French Research Institute for Exploitation of the Sea
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Seismogenic and rheological behaviours from time-dependent analysis of earthquake depth distribution in the Corinth Rift
No full textUnderstanding earthquake depth distribution is critical for improving seismogenesis models. While the spatiotemporal pattern of earthquakes is well studied, transient changes in depth distribution remain poorly explored. In this study, we investigate how crustal rheological parameters influence the depth of earthquakes through time, focusing on the Corinth rift, a well-monitored region experiencing a high-level seismic activity in a homogeneous extensional stress field.
To calculate crustal yield strength profiles, we compile geophysical and geological data, including heat flow, rock compositions and properties, Moho depth and strain rate. These estimates are then compared to a high-quality 11-year seismic catalogue of the region. An inversion approach is applied to identify crustal layers associated with persistent versus sporadic seismicity defined here instead of the conventional background versus clustered seismicity.
Our time analysis reveals that the persistent seismicity nicely matches the theoretical brittle–ductile transition and allows us to confidently define the seismogenic thickness, while sporadic seismicity is clustered at depths associated with swarm occurrences. Both distributions are subject to kilometer-scale changes after magnitude 4.0 – 5.5 earthquakes, evidencing a relaxation process even after moderate magnitude events. We conclude that in specific case studies aiming to compare depth distribution and yield strength in the crust, the application of declustering methods may not be optimal for examining the potential rheological controls on earthquake depth distribution and their temporal variations. Instead, the analysis of persistent and sporadic seismicity defined in this study is more accurate and reliable than a declustering approach and offers new and valuable insights for this comparison
Benthic ecological changes in response to fish farming waste deposition in tropical environment: combining field and modelling approaches
No full textWhile substantial progress has been made in evaluating the ecological carrying capacity (ECC) for fish farming in temperate regions, studies in tropical environment remain scarce, and benthic ecological thresholds are still lacking. This study combines spatial measurements of waste deposition (quantified with sediment traps and depositional modelling approaches), with measurements of sediment physical and biogeochemical properties and macrobenthic community structure at a shallow, non-dispersive site in Martinique. Despite minimal changes in sediment physical and biogeochemical properties, pronounced effects were observed on macrobenthic communities structure. At farm sites, benthic communities were highly perturbed (extremely low diversity and abundance of individuals) and dominated by few individuals of second-order opportunistic species. At sites located between 25 and 150 m from the farm, benthic communities were similar and characterised by higher diversity and abundance, with the presence of sensitive species to OM enrichment. The benthic response was strongly driven by organic waste deposition, which was elevated directly beneath and adjacent to the fish cages. The benthic response to depositional fluxes was best described by M-AMBI index. Notably, the transition from ‘Moderate’ to ‘Poor’ ecological status occurred within a depositional range of 1.2–3.0 kg m−2 year−1 for POM and 0.6–1.1 kg m−2 year−1 for TOC, with model predictions suggesting that these effects may extend up to 30 m from the farm. This study represents a step forward in defining benthic ecological thresholds for tropical fish farming and will help decision makers in fostering the sustainable development of aquaculture in these regions
Fostering Tropical Cyclone Research and Applications with Synthetic Aperture Radar
No full textWe examine how, over its first decade, the Sentinel-1 mission has advanced the estimation of ocean surface winds over tropical cyclones, supported their global monitoring, and fostered related research. C-band S1 Synthetic Aperture Radar have been instrumental in refining wind retrieval algorithms, relying on the co- and cross-polarized normalized radar cross-section sensitivity to the ocean wind–waves, especially for major category (3-5) tropical cyclones observed in wide swath modes. Systematic comparisons with airborne multi-frequency radiometer measurements confirm the ability of Synthetic Aperture Radar to provide estimates of the ocean surface wind field at kilometer resolution during a tropical cyclone (bias of 0.08 m/s, standard deviation of 3.84 m/s, correlation of 0.97) and to extract its main characteristics, including the center of the wind circulation, the maximum possible extent of a given wind speed around the tropical cyclone and the radius of maximum wind. Now available globally and in near-real time at operational tropical cyclone forecasting centers, Synthetic Aperture Radar observations are part of the mix used to diagnose the state of the tropical cyclones and issue warning bulletins. Sentinel-1 decametric-backscatter and kilometric-wind resolutions have also been shown to be a reference for interpreting and calibrating other satellite, in situ measurements, and algorithms. Sentinel-1 synoptic observations benefit from new observing systems. Their synergistic use enables us to provide improved temporal resolution of TCs inner core structural parameters. Research efforts exploiting Synthetic Aperture Radar measurements to document such a dynamical system, infer tropical cyclone boundary layer properties, TC-generated waves, and interactions with the upper ocean are presented. This growing increase in acquisitions from multiple C-band Synthetic Aperture Radar missions (e.g. the Radarsat Constellation Mission) over TCs (a factor of 4 over the last decade), combined with other observational data and numerical models, opens opportunities to revisit robust data-driven approaches. These advances shall support a better representation of tropical cyclones in digital twin frameworks. Both algorithm improvements on existing and future Synthetic Aperture Radar missions are attractive perspectives to provide more accurate predictions and a deeper understanding of these complex weather systems
