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First and disturbing records of the bivalve molluscs Potamocorbula amurensis (Schrenck, 1861) and Mulinia lateralis (Say, 1822) in the Bay of Biscay (France)
No full textInternational audienceThe bivalve mollusc Potamocorbula amurensis, a Corbulidae from the Asian coasts, was recorded for the first time in France in September 2023 in the Gironde estuary, and subsequently in September 2024 in Aiguillon Cove and Aytré Bay. In Aytré Bay, it was accompanied by another non-native bivalve not previously reported from French coasts, Mulinia lateralis, a Mactridae from the western Atlantic coasts. These two species were first recorded in Europe in 2018 in the Westerschelde (Netherlands, Belgium) and are known to be potentially highly invasive. Particular attention should be paid to monitor the spread and the establishment of these two euryoecious species along European coasts.</div
Seasonal dynamics of mudflat foraminifera linked to diatom species and traits
No full textInternational audienceThe trophic ecology of benthic foraminifera in intertidal mudflats is closely linked to diatoms, a dominant component of the microphytobenthos (MPB). Although experimental studies and metabarcoding have clarified foraminiferal diets, in situ assessments of the temporal dynamics of diatoms and foraminifera remain limited. In this study, we examined the seasonal dynamics of adult (> 150 µm) foraminiferal species over a notable 3.5-year monthly monitoring period at the La Coupelasse mudflat (Bay of Bourgneuf, French Atlantic coast). We related these dynamics to 25 environmental variables and to diatom assemblages, focusing on their traits (size, shape, and life-form). La Coupelasse exhibited a clear seasonal pattern driven by bay hydrodynamics, which regulated the availability of redox-sensitive metals, nutrients, and MPB biomass, thereby shaping the environmental context for benthic communities. Diatom traits, whether considered individually or in combination (“size + shape + life-form”), revealed distinct seasonal strategies that complemented species-level analyses. While species-level data provided a detailed understanding of foraminiferal temporal dynamics, combining diatom traits offered a more effective way to identify seasonal dietary shifts. The four dominant foraminiferal species occupied different seasonal niches, with Ammonia confertitesta and Haynesina germanica showing synchronized biannual peaks in spring and autumn, but differed in dietary responses, as H. germanica responded only to diatom shape. Elphidium oceanense displayed a single annual peak in early autumn, corresponding to a broader trophic flexibility across diatom traits, while Elphidium selseyense showed a late spring peak and remained enigmatic regarding its diatom food preferences. Overall, using combined diatom traits outperformed both species identity and MPB biomass in predicting foraminiferal patterns, highlighting their potential to simplify diatom–foraminifera trophic ecology by overcoming diatom taxonomic constraints. These findings shed light on our understanding of benthic ecology and suggest that trait-based approaches, when integrated with spatial and microbiome data, can enhance predictions of ecosystem responses to environmental change
H.E.S.S. detection and multi-wavelength study of the 1 blazar PKS 034627
No full textInternational audiencePKS 0346-27 is a Low Synchrotron Peaked (LSP) blazar at redshift 0.991. The very-high-energy (VHE, E > 100 GeV) spectra of blazars are always affected by absorption by the Extragalactic Background Light (EBL) and subsequently, no blazars have been detected in VHE -rays at redshifts exceeding 1. Extending the redshift range of VHE-detected blazars to will yield insights into the cosmological evolution of both the VHE blazar population and the EBL. This is the goal of a target-of-opportunity (ToO) programme by H.E.S.S. to observe flaring high-redshift () blazars. We report on H.E.S.S. ToO and multi-wavelength observations of the blazar PKS 034627. Along with H.E.S.S., simultaneous data from {\it Fermi}-LAT, {\it Swift} (XRT and UVOT), and ATOM have been analysed and modelled using single-zone leptonic and hadronic models. PKS~0346-27 has been detected by H.E.S.S at a significance of 6.3 during one night, on 3 November 2021, while for other nights before and after this day, upper limits on the VHE flux are determined. No evidence for intra-night -ray variability has been found. A flare in high-energy (HE, ~MeV) -rays detected by {\it Fermi}-LAT preceded the H.E.S.S. detection by 2 days. A fit with a single-zone emission model to the contemporaneous spectral energy distribution during the detection night was possible with a proton-synchrotron-dominated hadronic model, requiring a proton-kinetic-energy-dominated jet power temporarily exceeding the source's Eddington limit, although alternative (e.g. multi-zone) models can not be ruled out. A one-zone leptonic model is, in principle, also able to fit the flare-state SED, however, requiring implausible parameter choices, in particular, extreme Doppler and bulk Lorentz factors of
Modification of offshore wind flow and aeolian sand transport by artificial foredunes
