Factors involved in growth plasticity of cockles Cerastoderma edule (L.), identified by field survey and transplant experiments
In Arcachon Bay, a macrotidal coastal lagoon in southwest France, growth rates of cockles Cerastoderma edule (L.) differ greatly between locations. Sampling of populations at different tidal levels showed that the mean shell length was significantly and positively correlated with immersion time, whereas no correlation was found with population density and microphytobenthos biomass. Transplants of cockles between two intertidal sites were used to examine the relative importance of habitat and site of origin for growth rate and condition index. Artifacts due to manipulation were assessed, i.e. the impact of enclosures on growth, conditon index and mortality. During a 5-mo reciprocal transplant experiment, growth rates of the transplanted cockles and the cockles already present were similar, whereas the sites of origin did not affect growth rate. Condition index, however, displayed significant differences in relation to both transplant and origin sites. During a further 6-mo experiment in which cockles were transplanted from one site to four new sites, growth was mainly influenced by tidal level. These results indicate that net growth started when cockles were immersed 30% of the time. It is concluded that, on the scale of Arcachon Bay (156 km2), differences in growth and condition between cockle populations are largely phenotypic. Tidal level (i.e. food supply and emersion stress) accounts for most of these differences, but the existence of genetically or physiologically different populations cannot be excluded.
(Journal of Sea Research (JSR). vol. 36, n° 1385-1101, pp. 251-265, 01/12/1996)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Climatic interpretation of the recently extended Vostok ice records
(Climate Dynamics. vol. 12, n° 0930-7575, pp. 513-521, 01/06/1996)
LMCE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, URI, LGGE, OSUG, UJF, Grenoble INP, INSU - CNRS, IRSTEA, USMB [Université de Savoie] [Université de Chambéry], CNRS, INSU - CNRS, CNRS, AARI, Roshydromet, RAS, Penn State
The Quantitative Distribution of Subtidal Macrozoobenthic Assemblages in Arcachon Bay in Relation to Environmental Factors: a Multivariate Analysis
The species composition and spatial distribution of macrozoobenthic assemblages in the subtidal, unvegetated areas of Arcachon Bay (a mesotidal coastal lagoon on the SW coast of France) were investigated through a quantitative survey of 18 stations, sampled during a winter period. Factorial correspondence analysis (FCA) of the distribution of main species among stations and automatic hierarchical classification identified seven species groups and five station groups or faunal assemblages, the latter being also characterized in terms of species constancy and fidelity. These assemblages were: (1) aGastrosaccus spinifer –Nephtys cirrosacommunity on clean, medium sands in the deep entrance channel; (2) a fine –medium sand assemblage characterized by the amphipodsBathyporeia sarsiandMelita palmatain the two main tidal channels, which penetrates deeply in the bay along the hydrological axes of the system; (3) a very localized assemblage of epi- and infauna on a heterogeneous substratum; (4) a modifiedAbra albacommunity in the muddy, transverse channels; and (5) a facies of the latter dominated by the oligochaeteTubificoides benedeni.Multiple discriminant analysis including seven environmental variables revealed that the most important factors in the ordination of stations were the sediment parameters, especially organic matter andZosteradebris, followed by the salinity range and water depth. The spatial organization of subtidal infauna in Arcachon Bay appears to be characteristic of a mesotidal coastal lagoon with important water exchanges with the ocean. Average abundance and biomass of macrofauna amounted to 1719 individuals m−2and 6 ·10 gm−2DW, respectively. Density, biomass and species richness were, on average, higher in muddy sands than in clean, sandy bottoms. Comparison of available quantitative data for Arcachon Bay shows that abundance and biomass of macrozoobenthos are lower in subtidal areas than in intertidal habitats.