Environmental consequences of genetic improvement of growth and fillet yield in gilthead seabream: A life cycle assessment from breeding to plate
No full textSelective breeding plays a key role in the sustainable development of aquaculture by improving productivity and efficiency. While breeding programs have initially focused on growth traits, their potential to mitigate the environmental footprint of fish farming remains underexplored. Here, we present a case-study on the long-term environmental consequences of selective breeding during five generations (15 years) for growth and fillet yield in gilthead sea bream Sparus aurata by integrating genetic gain projections into a full supply chain Life Cycle Assessment (LCA), extending from hatchery to final consumer. The potential impacts were calculated in terms of 1 t of fish produced at the farm level and were also expressed per tonne of flesh consumed. Performance data and genetic parameters from families in a seabream breeding program were used to estimate breeding values and under different scenarios. Selection for growth significantly shortened the production cycle, while selection for fillet yield increased the proportion of edible product. Although environmental gains at the farm level were modest (<1 %), substantial reductions (up to 7 % in climate change impacts and cumulative energy demand) were observed when impacts were expressed per kilogram of fillet consumed. Feed production remained the dominant source of environmental burden across all scenarios. By explicitly accounting for post-farm stages - processing, distribution, consumption, and waste management -our study demonstrates that genetic improvement, particularly for fillet yield, can meaningfully reduce the environmental footprint of aquaculture products delivered to the consumer. This case study underlines the importance of integrating full supply chain assessments into genetic selection strategies to drive sustainable innovation in aquaculture
The Overlooked Threat of Global Warming on Elasmobranch Fertility
No full textClimate change is increasingly recognised as a critical threat to global biodiversity, yet its impacts on reproductive processes remain poorly understood in many marine taxa. Elasmobranchs (sharks, skates and rays) represent a particularly vulnerable group due to their peculiar life histories, low fecundity, and diverse reproductive modes. In this review, we synthesise current knowledge on how rising ocean temperatures may affect elasmobranch fertility across key stages of the reproductive cycle, including gametogenesis, mate searching, sperm storage, fertilisation, embryonic development, and offspring production. Evidence from 88 species suggests that thermal stress could impair sperm and oocyte quality, disrupt reproductive timing, alter embryonic growth and survival, and potentially exacerbate sexual conflict. While some reproductive strategies such as embryonic diapause, sperm storage, or behavioural thermoregulation may provide short‐term buffering capacity, their effectiveness under rapid and sustained warming remains uncertain. We further highlight the macroevolutionary significance of elasmobranch reproductive diversity, as well as the conservation implications of fertility constraints under global change. Addressing these knowledge gaps is essential to refining demographic models, improving extinction risk assessments, and guiding the design of climate‐resilient management strategies, including fisheries regulations and marine protected areas. By explicitly linking reproductive biology with conservation policy, we argue that understanding thermal fertility limits is key to predicting elasmobranch population trajectories in a warming ocean
Benchmarking the Taxonomic Resolution of Fish eDNA Metabarcodes Against COI Barcodes
No full textEven though environmental DNA metabarcoding is revolutionizing biomonitoring, many critical steps remain unstandardized, leading to arbitrary choices, particularly regarding the selection of metabarcode, clustering method and similarity threshold, among others. Additionally, these studies were hindered by biases resulting from the presence of mislabeled sequences in international databases such as GenBank and the lack of explicit definitions for taxonomic resolution. To address these issues, we developed a robust framework to compare the performance of 22 metabarcodes derived from the same mitogenomes (all available for Actinopterygians in NCBI) against a standardized taxonomic baseline based on COI Barcode Index Numbers (BINs). This framework allows for the separate quantification of over‐splitting (splitting the same taxon/BIN) and over‐merging (merging different taxon/BIN). Comparison of OTUs obtained with multiple de novo clustering methods to BINs confirmed the metabarcode ranking based on error sums. Although each metabarcode exhibited varying sensitivities to over‐merging or over‐splitting errors, the clustering threshold emerged as the most important factor influencing biodiversity estimates whatever the clustering method. This led us to propose optimal thresholds for each metabarcode to delineate taxonomic levels (metabarcode gaps). Additionally, we found that taxonomic resolution varied significantly among genes, orders and community diversity, but independently of metabarcode length. Overall, the choice of metabarcode and clustering threshold should aim to minimize over‐merging or over‐splitting while ensuring accurate lower taxonomic delineations. A set of documented R functions makes this evaluation of taxonomic resolution easily applicable to any other taxonomic group for which a representative set of full genes or mitogenomes is available
Optimised use of passive samplers enabled early detection of SARS-CoV-2 variants BA.4 and BA.5 in sewage water
