Evolution of the Nile deep-sea turbidite system during the Late Quaternary: influence of climate change on fan sedimentation
This paper presents an overview of the evolution of the Nile deep-sea turbidite system during the last 200 kyr, over a series of glacial to interglacial cycles. Six individual deep-sea fans were identified from an extensive field data set. Each fan comprises a canyon, channel system and terminal lobes. Two of these fan systems were possibly active at the same time, at least during some periods. Large-scale slope failures destroyed channel segments and caused the formation of new submarine fan systems. These slope failures thus played an important role in the overall evolution of the turbidite system. During the last glacial maximum (ca 25 to 14·8 ka) the central and eastern parts of the Nile deep-sea turbidite system were relatively inactive. This inactivity corresponds to a lowstand in sea-level, and a period of arid climate and relatively low sediment discharge from the Nile fluvial system. Rapid accumulation of fluvial flood-derived deposits occurred across the shallower part of the submarine delta during sea-level rise between ca 14·8 and 5 ka. The most recent deep-sea channel–lobe system was very active during this period of rising sea-level, which is also associated with a wetter continental climate and increased sediment and water discharge from the Nile. Increased sediment deposition in shallower water areas led to occasional large-scale slope failure. The Nile deep-sea turbidite system was largely inactive after ca 5 ka. This widespread inactivity is due to retreat of the coastline away from the continental shelf break, and to a more arid continental climate and reduced discharge of sediment from the Nile. The Nile deep-sea turbidite system may be more active during periods of rising and high sea-level associated with wetter climates, than during lowstands, and may rapidly become largely inactive during highstands in sea-level coupled with arid periods. These acute responses to climate change have produced sedimentary/stratigraphic features that diverge from traditional sequence models in their nature and timing. This large-scale sedimentary system responded to monsoon-driven climate change and sea-level change in a system-wide and contemporaneous manner.
(Sedimentology. vol. 56, n° 0037-0746, pp. 2061-2090, 08/05/2009)
GEOAZUR 6526, IRD, UPMC, UNS, INSU - CNRS, UniCA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, INTECHMER, Cnam, ISMAR, ISMAR, CNR, ETH Zürich
Testing the enemy release hypothesis: trematode parasites in the non-indigenous Manila clam Ruditapes philippinarum
The present study tested the ‘Enemy Release Hypothesis’ (ERH) which states that the success of an introduced species is related to the scarcity of natural enemies in the introduced range compared with the native range. Digeneans are dominant macroparasites of molluscs; therefore, the interaction between R. philippinarum and these parasites was ideal for investigation. A two-year monitoring in Arcachon Bay (SW France) was performed to estimate digenean loads in R. philippinarum and in three infaunal native bivalves (R. decussatus, Paphia aurea, Cerastoderma edule). A laboratory experiment allowed comparison of infection success among these bivalves (except P. aurea) by generalist digenean larvae (Himasthla elongata cercariae). R. philippinarum digenean abundance in Arcachon Bay was much lower than in native bivalves, with values depending on species, sites and time. Similarly, mean digenean species richness per host individual was always lower in R. philippinarum than in sympatric bivalves. A comparison of digenean metacercariae abundance between R. decussatus and C. edule in Mundaka Estuary (Spain) showed that both species had similar digenean loads but that R. decussatus was depleted in digenean species encysting in host tissues (the non-gymnophallid species). Experimental infection confirmed that the two species of the genus Ruditapes (and not R. philippinarum only) were resistant to encysting digeneans, with an infection success 3–5 times lower than that of C. edule. The lack of infection that was observed in the field would therefore be the consequence of a tissue barrier, R. philippinarum epithelium being too tough for cercariae penetration. Concordantly, according to the literature, digenean infection in the native range of R. philippinarum is also low. Consequently, the ERH, as an explanation for R. philippinarum success in Europe, is not totally consistent in the case of digenean trematodes as enemies, R. philippinarum hosting low load of digeneans in its native as well as colonized range.
(Hydrobiologia. vol. 630, n° 0018-8158, pp. 139-148, 03/05/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Deposits related to the failure of the Malpasset Dam in 1959. An analogue for hyperpycnal deposits from jökulhlaups
Sediment cores collected in the Gulf of Fréjus (SE France) contain submarine deposits related to the failure of the Malpasset Dam in 1959. These deposits constitute a dark, sandy terrigeneous layer of 10–40 cm thickness lying above an erosion surface. The deposits are composed of ungraded, non-bioturbated sands and silts displaying no apparent sedimentary structure, but rich in organic matter and rock or shell fragments. During the event, this layer prograded onto the inner continental shelf and froze rapidly. These hyperconcentrated flow deposits are related to an unsteady inertia flow generated by a surge-like flood and bedload-dominated hyperpycnal flow. Rapid freezing on flow sides generated lateral, coarse-grained, levee-shape deposits. The deposits related to the failure of the Malpasset Dam are drastically different from classical suspended-load-dominated hyperpycnites deposited by a steady, flood-generated, hyperpycnal flow. However, they are comparable with present-day deposits on a volcanic, ice-covered margin (Icelandic jökulhlaups), with ancient deposits resulting from the pulsating output of subglacial lakes during a deglaciation, or with Martian landforms resulting from sporadic ice–melt events during early Martian times.
(Marine Geology. vol. 260, n° 0025-3227, pp. 81-89, 01/05/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A round-the-world tour almost completed: first records of the invasive mussel Musculista senhousia in the north-east Atlantic (southern Bay of Biscay)
The Asian date mussel Musculista senhousia, previously recorded from the Pacific coast of North America, Australasia and the Mediterranean, is reported for the first time from the Atlantic coast of Europe in Arcachon Bay, where it occurs intertidally and to depths of 5 m. It has been present in Arcachon Bay since 2002 and has since been found in 2006 within two further inlets of the Bay of Biscay, Hossegor Lake and the Bidasoa estuary. Their appearance is probably associated with oyster transfer from Thau lagoon in the Mediterranean Sea to Arcachon Bay.
(Marine Biodiversity Records. vol. 2, n° 1755-2672, 01/05/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Brown Muscle Disease and Manila Clam Ruditapes philippinarum Dynamics in Arcachon Bay, France
Brown Muscle Disease (BMD) affects Manila clam Ruditapes philippinarum. It was described for the first time in 2005 in Arcachon Bay, France. The pathology consists in a progressive necrosis of the posterior adductor muscle, valve gaping, clam migration to the sediment surface, and death. This study aims to quantify the prevalence of BMD in the bay and to evaluate the effect of BMD on Manila clam dynamics. The prevalence was assessed on 50 stations spread within Arcachon Bay. About 62% of Manila clam habitat surface was infected by BMD. A survey of buried and surface clams was conducted from November 2006 to March 2008 in Lanton, a site infected by BMD. Modal progression analysis separated confidently cohorts from 2003 to 2005 recruitments. This pathology only affected adult clams (>25 mm, >2 years). For both buried and surface individuals, shell length was significantly correlated with BMD infection. Surface clams had prevalence (67%) higher than buried clams (23%) and showed greater mortality rate after 15 d in running water: 82% against 12% for buried individuals. The final disease index (FDI) and the condition index (CI) were monthly evaluated on 50 clams located at each position in the sediment. CI displayed a significant decrease after BMD's infection from light to severe disease stages. Length data analysis through Bhattacharya's method (FISAT II software) allowed identifying four cohorts. The 2003s cohort enabled to calculate mortality rate that was 39% for 5 months and to estimate that BMD was responsible of 95% of that mortality. The temperature was certainly an important factor in BMD transmission, because cohort dynamics results argued that BMD developed during spring and summer.
(Journal of Shellfish Research. vol. 28, n° 0730-8000, pp. 355-362, 26/04/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Particle fluxes and recent sediment accumulation on the Aquitanian margin of Bay of Biscay
(Continental Shelf Research. vol. 29, n° 0278-4343, pp. 1044-1052, 01/04/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BIAF, UA, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Planktic foraminiferal production along an offshore–onshore transect in the south-eastern Bay of Biscay
(Continental Shelf Research. vol. 29, n° 0278-4343, pp. 1123-1135, 01/04/2009)
BIAF, UA, NOC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Digenean trematode species in the cockle cerastoderma edule: Identification key and distribution along the North-Eastern Atlantic Shoreline
We describe the digenean fauna of one of the dominant intertidal hosts, the common cockle Cerastoderma edule, in terms of biomass, off north-eastern Atlantic shores. Using published and unpublished literature we have prepared an identification key and provide an up-date of the large-scale distributional patterns of digenean species of the common cockle. At least sixteen digenean species, belonging to seven families, use cockles as intermediate host. Among these species two utilize cockles as first intermediate host only, whereas two species utilize cockles as both first and second intermediate host. The remaining eleven species have cockles as their second intermediate host. Water birds and fish are the definitive hosts to twelve and four species, respectively.Cockles are infected with digeneans along the latitudinal gradient from southern Morocco to the western region of the Barents Sea often with high infection levels. Whereas some of these digenean species occur along most of the latitudinal gradient others show a more restricted northern or southern distribution mostly caused by an underlying latitudinal gradient of host species.Knowledge of digenean species and their large-scale distribution pattern may serve as a baseline for future studies dealing with the effects of climate change on parasite–host systems. For such studies the cockle and its digenean community could be an ideal model system.
(Journal of the Marine Biological Association of the United Kingdom. vol. 89, n° 0025-3154, pp. 543, 26/03/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Biodynamics, subcellular partitioning, and ultrastructural effects of organic selenium in a freshwater bivalve
Selenium is a trace element characterized by concentrations that narrowly range between being essential and being toxic. Even though inorganic selenite and selenate are the predominant chemical forms of Se in surface waters, the toxicity of Se to aquatic organisms is mostly governed by the bioavailability of organic selenium within food webs. The present study was designed to evaluate organic selenium bioaccumulation and toxicity patterns in the freshwater sentinel species Corbicula fluminea. Waterborne selenomethionine (SeMet) exposure was used to mimic dietary organo-Se uptake. Our results demonstrate that SeMet is accumulated to a relatively high extent with a concentration factor of 770 (wet weight basis). Higher uptake than depuration rates suggest that bivalves deal with high Se amounts using a strategy of detoxification based on Se sequestration that could involve granules, as shown by a strong increase of Se in the particulate subcellular fraction. Selenium is persistent in the cytosol of bivalves exposed to SeMet where it is found in proteins of a wide range of molecular mass, indicating a possible replacement of methionine by selenomethionine. A subsequent alteration of protein function might be one of the mechanisms of Se toxicity that could explain the histopathological effects we observed in gills by using transmission electronic microscopy. Those analyses showed changes in gill filament ultrastructure and suggested mitochondria as the first target for SeMet cytotoxicity, with alterations of the outer membrane and of cristae morphology. Organo-Se would thus not only be toxic via indirect mechanisms of maternal transfer as it was suggested for fish but also directly. Our results on Se distribution agree with studies that used dietary Se transfer, and highlight the relevance (and less expensive way) of using SeMet water-only exposure protocols to mimic the real environment. © 2009 American Chemical Society.
(Environmental Science and Technology. vol. 43, n° 0013-936X, pp. 2112-2117, 15/03/2009)
IRSN/DEI/SECRE/LRE, IRSN/DEI/SECRE, IRSN, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Properties of fluorescent dissolved organic matter in the Gironde Estuary
The isolation, characterization and study of the properties of aquatic dissolved organic matter (DOM) still represent a challenge because of the heterogeneity, complexity and low concentration of organic material in natural waters. Based on its ability to interact with contaminants and thus to modify their transport and bioavailability, DOM is of interest for environmental purposes. The objective of this work was to better characterize DOM in the Gironde Estuary (southwestern France). The estuary represents an exchange zone between the continent and the Atlantic Ocean and conditions the transfer of organic and inorganic substances from the continental to the oceanic environment. Several samples were collected along the estuary during three cruises in 2002 and 2006. They were analysed using excitation-emission matrix (EEM) spectroscopy, a sensitive technique that allows direct analysis of water samples. Fluorescent DOM and dissolved organic carbon (DOC) did not behave conservatively in this estuarine system, i.e. the organic material did not undergo simple dilution from the upstream to the downstream part of the estuary. A seasonal variability in DOC content was pointed out, whereas few seasonal variations in DOM fluorescence were observed. DOM sources and processing in the estuary were further evaluated by determining two fluorescence indices - the humification index (HIX) and the index of recent autochthonous contribution (BIX). By applying these indices, the relative degree of humification (HIX) and autotrophic productivity (BIX) could be assessed. Based on the fluorescence and DOC results, the estuary was divided into three zones depending on salinity (S) and characterized by specific DOM: (i) A turbid zone of low salinity (S < 5) and high suspended particulate matter concentration with increase in the intensities of the α′ and α fluorophores, characteristic of humic-like compounds. (ii) A mid-estuarine zone (5 < S < 25) characterized by low autotrophic productivity and containing strongly degraded organic material, as shown by the low values of BIX and high values of HIX. (iii) A higher salinity area (S > 25) characterized by increased autotrophic productivity and a marked marine influence, and associated with high and low values of BIX and HIX, respectively. The HIX and BIX indices were shown as useful tools for readily defining and classifying DOM characteristics in estuarine waters.
(Organic Geochemistry. vol. 40, n° 0146-6380, pp. 706-719, 12/03/2009)
ISM, UB, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS