French Research Institute for Exploitation of the Sea
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Exploring the inhibition of targeted microalgae by a Cylindrotheca closterium non-axenic biofilm
No full textWhile most studies on allelopathic interactions among autotrophic microorganisms focus on free-living aquatic species, little is known about microalgal biofilms, where chemical communication is enhanced by spatial proximity. A co-culture protocol using a disc diffusion method was developed to assess the inhibitory potential of the marine diatom Cylindrotheca closterium growing in non-axenic conditions, against different targeted algal strains. The biofilm exhibited an inhibitory effect on the individual growth of two algal strains, Nannochloropsis oculata and Tetraselmis striata, but did not affect the microalga Porphyridium purpureum. The findings highlight the potential of such allelopathic interactions, making C. closterium a candidate for contamination-resistant algal biofilm technologies. Further research is needed to identify the inhibitory compounds and their microbial producers within the growing biofilm
Migrating Turnstones use Tromelin Island as an opportunistic stopover site during pre-breeding migration
No full textMigrating waders fly huge distances over the sea with no or limited stopovers (Gill et al. 2005, Alves et al. 2016). These birds have behavioral and physiological adaptations limiting the energetic costs of these long and demanding flights (Scheiffarth et al. 2002, Helseth et al. 2005), but it is likely that some birds become disoriented during the flights, occasionally resulting in loss and mortality (Cayford 1993, Melville 1997, Amano et al. 2010, Thompson et al. 2012). In this context, remote islets or islands along the oceanic routes may provide sites for opportunistic stopovers where birds can rest and restore their body condition.
Temporal scales of variability in Regions Of Freshwater Influence on the French continental shelf over two decades
No full textThe Regions Of Freshwater Influence (ROFIs) are defined as the area on the continental shelf in the vicinity of estuaries, where freshwater from the river significantly influence water properties and circulation. These regions are subject to a variety of dynamic forcings, including tides, winds and river runoffs, which exhibit considerable variability. The objective of this study is to identify the dominant time scales of variability of the three major ROFIs (Seine, Loire, and Gironde) of the French continental shelf and their evolution over the last two decades. In order to address these questions, we developed a high-resolution numerical simulation of the physical dynamics of the Bay of Biscay and the English Channel. The results demonstrate that the three ROFIs oscillate on the same two cycles: the semidiurnal cycle, caused by tides, and the annual cycle, linked to the seasonal variation in runoff. At the weekly and monthly time scales, two contrasting dynamics emerge. The Seine ROFI, situated in the eastern English Channel, is predominantly influenced by tides and exhibits a third oscillatory cycle, namely the fortnightly cycle. In the Bay of Biscay, the Loire and Gironde ROFIs are more influenced by wind events that shape their monthly variations. The interannual variations are primarily driven by runoff, with an observed reduction in ROFIs extension over the twenty years simulated correlated with a decrease in runoff. However, the combination of shorter timescale events impacts the interannual variability, leading to years with distinctive dynamics of the ROFIs
Seismicity and thermal structure of the St. Paul Transform System, equatorial Atlantic: Insights from focal depth analysis
No full textThe slow-spreading Mid-Atlantic Ridge is segmented and offset by transform faults. Among these, the St. Paul Transform System (SPTS), located in the equatorial Mid-Atlantic Ridge, is a complex multi-fault system with four transform faults (Transform A, B, C, and D) and three intra-transform spreading segments with a cumulated offset of 630 km. The SPTS is seismically active, with strong strike-slip earthquakes reaching moment magnitudes of 6.9. In this study, we have re-analyzed the focal depth of 35 earthquakes of the Global Centroid Moment Tensor (GCMT) catalog with 5.3³Mw³6.9 occurring at Transform A, B, and C since 2004, using regional surface waveform modelling. In addition, we derived a 3-dimensional half-space cooling thermal structure along the transform system that relates the focal depths to the temperature structure. Our results of focal depths indicated that the seismogenic zone of both Transform A, B, and C reaches from 5 to 18 km below the seafloor, with the deepest earthquakes located at the center area of the strike-slip segments, and shallower earthquakes occur towards the ridge-transform intersections. The comparison with the half-space cooling indicates that the deepest earthquakes are located in a cooler lithosphere located near the center of the transform segments, with their deformations reaching 600–900 °C. These observations challenge previous viscoplastic mantle geodynamic models that indicated a warm temperature toward the center of a transform fault. The main features found at the SPTS are supported by previous studies of focal depth in other transform faults in the Atlantic Ocean, supporting a global pattern and the occurrence of a cooler mantle at the center of the oceanic transform faults
Global calibration of archaeal GDGT-based ocean paleotemperature proxy
No full textTEX₈₆ paleotemperature proxies, derived from GDGTs produced by marine archaea, are widely used to reconstruct past ocean temperatures. However, existing global calibrations often exhibit regionally biased residuals, notably overestimating temperatures in polar regions, and the depth origin of the TEX₈₆ signal remains debated. Here, we compile a global dataset of GDGT distributions from 1,648 surface sediment sites to refine calibration. We find that GDGT-derived indices correlate most strongly with upper ocean (0–200 m) temperatures, with TEX₈₆ᴹᴰ showing the highest correlation with thermocline temperatures and the most uniform residual distribution (R² > 0.86). Application of TEX₈₆ᴹᴰ to sediment cores from tropical and polar regions yields consistent and realistic reconstructions, demonstrating its robustness as a subsurface temperature proxy. We propose a new global calibration for TEX₈₆ᴹᴰ: T_thermocline = 57.3005 × TEX₈₆ᴹᴰ + 36.7460 (R2=0.867, RMSE=3.346℃), which offers improved performance across diverse oceanographic settings and provides a physically grounded approach for reconstructing subsurface paleotemperatures
Zinc stable isotopes in mangrove crabs as tracers of anthropogenic contamination in a tropical estuary
No full textOur study presents a novel approach for tracing anthropogenic zinc (Zn) bioaccumulation in mangrove crabs using Zn stable isotope compositions (δ66Zn). We analyzed δ66Zn and elemental composition in crab tissues from Brazilian mangroves within a coastal lagoon historically impacted by electroplating waste. Crabs from the mangrove area near the old electroplating plant exhibited the highest Zn concentrations in both muscle and hepatopancreas, likely reflecting the high Zn bioavailability in these sediments. In contrast, crabs from other mangrove sites showed minimal variations in Zn concentrations, despite prominent differences in sediment Zn levels. This suggests that crabs regulate their internal Zn concentrations within a specific range, not correlating with external Zn bioavailability. The tissues of crabs from contaminated sites bore heavier δ66Zn, consistent with the δ66Zn left by industrial Zn pollution in sediments. However, δ66Zn did not correlate directly with either bioaccumulated Zn or sediment Zn levels, making it challenging to distinguish between stations with varying contamination degrees. Shifting δ66Zn in crab tissues toward lighter isotopes compared to sedimentary Zn indicates the influence of diet, internal biological fractionation, specific bioaccumulation pathways, or additional Zn sources. Biological fractionation within crabs likely caused muscle tissues to be isotopically lighter than the hepatopancreas, especially in moderately contaminated areas. This first systematic study of δ66Zn within mangrove crabs highlights the need for further research to fully understand isotopic variations in crab tissues and their relationship with environmental, ecological, and physiological factors. Initial findings suggest that sources, bioaccumulation routes, and regulatory mechanisms shape δ66Zn within crab tissues
The fate of carbon, nitrogen and phosphorus in freshwater polyculture mesocosms using both nutrient-balance and stable-isotope assessment
No full textFreshwater polyculture can increase nutrient use by rearing species from different trophic levels. The aim of this study was to quantify nutrient balances and determine the food sources of fish using nitrogen (N) and phosphorus (P) nutrient balances and carbon (δ13C) and N (δ15N) stable isotopes. The contributions of food sources to fish diets were estimated using stable-isotope mixing models. Three treatments were compared in mesocosms: fish-only (F treatment: common carp, roach and largemouth bass), fish-macrophyte (FM treatment) and macrophyte-only (M treatment). Fish were fed with commercial pellets. The results showed that adding macrophytes to the fish did not improve water quality. Chlorophyll-a concentration in F and FM treatments was significantly higher than that in treatment M (8.1, 8.3 and 0.6 µg l−1, respectively). Regardless of the treatment, sediment contained most of the total N and P at harvest (93.5 and 89.7 %, respectively). Carp, roach and bass had a similar specific growth rate in F and FM treatments (1.19, 0.36, 0.94 % day−1, respectively). Carp consumed 90 % commercial feed and 8 % macrobenthic invertebrates, while roach consumed 50 % commercial feed and supplemented their diet with macrophytes (15 %), macrobenthic invertebrates (12 %) and large zooplankton (11 %). Juvenile roach and bass had higher δ15N values than carp and roach did (12.31, 14.55, 7.54, 10.44 ‰, respectively). Bass consumed mainly juvenile roach (59 %), followed by macrobenthic invertebrates (25 %). Combining the nutrient balances and stable isotopes showed that sediment was the main nutrient pool, but that organisms in the mesocosms consumed little sediment organic matter
Cartographie et enjeux de la «BlueTech» en Nouvelle-Calédonie. Pourquoi ce territoire est-il d’innovation en matière marine et maritime ? Vers l’élaboration d’une Directory de ses acteurs et projets
No full textThis article was written in the framework of a mission entrusted to the author by the French Tech New Caledonia. The purpose of this mission is, on the one hand, to investigate why the territory of New Caledonia, as an archipelago in the South Pacific, is a territory of blue innovation. On the other hand, it is to draw up a catalogue of innovative Caledonian projects in terms of «Blue Tech». The article summarizes the work carried out at the end of May 2025 for a presentation to be made during a “side event” of UNOC-3 in Nice, entitled: «The blue economy in the Pacific: Ocean of Innovation, territories of solutions», then an intervention in the framework of the “Pacific Tech Village” under the theme: “Connecting Pacific Minds – Creating global impact”, at the international Innovation Fair VIVA Technologies 2025 in ParisCet article a été rédigé dans le cadre d’une mission confiée à l’auteur par la French Tech Nouvelle-Calédonie. Celle-ci a pour objet : d’une part d’instruire les raisons pour lesquelles le territoire de la Nouvelle-Calédonie, en tant qu’archipel du Pacifique Sud, est un territoire d’innovation bleue. D’autre part il est de dresser un catalogue de projets innovants néocalédoniens en matière de « Blue Tech ». L’article résume le travail effectué en date de fin mai 2025 en vue d’une présentation qui sera effectuée à la faveur d’un « side event » de l’UNOC-3 à Nice, intitulé : « L’économie bleue dans le Pacifique : Océan d’Innovation, territoires de solutions » puis d’une intervention dans le cadre du « Pacific Tech Village » sous le thème : « Connecting Pacific Minds – Creating global impact », à la faveur su salon international de l’Innovation VIVA Technologies 2025 à Pari