No full textWastewater-based epidemiology emerged as a valuable method to monitor the COVID-19 epidemic and the dynamic of SARS-CoV-2 variants. Because of its ease of deployment and low cost, membrane-based passive sampling is a prime alternative for deploying a monitoring network in wastewater, especially when automatic samplers cannot be used. However, the performance of these strategies for the identification of low-abundance viruses needs to be evaluated. Passive sampling using nylon membranes and grab sampling were carried out in parallel in the sewers of two French cities in April and May 2022, for the detection of norovirus GII (NoV GII) and SARS-CoV-2. SARS-CoV-2 sequencing was performed to compare the performance of passive samplers and their paired grab sampler in identifying Omicron sub-lineages. Direct lysis and elution methods from nylon membranes were equally effective for virus recovery and SARS-CoV-2 sequencing. For all sites, the virus concentrations in passive and grab samples were very similar. A near-complete genome coverage at a depth of 30 was obtained for most samples, using ARTIC multiplex PCR (V4.1) and Illumina MiSeq. There was a high proportion of low-frequency mutations for both methods and rare mutations in the S gene were detected, which could reflect the presence of cryptic lineages. Even though a large proportion of BA.2 lineage was detected in sewage, most importantly this study provides the first evidence that the use of passive sampling enables early detection of SARS-CoV-2 variants BA.4 and BA.5, that is, before they are identified in the population
Smoked fish from Gabon: nutritional benefits vs. contaminant risks
No full textSmoked fish is the most common form of fish consumption in many African countries. Smoking is likely to cause changes in nutritional value and in the concentration of certain toxic elements. We assessed these changes in the Bonga shad (Ethmalosa fimbriata, Bowdich 1825). Fatty acids (26), vitamin A, trace elements (14) and polycyclic aromatic hydrocarbons (PAHs, 24) were examined in E. fimbriata at different smoking durations (fresh, 24 h, 48 h and 72 h). Composition of smoked fish revealed high inter-individual variability. Smoking did not affect total fatty acid concentrations, but it led to a 4.5-fold decrease in vitamin A and a decrease in the concentrations of Ca, Mg, Mn, Pb and Sr. Meanwhile, it increased the concentrations of PAHs (by a factor of 42), Cd, Mo and Na. Despite these changes, toxic metals (As, Cd and Pb) and PAHs levels remained within safety limits, except for the B(a)P Toxic Equivalent (TEQ) in 72 h-smoked fish. High inter-individual variability in toxic metals, PAHs and nutrients concentrations is suspected to originate from the heterogeneity of the smoking process, and to natural variation in fish. Overall, our results highlight the safety of artisanal smoked fish for human consumption when processed under certain conditions. To further enhance consumer safety, dietary recommendations would advise ensuring fish skin integrity in order to reduce flesh contamination
Growth, metabolic, and immune responses of lean and fat rainbow trout lines during a starvation-refeeding cycle
No full textUnderstanding how fish with divergent energy reserve profiles respond to feed deprivation is critical for optimizing aquaculture feeding strategies. In this study, we compared two rainbow trout (Oncorhynchus mykiss) lines selected for low (lean, L) or high (fat, F) muscle lipid content. Both lines underwent a 3-week starvation period followed by 3 weeks of refeeding using self-feeders. The L line exhibited faster post-refeeding growth, higher post-refeeding weight gain, and earlier feeding activity concentrated in the morning. Conversely, the F line showed greater weight loss during starvation, reduced haematocrit and innate immune parameters, and limited metabolic recovery. Starvation induced distinct changes in lipid and protein metabolism, hydromineral regulation, and immune responses, with the F line being more metabolically and immunologically impacted. Plasmatic concentrations of calcium and sodium decreased, while chlorides concentrations increased transiently. Principal Component Analysis revealed stronger physiological disruption in the F line during starvation. These findings highlight how fat reserves influence recovery from nutritional stress, offering perspectives for genotype-specific feed management in aquaculture
Sentinel-1 Wave Mode Sar Monitoring of Icebergs Around the Antarctica
No full textThe high-quality global wave mode synthetic aperture radar (SAR) vignettes routinely collected by Sentinel-1 is today extensively exploited for various oceanic and atmospheric phenomena. Yet, these observations still remain largely untapped for iceberg monitoring in the Southern Ocean. As a follow-up to our previous work (Wang et al., 2019b), a dedicated SAR image classifier is built to detect small-sized icebergs (<5 km) that are commonly underrepresented in current recording systems. It has been fine-tuned from the Inception-v3 deep convolutional neural network using a curated dataset of 2,062 iceberg and 15,338 non-iceberg cases. Independent evaluations, based on three additional datasets, achieve high precision and recall rates above 90%. Applied to all WV images acquired between 2016 and 2018 unveils iceberg occurrences around Antarctica. About ~7.5% of the detected icebergs drift into 40°S to 50°S latitudes, while the majority are concentrated poleward of 55°S. The seasonal patterns of SAR icebergs are generally consistent with altimeter-detection estimates, and exhibit advances over the sea ice regions. Linking these SAR icebergs to the reported large icebergs reveals that small icebergs are more likely located to the east of large iceberg trajectories, suggesting the primary driver of underlying ocean currents to their drift. Although precise identification of the shape and position of these small icebergs remains challenging, WV SAR vignettes provide added values to iceberg investigations at scales beyond current operational reports. Not only relevant for the precise monitoring of icebergs across a wider range of sizes, it can become instrumental for our understanding of iceberg tracking, associated dissolution, along with freshwater transport, and their broader impact on global and local climate processes