Goldmining and mercury contamina- tion of freshwater systems in French Guiana : a statistical analysis based on the piscivorous fish Hoplias aimara
(22/03/2001)
LMBA, UBS, UBO EPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UB
Why does the introduced gastropod Crepidula fornicata fail to invade Arcachon Bay (France)?
Arcachon Bay was the last important shell culture area of the French Atlantic coast without a stock assessment of the accidentally introduced Crepidula fornicata (Gastropoda). Following a stratified sampling strategy, 205 stations were sampled with a dredge. The total biomass of C. fornicata was estimated at 155 tn (confidence limits: 72 tn) scattered on 2·4 km2, i.e. about 5% of the infralittoral area. This biomass is very low compared to other exploited shellfish sites. Amongst mean environmental parameters (such as bathymetry, temperature, salinity, sediment grain-size, anthropic activity), the major keyfactors differentiating Arcachon Bay from other French sites were searched to explain the differences in C. fornicata colonization pattern. It seems that the low biomass of C. fornicata, 30 y after its occurrence was first recorded in the bay, could be correlated to: (1) the scarcity of subtidal muddy sediments which are suitable for C. fornicata settlement; (2) the presence of large Zostera spp. beds on both intertidal and subtidal areas; and (3) the absence of bottom trawl fishing. Growth, production and productivity (P/B) ratios were compared between five stations characterized by different hydrological and sediment parameters. Growth and productivity (0·3 y−1) were not affected by mean biomass suggesting a lack of population regulation by intraspecific competition.
(Journal of the Marine Biological Association of the United Kingdom. vol. 81, n° 0025-3154, pp. 97-104, 01/02/2001)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
LES SYSTEMES TURBIDITIQUES PROFONDS DE LA MARGE CELTIQUEARMORICAINE (GOLFE DE GASCOGNE) : PHYSIOGRAPHIE ET EVOLUTION AU COURS DES DERNIERS 30 000 ANS
Ce travail, basé sur l'analyse et l'interprétation de données acoustiques (sismique 3.5 kHz et multifaisceaux EM12) et de prélèvements (carottes Kullenberg), propose une reconstruction du fonctionnement sédimentaire récent (derniers 30 000 ans) du domaine profond de la Marge Celtique-Armoricaine. Les résultats obtenus ont permis d'interpréter l' ensemble des systèmes turbiditiques localisés au sein de la marge, comme un système multi-source de type "rampe". En effet, contrairement à la majorité des systèmes turbiditiques modernes, alimentés par une source ponctuelle, le domaine profond de la Marge Celtique-Armoricaine semble équitablement alimenté et abrite plusieurs systèmes turbiditiques de taille réduite, localisés au débouché de chaque canyon majeur. L' analyse détaillée des facièse t séquences sédimentaires a permis de mettre en évidence un fonctionnement sédimentaire lié aux conditions environnementales régnant au sein de la plateforme continentale Celtique. En bas niveau marin, la position du Delta de la Mer Celtique associé à de forts courants tidaux, semble représenter le facteur dominant contrôlant les apports sédimentaires vers le domaine profond. Cette configuration a entraîné, au cours du Stade isotopique 2, d' importants apports sédimentaires d' origine fluv-dioeltaïque qui se sont traduits par des séquences turbiditiques argilo-silteuses déposées sur les levées. En haut niveau marin, malgré la disparition de la totalité des réseaux hydrographiques, des apports sableux récents témoignent d' une alimentation épisodique du domaine profond. Ces apports, mis en évidence par des niveaux sableux centimétriques à métriques intercalés dans des argiles d' origine hémipélagique, témoignent d' écoulements turbiditiques de haute densité. Ce deuxième type de fonctionnement semble lié à la présence de corps sableux tidaux localisés sur la plateforme externe, ainsi qu' au transport sableux résiduel, orienté actuellement pour l' ensemble de la Mer Celtique vers le rebord de pente.
(05/01/2001)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The deep-sea Armorican depositional system (Bay of Biscay), a multiple source, ramp model
The deep-sea Armorican depositional system, located in the central part of the Bay of Biscay, is a medium-sized turbidite system with a surface area of more than 30,000 km2. The whole system is a mud/sand-rich submarine ramp on a passive margin. The medial ramp is characterised by the presence of six distinct tributary channels which form three systems: the Guilcher, Crozon and Cornouaille systems. The distal ramp corresponds to divergent braided secondary channels and associated lobes. Variations in hydrodynamic conditions on the outer Armorican Shelf during the last climatic cycle are the major factor controlling facies shifts and system growth. Thus, the Armorican depositional system is a delta-fed submarine ramp during low sea-level glacial conditions, and an outer shelf-fed submarine ramp at times of sea-level rise.
(Geo-Marine Letters. vol. 20, n° 0276-0460, pp. 219-232, 04/01/2001)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Artificial cold-adapted microbial mats cultured from Antarctic lake samples. 1. Formation and structure
(Aquatic Microbial Ecology. vol. 26, n° 0948-3055, pp. 115-125, 21/02/2026)
LEFE, INEE-CNRS, CNRS, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse, ECOLAG, UM2, IFREMER, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Contribution of ciliated microprotozoans and dinoflagellates to the diet of three Copepod species in the Bay of Biscay.
Predation of three calanoid copepods (Calanus helgolandicus, Temora longicornis, and Centropages chierchiae) on phytoplankton, dinoflagellates, and ciliates was estimated in the Gironde estuarine plume (Bay of Biscay) during winter by means of in situ incubations. Both phytoplankton and ciliates were part of the diet of those three species, while only Centropages chierchiae also included a significant portion of dinoflagellates in its diet. The clearance rates of Calanus helgolandicus for ciliates and phytoplankton reached 2.8 and 4.0 ml copepod-1 h-1 respectively, those of Temora longicornis were 3.2 and 1.8 ml copepod-1 h-1, and those of Centropages chierchiae were 4.3 and 0.8 ml copepod-1 h-1 . Neither Calanus helgolandicus nor Temora longicornis selected dinoflagellates, given the low clearance rates measured for this prey category (0.05 and 0.03 ml copepod-1 h-1, respectively). By contrast, Centropages chierchiae included dinoflagellates in its diet, with a clearance rate of 4.9 ml copepod-1 h-1. Within a given prey category (ciliates or dinoflagellates), all three copepods selected larger prey types (> 40 µm) over smaller ones (´ 40µm). This implies a better detection and capture of larger motile prey compared to small ones. The results are discussed with regard to the omnivorous feeding behavior of these copepods observed here, during a late winter phytoplankton bloom
(Hydrobiologia. vol. 443, n° 0018-8158, pp. 193-204, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ELICO, ULCO, CNRS, LBEML, ULR, CNRS
Contrasting life-histories, secondary production, and trophic structure of Peracarid assemblages of the bathyal suprabenthos from the Bay of Biscay (NE Atlantic) and the Catalan Sea (NW Mediterranean)
The life-histories and the secondary production of four dominant peracarid crustaceans (the mysids Boreomysis arctica and Parapseudomma calloplura, the amphipod Rhachotropis caeca, and the isopod Ilyarachna longicornis) in bathyal depths of the Bay of Biscay (NE Atlantic; between 383 and 420 m) and the Catalan Sea (Northwestern Mediterranean; between 389 and 1355 m) were established. Both the Atlantic and the Mediterranean populations of the major part of the target-species had two generations/year with mean cohort-production intervals (CPI) ranging from 5.5 mo for Ilyarachna longicornis to 6.3 mo for Parapseudomma calloplura. The Hynes method showed secondary production to vary in the Bay of Biscay between 0.113 mg DW m -2 yr -1 for I. longirostris and 3.069 mg DW m -2 yr -1 for P. calloplura, with P/ B ratios between 4.57 ( I. longirostris) and 7.93 ( Boreomysis arctica). In the Catalan Sea, production varied between 0.286 mg DW m -2 yr -1 for I. longirostris and 1.096 mg DW m -2 yr -1 for P. calloplura, with P/ B between 5.72 ( I. longirostris) and 6.66 ( P. calloplura). Application of two different empiric models to the whole peracarid assemblage gave similar levels of secondary production in both study areas (between 29.26 and 32.14 mgDWm -2 yr -1 in the Bay of Biscay; between 26.23 and 26.54 mg DW m -2 yr -1 in the Catalan Sea). From the analysis of gut contents of 22 species the dominant species in each study area were assigned to two basic trophic levels, detritus feeders and predators. Also, cumulative curves of dominance showed high diversity (low dominance) for peracarid assemblages distributed at mid-bathyal depths (524-693 m) both in the Bay of Biscay off Arcachon and in the Catalan Sea off Barcelona. We also discuss and compare, both within and between areas, how environmental features may explain the observed diversity patterns, the trophic structure, and the production results obtained for the suprabenthos assemblages.
