Variations in food intake of Pecten maximus (L.) from the Bay of Brest (France): influence of environmental factors and phytoplankton species composition

International audienc

Modeling surface defects in fused silica optics for laser wave propagation

International audienceModulation of the laser intensity caused by surface defects on optical components is a main concern for high-power lasers. Among the consequences of this effect, the laser damage occurrence can be magnified on the downstream components in the laser chain. In order to understand the impact of defects on wave propagation, a specific numerical approach has been developed. The defects are modeled as phase perturbations that are used as inputs in either a 1D axi-symmetric code based on finite differences or a 2D code that uses fast Fourier transform. The computations are then used to evaluate the laser intensity modulations generated by CO 2 laser-induced defects at the surface of fused silica optics. A dedicated damage experiment at 355 nm has been carried out for various defect dimensions. Consistent results are found between experiments and simulations, both on the quantitative values of magnitude and positions of the modulations. This study proves that, for short propagation distances, it is necessary to use the exact shape of the defect in the simulations, especially the complex rim structure characteristic of CO 2 laser craters

Understanding virulence and pathogenesis in controlled conditions: The case of brown ring disease causing immunodepression in clams

International audienc

Deepwater mantle 3 He plumes over the northern Mid-Atlantic Ridge (36°N-40°N) and the Azores Platform

International audienceAs part of a multidisciplinary project aimed at studying mid-ocean ridge processes near the Azores, fifty water column profiles were analyzed for 3 He/ 4 He ratios in dissolved helium (a well-known hydrothermal tracer) from 36°N to 40°N along the Mid-Atlantic Ridge (MAR) and over the Azores Plateau. As expected, large d 3 He anomalies could be observed over the Rainbow, Lucky Strike, and Menez Gwen hydrothermal sites. The main finding of the present study is the discovery of a large hydrothermal 3 He plume north of the Açor Fracture Zone (north AFZ site), with a CH 4 / 3 He ratio indicative of a basaltichosted hydrothermal system. Clear 3 He and CH 4 anomalies, likely corresponding to unknown venting sites too, were also detected in the Amar Minor segment and south of the Kurchatov Fracture Zone. Evidence for substantial mantle helium degassing was also observed in the deep nodal basins along the Terceira Rift. On the basis of 3 He plumes over the total length of the surveyed segments, the distribution of hydrothermal sites corresponds to a site frequency of 1.3 ± 0.2 site/100 km, in good agreement with the global vent field statistics of Baker and German (2004). For the Rainbow, Lucky Strike, and Menez Gwen sites, the application of a plume model based on the conservation of mass, heat, and momentum shows that the heat output computed by the model is only an estimation of the heat released by the focused part of the flow imputable to one single vent. Applied to the north AFZ venting site for which the height of the plume is not known precisely, the model does not allow us to discriminate between a Menez Gwen/Rainbow type of venting or a more focused vent complex such as the one observed at the TAG site (26°N)

Differential d¹³C and d¹⁵N signatures among scallop tissues: implications for ecology and physiology

There have been several studies where the isotopic composition of organisms has been determined seasonally, but fewer have examined separate organs. In this context, separate organs (e.g. gonad, digestive gland and muscle) of a suspension-feeder, the scallop Pecten maximus, were used to assess seasonal changes of both stable isotopes and biochemical components. Our study used multiple indicators [stable carbon and nitrogen isotope ratios, biochemical components and seston chlorophyll-a (chl a)] to track nutritive activity and energy allocation in P. maximus from the Bay of Brest (France). In addition to seasonal variation in the isotopic composition of P. maximus tissues, we found strong differences in the mean isotopic signatures of different organs. This has serious implications for interpretation of animal diets and potential use in animal physiology. Furthermore, we present evidence that seasonal variations of metabolism will cause changes in the isotopic composition not related to changes in the diet. Interpretation of isotopic data may require consideration of values from several separate organs. Finally, d15N appears powerful to track metabolite fates in the scallop P. maximus

Observations of plankton communities in the Senegalese upwelling system

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201

Observations of plankton communities in the Senegalese upwelling system

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201

International conference ICAWA 2016 : extended book of abstract : the AWA project : ecosystem approach to the management of fisheries and the marine environment in West African waters

Two main reason make phytoplankton communities' key components of upwelling ecosystems. First of all they are closely linked to small pelagic fish which are microphageaous planktivores and dominate these oceanic provinces. They are also tightly coupled to physical and chemical conditions and hence very sensitive to climate change. During the last 5 years a significant effort of observation of these communities has been conducted in the Senegalese coastal waters. During five field trips conducted over the last 5 years (4 during the upwelling season and one at the end of the rainy season), we collected concentrations through underway fluorimetry (Scanfish ondulating vehicule, ship fluorometer, fluoroprobe), ocean colour and pigment analyses (HPLC, cytometry). The phytoplankton biodiversity was studied through pigments, microscope taxonomy and metagenomics. We will present here an overview of the different analysis and the actual results obtained in the southern Senegal coastal region

Changes in motility, ATP content, morphology and fertilisation capacity during the movement phase of tetraploid Pacific oyster [i](Crassostrea gigas)[/i] sperm

Changes in sperm features during the movement phase are especially interesting to study in external fertilization species whose sperm duration movement is long because this implies a significant adaptation of moving cells to the external medium. This study describes the changes in tetraploid Pacific oyster sperm characteristics in relation to time post activation. Sperm individually collected on three tetraploid males were activated in seawater. Their features were analysed over a 24 h period and compared to a sperm pool collected on three diploid males as a reference. The percentage of motile spermatozoa, the intracellular ATP content, and the fine structure of spermatozoa were studied in relation to time post activation. Furthermore, the fertilisation capacity of sperm individually collected on five diploid males was assessed after 1 and 24 h post activation. A forward progressive movement was maintained for at least a 20 h duration. Compared to diploid males, the percentage of motile spermatozoa was lower in tetraploid males. The intracellular ATP concentration was higher in spermatozoa from tetraploid males than in spermatozoa from diploid males. A decrease in ATP content was observed in the first 6 h post activation and severe alterations were observed in sperm morphology after 24 h. Then, a lower fertilisation capacity of sperm from diploid males was observed at the end of the movement phase. The cessation of Pacific oyster sperm motility was unlikely caused by ATP consumption as ATP concentration was still high at the end of sperm movement but rather caused by drastic changes in sperm morphology. Compared to sperm collected on diploid males, the lower quality of sperm from tetraploid males was emphasized by a shorter movement duration and deeper morphological alterations at the end of the movement phase. (C) 2010 Elsevier Inc. All rights reserved

Marathon vs sprint racers: an adaptation of sperm characteristics to the reproductive strategy of Pacific oyster, turbot and seabass

International audienceThis work assesses the present knowledge on Pacific oyster sperm biology in comparison to two marine fish species (turbot and seabass) whose sperm characteristics are well described. Sperm morphology mainly differs by the presence of an acrosome in Pacific oyster which is absent in both fish species. In turbot as in Pacific oyster, a sperm 'maturation process' along the genital tract is observed. Sperm motility is triggered by changes in osmolality for seabass and turbot and in pH for Pacific oyster. However, complementary factors are involved to maintain sperm immotile in the genital tract. Sperm movement duration is very long in Pacific oyster (20-24 h), compared to turbot (3-5 min) and seabass (40-50 s). A high capacity of ATP regeneration is observed in Pacific oyster sperm, sustained by the limited changes in its morphology observed at the end of the swimming phase. Then, the total distance covered by spermatozoa is very different among the studied species (seabass: 2 mm, turbot: 12 mm, Pacific oyster: 1 m). Considering the main characteristics of sperm movement, the three studied species can be separated in two groups: the sprint racer group (seabass: high velocity and short distance covered) and the marathonian racer one (Pacific oyster: low velocity but covering long distances). To an intermediate extent, turbot sperm belongs to the sprint racer group. Then, the two different sperm movement strategies observed in the three species, are compensated by the behaviour of the breeders