Evaluating migration hazard for recently remobilized managed coastal dunes
Sparsely vegetated or unvegetated coastal dunes are inherently dynamic, regardless of their size (Hesp et al., 2022). A salient characteristic of these dunes is their landward migration, driven by prevailing onshore winds, at rates that can exceed several meters per year. The rapid evolution of freely evolving coastal dunes inevitably raises concerns about the burial of infrastructure and more generally, the back dune areas. In a context where dune system remobilization is emerging as a nature-based management solution with multiple benefits (ecological reconnection, chronic marine erosion and sea-level rise effects mitigation), precise, spatially explicit quantitative assessments of dune migration hazards are essential. This is more critical given the trends of increasing urbanization and the concentration of socio-economic interests in coastal zones. Along the 230 km of the Aquitaine coast (southwest France), coastal dunes, which landscape is largely inherited from nearly two centuries of management, stabilization, and episodic mechanical re-profiling, have undergone spontaneous remobilization over the past decade (Nicolae Lerma et al., accepted). Across extensive sectors, dunes have transitioned from geometrically fixed, vegetated forms to aerodynamic, transgressive dunes (Figure 1a). This shift presents both opportunities and challenges for short- and long-term management strategies but also raises critical questions about accommodating rapid migration rates and evolving dune morphology. Current approaches to assessing burial hazards often overlook key parameters, such as interannual wind variability, climate change-induced trends in forcing, dune and back-dune morphology, and sediment budgets. Furthermore, methods relying on historical migration rates are inapplicable in regions where dunes were artificially stabilized during the 20th century through management interventions. Using annual airborne LiDAR data (Figure 1b.) and simulations with the morphodynamic model DUNA (Kombiadou et al., 2023, Figure 1c.), we analyze the factors influencing the migration speed of recently unvegetated dunes. We also investigate the impact of hybrid management strategies (designed to either accelerate or mitigate dune remobilization) at large spatial scales (hundreds of meters to tens of kilometers).
(13/07/2026)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ONF
Impact of combined atmospheric and marine heatwaves on the filtration activity of the invasive Asian date mussel, Arcuatula senhousia.
The Asian date mussel, Arcuatula senhousia, originated from East Asia, is a highly invasive species that severely affects ecosystem functioning and biodiversity in various ecosystems in America and Europe. In recent decades, heatwave events have increased in severity and frequency, causing additional stress for intertidal organisms living in one of the most thermally challenging habitats. Therefore, understanding the impact of stressful environmental conditions on species' behavioural responses is essential for predicting the effects of biological invasions in the context of climate change. This study aimed to evaluate the response of A. senhousia filtration activity under two levels of realistic combined marine and atmospheric short-term heatwaves (strong and extreme), performed during spring and summer conditions. Although numerous intertidal organisms have been shown to suffer greatly from heatwaves, the results indicate that A. senhousia is able to withstand short-term heatwaves. The results showed that, for all intensities and seasons, heatwaves had no significant effect on the clearance rate. Although there was no distinct general trend regarding the influence of heatwaves on the behaviour of valve opening in spring, strong heatwave conditions significantly increased the valve gaping activity (e.g., increasing valve opening and time of active filtration) during the summer experiment without significant difference on the clearance rate. This highlights the importance of considering the season when attempting to understand and predict the impacts of heatwaves. Therefore, this species exhibits a high filtration rate as well as tolerance to heatwaves. However, future investigations should investigate if this resistance have an impact on the species growth and survival at a longer term. In the context of climate change, this species may have advantage over native ones, and its abundances may significantly rise, leading to important ecological consequences in terms of communities structures and habitat modifications.
(Estuarine, Coastal and Shelf Science. vol. 332, n° 0272-7714, pp. 109767 (14p.), 01/05/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PatriNat, MNHN, IRD, CNRS, OFB - DSUED, OFB, LERAR, COAST, IFREMER
Deciphering copper and zinc leaching from antifouling paints with different operating modes: flux determination and toxicity evidence
Laboratory experiments were performed using 3 antifouling paints with different operating modes immersed in seawater for 7 days, to estimate copper and zinc fluxes and determine the scale of the related contamination. The toxicity of antifouling paints leachates was also assessed for natural bacterioplanktonic and phytoplanktonic communities. Given the increase in copper and zinc concentrations (4 to 1750-fold enrichment in dissolved Cu and to 7 to 200-fold enrichment in dissolved Zn), a systematic mortality upon phytoplankton was evidenced within 2 days of exposure to leachates produced from 1 hour to 2 days of immersion, whatever the paint. This went oppositely with the environmental risks calculated according to European guidelines, demonstrating an acceptable risk for the environment. Considering that 1 hour of leaching from a 7 cm² painted disk polluted 0.5L of seawater with Cu in our experimental conditions whatever the paint used, we estimated that a painted ship hull of 15 m² can pollute more than 10 m 3 of seawater within the same time. Leachates produced after only 20 minutes even yielded phytoplankton growth inhibition or mortality for insoluble and self-polishing paints, respectively, shortening the time needed for a freshly painted ship hull of 15 m² to pollute 10 m 3 . The bacterioplanktonic community appeared less sensitive than phytoplankton but demonstrated the same hierarchy: the highest toxicity was observed for the insoluble matrix and the lowest toxicity for the soluble one. This study therefore brings added value in terms of biocides flux determination, range of studied paints and concrete toxicity evaluation.
(Marine Pollution Bulletin. vol. 225, n° 0025-326X, pp. 119265, 01/04/2026)
MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Assessing spatiotemporal changes in the benthic habitats of the West Gironde Mud Patch through the analyses of surface sediments, benthic macrofauna and sediment profile images
This work aims to refine the current assessment of spatiotemporal changes in the benthic habitats of the West Gironde Mud Patch. It follows a survey based on the analysis of surface sediment characteristics and benthic macrofauna composition at 5 stations located along a depth gradient, which was achieved between 2010 and 2018. The present work extends this observation period to 2021 and includes the indirect assessment of bioturbation through the analysis of sediment profile image characteristics. Temporal changes in surface sediment characteristics were essentially seasonal with strong increases in chloropigment concentrations in spring. Temporal changes in benthic macrofauna composition were mostly interannual with a major difference between 2010 and 2016-2021 currently attributed to the impact of a major physical disturbance during 2013-2014. In this study, extending the observation period shows that full recovery of benthic macrofauna composition had not yet been achieved by 2021. Sediment profile image characteristics (tube and organisms numbers, area of subsurface structures, oxic void depth and aRPD thickness) showed: (i) clear seasonal changes at the two deepest stations, mostly associated with a spring increase in tube numbers; and (ii) no significant difference between 2010 and 2016-2021, except at the deepest station. The discrepancy between benthic macrofauna composition and sediment profile image characteristics may result from differences in the recovery dynamics of benthic macrofauna composition and functionalities. Overall, results clearly call for a further extension of the WGMP observation period, which could consist in a yearly sampling at only two stations.
(Continental Shelf Research. vol. 298, n° 0278-4343, pp. 105637 (14p.), 01/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UA, CHROME, UNIMES, DYNECO, IFREMER
Dominance of cellulosic and synthetic microfibers in upper layers of the Atlantic Ocean: evidence from the Vendée globe 2020 race
This study investigates the large-scale assessment of microplastic and anthropogenic microfiber pollution across the Atlantic Ocean, using continuous upper layer (0-5 m) sampling device aboard a sailing vessel during the Vendée Globe race 2020. Building on 53 samples and around 64 m 3 of filtered seawater, we applied three-stage size filtration 300 μm, 100 μm and 30 μm to capture small-size particles typically undersampled in large-scale oceanic surveys. Microplastic concentrations were inversely proportional to particle size, with the 30-100 μm fraction reaching mean values of 65.09 MP/m 3 -three times higher than the 100-300 μm range and over 60 times higher than for particles >300 μm. Smaller fractions exhibited higher polymeric and morphological diversity, dominated by polyethylene, polypropylene, and epoxy resins, while larger particles were mainly polyester and polyamide microfibers from textile sources. In addition, cellulosic fibers represented 87 % of the anthropogenic microfibers >100 μm, surpassing synthetic counterparts. These included cotton, viscose, and other regenerated or natural fibers, indicating diverse potential sources such as clothes, hygiene products, and cigarette butts. Geographically, high microplastic concentrations were observed in the North Atlantic (~106.2 MPs/m 3 on average) near European coastal regions, whereas lower levels in the South Atlantic subtropical region (~49.8 MPs/m 3 on average) suggest vertical redistribution and spatial heterogeneity mediated potentially by ocean dynamics. These results highlight the need to incorporate all anthropogenic particles across fine-scale size classes into marine pollution international assessments. Continuous, opportunistic sampling using leisure, commercial or race vessels is shown to be a valuable approach for capturing particle diversity in remote and open oceanic regions.
(Marine Pollution Bulletin. vol. 225, n° 0025-326X, pp. 119173, 01/04/2026)
RDT, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CBMN, UB, ENITAB, INC-CNRS, CNRS, LOPS, IRD, IFREMER, INSU - CNRS, UBO EPE, CNRS
Observations and Modelling of Coastal Dune Dynamics Along the Gironde Coast, France
Considered as reservoirs of biodiversity, coastal dunes also represent natural barrier against coastal flooding and large source of sediment to mitigate coastal erosion. Dynamics of coastal dunes are forced and controlled by marine, aeolian and biological processes. A better understanding of the interactions between all these processes based on field observations or numerical modelling is crucial to define management strategies that aim to develop the resilience of coastal dune against sea level rise. The analysis of multi-annual topographic data collected along the Gironde coast in SW France show a strong landward migration of the coastal dunes caused by strong wind events and a decrease in vegetation cover. The same data were also used to calibrate and validate a numerical model, AeoLiS, that simulated Aeolian sediment transport. This model showed good performance to reproduce the landward migration of non-vegetated dune.
(. vol. 41, pp. 141-146, 05/03/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BRGM
Origin and evolution of giant comet marks along the North Atlantic Deep-Water flow on the Demerara plateau
The Demerara Plateau, located in the equatorial Atlantic, is particularly well-suited for recording the activity of the Deep Western Boundary Current (DWBC), which transports North Atlantic Deep Water (NADW) southward into the Atlantic basin. This current, active between 1500 and 3500 m depth, constitutes the deep part of the global thermohaline circulation and plays a crucial role in climate regulation. The Demerara Plateau is remarkable for the abundance and wide distribution of comet mark-type sedimentary structures, which can reach several kilometres in length. These hydrodynamic bedforms, interpreted as erosional features associated with strong bottom currents, are currently used as proxies for deep currents velocities, with minimum formation thresholds estimated between 0.60 and 0.75 m/s according to the literature (Rebesco et al., 2014; Werner et al., 1980). The DIADEM (Dive At DEMerara) oceanographic cruise (Basile and Loncke, 2023) enabled detailed investigation of one such structure using a combination of complementary tools with the aim of better understanding their functioning and evolution with in-situ observation, physical records, and sampling. Those new data were also combined with formerly acquired high-resolution seismic data, allowing a new vision of these bedforms their formation, and their evolution over time. The main findings are the following: (1) comet-marks localize on carbonate mass transported blocs outcropping on the seafloor; (2) Clearly show a polyphase evolution of the bedforms of comet mark presenting alternations of erosion and sedimentation phases. The bedforms therefore record long-term variations in bottom current activity with an alternation of intense hydrodynamic events (erosion) and quieter hydrodynamic periods (deposition) through time, reflecting a complex hydrodynamic history; (3) At present, comet-marks recorded a significant decrease in current velocity within the erosional zones located inside the comet tails associated with fined-grained sediments infill in this area, highlighting the need for cautious interpretation of such features as direct indicators of present-day current intensity; (4) Finally, a result that was not necessarily anticipated but documented by exploring those bedforms with the Nautile submersible, comet-marks host quite important benthic and epibenthic biodiversity with a wide variety of associated species.
(Marine Geology. vol. 493, n° 0025-3227, pp. 107717, 01/03/2026)
CEFREM, UPVD, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOCEAN-CYBIOM, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, LOCEAN-VALCO, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, LOPS, IRD, IFREMER, INSU - CNRS, UBO EPE, CNRS, GEO-OCEAN, UBS, IFREMER, INSU - CNRS, UBO EPE, CNRS, ENTROPIE [Réunion], IRD, UR, CNRS, ISTerre, IRD, INSU - CNRS, USMB [Université de Savoie] [Université de Chambéry], CNRS, Fédération OSUG, UGA
Multi-annual evolution of coastal dunes: Transition from fixed to transgressive dunes state
Most of coastal dunes located in temperate latitudes, especially in the Northern Hemisphere, are relatively stable. However, along the Gironde coast (SW France) substantial dune remobilization has been observed over the last decade following major marine erosion events during the 2013-2014 winter. This study is based on the analysis of a robust dataset including (i) 10 high-resolution Digital Terrain Models (DTMs) derived from airborne LiDAR surveys conducted over a 12-year period (2011-2023) and (ii) 7 Satellite-derived Digital maps of dune vegetation cover derived from Sentinel-2 satellite images acquired between 2017 and 2023. These morphological and biological parameters are linked to forcing parameters derived from observed wind data, to provide a comprehensive analysis of coastal dune changes related to the transition from vegetation-fixed dunes to the development of transgressive dunes. For the first time, morphological and vegetation dynamics are explored over a large spatial scale (tens of km), covering a range of initial dune morphology and sediment supply.
