HAL Université des Antilles
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High-resolution mapping of the carbonate system in mangrove porewaters
No full textInternational audienceMangrove ecosystems sequester blue carbon at exceptionally high rates, primarily within sediments. However, the extent and variability of carbon stocks and fluxes remain insufficiently addressed. Organic matter degradation governs dissolved inorganic carbon (DIC) production, while the proton balance of diagenetic reactions determines the proportions of CO₂, HCO₃⁻, and CO₃²⁻, influencing CO₂ flux and long-term carbon sequestration. Alkalinity, mainly controlled by HCO₃⁻, buffers pH fluctuations. Conventional techniques lack the spatial resolution to capture fine-scale geochemical gradients, where biologically driven perturbations and redox stratification create strong variability. This study introduces two-dimensional Diffusive Equilibrium in Thin-films (2D-DET) gels for high-resolution mapping of pH and alkalinity in mangrove porewaters. By combining in situ equilibration with colorimetric analysis, this approach provides sub-millimeter-scale insights into carbonate system dynamics. We applied this method to contrasting mangrove ecosystems along the Brazilian coast: Marapanim (MAR, Pará), a macrotidal coastal plain influenced by seasonal Amazonian rainfall, and Mamanguá (MAM, Rio de Janeiro), a sheltered bay with narrow shorelines and moderate tidal dynamics. Our results reveal substantial microscale and regional heterogeneity in pH and alkalinity. In MAM, sediments exhibit an acidic zone (pH ~5.5–6.0) transitioning to neutral conditions (pH ~7.5–8.0) towards the water column, with bioturbation enhancing mixing. Weaker hydrodynamics contribute to sharp pH gradients
Temporalité et contenu des notifications d’alerte cyclonique diffusées à la population à La Réunion et Mayotte (2023-2025) : des exemples à suivre ?
No full textInternational audienceNumerous alerts (n=10) were broadcasted with the FR-Alert solution during the passage of several cyclonic hazards (n=5) near the islands of La Réunion and Mayotte, from December 2023 to February 2025. But when were these alerts triggered, and with which content ? To answer these questions, this article aims at : 1) analyzing the temporality of the warnings in relation to the vigilance levels set by Météo France, and 2) scoring the content of messages which often explained the nature of the phenomenon in progress and reminded people of the safety instructions expected. Several notifications were sent out 3 hours before the red alert level, allowing time for confinement, and such a practice (introduced in the ORSEC Cyclones plan) can be put into perspective in relation to the kinetics of other dangerous hazards, which could also be the subject of mass alerts.Cet article analyse la temporalité et le contenu de 10 notifications d’alerte cyclonique qui ont été diffusées à la population lors du passage de 5 cyclones (Freddy, Belal, Chido, Garance et Dikeledi), sur les îles de La Réunion et Mayotte, entre décembre 2023 et février 2025. En mobilisant différentes sources de données (les horaires des vigilances de Météo France, les documents de planification opérationnelle en vigueur, le site internet du dispositif FR-Alert, et les résultats d’enquêtes menées auprès des autorités et de la population), cet article met en évidence des points de similitude, mais également certaines particularités territoriales et des évolutions au-fur-et-à-mesure de la pratique. Ces résultats invitent à débattre de la manière d’optimiser les alertes, dans ces territoires mais aussi sur l’ensemble du territoire national
Convergent morphology and divergent phenology: unravelling the coexistence of mimetic Morpho butterfly species
No full textAbstract The emergence and persistence of closely-related species in sympatry is puzzling because the potential gene flow and the common local selective pressures may lead to either merging or competitive exclusion. Some species of Morpho butterflies occurring in sympatry display highly similar wing colour patterns. Associated with erratic flight abilities, their bright colouration may limit predator success and discourage future attacks. The evolution of similar colouration in sympatric species is thus likely under local selection by predators (i.e. escape mimicry). Such phenotypic similarity may promote interspecific territoriality and/or reproductive interference, questioning how closely-related co-mimetic species become sexually isolated and coexist in sympatry. We performed a series of field experiments using flying Morpho dummies placed in a natural habitat where wild males commonly patrol. Analysing the interactions of wild Morpho with different dummies, we show that similarity in wing colour pattern leads to interspecific territoriality and courtship among sympatric species. Using genomic data, we then showed that sympatric Morpho species are surprisingly strictly isolated despite their close relatedness and the observed heterospecific interactions. Finally, using a mark-recapture experiment, we discovered a strong temporal segregation in patrolling activity of males from two co-mimetic sister species. Such divergence in phenology may favour sympatry between closely-related species, despite behavioural interferences induced by the local convergence in colour pattern. Altogether, our findings show that temporal segregation may facilitate the co-existence of closely-related species sharing the same ecological niche, suggesting that phenological shifts may represent an overlooked factor of sympatric speciation. Our study therefore highlights how the evolution of multiple traits may favour species diversification in sympatry by partitioning niche in different dimensions
Dlo la té dlo lanmè. Etude des relations des habitants aux milieux aquatiques en Martinique
No full textInternational audienc
A kinetic model of silica precipitation
No full textInternational audienceSilica precipitation is one of the main technical issues that geothermal plants have to deal with. Indeed, silica has a retrograde behavior, which means that its solubility decreases with decreasing temperature. Consequences of silica precipitation can be dramatic for the surface facilities of the geothermal plant or for the injectivity of reinjection wells.A new kinetic model is proposed to predict silica precipitation risks. It relies on simple relationships that link physical mechanisms (nucleation, aggregation, aging and growth) to physico-chemical parameters (pH, initial dissolved SiO2, ionic strength). The range of conditions of application are the following: 3 < pH < 8, 0 < m_(SiO2)init < 20.8 mmol•kg -1 , 0 < I < 0.5 mol•kg -1 , at 25°C
Shūdan kyūshoku: Ryōri sezu ni hito o yashinau to iu geijutsu
No full textInternational audienceFrench collective catering, once a tool of republican education and solidarity, has gradually been transformed into an industrialized logistics chain. Through relentless rationalization, cold chain systems, and outsourcing, it has lost its connection to life, flavor, and the transmission of knowledge. The cook has become a reheating technician, the child a standardized consumer. Nutritional requirements are dictated by spreadsheets rather than cultural or sensory realities. Yet alternatives do exist: some local authorities are returning to hands-on cooking, promoting local products, and placing food back at the heart of the educational mission. These initiatives show that it is possible to nourish differently: with meaning, flavor… and human warmth.La restauration collective française, longtemps outil d’éducation républicaine et de solidarité, s’est progressivement transformée en une chaîne logistique industrialisée. À force de rationalisation, de liaison froide et de sous-traitance, elle a perdu son lien au vivant, au goût, et à la transmission. Le cuisinier est devenu un opérateur de réchauffage, l’enfant un consommateur standardisé. Les impératifs nutritionnels sont dictés par des tableurs plutôt que par les réalités culturelles ou sensorielles. Pourtant, des alternatives existent : certaines collectivités remettent les mains dans les casseroles, valorisent les produits locaux et replacent l’alimentation au cœur du projet éducatif. Ces initiatives montrent qu’il est possible de nourrir autrement : avec sens, saveur… et chaleur humaine.かつてフランスの集団給食は、共和主義的な教育と連帯の手段として機能していましたが、徐々に産業化された物流チェーンへと変貌していきました。合理化、クールチェーン（冷却配送）、外部委託の進行により、「いのち」や「味」、「知識の継承」とのつながりが失われつつあります。料理人は再加熱作業の技術者となり、子どもは標準化された消費者となりました。栄養の基準は文化的・感覚的な現実ではなく、スプレッドシートによって決められています。しかし、代替手段も存在します。一部の自治体では再び自らの手で料理をし、地元の食材を重視し、食を教育の中核に据え直しています。こうした取り組みは、より意味があり、風味豊かで、人間味あふれる方法で人を養うことが可能であることを示しています
A South American sebecid from the Miocene of Hispaniola documents the presence of apex predators in early West Indies ecosystems
No full textInternational audienceAbsence of terrestrial apex predators on oceanic islands lead to the evolution of endemic secondary apex predators like birds, snakes, and crocodiles and loss of defense mechanisms among species. These patterns are well documented in modern and Quaternary terrestrial communities of the West Indies, suggesting that biodiversity there assembled similarly throughoverwater dispersal. Here, we describe fossils of a terrestrial apex predator, a sebecid crocodyliform with South American origins from the late Neogene of Hispaniola that challenge this scenario. These fossils, along with other putative sebecid specimens from Cuba and Puerto Rico, show that deep-time Caribbean ecosystems more closely resembled coeval localities in SouthAmerican than those of today. We argue that Plio-Pleistocene extinction of apex predators in the West Indies resulted in mesopredator release and other evolutionary patterns traditionally observed on oceanic islands. Adaptations to a terrestrial lifestyle documented for sebecids and the chronology of West Indian fossils strongly suggest that they reached the islands in the Eocene-Oligocene through transient land connections with South America or island hopping. Furthermore, sebecids persisted in the West Indies for at least five million years after their extinction in South America, preserving the last populations of notosuchians yet recovered from the fossil record
Derivation of a standardized index to explore spatial, seasonal and between-year variation of squid (Loligo spp.) abundance in the English Channel
No full textInternational audienceLong-finned squids are among the valuable resources exploited by English Channel demersal fisheries. This resource consists of two short-lived species (not distinguished in landings): Loligo forbesii and Loligo vulgaris, which differ in the timing of their life cycle. In the present study, we investigated spatial, seasonal and long-term biomass variation of Loligo spp. in the English Channel using 22 years (2000–2021) of commercial fishing data to compute biomass indices. Results indicated that landing per unit of effort (LPUE) indices (computed per month for each statistical rectangle of the English Channel), standardized by vector autoregressive spatio-temporal (VAST) method, provided an appropriate squid biomass estimator. Two distinct geographical patterns were observed in the English Channel, with low and stable biomass indices in the West and most of the fluctuations and seasonal variations in East. Within each year, the observed increase in abundance in June is likely to correspond to the recruitment of the loliginid squid into the fishery. Abundance typically rises from June to December and then gradually decreases from January to May. Over the 22-year series there has been an eastward shift in squid biomass since 2014. This information is valuable for fishers but also to manage fisheries, as it offers potential indices of squid availability to the fisheries and a direct quantification of loliginid biomass variability in the ecosystem
Factors Associated with Cognitive Impairment among Adults of 55 Years and Older in Cameroon
No full textInternational audienceIntroduction: Cognitive impairment is a major cause of dependency in older people. The aim of this study was to identify factors associated with severe cognitive decline, as assessed by the mini-mental state examination (MMSE), in communitydwelling adults aged 55+ in Cameroon. Method: Data are from a cross-sectional survey carried out in Cameroon. The cognitive status was assessed using the MMSE and a score of 18/ 30 or lower is considered as a proxy of severe cognitive decline. Result: A total of 403 adults participated in the study. Of these, 16 (3.9%) had an MMSE score <18 and were considered to have cognitive impairment. The rate of severe cognitive decline increased with rising age, from 2.1% in those aged 55-64 years, to 3.3% in those aged 65-74, and 11% in those aged 75 and older. The factors associated with cognitive impairment (MMSE score <18) by multivariate analysis in our population are level of education (OR 0.10 [95% CI: 0.02-0.37], p < 0.01), body mass index (BMI) (OR 0.88 [95% CI: 0.78-0.99], p = 0.03), and IADL score (OR 0.12 [95% CI: 0.03-0.38], p < 0.001). Conclusion: The three main factors associated with cognitive impairment were education, IADL (Instrumental Activity of Daily Living) dependency, and BMI. This study shows that among older people in sub-Saharan Africa, the effect of BMI, IADL dependency, and education on cognitive function appears similar to that observed in middle-and high-income countries.</div
Fusion de séries temporelles d’images satellites Sentinel-2 pour la production d’images et la cartographie des fonds marins de la surface jusqu’aux profondeurs mésophotiques dans le sud-ouest de l’océan Indien
No full textInternational audienceA l’échelle mondiale les écosystèmes sont confrontés à des perturbations et pressions croissantes, entraînant une dégradation globale de leur état de santé. Bien qu’occupant moins de 0,3% de la surface des océans, les récifs coralliens et les herbiers de phanérogames marines sont parmi les écosystèmes marins les plus importants en termes de biodiversité, de protection des côtes, d’alimentation, de sécurité économique et sont essentiels au bien-être de centaines de millions de personnes du monde entier. En raison de leur proximité avec les côtes, ces habitats sont parmi les plus vulnérables de la planète aux menaces liées au changement climatique et aux activités humaines. Cette situation génère un besoin urgent d'améliorer les connaissances pour maintenir leur intégrité et comprendre leur résilience aux différents facteurs de stress. La télédétection optique est couramment utilisée pour cartographier et surveiller les habitats benthiques côtiers. En raison des contraintes liées aux caractéristiques de l'eau sur les images satellites individuelles (effets de surface, atténuation dans la colonne d’eau), ces dernières ne sont souvent utiles que pour cartographier les eaux claires et peu profondes, lorsque les conditions d’acquisition et de luminosité sont les plus favorables. Grâce aux évolutions rapides des capteurs et à la multiplication des missions spatiales, des collections d'images homogènes à hautes résolutions spatiales et temporelles sont aujourd’hui disponibles sur les océans à l’échelle mondiale. Des nouvelles images des fonds marins ont été produites à partir de séries temporelles d'images satellites Sentinel-2.Les chaines de traitement spécifiques développées pour masquer les nuages, corriger les effets de surface, et calculer des statistiques temporelles sur des centaines d’images, ont permis d’améliorer le rapport signal sur bruit des données, révélant des informations sur les fonds marins mésophotiques (> 30m), à des profondeurs beaucoup plus importantes qu’avec les analyses traditionnelles d'images individuelles. Le nombre d'images fusionnées est déterminant pour la profondeur maximale de perception du fond (au-delà de 70 m par endroits). Cette méthode, appliquée sur des îles du sud-ouest de l'océan Indien (La Réunion, les Seychelles) a permis de produire des données d’intérêt dans des secteurs et à des profondeurs jusqu'à présent encore très mal cartographiés. La mise en production de cesalgorithmes sur de larges échelles spatiales permettra de générer des jeux de données de référence pour répondre aux besoins des scientifiques et des gestionnaires