French Research Institute for Exploitation of the Sea
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Anisotropic fluorescence emission by diatoms modifies the underwater oceanic light field
No full textFluorescence in phytoplankton and other autotrophic organisms originates within the cell chloroplasts, where a fraction of the absorbed solar radiation is reemitted at longer wavelengths by photopigments. While traditionally employed as an indicator of physiological status, emerging evidence suggests that natural chlorophyll fluorescence (ChlF) may also play unanticipated functional roles in the marine environment. Here, we examine the ChlF emission fields generated by pennate planktonic diatoms, a key phytoplankton group playing a critical role in global biogeochemical cycles. Using cell micromanipulation experiments, we demonstrate that the ChlF emitted by Pseudo-nitzschia fraudulenta (Bacillariophyceae) is markedly anisotropic, a feature attributed to both the cells’ elongated morphology and the arrangement of chloroplasts within the cytoplasm. In these diatoms, fluorescence is preferentially emitted in the transapical direction, accounting for up to 35% of total emission. However, peak ChlF intensities occur at the cell apices, suggesting that the silica frustule focuses fluorescent light emission along the longitudinal axis. At elevated cell densities (~10 6 cells/L), the underwater light field is modulated by the combined effects of ChlF emission anisotropy and preferential alignment of diatom cells within the water column. Numerical simulations indicate that ChlF intensity can vary by up to 15% depending on whether cells are predominantly aligned—commonly in stratified water columns—or randomly oriented. These results suggest that diatom-driven modulation of the light field through structured ChlF emission may influence microscale optical environments, with potential consequences for processes ranging from intercellular signaling to large-scale phytoplankton dynamics, including remote sensing–based assessments of phytoplankton physiology
Late autumn aerosol trace element composition and source tracking over the Southern Mozambique channel
No full textThe southern Mozambique Channel (20–30° S) receives a range of atmospheric influences, from desert dust and fire emissions through to industrial, mining and agricultural emissions, emitted from both Madagascar and southeastern Africa. Our study characterises the trace element composition of aerosols collected between the south of Madagascar and Durban, South Africa during the low dust season. Dust deposition fluxes (40–263 mg m-2 yr-1) calculated fell within the lower range of modelled fluxes estimates, confirming the absence of major dust or fire events during the study. While prevailing air-masses affecting our samples were modelled to originate from long-range particulate transport over the Southern Ocean, a holistic understanding of our sample composition could only be obtained when accounting for sporadic aeolian inputs from the two local landmasses. Notably, we found surprising high levels of Cr (4 ± 2 ng m-3) and Cd (0.02 ± 0.01 ng m-3) in the atmosphere over the southern Channel which could be, at least in part, attributed to emissions from mining (chromite and gold, respectively) and smelting activities (Cu, Zn and Cd co-emission) on both neighbouring landmasses. Our results emphasise the difficulty to track such specific and overlooked atmospheric sources in the absence of known atmospheric tracers. We also stress the need for multi-elemental studies and encourage the use of detailed (cluster) air-mass transport model analysis in regions dominated by the long-range atmospheric transport as complex atmospheric circulation and minor (sporadic) inputs from terrestrial air-masses may have disproportionate impact on the atmospheric composition
Production of 13C-labeled docosahexaenoic acid from heterotrophic marine microorganisms Aurantiochytrium mangrovei and Crypthecodinium cohnii enabling fluxomic applications
No full textDocosahexaenoic acid (DHA, 22:6n-3) is the predominant polyunsaturated fatty acid in the human brain and eyes, playing a crucial role in vision and cognitive development. DHA deficiency has been associated with ocular diseases, such as macular degeneration and glaucoma, as well as neurodegenerative disorders. Since the human body has a limited ability to synthesize DHA from its precursor, alpha-linolenic acid (ALA, 18:3n-3), targeted DHA supplementation is essential for these patients. To investigate DHA metabolism and integration, researchers commonly use stable ( 2 H, 13 C) or radioactive ( 3 H, 14 C) isotopes, which are expensive and not widely accessible, restricting the scope and duration of studies. This study aimed to develop a sustainable method for biosynthesizing uniformly labeled 13 C-DHA by culturing the heterotrophic protists Aurantiochytrium mangrovei and Crypthecodinium cohnii with 13 C-glucose. The major fatty acids (FA) of A. mangrovei included 16:0, 22:5n-6 (DPA), and DHA, with DHA accounting for 50.5% ± 4.9% of the total FA. Gas Chromatography-Mass Spectrometry (GC-MS) analysis revealed a 13 C-enrichment of DHA at 96.7% ± 0.4% after the effective High Performance Liquid Chromatography (HPLC) purification. The predominant FA of C. cohnii were 12:0, 14:0, 16:0, and DHA, with DHA representing around 27% of the total FA and exhibiting a 13 C-enrichment of 86.3% ± 1.6%. Based on FA content, A. mangrovei showed a balanced distribution of neutral and polar lipids, with DHA predominantly in the polar fraction (57.8% ± 3.1%), whereas C. cohnii exhibited a predominance of neutral lipids (82.4% ± 0.3%), which contained the majority of its DHA (57.5% ± 1.0%)
Unveiling the global urban virome through wastewater metagenomics
No full textUnderstanding global viral dynamics is critical for public health. Traditional surveillance focuses on individual pathogens and symptomatic cases, which may miss asymptomatic infections or newly emerging viruses, delaying detection and response. Wastewater-based epidemiology has been used to track pathogens through targeted molecular assays, but its reliance on predefined targets limits detection of the full viral spectrum. Here, we analyse longitudinal wastewater samples from 62 cities across six continents (2017–2019) using metagenomics and capture-based sequencing with probes targeting viruses associated with gastrointestinal disease. We detect over 2500 viral species spanning 122 families, many with human, animal, or plant health relevance. The bacteriophage family Microviridae and plant virus family Virgaviridae dominate the metagenomic dataset, while Astroviridae and Picornaviridae prevail in the capture-based sequence dataset. Virus distributions are broadly similar across continents at the family and genus levels, yet distinct city-level fingerprints reveal geographical and temporal variation, enabling spatiotemporal surveillance of viruses such as astroviruses and enteroviruses. Global wastewater-based epidemiology enables early detection of emerging viruses, including Echovirus 30 in Europe and Tomato brown rugose fruit virus. These findings highlight the potential of wastewater sequencing for the early detection of emerging viruses and population-wide virome monitoring across diverse hosts
Rapport d’expertise concernant l’évaluation initiale de la contamination chimique de lagunes permanentes d’Occitanie (narbonnais), dans le cadre du Life Marha en 2024
No full textCette étude a été réalisée lors de l'évaluation de l'état de conservation des lagunes côtières méditerranéennes, habitat d'intérêt communautaire UE-1150, dans le cadre du Life Marha (2018-2025). Le présent rapport fait le bilan des protocoles utilisés, des résultats obtenus et des indicateurs d’état pour 4 masses d’eau de transition (les étangs de l’Estarac, du Grazel, de Gruissan et de St Paul) dont c’est le premier diagnostic chimique (sauf pour Gruissan). Pour cela, les protocoles DCE « lagune » et OBSLAG ont été mis en oeuvre pour caractériser l’état chimique de ces masses d’eau, à partir de la phase aqueuse via l’emploi d’échantillonneurs intégratifs POCIS, DGT et SBSE
Automatic Analysis of Hydroacoustic Signals Related to the Activity of the Fani Maoré Submarine Volcano
No full textDue to the properties of sound propagation underwater, including the existence of the SOFAR channel, sounds in the ocean can propagate over large distances with little attenuation. This makes passive acoustics a relevant method for monitoring natural events such as ice calving, earthquakes, and underwater volcanic eruptions. However, the lack of automated techniques (e.g., such as beamforming for small‐aperture array) for large (50 km) hydrophone arrays makes the data analysis very time‐consuming; indeed, analysts must recognize signals such as earthquake T‐phases on several hydrophones, manually pick and associate their arrival times to build event catalogs. This lengthy iterative process by trial and error often leads to underutilization of the recorded data and exposes the resulting catalogs to the analyst's subjectivity. Here we propose a pipeline that fully automates the creation of event catalogs from continuous hydroacoustic data in two steps: (a) detection of events at each recording station and (b) association of detections at multiple stations to trilaterate the source. In order to evaluate this approach, we tested it on real data recorded by the Mayotte Hydrophone Network (MAHY), which monitors the activity of the new underwater volcano off Mayotte Island in the Mozambique Channel. Its seismicity and volcanic activity were analyzed with the catalogs obtained
SWOT Satellite Altimetry Observations and Source Model for the Tsunami from the 2025 M 8.8 Kamchatka Earthquake
No full textOn 29 July 2025, an Mw 8.8 earthquake struck off Kamchatka, Russia, generating a Pacificwide tsunami and marking the largest earthquake since the launch of the surface water and ocean topography (SWOT) satellite in 2022. We analyze tsunami observations from SWOT together with three nearby deep-ocean assessment and reporting of tsunamis (DART) buoys to resolve the source of the event. SWOT provided the first high-resolution spaceborne track of a great subduction-zone tsunami, capturing waveforms that reveal complex propagation, dispersion, and scattering. Inversion of the DART time series using Gaussian unit sources shows that the rupture extended 400 km along strike, with peak uplift of 4 m, significantly different from the published finite-fault model. A blended source that combines the DART-inverted uplift with subsidence from the seismic-geodetic model best matches both datasets and reproduces the SWOT observations. Comparison with reconstructions of the 1952 Mw 9.0 Kamchatka earthquake indicates that the 2025 rupture likely reactivated significant portions of the megathrust that broke in 1952 but occurred farther down-dip and with little to no near-trench slip, consistent with its smaller tsunami impact. These findings highlight the hazard implications of short recurrence intervals of great earthquakes and show how rupture style governs tsunami severity. They also demonstrate the value of satellite altimetry for improving tsunami source characterization, post-event forecasting, and understanding of hydrodynamic processes
Nitrogen deposition reveals global patterns in plant and animal stoichiometry
No full textThe elemental content of organisms links cellular biochemistry to ecological processes, from physiology to nutrient dynamics. While plant stoichiometry is thought to vary with climate and nutrient availability across latitudes, the consistency of these patterns across trophic groups and realms remains unclear. Using the StoichLife database, which includes nitrogen and phosphorus content data for 5443 species across 1390 sites, we examine how solar energy (temperature, radiation) and nutrients (nitrogen and phosphorus) influence stoichiometric variation. We find that plant stoichiometry in terrestrial and freshwater ecosystems is more strongly associated with environmental gradients, particularly nitrogen deposition, than animal stoichiometry. Contrary to expectations, temperature, radiation, and labile P show limited global effects. Latitudinal patterns in stoichiometry are more closely associated with species turnover rather than intraspecific variation. Given the strong links between stoichiometry and organismal performance, these findings underscore the need to predict the ecological consequences of anthropogenic disruption to global biogeochemical cycles
Façade Atlantique. 2024. Activité des navires de pêche.
No full textCe document est réalisé dans le cadre du projet « Système d’Informations Halieutiques » (SIH) de l’Ifremer, qui constitue le réseau d’observation des ressources halieutiques et des usages associés. Ce projet s’inscrit dans la mission de service d’intérêt public de l’Ifremer consistant à « connaître, évaluer et mettre en valeur les ressources des océans et permettre leur exploitation durable ». Outre la collecte des données pertinentes permettant l’analyse du secteur des pêches, le SIH a en charge l’élaboration d’indicateurs sur les flottilles de pêche et leur restitution sous forme de synthèses aux différents acteurs de la filière pêche et du grand public
Façade Méditerranée. 2024. Activité des navires de pêche.
No full textCe document est réalisé dans le cadre du projet « Système d’Informations Halieutiques » (SIH) de l’Ifremer, qui constitue le réseau d’observation des ressources halieutiques et des usages associés. Ce projet s’inscrit dans la mission de service d’intérêt public de l’Ifremer consistant à « connaître, évaluer et mettre en valeur les ressources des océans et permettre leur exploitation durable ». Outre la collecte des données pertinentes permettant l’analyse du secteur des pêches, le SIH a en charge l’élaboration d’indicateurs sur les flottilles de pêche et leur restitution sous forme de synthèses aux différents acteurs de la filière pêche et du grand public