Effects of epibionts on Sabellaria alveolata (L.) biogenic reefs and their associated fauna in the Bay of Mont Saint-Michel     

Stanislas Dubois  John A. Commito  Frdric Olivier  Christian Retire 《Estuarine, Coastal and Shelf Science》2006,68(3-4):635

Biogenic structures built by ecosystem engineers such as corals, bivalves, polychaetes, and sea grasses provide habitat for benthic vertebrates and invertebrates. The polychaete Sabellaria alveolata is an important foundation species whose reef structure adds topographic complexity and high levels of biodiversity to the otherwise low-relief, low diversity, soft-bottom environments in the Bay of Mont Saint-Michel, France, where the largest such reef formations in Europe are found. In this bay, reefs are being increasingly colonised by oysters (Crassostrea gigas) from local aquaculture operations and by green algae (Ulva sp.) due to the increasing inputs of nitrates from terrestrial origin. The purpose of this study was to investigate the possible impacts of epibiotic oysters and green algae on the S. alveolata population and reef community structure in the Bay of Mont Saint-Michel, France. Univariate and multivariate comparisons of macrofauna were conducted for five reef types: controls (no epibionts), low oyster density, high oyster density, green algae, and oyster and green algae. Results showed that all the three reef types with oysters had significantly higher species richness and diversity values than control and algae-only reef types. Pairwise ANOSIM and SIMPER comparisons of controls versus the four reef types with epibionts revealed that all three of the reef types with oysters were significantly different from controls, but there was no significant difference between controls and algae-only reef types. A striking feature of the reef comparisons is that no single species in this species-rich system contributed more than 8.86% to the dissimilarity between the reef types. Thus, k-dominance curves for species abundances were not effective in revealing differences among the reef types. Our results demonstrate that recent anthropogenic inputs of oysters affect the reef species assemblage more strongly than algal epibionts. In addition, epibionts, especially green algae, alter S. alveolata population structure, causing a reduction in new recruits that over the long run may cause significant damage to the reef structure itself. These results are a first step towards understanding anthropogenic threats to S. alveolata reefs and may be useful in the development of strategies for their protection and management.  相似文献   

Physical modelling of fault scarp degradation under freeze–thaw cycles     

M. Font  J.‐L. Lagarde  D. Amorese  J.‐P. Coutard  A. Dubois  G. Guillemet  J.‐C. Ozouf  E. Vedie 《地球表面变化过程与地形》2006,31(14):1731-1745

Physical modelling has been developed in order to simulate the effects of periglacial erosion processes on the degradation of slopes and scarps. Data from 41 experimental freeze–thaw cycles are presented. They attest to the efficiency of periglacial processes that control both erosion and changes in scarp morphology: (i) cryoexpulsion leads to an increase of scarp surface roughness and modifies significantly the internal structure of the active layer; (ii) combined effects of frost creep and gelifluction lead to slow and gradual downslope displacements of the active layer (0·3 cm/cycle); (iii) debris flows are associated with the most significant changes in scarp morphology and are responsible for the highest rate of scarp erosion; (iv) quantification of the erosion rate gives values close to 1 cm³ cm^?2 for 41 freeze–thaw cycles. These experimental results are consistent with field data acquired along the La Hague fault scarp (Normandy, France) where an erosion rate of 4·6 ± 1 m³ m^?2 per glacial stage has been computed from the volume of natural slope deposits stored during the Weichselian glacial stage. These results show that moist periglacial erosion processes could lead to an underestimation of Plio‐Quaternary deformation in the mid‐latitudes. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Landslides : José Chacon, Clemente Irigaray and Tomas Fernandez (Editors). A.A. Balkema, Rotterdam, 1996, xiv + 393 pp., 218 figs., 51 tables, $US 95.00, ISBN 90-5410-832-0.     

Jean-Mars M. Dubois 《Geomorphology》1998,22(3-4)

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Free Radicals and Fast Photochemistry during BERLIOZ   总被引：4，自引：0，他引：4  

U. Platt  B. Alicke  R. Dubois  A. Geyer  A. Hofzumahaus  F. Holland  M. Martinez  D. Mihelcic  T. Klüpfel  B. Lohrmann  W. Pätz  D. Perner  F. Rohrer  J. Schäfer  J. Stutz 《Journal of Atmospheric Chemistry》2002,42(1):359-394

The free radicals OH, HO₂, RO₂, and NO₃ are known to be the driving force for most chemical processes in the atmosphere. Since the low concentration of the above radicals makes measurements particularly difficult, only relatively few direct measurements of free radical concentrations have been reported to date.We present a comprehensive set of simultaneous radical measurements performed by Laser Induced Fluorescence (LIF), Matrix Isolation –Electron spin Resonance (MI-ESR), Peroxy Radical Chemical Amplification (PERCA), and Differential Optical Absorption Spectroscopy (DOAS) during the BERLIner OZonexperiment (BERLIOZ) during July and August of 1998 near Berlin, Germany. Most of the above radical species were measured by more than one technique and an intercomparison gave good agreement. This data set offered the possibility to study and quantify the role of each radical at a rural, semi-polluted site in the continental boundary layer and to investigate interconnections and dependencies among these free radicals.In general (box) modelled diurnal profiles of the different radicals reproduced the measurements quite well, however measured absolute levels are frequently lower than model predictions. These discrepancies point to disturbing deficiencies in our understanding of the chemical system in urban air masses.In addition considerable night-time peroxy radical production related to VOC reactions with NO₃ and O₃ could be quantified.  相似文献   

Assessment of seawater pollution by heavy metals in the neighbourhood of Algiers: use of the sea urchin, Paracentrotus lividus, as a bioindicator     

Soualili  Dina; Dubois  Philippe; Gosselin  Pol; Pernet  Philippe; Guillou  Monique 《ICES Journal of Marine Science》2008,65(2):132-139

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Increased phagocytic activity in contaminated seastars (Asterias rubens) collected in the Southern Bight of the North Sea     

Coteur G  Danis B  Wantier P  Pernet P  Dubois P 《Marine pollution bulletin》2005,50(11):1295-1302

In invertebrates, the phagocytosis exerted by immune cells constitutes the main line of internal defence against offending microorganisms. This study assessed during two consecutive years the phagocytic activity in seastars (Asterias rubens) collected in stations along the Belgian and Dutch coasts. The contamination of these seastars by metals and PCBs were measured in parallel. Increased phagocytic activities were found in seastars collected in the plume of the Scheldt river. This correlated with the contamination of seastars by metals, mainly Pb, but not with the contamination by the analysed PCB congeners. Furthermore, the relationship between phagocytosis and metal contamination was reproducible from one year to another. The possible mechanisms explaining this effect are discussed in light of a direct or indirect link between phagocytic activity and metal contamination of seastars.  相似文献   

Evaluating Cenozoic equatorial sediment deposition anomalies for potential paleoceanographic and Pacific plate motion applications     

Neil C. Mitchell  Nathalie Dubois 《Marine Geophysical Researches》2014,35(1):1-20

If equatorial sediments form characteristic deposits around the equator, they may help to resolve the amount of northwards drift of the Pacific tectonic plate. Relevant to this issue, it has been shown that ²³⁰Th has been accumulating on the equatorial seabed faster than its production from radioactive decay in the overlying water column during the Holocene (Marcantonio et al. in Paleoceanography 16:260–267, 2001). Some researchers have argued that this reflects the deposition of particles with adsorbed ²³⁰Th carried by bottom currents towards the equator (“focusing”). If correct, this effect may combine with high pelagic productivity, which is also centered on the equator, to yield a characteristic signature of high accumulation rates marking the paleoequator in older deposits. Here we evaluate potential evidence that such an equatorial feature existed in the geological past. Seismic reflection data from seven meridional transects suggest that a band of equatorially enhanced accumulation of restricted latitude was variably developed, both spatially and temporally. It is absent in the interval 14.25–20.1 Ma but is well developed for the interval 8.55–14.25 Ma. We also examined eolian dust accumulation rate histories generated from scientific drilling data. A dust accumulation rate anomaly near the modern equator, which is not obviously related to the inter-tropical convergence zone, is interpreted as caused by focusing. Accumulation rates of Ba and P₂O₅ (proxies of export production) reveal a static equatorial signature, which suggests that the movement of the Pacific plate over the period 10–25 Ma was modest. The general transition from missing to well-developed focusing signatures around 14.25 Ma in the seismic data coincides with the mid-Miocene development of the western boundary current off New Zealand. This current supplies the Pacific with deep water from Antarctica, and could therefore imply a potential paleoceanographic or paleoclimatic origin. At 10.05–14.25 Ma, the latitudes of the seismic anomalies are up to ~2° different from the paleoequator predicted by Pacific plate-hotspot models, suggesting potentially a small change in the hotspot latitudes relative to the present day (although this inference depends on the precise form of the deposition around the equator). The Ba and P₂O₅ anomalies, on the other hand, are broadly compatible with plate models predicting slow northward plate movement over 10–25 Ma.  相似文献   

RAPID EVALUATION OF SEDIMENT BUDGETS by Leslie M. Reid and Thomas Dunne,Catena Verlag,Reiskirchen, 1996. No. of pages: x + 164. Price: $49. ISBN 3‒923381‒39‒5     

J‐M.M. Dubois 《地球表面变化过程与地形》2000,25(11):1275-1275

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