No full textInternational audienceAirflow dynamics and aeolian sand transport under offshore wind conditions have primarily been examined over relatively large coastal dunes, where dune morphology significantly alters flow structure and sediment pathways. In contrast, the role of smaller-scale, anthropogenically constructed coastal sand dunes, remains relatively understudied. This study investigates airflow patterns and sand transport over a low (<2.5 m) artificial foredune in Leucate (South of France), exposed to dominant offshore winds. A high resolution network of anemometers and aeolian sand traps was deployed along a cross-shore transect during four field campaigns. Results indicate that the direction of incident offshore winds generated distinct patterns of airflow and sediment transport from the dune's lee slope to the beach. When wind approached within 20 • of crest-normal, flow separation occurred on the lee side, with wind speeds reduced to 10-20 % of crest values. For angles >20 • , flow remained attached but deviated alongshore, with wind speeds reaching 35-50 % of crest values at the dune seaward toe. Wind velocity consistently increased seaward, enhancing sand transport toward the berm, with maximum transport rates exceeding 300 kg/m/h. This seaward-directed transport contributed to a negative sediment budget under persistent offshore wind dynamics. These findings highlight the capacity of small, artificial dunes to modify offshore wind dynamics and sediment pathways, with implications for dune management and coastal sediment budgets.</div
Modeling the thermo-mechanical behavior of porous lava under reservoir conditions
No full textInternational audienceHarnessing geothermal energy and storing carbon dioxide in volcanic systems require reliable constitutive models to predict rock deformation and failure under extreme pressure and temperature. However, existing models are limited, especially when compared to the more advanced predictive tools available for sedimentary rocks. In this study, we integrate elastoplasticity, strain hardening, nonassociative plasticity, phenomenological thermomechanics, and bifurcation analysis to establish a novel constitutive model for porous lava. The model is calibrated against a unique dataset that provides the stress–strain and strain localization responses of porous andesite deformed at temperatures ranging from room temperature up to 800 °C and at effective confining pressures from room pressure to 50 MPa. These mechanical and thermal conditions are representative of deep geothermal reservoirs. Finite element simulations of laboratory experiments are used to demonstrate the model’s capabilities in terms of reproducing key mechanical characteristics, including the differential stress required for the first stress drop and deformation mechanisms, across varying pressure and temperature conditions. Further validation via full-field finite element computations, simulating borehole excavation in low- to high-temperature systems, underscores the model’s predictive capabilities. In particular, the field-scale simulations demonstrate the model’s efficacy in reproducing variable forms of deformation structures and deformation modes around boreholes with capabilities to provide more information about the displacement in the borehole walls. The proposed modeling framework can be integrated into commercial numerical tools and used to facilitate the engineering of safe and cost-effective geothermal energy production and carbon geostorage, as well as numerical models designed to better understand the stability and therefore the hazard potential of volcanic structures
The role of biomolecules produced by invasive macrophytes in lake ecosystem processes
No full textEgeria densa and Lagarosiphon major are the main invasive hydrophytes in French Atlantic Lakes. These exotic species can modify trophic levels by producing large quantities of biomass in lakes; previous investigations revealed the occurrence of endogenous metabolites in these plants known to be able to affect epiphytic communities, phytoplankton, or other plants, through allelopathic activity. Nevertheless, the actual excretion and environmental occurrence of these metabolites remain poorly documented. In order to gain knowledge of the concrete occurrence and potential ecological impact of E. densa and L. major exometabolome, untargetedmetabolomics using high-resolution mass spectrometer and chemometrics approaches is relevant through its ability to depict, as a first step, the exometabolome chemical landscape
Differences in telomere length and telomerase gene expression with age and among tissues in the Pacific oyster
No full textInternational audienceMarine organisms are continuously exposed to chemical stressors, highlighting the need for operational biomarkers that can be reliably implemented in biomonitoring programmes. Telomere length (TL) has emerged as a promising biomarker of cumulative stress, but its application in ecotoxicology remains limited due to two main challenges: (i) methodological difficulties in obtaining reliable TL measurements from preserved samples, and (ii) incomplete understanding of telomere dynamics across tissues and life stages in sentinel marine species.In this study, we addressed both limitations in the Pacific oyster Crassostrea gigas. First, we compared different DNA extraction methods and selected a protocol suitable for isolating high-molecular-weight DNA from frozen oyster tissues. The qPCR assay was then optimized to minimise technical biases and ensure accurate TL quantification. Using this optimized method, we assessed TL variation across tissues and age classes. Significant tissue-specific differences were observed, with the digestive gland exhibiting the shortest telomeres. In addition, a clear age-related decrease in TL was detected across all tissues. Finally, RT-qPCR analyses revealed lower expression of the telomerase gene in adult tissues compared to early developmental stages, in line with the absence of detectable telomerase activity in adults.Together, these findings provide a methodological and biological framework for future investigations into the effects of chemical stress on telomere dynamics in oysters
Metrological concepts applied to Total Alkalinity measurements in seawater: reference materials, inter-laboratory comparison and uncertainty budget
No full textInternational audienceAbstract. Total alkalinity (TA) measurements in seawater are crucial for characterizing and monitoring the oceanic carbonate system. While international best practices and guidelines exist, the field still lacks widely available traceable reference materials and a well-established uncertainty budget of the measurement method. In this study, we applied key metrological principles – development of reference materials, inter-laboratory comparison and uncertainty quantification – to TA measurements. We developed two reference materials, including an artificial material with a rigorously characterized reference value and an associated uncertainty budget, being traceable to the International System of units (SI). These materials were tested in an inter-laboratory comparison involving five laboratories and demonstrated the applicability of the reference materials developed for quality control. Additionally, we established an uncertainty budget for the TA measurement method using two metrological approaches. The resulting expanded uncertainty was 5 µmol kg−1 (with a coverage factor k=2) in TA, approaching the 4 µmol kg−1 target set by the Global Ocean Acidification Observing Network for climate monitoring. These findings mark a significant step toward improving the quality and comparability of TA measurements, thereby strengthening long-term ocean carbonate system monitoring
Dissipative Solutions to a Compressible Non-Newtonian Korteweg System with Density-Dependent Viscous Stress Tensor
No full textThe main objective of this paper is to prove that if capillarity effect is taken into account then there exist dissipative solutions to a system describing viscoplastic compressibleflows with density dependent viscosities in a periodic domain \T^d with . We calculate the relative entropy inequality and in consequence show existence of dissipative solutions and the weak-strong uniqueness for this system. Our result extends the recent result concerning the link between Euler--Korteweg and Navier--Stokes--Korteweg systemsfor Newtonian flows (when the viscosity depends on the density) [See D.~Bresch, M. Gisclon, I. Lacroix-Violet, {\it Arch. Rational Mech. Anal.} (2019)] to non-Newtonian flows
Refining near-infrared spectroscopy for collagen quantification: A new predictive model for archaeological bone
No full textInternational audienceCollagen is a vital archaeological material, preserving biochemical signatures that provide insights into past environments, diets, and human-animal interactions. However, diagenesis can lead to rapid and inconspicuous collagen degradation. Given the variability in collagen preservation and its significance for analyses such as radiocarbon dating, stable isotope analysis, and ZooMS, researchers have developed prescreening techniques to assess collagen preservation before destructive sampling. Current prescreening approaches, including %N and C:N ratios, typically require sample destruction and access to equipped laboratories. Spectroscopic techniques such as Raman spectroscopy and Fourier Transform Infrared spectroscopy have been explored as alternatives, but they are limited in penetration depth, generalizability (at present at least), and are often still destructive, if minimally.Here, we further develop single-point near-infrared (NIR) spectroscopy as a fully non-destructive, rapid, and field-portable method for prescreening bone for collagen preservation. Unlike FTIR and Raman spectroscopic techniques, NIR light penetrates below the surface of bone, enabling assessment of internal collagen preservation without destructive sample preparation. Using Partial Least Squares Regression (PLSR) and Random Forest (RF) modeling, we trained predictive models on whole bones with known collagen yields and validated the models on an independent archaeological collection. Both PLSR and RF models, when restricted to the 2030–2060 nm range, demonstrate strong and comparable performance while avoiding wavelengths associated with consolidants in our reference library. The models outperform traditional % N-based methods in identifying suitable samples for radiocarbon dating. These models enable the high-throughput screening of large collections of bone, improving sample selection and minimizing unnecessary destructive analysis