(Estuarine, Coastal and Shelf Science. vol. 42, n° 0272-7714, pp. 371-391, 01/03/1996)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A Late Pleistocene-Holocene lacustrine record from Lake Manas, Zunggar (northern Xinjiang, western China)
(Palaeogeography, Palaeoclimatology, Palaeoecology. vol. 120, n° 0031-0182, pp. 105-121, 01/02/1996)
CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS, UP11, CAS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IDES, UP11, INSU - CNRS, CNRS, MNHN, UP11
Hydrographic changes of the Southern Ocean (southeast Indian Sector) Over the last 230 kyr
(Paleoceanography. vol. 11, n° 0883-8305, pp. 57-76, 01/02/1996)
CFR, CEA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Le Quaternaire littoral girondin.
Nous présentons la situation géographique, l'histoire géologique, les traces d'occupations humaines, l'histoire contemporaine et le vin en Médoc.
(23/05/1996)
PACEA, UB, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Morphologie, paysages et occupations du sol entre Atlantique et Gironde aux époques historiques
(pp. p. 206-211, 23/05/1996)
ArScAn, UP1, UP8, UPN, MCC, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Morphogenèse, paysage et peuplement en Aquitaine
(23/05/1996)
ArScAn, UP1, UP8, UPN, MCC, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Lacustrine organic fluxes and palaeoclimatic variations during the last 15 ka: Lac du bouchet (Massif Central, France)
To assess the influence of climatic changes on organic lacustrine sedimentation, two cores recovered from the centre of the Lac du Bouchet were studied by petrographical (palynofacies) and geochemical methods. Only core LDB H was used for estimation of the organic fluxes. The variation of these fluxes with climo-stratigraphic periods showed: low organic fluxes during the Lateglacial, an increase at the beginning of the Holocene, a minimum at the end of the Atlantic period resulting from the climatic cooling, and a maximum at the end of the Sub-Boreal related to the installation of the present climatic conditions.
(Quaternary Science Reviews. vol. 15, n° 0277-3791, pp. 203-211, 23/05/1996)
PALEOTROPIQUE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ISTO, INSU - CNRS, UO, CNRS
Experimental evidence of complex interactions between biotic and abiotic factors in the dynamics of an intertidal population of the bivalve Cerastoderma edule.
Densities of the suspension-feeding bivalve Cerastoderma edule (L.) were manipulated inside field enclosures at two tidal elevations (low water level, LWL, and mid-tide level, MTL) on an intertidal sand flat in Arcachon Bay to test the influence of both adult densities and emersion time on (1) individual growth rate, (2) settlement rate, and (3) survival rate of cockles. These experiments were conducted during two consecutive years, in plots with ambient (Ix) and modified (1/3x, 3x, or 10x) densities of adult cockles. Growth rate and condition index of both adults and juveniles were significantly higher at the lowest tidal elevation (LWL), which is in accordance with the feeding mode of the species. The highest juvenile growth rate was recorded in the low-density treatments (160-200 adults m(-2)), which suggests a competitive interaction with adults; for the latter, growth rate was depressed only at the highest density (2000 m(-2)). survival of-adults was affected neither by immersion time nor by densities. Contrasted results were found for the settlement rate and the survival of recruits. During the first year of-experiment, density-treatments had no effect on settlement at MTL, whereas high adult densities negatively influenced settlement at LWL, but only during the period of high settlement; during the second year, a significant effect of-adult densities on settlement was found on a single occasion at MTL. However, at the end of-both experiments (195 and 252 d, respectively), recruit densities did not significantly differ between density-treatments. Although the difference in tidal elevation between the two experimental sites was only 1.0 m, settlement peaks were clearly distinct: they occurred in April (approximate to 4000 m(-2)) at LWL but not earlier than July (approximate to 12000 m(-2)) at MTL; however, the final recruitment was higher at LWL than at MTL. Preliminary results of a laboratory flume study show that, in conditions of smooth turbulent flow (u* = 0.51 cm s(-1), Re* = 1.8), juvenile cockles are able to leave the substratum, to migrate by byssus drifting into the water column over several metres and to avoid resettlement in areas with high densities of conspecific adults. Although competition with adults may occur during larval settlement, subsequent migration of juveniles between different tidal levels is likely to affect significantly the growth and recruitment of intertidal cockle populations.
(Oceanologica Acta, n° 0399-1784, 23/05/1996)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS