The proliferating Gastropoda Crepidula fornicata may stimulate macrozoobenthic diversity
Since the late 19th century, the accidentally introduced Gastropoda Crepidula fornicata has been invading sheltered coastal waters of western Europe. The consequences of this proliferation on macrozoobenthic communities were studied in the Bay of Marennes-Oléron, France. Crepidula fornicata was found in a wide range of sediment grain sizes and depths, with however, a predilection for shallow muddy areas where abundance and biomass reached 4770 ind m−2 and 354 g DW m−2, respectively. Soft-sediment macrofaunal assemblages were compared in similar habitats, in the presence and absence of C. fornicata. In muddy and medium sand areas, abundance, biomass and species richness of macrofauna were generally greater in presence of C. fornicata, with Annelida dominating, although the differences were significant (P<0.05) only in one location out of five. The species composition was moderately different in the presence of C. fornicata. In coarse sand, the abundance of C. fornicata was low and did not affect abundance, biomass and species richness of the macrofauna. However, species composition differed where C. fornicata was absent, with a higher proportion of mobile Crustaceana. The effect of C. fornicata on benthic communities differs in relation to the habitat they colonize: in muddy sediments, the presence of C. fornicata apparently stimulates zoobenthic community diversity and abundance (mostly deposit-feeders), whereas in coarser sediments, macrofauna community is different (more suspension-feeders) from the community associated with C. fornicata.
(Journal of the Marine Biological Association of the United Kingdom. vol. 79, n° 0025-3154, pp. 1069-1077, 01/12/1999)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS
Présentation du logiciel SnB ( Shake and Bake ) Exemples d'applications
On présentera le principe de fonctionnement du programme de résolution de structures cristallographiques par méthode directe SnB (Shake and Bake) développé par une équipe de l'Université de Buffalo. Des exemples d'application aux petites protéines seront donnés, ainsi qu'à deux structures d'antibiotiques résolues au LMCP grâce à SnB. A cette occasion on passera rapidement en revue les caractéristiques de ces Pristinamycines.
(26/11/1999)
LMCP, UPMC, UPD7, IPG Paris, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Anomalous directions of the natural remanent magnetization in Late Pleistocene marine sediments from the coast of Mauritania (West Africa)
(Physics of the Earth and Planetary Interiors. vol. 115, n° 0031-9201, pp. 81-100, 01/09/1999)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GEOTRAC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Effects of metallic waterborne exposure of fisch (rainbow trout and carp) Implacations for radionuclide monitoring
(25/05/1999)
IRSN/PRP-ENV/SERIS/LECO, IRSN/PRP-ENV/SERIS, IRSN, UM2, INERIS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A comparison between oyster (Crassostrea gigas) and sea urchin (Paracentrotus lividus) larval bioassays for toxicological studies
The respective sensitivity of oyster (Crassostrea gigas) and sea urchin (Paracentrotus lividus) embryos and larvae to salinity, and to various micropollutants (four heavy metals, three pesticides) and to two polluted sediments were compared with a simplified bioassay method. C. gigas embryos and larvae were more sensitive to copper; the sensitivity of both species to tributyltin (TBT) was practically the same; P. lividus was more sensitive to lead and mercury. The only pesticide found to be toxic was a herbicide, Dinoterbe, to which oyster larvae were more sensitive than sea urchin plutei. Of the two sediments tested, the first one had effects on P. lividus embryogenesis only; C. gigas embryos and larvae were more affected by the second sediment which was originated from a harbour and was polluted by heavy-metals. The choice of species for biomonitoring may be based on biological considerations, such as the availability of mature adults for obtaining gametes, or on the salinity of the studied area; the oyster bioassay seems to be more suitable for coastal and estuarine brackish waters, because of the broader salinity tolerance of estuarine bivalve larvae as compared to sea urchin larvae.
(Water Research. vol. 33, n° 0043-1354, pp. 1706-1718, 01/05/1999)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Effect of intermediate host size (cerastoderma edule) on infectivity of cercariae of three himasthla species (echinostomatidae, trematoda)
To understand prevalence patterns of parasites in marine host populations experimental infection studies are required. Bivalves are important host organisms to a variety of trematodes species and in our study area (Wadden Sea) three different Himasthla species co-occur in cockle populations. These species are morphologically very similar but differ with respect to various morphometric dimensions. To study the possible functional importance of differences between Himasthla cercariae (the free-living stage shed from prosobranch snails and encysting as metacercariae in bivalves), we experimentally measured the infectivity of the three congeners in regard to different size groups of juvenile cockles. The smallest species, H. interrupta, has a high infectivity in small cockles (optimum around 4 mm), whereas the two other congeners H. continua and H. elongata exhibit low infection efficiencies in cockles less than 6 mm and higher efficiencies in larger cockles. Behavioural experiments were performed to identify proximate causes underlying the observed infection patterns. Parasite avoidance behaviour of the cockle varies in a host–parasite size-dependent manner so that a large cercaria tend to provoke an avoidance response in a small cockle. The possible consequences of the observed host size preferences in relation to definitive host species (waterbirds) are discussed and it is suggested that one or more of the parasite species are adapted to other host species and that their sympatric occurrence in cockles in our study area is a result of a spinoff from their main cycle mediated through migratory birds.
(Journal of Experimental Marine Biology and Ecology. vol. 238, n° 0022-0981, pp. 259-269, 01/05/1999)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Molecular gene organisation and secondary structure of the mitochondrial large subunit ribosomal RNA from the cultivated Basidiomycota Agrocybe aegerita: a 13 kb gene possessing six unusual nucleotide extensions and eight introns.
The complete gene sequence and secondary structure of the mitochondrial LSU rRNA from the cultivated Basidiomycota Agrocybe aegerita was derived by chromosome walking. The A.aegerita LSU rRNA gene (13 526 nt) represents, to date, the longest described, due to the highest number of introns (eight) and the occurrence of six long nucleotidic extensions. Seven introns belong to group I, while the intronic sequence i5 constitutes the first typical group II intron reported in a fungal mitochondrial LSU rDNA. As with most fungal LSU rDNA introns reported to date, four introns (i5-i8) are distributed in domain V associated with the peptidyl-transferase activity. One intron (i1) is located in domain I, and three (i2-i4) in domain II. The introns i2-i8 possess homologies with other fungal, algal or protozoan introns located at the same position in LSU rDNAs. One of them (i6) is located at the same insertion site as most Ascomycota or algae LSU introns, suggesting a possible inheritance from a common ancestor. On the contrary, intron i1 is located at a so-far unreported insertion site. Among the six unusual nucleotide extensions, five are located in domain I and one in domain V. This is the first report of a mitochondrial LSU rRNA gene sequence and secondary structure for the whole Basidiomycota division.
(Nucleic Acids Research. vol. 27, n° 0305-1048, pp. 1754-1761, 01/04/1999)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Chemical and isotopic constraints to varied formation processes for the brines of different deeps in the Red Sea.
Almost all Red Sea deeps contain metal-rich sediments covered by brine pools. It is generally agreed that these metal-rich deposits precipitated from overlying metal-rich brines that originated from migrating hydrothermal fluids. No brine pool has ever been reported in Thetis Deep, inciting us to evaluate if such a brine layer ever occurred in the deep during the past. In order to address that questioning, a study combining mineralogical, geochemical (major-, minor-, rare-earth elements) and isotopic (Sr. Nd. Pb) approaches was completed on cored sediments and extracted interstitial waters from inside and outside the deep.;The sediments have an overall hydrothermal origin, as shown by the REE concentrations and patterns, metal contents, and Pb-Nd isotopic data, all pointing to a mantle signature. The intensity of the hydrothermal activity varied with time in the deep; the most intense episode resulting in an almost pure Fe-oxi-hydroxide layer. Varied chemical arguments, especially the Zr and REE data of the sediments, favor the fact that the whole sedimentation in Thetis Deep occurred in the absence of a stable, salt-rich and mineralized brine pool, and that no brine layer ever existed. This conclusion is supported by the constant Sr isotope composition of the sediment and its interstitial waters that are almost identical to that of the Red Sea seawater. The study also suggests that hydrothermal activity monitored fluid supplies that interacted differently with seawater in the different Red Sea deeps, resulting in an overall formation of metal-rich sediments, but along varied local conditions. (C) 2009 Elsevier B.V. All rights reserved.
(28/03/1999)
LHyGeS, ENGEES, UNISTRA, INSU - CNRS, CNRS, UAG, INSU - CNRS, UM, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Does the slipper limpet (Crepidula fornicata, L.) impair oyster growth and zoobenthos biodiversity? A revisited hypothesis
The Prosobranch Gastropod Crepidula fornicata was introduced into Great Britain at the end of the 19th century from North America, upon imported oysters Crassostrea virginica. Since then, it has invaded sheltered coasts of the North West Atlantic and Mediterranean Sea. C. fornicata proliferation has often generated social conflicts due to three main causes: (1) trophic competition with other suspension feeders, e.g. the cultivated oyster Crassostrea gigas; (2) spatial competition with macrozoobenthos; and (3) enhancement of silt and clay sedimentation. The effects of C. fornicata on C. gigas growth and on macrozoobenthic density and diversity have been documented through field experiments in an oyster park of Arcachon Bay (France). Densities of C. gigas and biomass of C. fornicata were manipulated over a period of 247 days within field enclosures at low water level to test: (1) oyster growth, condition index and mortality; (2) zoobenthic community alterations (abundance, biomass, species richness). From this small-scale experiment, it was shown that none of these investigated parameters was significantly affected by the presence of C. fornicata. However, faunal assemblages were modified in enclosures compared to external bare sands, due to adding a hard substrata over a soft sediment.
(Journal of Experimental Marine Biology and Ecology. vol. 235, n° 0022-0981, pp. 105-124, 01/03/1999)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Fine-grained sediment budget on the continental margin of the Bay of Biscay
Under present-day conditions, rivers are the main source of fine sediments dispersed to the Bay of Biscay. They deliver about 2.5×10 6 t yr -1 of continental fine sediments, 60% of which is derived from the Gironde estuary. Of this flux, 65% is believed stored on the shelf. Two kinds of mud fields can be found in the Bay of Biscay: coastal mud and shelf mud belts. The total mass of fine sediments stored during the past 2000 years is 3.2×10 9 t. Consequently, about 0.9×10 6 t yr -1 could reach the shelf edge and eventually the open sea. From this amount of displaced material and the deposition surface areas, an evaluation of sediment fluxes across the margin during the late Holocene period is discussed. This evaluation is compared with results obtained from ECOsystéme du canyon du cap-FERret (ECOFER) data from sediment traps and surficial box cores.
(Deep Sea Research Part II: Topical Studies in Oceanography. vol. 46, n° 0967-0645, pp. 2205-2220, 18/05/1999)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS