Influence of the parasite worm Polydora sp. on the behaviour of the oyster Crassostrea gigas: a study of the respiratory impact and associated oxidative stress
The aim of this study was to investigate how the worm Polydora sp., which induces oysters into creating mud blisters in response to an irritation within their shells, could interfere with the oyster Crassostrea gigas physiology and ethology. The impact was characterized by studying two groups of oysters (non-parasitized and parasitized) during a 30 days period: (1) the animal behaviour by analysing their valve activity (valvometry), and (2) the animal respiratory physiology by measuring in vivo the oxygen partial pressure and the specific oxygen consumption in selected tissues (heart, fast and slow adductor muscle). We also researched a putative impact on the expression of several oxidative stress genes at the heart level. Our results show that Polydora sp. is clearly an oyster’s parasite as it induces a decrease in oyster growth according to the infestation intensity. Moreover, it modifies the behaviour and the respiratory physiology of the molluscs. Infested animals opened more frequently but for less time and their level of blood oxygenation was systematically higher than healthy molluscs. These high levels of oxygenation had no effect on the oxidative metabolism of the tissues studied but they induced oxidative stress. Indeed, the superoxide dismutase gene showed a threefold increase in expression in the heart of infested oysters. A putative scenario of the weakening mechanism is proposed.
(Marine Biology. vol. 152, n° 0025-3162, pp. 329-338, 09/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Climate variability of the last five isotopic interglacials: Direct land-sea-ice correlation from the multiproxy analysis of North-Western Iberian margin deep-sea cores
(pp. 375-386 (chapter 25), 09/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Gas transfer velocities of CO2 and CH4 in a tropical reservoir and its river downstream
We have measured simultaneously the methane (CH4) and carbon dioxide (CO2) surface concentrations and water–air fluxes by floating chambers (FC) in the Petit-Saut Reservoir (French Guiana) and its tidal river (Sinnamary River) downstream of the dam, during the two field experiments in wet (May 2003) and dry season (December 2003). The eddy covariance (EC) technique was also used for CO2 fluxes on the lake. The comparison of fluxes obtained by FC and EC showed little discrepancies mainly due to differences in measurements durations which resulted in different average wind speeds. When comparing the gas transfer velocity (k600) for a given wind speed, both methods gave similar results. On the lake and excluding rainy events, we obtained an exponential relationship between k600 and U10, with a significant intercept at 1.7 cm h− 1, probably due to thermal effects. Gas transfer velocity was also positively related to rainfall rates reaching 26.5 cm h−1 for a rainfall rate of 36 mm h− 1. During a 24-h experiment in dry season, rainfall accounted for as much as 25% of the k600. In the river downstream of the dam, k600 values were 3 to 4 times higher than on the lake, and followed a linear relationship with U10.
(Journal of Marine Systems. vol. 66, n° 0924-7963, pp. 161-172, 09/04/2026)
LAERO, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LAERO, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNRS, CNRM, INSU - CNRS, CNRS, Comue de Toulouse, IREQ
A fourth-order compact finite volume scheme for fully nonlinear and weakly dispersive Boussinesq-type equations. Part II : boundary conditions and validation
This paper supplements the validation of the fourth-order compact finite volume Boussinesq-type model presented by Cienfuegos et al. We discuss several issues related to the application of the model for realistic wave propagation problems where boundary conditions and uneven bathymetries must be considered. We implement a moving shoreline boundary condition following the lines given by Lynett et al., while an absorbing-generating seaward boundary and an impermeable vertical wall boundary are approximated using a characteristic decomposition of the Serre equations. Using several benchmark tests, both numerical and experimental, we show that the new finite volume model is able to correctly describe nonlinear wave processes from shallow waters and up to wavelengths which correspond to the theoretical deep water limit. The results compare favourably with those reported using former fully nonlinear and weakly dispersive Boussinesq-type solvers even when time integration is conducted with Courant numbers greater than 1.0. Furthermore, excellent nonlinear performance is observed when numerical computations are compared with several experimental tests on solitary waves shoaling over planar beaches up to breaking. A preliminary test including the wave-breaking parameterization described by Cienfuegos (Fifth International Symposium on Ocean Wave Measurement Analysis, Madrid, Spain, 2005) shows that the Boussinesq model can be extended to deal with surf zone waves. Finally, practical aspects related to the application of a high-order implicit filter as given by Gaitonde et al. to damp out unphysical wavelengths, and the numerical robustness of the finite volume scheme are also discussed.
(International Journal for Numerical Methods in Fluids. vol. 53, n° 0271-2091, pp. 1423-1455, 09/04/2026)
LEGI, UJF, Grenoble INP, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
H4 abrupt event and late Neanderthal presence in Iberia
Heinrich event 4 (H4) is well documented in the North Atlantic Ocean and the adjacent continents as a cooling event 39,000 yr before present (BP). To quantify the impact of this event with respect to climate and vegetation over the Iberian Peninsula, we perform numerical experiments using a high-resolution general circulation model forced by sea surface temperatures before and during H4. Our model simulates an expansion of aridity over the peninsula during H4, a desertification of the south, and a replacement of arboreal by herbaceous plants in the north, all of which are in agreement with contemporaneous pollen sequences from marine cores located off the Iberian Peninsula. Our simulations demonstrate that the H4 marine event imprinted drastic changes over Southern Iberia, which would not have favoured its occupation by Anatomically Modern Humans, therefore providing a plausible explanation for the delayed extinction of Neanderthals in this region inferred from the archaeological record.
(Earth and Planetary Science Letters. vol. 258, n° 0012-821X, pp. 283 à 292, 09/04/2026)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, ArScAn, UP1, UP8, UPN, MCC, CNRS, LGGE, OSUG, UJF, Grenoble INP, INSU - CNRS, IRSTEA, USMB [Université de Savoie] [Université de Chambéry], CNRS, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PACEA, UB, CNRS, GW
HYDROBIA ULVAE: A DEPOSIT-FEEDER FOR CLEANING LIVING HARD-SHELLED FORAMINIFERA
This study proposes a new method for fast and inexpensive extraction of a large number of living foraminifera for laboratory cultures. The method is a significant improvement over current extraction methods, which are highly time-consuming. Several treatments were designed to test the method. Sediment bearing foraminifera from Brouage Mudflat (Atlantic coast of France) was washed through a 50-µm sieve and distributed in glass Petri dishes with 20, 40 and 80 specimens of Hydrobia ulvae, a common gastropod from European intertidal mudflats. As a control experiment, one dish was treated similarly but maintained without Hydrobia. After two days, most of the sediment in the Hydrobia treatments was compacted into small cylindrical gastropod feces and the tests of living benthic foraminifera (Ammonia tepida and Haynesina germanica) were clean and easily visible. Additional experiments showed that the foraminifera were not ingested by Hydrobia ulvae, and could be picked quickly and easily.
(Journal of Foraminiferal Research, n° 0096-1191, 09/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS, UAG, UPMC, UNS, CNRS, BIAF, UA
Study of secondary relaxations in poly(vinyl chloride) by phosphorescence decay: Effect of the chemical structure and the concentration of luminescent probes
The phosphorescence emission of both naphthalene and pyridine can be used to detect the secondary (β) relaxation of PVC, as this relaxation manifests by a decrease in the emission from the grafted probe at the temperatures at which the local motion at the backbone begins. In this work, an extensive study of the kinetic and spectral features of the phosphorescence of 4-mercaptopyridine, 4-methoxybenzenethiol and 4-mercaptophenol groups as a function of temperature is presented. These three luminescent probes have been grafted onto PVC, with modification levels ranging from 3% up to 46%. The phosphorescence decay from −130 °C up to 30 °C has been followed and both the intensity of the emission and the spectral features have been studied as a function of temperature. The interaction between probes as the concentration increases leads in all cases to the emission from aggregates or excimers, which have features different to those of the isolated probe. Side reactions occur when grafting the hydroxyl containing probe, what also leads to surprising phosphorescence spectral and decay rate features.
(Journal of Photochemistry and Photobiology A: Chemistry. vol. 187, n° 1010-6030, pp. 222-232, 09/04/2026)
LAPLACE-DSF, LAPLACE, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRSTEA, LOB, INSU - CNRS, CNRS
Simulation of the chemical fate and bioavailability of liquid elemental mercury drops from gold mining in Amazonian freshwater systems
Elemental mercury (Hg°) for gold amalgamation is the main process applied by artisanal gold miners in South America, leading to important discharges into freshwater ecosystems. Through a 28-day experimental approach based on indoor microcosms, we simulated the chemical fate and bioavailability of Hg° droplets in the presence or absence of sediment collected from a typical forest creek that is unaffected by gold mining activities. Our results clearly showed significant mercury transfers in the water column in both the dissolved gaseous Hg° and oxidized (Hg(II)) forms, with a marked effect of the presence of sediment. After 28 days, Hg total (HgT) concentration in the water column was 25 times higher in sediment-free units (108 ± 17 vs 4 ± 0.4 nM). Methylmercury (MeHg) determinations in the dissolved fraction showed a significant increase only in the presence of sediment after 7 and 14 days. Zebrafish (Danio rerio) were used as indicators for mercury bioavailability. The HgT determinations in four organs revealed significant accumulation levels as early as 7 days exposure, with marked differences in favor of fish collected from the sediment-free units. Significant MeHg increases were observed in the four organs only when sediment was present. Genomic tools applied to estimate sulfate-reducing bacteria communities showed mercury impacts on their diversity and distribution in the different compartments (water, sediment, biofilm, fish gut).
(Environmental Science and Technology. vol. 41, n° 0013-936X, pp. 7322-7329, 09/04/2026)
IPREM, UPPA, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
New insights in the French Guiana continental shelf circulation and its relation to the North Brazil Current retroflection
Moored current measurements carried out from 6 October 2003 to 18 February 2004 over the French Guiana continental shelf are presented. Two contrasted situations have been evidenced in which the currents were either weak and oscillating during the first period ( from October to early December) or strong and northwestward during the rest of the survey. Further analysis of these measurements in light of Moderate Resolution Imaging Spectroradiometer satellite images have revealed that these situations are mainly due to the motion of an outer shelf mesoscale feature: the North Brazil Current (NBC) retroflection. Two other main results have also been evidenced in this survey: ( 1) When the NBC retroflection occurs northwestward of the French Guiana continental shelf, part of the NBC climbs over the shelf slope and propagates to the inner shelf, and ( 2) the "Guyana current'' does not persist throughout the year at a 22 m depth and below. Finally, the location of the NBC retroflection has also a strong impact on the spread of the Amazon plume over the French Guiana continental shelf and is felt to have an influence on the nutrient supply in this region.
(Journal of Geophysical Research. vol. 112, n° 0148-0227, 09/04/2026)
LOB, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UMR EME, IRD, IFREMER, UM, COM, INSU - CNRS, CNRS
Inverse analysis of the planktonic food web dynamics related to phytoplankton bloom development on the continental shelf of the Bay of Biscay, French coast
Along the French coast of the Bay of Biscay, the seasonal progression of phytoplankton presents specific hydrographic conditions compared to other temperate areas due to the influence of two large river plumes (Loire and Gironde). However, in spite of the occurrence of a microphy-toplankton bloom during winter and phosphate limitation in spring, the dynamics of the planktonic food web on the continental shelf of the Bay seem to correspond with the characteristics typical of temperate oceans with the dominance of herbivory during spring and the development of the microbial food web under the stable post-bloom environment. Existing plankton data from recent scientific cruises were combined with inverse and network analyses to construct five model ecosystems between late winter and late spring and to investigate the structure and the function of the food web. The analysis of those models confirmed that the absolute amount of biogenic carbon export from the planktonic food web follows a continuum from high carbon export to depth when the microphytoplankton winter bloom is not consumed by grazers to carbon recycling within the microbial food web after the spring bloom when the water column is strongly stratified. Therefore, the winterespring period corresponds to a situation of high export. The particular hydrological conditions of the Bay of Biscay are not altering the capacity of the planktonic food web to export the greatest absolute amount of carbon during spring to plankton predators such as small pelagic fishes. However, this study showed that, in proportion to the primary production, the relative amount of biogenic carbon export to higher trophic levels does not vary considerably among the three types of planktonic food web function. Bacterial activity seems to have a higher control on relative export than phytoplankton size structure.
(Estuarine, Coastal and Shelf Science, n° 0272-7714, 09/04/2026)
LBEM, ULR, UNICAEN, NU, IFREMER, LIENSs, INSU - CNRS, ULR, CNRS, UMR MARBEC, IRD, IFREMER, UM, CNRS, MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS