diel variations in the upper mixed water column with higher activities at night. Under mesotrophic conditions, the contribution of attached bacteria to total bacterial activity increased from less than 10% at day time to 83% at night time. At high chlorophyll a concentration, the highest cell-specific activities and contribution to total bacterial activity were due to free-living bacteria at day and to attached bacteria at night. Under summer oligotrophic conditions, free-living bacteria dominated and contributed to the most important part of the bacterial activity at both day and night, whereas attached bacteria were much less abundant but presented the highest cell-specific activities. These diel and seasonal variations in activities were concomitant to changes in bacterial community structure, mainly in the upper layer. The number of attached ribotypes was fairly constant suggesting that particles are colonized by a relatively limited number of ubiquitous ribotypes. Most of these ribotypes were also free-living ribotypes suggesting that attached bacteria probably originate from colonization of newly formed particles by free-living bacteria in the upper layer. These results reinforce the biogeochemical role of attached bacteria in the cycling of particulate organic carbon in the NW Mediterranean Sea and the importance of diel variability in these processes.
An integrated analysis of the pelagic ecosystems of the Ligurian Sea is performed combining time series (1995–2005) of several zooplankton groups (one group for copepods smaller than 0.724 mm3 and ...nine groups for individuals larger than 0.724 mm3, i.e. large copepods, decapod larvæ, other crustaceans, chaetognaths, appendicularians, pteropods, thaliaceans, gelatinous predators and other zooplankton), chlorophyll-a, nutrients, salinity, temperature, density, and local weather at Point B coastal station (Northern Ligurian Sea). From 1995 to 2000 winters were wet and mild resulting in lower winter sea surface density. These years showed lower than average nutrients and zooplankton concentrations while chlorophyll-a biomass was high. After 2000, winters were colder and dryer resulting in higher sea surface density. Nutrients and zooplankton showed higher concentrations while chlorophyll-a was lower than average. The ca. 2000 change was observed for most zooplankton groups with a one-year delay for some groups. Inter-annual variability within each period was also observed. The observed patterns suggest that the pelagic ecosystem trophic state at the studied point is mostly set by the winter forcing on the vertical mixing that upwells nutrients to the surface sustaining primary production. Surprisingly, low chlorophyll-a biomass in high nitrate and zooplankton conditions during the well mixed years suggest that phytoplankton biomass is controlled by grazers. The proposed mechanisms of stronger winter vertical mixing hold for most of the time series, but specific years with contradicting patterns suggest also the possible influence of the summer climate. A review of recent literature suggests that changes in the pelagic ecosystem are not limited to the studied site but concern also the central Ligurian Sea.
Lipid class profiles and total fatty acid composition of particulate matter were studied in the northeast Atlantic during the spring bloom and fall. Eddies of known physical and chemical properties ...were sampled at different depths. HPLC pigment data were used to characterize the phytoplankton communities. In spring, a dominance of prymnesiophytes was recorded at all depths, while in fall prochlorophytes dominated near the surface and prymnesiophytes only at deep chlorophyll maximum. Lipid classes included triglycerides, sterols, glycolipids and phospholipids. A differential relationship between phytoplankton abundance and lipid accumulation was observed: spring lipid concentrations were positively related to phytoplankton biomass, while fall particulate lipid did not show any relationship. The main feature was a northward increase in lipid concentrations unrelated to the mesoscale hydrological structures. Polar lipids dominated over neutral acyl-glycerols with phospholipids dominating over glycolipids in spring, while glycolipids dominated in fall. This resulted from different nutrient availability with a dominance of flagellates associated with mesotrophy in spring and of picophytoplankton associated with oligotrophy in fall. In terms of fatty acids, factorial correspondence analyses illustrate the influence of seasonally changing assemblages: (1) in spring, the main source of variability was the bloom with an opposition between bloom sites characterized by n-3 and n-6 PUFA, and more detrital deep samples characterized by saturated, monoenoic and branched acids; (2) fall fatty acid profiles were similar at all depths and very close to those observed for spring deep samples. Comparison of pigment and fatty acids using redundancy analysis suggested that pelagophytes were linked to saturated and branched acids. It also showed that prymnesiophytes and prochlorophytes were significantly associated with n-6 and n-3 PUFA. The spring period illustrated the complexity of these relationships with dinoflagellates and prymnesiophytes linked with n-3 PUFA, diatoms linked with palmitoleic and myristic acids, and pelagophytes linked with n-6 PUFA and higher-chain-length monoenes.
Short term changes in zooplankton community were investigated at a fixed station in offshore waters of the Ligurian Sea (DYNAPROC 2 cruise, September–October 2004). Mesozooplankton were sampled with ...vertical WP-II hauls (200 μm mesh-size) and large mesozooplankton, macrozooplankton and micronekton with a BIONESS multinet sampler (500 μm mesh-size). Temporal variations of total biomass, species composition and abundance of major taxa were studied. Intrusions of low salinity water masses were observed two times during the cruise. The first one, which was the most intense, was associated with changes in zooplankton community composition. Among copepods, the abundance of Calocalanus, Euchaeta, Heterorhabdus, Mesocalanus, Nannocalanus, Neocalanus, Pleuromammaand also calanoid copepodites increased markedly. Among non-copepod taxa, only small ostracods abundance increased. After this low salinity event, abundance of all taxa nearly returned to their initial values. The influence of salinity on each zooplankton taxon was confirmed by a statistical analysis (Perry's method). The Shannon diversity index, Pielou evenness and species richness were used to describe temporal variations of large copepod (>500 μm) diversity. The Shannon index and Pielou evenness decreased at the beginning of the low salinity water intrusions, but not species richness. We suggest that low salinity water masses contained its own zooplankton community and passed through the sampling area, thus causing a replacement of the zooplankton population.
Évaluation d’un nouveau test : Acaritest® pour la recherche des allergènes d’acariens dans des poussières caractérisées par dosages Elisa.
Trente-deux échantillons de poussières ont été ...sélectionnés sur la base d’une concentration en Derp 1 et Derf 1 supérieure au seuil de détection du dosage Elisa (0,039μg/g). Les recueils de poussières étaient réalisés selon les recommandations internationales. L’Acaritest® est une méthode immunochromatographique. L’échantillon migre dans une membrane de nitrocellulose et l’intensité de la réponse est proportionnelle à la quantité d’allergènes présente. Les résultats sont interprétés en comparant la ligne test (T) à la ligne contrôle (C) :
– T>C : taux important d’acariens (>2μg d’allergènes du groupe 1/g de poussière) ;
– T<C : faible taux d’acariens (<2μg d’allergènes du groupe 1/g de poussière).
Les tests ELISA et Acaritest® ont été réalisés selon les recommandations des fabricants.
Selon l’Acaritest, 25 poussières ont un taux important d’allergènes d’acariens, parmi elles 17 présentent une concentration>2μg/g en ELISA et 8 une concentration comprise entre 0,97 et 1,76μg/g. Les 7 poussières avec un taux d’allergènes d’acariens faible selon Acaritest, présentent des concentrations<0,37μg/g en Elisa.
Acaritest® semble un dispositif intéressant pour évaluer l’exposition des patients, mais des essais complémentaires devront le confirmer. En effet, la mesure de l’exposition aux allergènes d’acariens est un élément important dans le diagnostic de l’allergie aux acariens et dans le suivi des mesures d’éviction.
Adhesively bonded glass-epoxy lap joints are transversely impacted in order to determine the modes of damage resulting from out-of-plane impacts to the overlap region and to identify mechanisms by ...which damage formation occurs. Impacts over an energy range of 10-50 J are produced using a low-velocity, highmass drop weight tower. Woven glass-epoxy joints bonded together with an epoxy adhesive film are tested. Localized debonding is observed for lower energy impacts in the region surrounding the impact point. These debonds, attributed to the transverse shear stress developed within the adhesive, are typically circular and concentric to the impact point, and can exist in the absence of debonds growing from the joint free edges (overlap boundaries). Debonds growing from the free edges initiate at the backside of the specimen (i.e., away from the impact side) where tensile peel stress in combination with shear stress causes failure of the adhesive at this location. Finite element analysis is used to determine the stresses that develop in the adhesive during impact, and to corroborate experimentally based conclusions on the mechanisms of damage formation. For bonded joint impacts, it is possible to experimentally establish damage threat thresholds at which impact damage initiates. Such thresholds are important for joint design, and also when making decisions related to the maintenance and repair of composite bonded joints. This is an important safety feature of bonded composite structures since partial joint-width debonding can occur at moderate impact energy levels, and the resulting damage is difficult (perhaps impossible) to detect by visual inspection.
The semi-enclosed nature of the Mediterranean Sea, together with its smaller inertia due to the relative short residence time of its water masses, make it highly reactive to external forcings, in ...particular variations of water, energy and matter fluxes at the interfaces. This region, which has been identified as a “hotspot” for climate change, is therefore expected to experience environmental impacts that are considerably greater than those in many other places around the world. These natural pressures interact with the increasing demographic and economic developments occurring heterogeneously in the coastal zone, making the Mediterranean even more sensitive. This review paper aims to provide a review of the state of current functioning and responses of Mediterranean marine biogeochemical cycles and ecosystems with respect to key natural and anthropogenic drivers and to consider the ecosystems’ responses to likely changes in physical, chemical and socio-economical forcings induced by global change and by growing anthropogenic pressure at the regional scale. The current knowledge on and expected changes due to single forcing (hydrodynamics, solar radiation, temperature and acidification, chemical contaminants) and combined forcing (nutrient sources and stoichiometry, extreme events) affecting the biogeochemical fluxes and ecosystem functioning are explored. Expected changes in biodiversity resulting from the combined action of the different forcings are proposed. Finally, modeling capabilities and necessity for modeling are presented. A synthesis of our current knowledge of expected changes is proposed, highlighting relevant questions for the future of the Mediterranean ecosystems that are current research priorities for the scientific community. Finally, we discuss how these priorities can be approached by national and international multi-disciplinary research, which should be implemented on several levels, including observational studies and modeling at different temporal and spatial scales.
Coastal marine ecosystems, which play a crucial role in the biogeochemical and ecological functioning of the Earth, are highly sensitive to the combined effects of climate and human activities. ...Because of their location, coastal ecosystems are directly influenced by human activities, but it remains challenging to assess the spatial and temporal scales at which climate influences coastal ecosystems. We monitored 12 sampling stations, distributed in 8 ecosystems in France, over 2 decades for physico-biogeochemical parameters (temperature, salinity, concentrations of dissolved oxygen, nutrients and particulate material). The study encompasses a large diversity of temperate coastal ecosystems with respect to e.g. geomorphology, trophic status, tidal regime, river influence and turbidity. Time-series analysis coupled with standardised 3-mode principal component analyses, partial triadic analyses and correlations were used to assess bi-decadal variability and ecosystem trajectories, and to identify large-scale, regional and local drivers. Our results highlighted 2 abrupt changes in 2001 and 2005. The bi-decadal changes were related to changes in large-scale and regional climate, detected through proxies of temperature and atmospheric circulation, as well as through river discharge. Ecosystem trajectories tended to move towards an increase in temperature and salinity, and/or a decrease in chlorophyll
a
, nutrients and particulate matter. However, the magnitude of change, the year-to-year variability and the sensitivity to the 2001 and 2005 changes varied among the ecosystems. This study highlights the need for establishing long-term time series and combining data sets as well as undertaking multi-ecosystem and local studies to better understand the long-term variability of coastal ecosystems and its associated drivers.
We examined the mesoscale distribution of zooplankton populations using a continuous recording system: the optical plankton counter (OPC). Data were collected in the mid-latitude northeast Atlantic ...inter-gyre region in April and September 2001 during the P
OMME 2 and P
OMME 3 cruises. This sector of the North Atlantic system is characterized by subduction phenomena and mesoscale eddies. Estimated mean biomass was 2.88
DW
g
m
−2 in April and 1.64
DW
g
m
−2 in September with populations dominated by small copepods of the genera,
Clausocalanus,
Paracalanus and
Oithona. Day–night changes in vertical distribution appeared to be seasonally variable. During April, absolute concentrations within the upper layer above 50
m were higher at night. During September, vertical profiles of relative biomass were quite similar for day and night. Highest depth-integrated biomasses were located mainly on the periphery of anticyclonic eddies, with maxima related to the increase in depth range of vertical distribution. This pattern suggested that maximum biomass was associated with the most dynamic parts of the frontal features. Other zones of high zooplankton biomass were associated with the centers of cyclonic eddies and high fluorescence values. Using a 3D view, we found that zooplankton distribution showed a more complex pattern than in a 2D view with variable vertical distribution. Hence, proper description of the distribution of zooplankton underlines the need to describe this submesoscale with an order of magnitude around 10 nautical miles.
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