(Deep Sea Research Part I: Oceanographic Research Papers. vol. 48, n° 0967-0637, pp. 2209-2232, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Artificial cold-adapted microbial mats cultured from Antarctic lake samples. 2. Short-term temperature effects on oxygen turn-over
(Aquatic Microbial Ecology. vol. 26, n° 0948-3055, pp. 127-138, 21/02/2026)
ECOLAG, UM2, IFREMER, CNRS, LEFE, INEE-CNRS, CNRS, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
ROBUST: The ROle of BUffering capacities in STabilising coastal lagoon ecosystems
Buffer capacities" has been defined in ecology as a holistic concept (e.g., Integration of Ecosystem Theories: A Pattern, second ed. Kluwer, Dordrecht, 1997, 388pp), but we show that it can also be worked out in mechanistic studies. Our mechanistic approach highlights that "buffering capacities" can be depleted progressively, and, therefore, we make a distinction between current and potential "buffering capacities". We have applied this concept to understand the limited "local stability" in seagrass ecosystems and their vulnerability towards structural changes into macro-algal dominated communities. We explored the following processes and studied how they confer buffering capacities to the seagrass ecosystem: (i) net autotrophy is persistent in Zostera noltii meadows where plant assimilation acts as a sink for nutrients, this contrasted with the Ulva system that shifted back and forth between net autotrophy and net heterotrophy; (ii) the Z. noltii ecosystem possesses a certain albeit rather limited capacity to modify the balance between nitrogen fixation and denitrification, i.e., it was found that in situ nitrogen fixation always exceeded denitrification; (iii) the nitrogen demand of organoheterotrophic bacteria in the sediment results in nitrogen retention of N in the sediment and hence a buffer against release of nitrogen compounds from sediments, (iv) habitat diversification in seagrass meadows provides shelter for meiofauna and hence buffering against adverse conditions, (v) sedimentary iron provides a buffer against noxious sulfide (note: bacterial sulfide production is enhanced in anoxic sediment niches by increased organic matter loading). On the other hand, in the coastal system we studied, sedimentary iron appears less important as a redox-coupled buffer system against phosphate loading. This is because most inorganic phosphate is bound to calcium rather than to iron. In addition, our studies have highlighted the importance of plant-microbe interactions in the seagrass meadows.
(CONTINENTAL SHELF RESEARCH. vol. 21, pp. 2021-2041, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Primary or secondary distal volcaniclastic turbidites: how to make the distinction? An example from the Miocene of New Zealand (Mahia Peninsula, North Island)
Miocene marine volcaniclastic deposits occur in Mahia Peninsula (North Island, New Zealand) and were sedimented in a forearc setting related to the Hikurangi trench subduction system. These deposits are interbedded with hemipelagic marls, and correspond to simple or amalgamated centimetric- to metric-thick turbiditic sequences. Volcaniclastic material is mainly composed of vitric particles, with crystals (quartz, plagioclase with minor biotite, amphibole, pyroxene and oxides), which are well represented in the coarse-grained fraction. The glass shards are mainly rhyolitic in composition. Three types of volcaniclastic turbidites were distinguished with geochemical data, because distinction is impossible on sedimentary characteristics. (1) Primary monomagmatic turbidites contain both magmatic (bubble wall pumice and shards) and phreatomagmatic (blocky shards with few vesicles and hydroclastically fragmented pyroclasts) vitric particles. The chemical compositions of the vitric particles and the crystals are very homogeneous suggesting a cogenetic origin. These turbidites directly result from unique eruptive events and are probably related to the entrance of hot subaerial pyroclastic flows into the sea, which also led to their transformation into subaqueous gravity flows. (2) Secondary monomagmatic turbidites never contain phreatomagmatic pyroclasts and the glass compositions display a trend from andesites to rhyolites. There is a strong linear correlation in the compositions that suggest that the glass particles are derived from the same magma. Crystals also show a compositional homogeneity. These deposits reflect the succession of several eruptions related to a unique magmatic system and result of the reworking of volcaniclastic material after relatively short storage on the shelf. (3) Secondary multimagmatic turbidites do not display compositional homogeneity of their vitric and mineral components. This implies that the volcaniclastic material has been stored during a relative long period on the shelf before remobilization, and that this sedimentation records the volcanic activity of multiple magmatic sources. Consequently, it has been possible to distinguish primary volcaniclastic turbidites that are directly related to the volcanic activity, from secondary turbidites that result from reworking of previously deposited material on the shelf. Monomagmatic turbidites can be used as stratigraphic and magmatic markers whereas multimagmatic cannot. Multimagmatic turbidites, however, record the evolution of the volcanic arc during longer periods. This leads to the conclusion that the Mahia Peninsula volcaniclastic turbidites distally record the evolution of the source volcanic arc.
(Sedimentary Geology. vol. 145, n° 0037-0738, pp. 1-22, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GR, UR, INSU - CNRS, CNRS