Impact of freshwater on a subarctic coastal ecosystem under seasonal sea ice (southeastern Hudson Bay, Canada) : 3. Feeding success of marine fish larvae

We monitored the feeding success (percent feeding incidence at length and mean feeding ratio at length) of Arctic cod (#Boreogadus saida) and sand lance (#Ammodytes sp. larvae in relation to prey density, light, temperature and potential predator density under the ice cover of southeastern Hudson Bay in the spring of 1988, 1989 and 1990. Both prey density and light limited larval fish feeding. The relationship between feeding success and actual food availability (nauplii density x irradiance) was adequately described by an Ivlev function which explained 64 and 76% of the variance in Arctic cod and sand lance feeding success respectively. By affecting both prey density and irradiance, the thickness of the Great Whale River plume (as defined by the depth of the 25 isohaline) was the main determinant of prey availability. Arctic cod and sand lance larvae stopped feeding when the depth of the 25 isohaline exceeded 9 m. Limitation of feeding success attributable to freshwater inputs occurred exclusively in 1988, the only time when the depth of the 25 isohaline exceeded the 9 m threshold. The close dependence of larval fish feeding success on the timing of the freshet and plume dynamics suggests a direct link between climate and survival of Arctic cod and sand lance larvae. The actual impact of climate fluctuations and/or hydro-electric developments on recruitment will depend on the fraction of the larval dispersal area of the two species that is affected by river plumes. (Résumé d'auteur

Cartographie AMT du biseau salé sur le flanc sud du Piton de la Fournaise (Ile de la Réunion)

Dans le secteur du Baril, situé sur la planèze sud du volcan de la Fournaise, l'interprétation unidimensionnelle (1-D) de 34 sondages AMT montre une séquence à trois terrains, avec disparition du deuxième dans la zone côtière. Cette séquence comprend un horizon supérieur résistant (> 1000 Ohm.m), un horizon intermédiaire plus conducteur (100 à 600 Ohm.m), et un substratum très conducteur (< 10 Ohm.m). Les résistivités obtenues permettent d'assimiler ce substratum au biseau salé. Les variations importantes dans la topographie du toit du biseau salé apportent des données nouvelles concernant les phénomènes de pénétration saline dans les aquifères volcaniques et, indirectement, une meilleure connaissance de la géométrie et du fonctionnement de l'aquifère sus-jacent. (Résumé d'auteur

The secretion inhibitor Exo2 perturbs trafficking of Shiga toxin between endosomes and the trans-Golgi network

The small-molecule inhibitor Exo2 {4-hydroxy-3-methoxy-(5,6,7,8-tetrahydrol[1]benzothieno[2,3-d]pyrimidin-4-yl)hydraz-one benzaldehyde} has been reported to disrupt the Golgi apparatus completely and to stimulate Golgi–ER (endoplasmic reticulum) fusion in mammalian cells, akin to the well-characterized fungal toxin BFA (brefeldin A). It has also been reported that Exo2 does not affect the integrity of the TGN (trans-Golgi network), or the direct retrograde trafficking of the glycolipid-binding cholera toxin from the TGN to the ER lumen. We have examined the effects of BFA and Exo2, and found that both compounds are indistinguishable in their inhibition of anterograde transport and that both reagents significantly disrupt the morphology of the TGN in HeLa and in BS-C-1 cells. However, Exo2, unlike BFA, does not induce tubulation and merging of the TGN and endosomal compartments. Furthermore, and in contrast with its effects on cholera toxin, Exo2 significantly perturbs the delivery of Shiga toxin to the ER. Together, these results suggest that the likely target(s) of Exo2 operate at the level of the TGN, the Golgi and a subset of early endosomes, and thus Exo2 provides a more selective tool than BFA for examining membrane trafficking in mammalian cells

Spatial and temporal variability in coccolithophore abundance and distribution in the NW Iberian coastal upwelling system

A systematic investigation of the spatial and temporal variability in coccolithophore abundance and distribution through the water column of the NW Iberian coastal up-welling system was performed. From July 2011 to June 2012, monthly sampling at various water depths was conducted at two parallel stations located at 42 degrees N. Total coccosphere abundance was higher at the outer-shelf station, where warmer, nutrient-depleted waters favoured coccolithophore rather than phytoplanktonic diatom blooms, which are known to dominate the inner-shelf location. In seasonal terms, higher coccosphere and coccolith abundances were registered at both stations during upwelling seasons, coinciding with high irradiance levels. This was typically in conjunction with stratified, nutrient-poor conditions (i.e. relaxing upwelling conditions). However, it also occurred during some upwelling events of colder, nutrient-rich subsurface waters onto the continental shelf. Minimum abundances were generally found during downwelling periods, with unexpectedly high coccolith abundance registered in subsurface waters at the inner-shelf station. This finding can only be explained if strong storms during these downwelling periods favoured resuspension processes, thus remobilizing deposited coccoliths from surface sediments, and hence hampering the identification of autochthonous coccolithophore community structure. At both locations, the major coccolithophore assemblages were dominated by Emiliania huxleyi, small Gephyrocapsa group, Gephyrocapsa oceanica, Florisphaera profunda, Syracosphaera spp., Coronosphaera mediterranea, and Calcidiscus leptoporus. Ecological preferences of the different taxa were assessed by exploring the relationships between environmental conditions and temporal and vertical variability in coccosphere abundance. These findings provide relevant information for the use of fossil coccolith assemblages in marine sediment records, in order to infer past environmental conditions, of particular importance for Paleoceanography. Both E. huxleyi and the small Gephyrocapsa group are proposed as proxies for the upwelling regime with a distinct affinity for different stages of the upwelling event: E. huxleyi was associated with warmer, nutrient-poor and more stable water column (i.e. upwelling relaxation stage) while the small Gephyrocapsa group was linked to colder waters and higher nutrient availability (i.e. early stages of the upwelling event), similarly to G. oceanica. Conversely, F. profunda is suggested as a proxy for the downwelling regime and low-productivity conditions. The assemblage composed by Syracosphaera pulchra, Coronosphaera mediterranea, and Rhabdosphaera clavigera may be a useful indicator of the presence of subtropical waters conveyed northward by the Iberian Poleward Current. Finally, C. leptoporus is proposed as an indicator of warmer, saltier, and oligotrophic waters during the downwelling/winter regime.EXCAPA project - Xunta de Galicia [10MDS402013PR]; CALIBERIA project (Fundacao para a Ciencia e a Tecnologia - Portugal) [PTDC/MAR/102045/2008]; CALIBERIA project [COMPETE/FEDER-FCOMP-01-0124-FEDER-010599, BI/PTDC/MAR/102045/2008/2010-016, BI/PTDC/MAR/102045/2008/2010-022, BI/PTDC/MAR/102045/2008/2011-027]; Ministerio de Economia y Competitividad [CGL2015-68459-P]; Ministry of Education of Spain [AP2010-2559]; ETH Zurich Postdoctoral Fellowship from the Swiss Federal Institute of Technology in Zurich (ETHZ); Xunta de Galicia (Spain); FCT [SFRH/BPD/111433/2015]; Plurianual/Estrategico project [UID/Multi/04326/2013]info:eu-repo/semantics/publishedVersio

The assessment of neuromuscular fatigue during 120 min of simulated soccer exercise

Purpose This investigation examined the development of neuromuscular fatigue during a simulated soccer match incorporating a period of extra time (ET) and the reliability of these responses on repeated test occasions. Methods Ten male amateur football players completed a 120 min soccer match simulation (SMS). Before, at half time (HT), full time (FT), and following a period of ET, twitch responses to supramaximal femoral nerve and transcranial magnetic stimulation (TMS) were obtained from the knee-extensors to measure neuromuscular fatigue. Within 7 days of the first SMS, a second 120 min SMS was performed by eight of the original ten participants to assess the reliability of the fatigue response. Results At HT, FT, and ET, reductions in maximal voluntary force (MVC; −11, −20 and −27%, respectively, P ≤ 0.01), potentiated twitch force (−15, −23 and −23%, respectively, P < 0.05), voluntary activation (FT, −15 and ET, −18%, P ≤ 0.01), and voluntary activation measured with TMS (−11, −15 and −17%, respectively, P ≤ 0.01) were evident. The fatigue response was robust across both trials; the change in MVC at each time point demonstrated a good level of reliability (CV range 6–11%; ICC2,1 0.83–0.94), whilst the responses identified with motor nerve stimulation showed a moderate level of reliability (CV range 5–18%; ICC2,1 0.63–0.89) and the data obtained with motor cortex stimulation showed an excellent level of reliability (CV range 3–6%; ICC2,1 0.90–0.98). Conclusion Simulated soccer exercise induces a significant level of fatigue, which is consistent on repeat tests, and involves both central and peripheral mechanisms

Debris avalanches on the western flank of Piton des Neiges shield volcano (Reunion Island)

Les faciès bréchiques reconnus à terre dans la région littorale de Saint-Gilles, sur le flanc ouest du volcan Piton des Neiges, sont clairement identifiés comme des dépôts d’avalanche de débris. Leur étude pétrographique, texturale et structurale permet de montrer, grâce à la présence de coulées autochtones interstratifiées, qu’au moins quatre glissements successifs se sont produits. Le premier est de grande ampleur puisqu’il affecte la zone centrale hydrothermalisée du volcan. Il est proposé que ce premier glissement, favorisé par la présence de matériaux ayant subi une importante altération hydrothermale, crée une zone d’instabilité qui influe sur le comportement ultérieur du Piton des Neiges. Dans ce même secteur, les glissements postérieurs concernent uniquement des domaines plus superficiels, mettant en jeu des matériaux non hydrothermalisés et vacuolaires. La bréchification des formations, et en particulier la désagrégation progressive des “blocs” durant le transport de l’avalanche de débris, implique une vitesse de progression élevée. Dans la zone du Cap La Houssaye, l’abrasion et la striation des formations laviques situées sous les unités bréchiques, ainsi que les phénomènes de tassement observés, sont interprétés comme des figures d’arrêt de l’avalanche

Benthic oxygen fluxes in a coastal upwelling system (Ria de Vigo, NW Iberia) measured by aquatic eddy covariance

Organic carbon mineralization and nutrient cycling in benthic environments are critically important for their biogeochemical functioning, but are poorly understood in coastal up - welling systems. The main objective of this study was to determine benthic oxygen fluxes in a muddy sediment in the Ria de Vigo (NW Iberian coastal upwelling), by applying the aquatic eddy covariance (AEC) technique during 2 campaigns in different seasons (June and October 2017). The main drivers of benthic fluxes were studied and compared among days in each season and between seasons. The 2 campaigns were characterized by an upwelling-relaxation period followed by a downwelling event, the last of which was due to the extratropical cyclone Ophelia in October. The mean (±SD) seasonal benthic oxygen fluxes were not significantly different for the 2 campaigns despite differences in hydrodynamic and biogeochemical conditions (June: -20.9 ± 7.1 mmol m-2d-1vs. October: -26.5 ± 3.1 mmol m-2d-1). Benthic fluxes were controlled by different drivers depending on the season. June was characterized by sinking labile organic material, which enhanced benthic fluxes in the downwelling event, whereas October had a significantly higher bottom velocity that stimulated the benthic fluxes. Finally, a comparison with a large benthic chamber (0.50 m2) was made during October. Despite methodological differences between AEC and chamber measurements, concurrent fluxes agreed within an acceptable margin (AEC:benthic chamber ratio = 0.78 ± 0.13; mean ± SD). Bottle incubations of water sampled from the chamber interior indicated that mineralization could explain this difference. These results show the importance of using non-invasive techniques such as AEC to resolve benthic flux dynamicsPostprin