Dunes have transitioned from stable to transgressive states primarily driven by sediment stoss slope recycling process (cannibalism) across a gradient of alongshore variable dune sediment budget, ranging from slightly negative to notably positive (+10 to 15 m 3 /m/yr), Along this coast, transgressive dunes defined as dune migrating via similar stoss and lee slope migration rates, have tripled in number over the last 10 years (reaching ≈ 15 km or 17.3 % of the studied coast). At the center of the Gironde coast where dunes are heavily remobilised, the lee slope of the dune translates landward at a rate of several meters to more than 10 m/year. In the following years, dunes will probably continue to migrate and remobilise across a broader scale if no re-stabilization management plan is implemented.
(CATENA. vol. 264, n° 0341-8162, pp. 109787, 01/03/2026)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CEFREM, UPVD, INSU - CNRS, CNRS, ONF
Drastic changes in tidal hydrodynamics following seagrass decline and their seasonal variations in a shallow lagoon
Over the past decades, seagrasses have drastically declined worldwide, reducing their capacity to regulate flow conditions. Intertidal species have been particularly affected by this decline, yet there is limited understanding of how intertidal seagrass loss influences hydrodynamics in shallow coastal lagoons. In this study, we use a 3D flow-vegetation model that accounts for vegetation effect on mean and turbulent flow, as well as flow-induced leaf bending, to investigate how tidal hydrodynamics respond to seasonal and multi-decadal changes in intertidal seagrass characteristics. The model is applied to the Arcachon lagoon (France), colonized by extensive Zostera noltei and Zostera marina meadows. This study reveals that a short-leaf and flexible seagrass species such as Zostera noltei can regulate tidal hydrodynamics throughout the lagoon due to the presence of broad and dense meadows on the tidal flats. In summer, seagrass decline leads to a significant increase in the 75th percentile in bottom flow velocities (+100 %) on the tidal flats, but to a decrease in the channels (−20 %). However, in winter, the response of tidal hydrodynamics to the reduction in seagrass coverage is far less pronounced. Comparison of simulated scenarios reveals that the multi-decadal decline of Zostera meadows with summer characteristics and the seasonal loss between summer and winter lead to modifications in tidal-flow parameters (current velocities, tidal asymmetry, high-tide water level) of a comparable magnitude. These changes in hydrodynamics likely enhance suspended sediment concentration, reducing light availability, contributing to further seagrass loss, and modifying sediment management for stakeholders due to enhanced siltation in channels.
(Coastal Engineering. vol. 205, n° 0378-3839, pp. 104948 (34p.), 01/03/2026)
LERAR, COAST, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Seasonal dynamics of cable bacteria in an estuarine intertidal mudflat subject to green tides: Implications for the foraminiferal community and test preservation
As many coastal areas draining intensive agricultural activities, Ledano estuary mudflats (French Brittany) experience Ulva proliferation, causing green tides. We studied the seasonal dynamics of sulphoxidizing cable bacteria from April 2019 to July 2020 using microsensors (O 2 , pH, H 2 S). The activity of these filamentous bacteria, called electrogenic sulphur oxidation (eSOx), results in strong acidification and in pore-water CO 3 2depletion in the first few centimeters of sediment (within the suboxic zone). Living and dead benthic foraminiferal assemblages were studied in July 2020 to observe the effects of eSOx on the calcareous meiofauna and their shell preservation in the sediment. eSOx was patchy on the mudflat but persistent throughout the year. It contributed up to 45% of oxygen consumption during the algal mat decay, and exceeded 100% during the flooding period suggesting stimulation by nitrate inputs. The corrosive effect was maximal in July 2020 (ΔpH ~ 1.7, [CO$_3^{2-}$]calc < 10 μM). The living foraminiferal community was sparse and nearly monospecific, dominated by the calcareous species Haynesina germanica, probably due to green tides coupled with eSOx-driven acidification. However, living specimens of H. germanica showed no signs of advanced dissolution of their shell suggesting a biological capacity to survive in such environmental acidification, potentially linked to their photosynthetic capability. In contrast, the dead assemblages displayed greater diversity despite a loss of about 20% of the calcareous shell recording with depth due to the synergetic effect of low salinity and eSOx. Overall, this study shows that green tides strongly influence cable bacteria activity and then, sedimentary biogeochemical processes in eutrophic coastal environments.
(Journal of Sea Research (JSR). vol. 210, n° 1385-1101, pp. 102683, 01/03/2026)
LPG, UM, UA, INSU - CNRS, CNRS, Nantes univ - UFR ST, Nantes Univ, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS