French Research Institute for Exploitation of the Sea
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Effects of Rain on the Ocean Radar Backscatter at Near-Nadir Incidence Angles: Insights From the Ku-Band SWIM/CFOSAT Under Low to Strong Wind Observations
No full textThe surface wave investigation and monitoring (SWIM) instrument, onboard China and France Oceanography Satellite (CFOSAT), is a Ku-band real-aperture radar, with six beams that illuminate the ocean surface at near-nadir incidences ranging from 0° to 10°. In this study, we investigate the effect of rain on the normalized radar cross section (NRCS) measured by SWIM under both tropical cyclone (TC) and non-TC conditions. Rain primarily attenuates the radar backscatter from the ocean surface. Under non-TC conditions, when wind speeds are below 21 m/s, the NRCS reduction is small (4–5 dB) under heavy rain (>15 mm/h) conditions. The impact of rain generally decreases as wind speed increases, especially at the smallest incidence angle. At low wind speeds, the NRCS reduction is also sensitive to the incidence angle. Based on a simplified model and the differing sensitivities of NRCS to surface roughness at two near-nadir incidence angles, we find that rain also influences the surface signal at incidence angles below 10°, in addition to the dominant effect of atmospheric attenuation, which leads to a consistent NRCS reduction across all wind speeds and incidence angles. Specifically, it contributes positively to NRCS at wind speeds above 7 m/s and negatively at lower wind speeds. This behavior is attributed to increased surface roughness from splashes and ring waves at low wind speeds, and to decreased roughness due to wave damping at moderate and high wind speeds. In TC environments, the NRCS tends to saturate under light to moderate rain rates (15 mm/h) conditions, the NRCS continues to decrease as wind speed increases. In both TC and non-TC conditions, beyond atmospheric attenuation, the impact of rain on surface roughness must be considered to fully explain the observed NRCS variations with wind and rain rate
Mixed messages: Eco-engineered tide pools can provide both positive and negative contributions, with the possibility of increasing introduced species diversity
No full textWith marine urbanisation on the rise, decision makers and managers are aiming to mitigate and offset impacts arising from the destruction of natural habitats. Among the potential solutions features marine eco-engineering, which aims to increase the structural complexity of marine infrastructure to enhance bioreceptivity or to diversify ecological niches. However, despite previous scientific efforts showing an increase of biodiversity and functions on such eco-engineered structures, studies rarely consider potential adverse effects such as increased introduced species diversity. In the present study we investigated whether negative contributions (i.e. increased introduced species diversity) were associated with positive ones (i.e. increased total and native epibenthic biodiversity) in two eco-engineering projects involving artificial intertidal concrete pools in two biogeographic provinces. We showed that species diversity and beta diversity were both higher on the eco-engineered sites compared to the unengineered sites, and species diversity was comparable to that of natural intertidal rocky environments. However, introduced species diversity was sometimes higher than in unengineered habitats, with some introduced species being exclusively associated with the artificial pools in one province. Furthermore, community structures on the eco-engineered sites remained distinct from natural ones, with artificial pools containing typical urban fouling species. For these reasons, we make the case that artificial pools should not be considered as offsetting the destruction of natural habitats. Eco-engineering can however be viewed as a means of increasing the attractivity of marine urban habitats, akin to city parks and green rooftops
Working Group on the Biology and Assessment of Deep Sea Fisheries Resources (WGDEEP)
No full textThe ICES working group on biology and assessment of deep-sea fisheries resources (WGDEEP) provides scientific advice on 25 assessment units including stocks of deep-water species and those on deep shelf areas. Overall, 14 stocks are assessed relative to MSY or a suitable proxy reference points. Full analytical assessments (Category 1) are currently conducted for 3 stocks (aru.27.5b6a, lin.27.5b, bli.27.5b6712).Non-straddling fish stocks in the northwestern Northeast Atlantic Ocean that were historically assessed by WGDEEP, including Greater silver smelt (aru.27.5a14), Blue ling (bli.27.5a14), Atlan-tic wolffish (caa.27.5a), Ling (lin.27.5a), and Tusk (usk.27.5a14), were assessed in 2025 by the Northwestern Working Group (NWWG), and can be found in their report at the following link: https://doi.org/10.17895/ices.pub.29086181 The working group received an update from two benchmarks in 2025: Benchmark workshop on selected deep-sea fisheries stocks (WKBDEEP) for black scabbardfish and Benchmark workshop on application of Stock Synthesis (SS3) on selected stocks (WKBSS3) for blackspot seabream in area 9. Available time-series for international landings and discards, fishing effort, survey indices and biological information were updated for all stocks. The first draft of advice was prepared for 11 stocks this year and the main conclusions are as follows.Black scabbardfish in the Northeast Atlantic has been showing a reduction in abundance, mostly driven by the decrease of fishing effort and catches in the Northern component, proba-bly associated with the ban of trawling below 800 m. As a consequence of changes in effort tar-geted to black scabbardfish of the French trawl fleet that operates in the Northern component, the accepted assessment model could not be updated. The rfb rule was applied for the first time this year to the whole NE Atlantic combined (ICES Division 5.b, subareas 6–7, and Divi-sion 12.b, corresponding to the Northern component; Subarea 8 and Division 9.a, correspond-ing to the Southern component; and Division 27.3.a and subareas 27.1, 27.2, 27.4, 27.10, and 27.14). The length-based fishing pressure proxy (LF = M/Lmean) is below FMSY proxy. Fishing mortality and the spawning stock biomass of greater silver smelt in ICES divisions 5.b and 6.a are estimated to be at sustainable levels. Over the last 30 years, recruitment has varied but maintains the same temporal pattern. Upon applying the MSY approach, the catch advice decreased compared to the previous advice. For greater silver smelt in 6b, 7, 8, 9, 10 and 12 the rfb rule was applied for the second time for the trend-based advice. The survey index from 2024 was agreed not to be valid by the working group, hence the rfb-rule is conducted for the stock with only survey data from 2023 as index A. The fisheries from this area are very minor and there are no directed fisheries. Mean discard rate for the years 2015 to 2024 is 81%. Although the present catches are minor, only 150 kg in 2024, it is important to monitor and follow if new fisheries emerge, as catches have been considerable in the past. For ling in subareas 1 and 2, the biomass index based on the targeted fishery by the Norwegian longliners increased steadily, from 2001 and peaked in 2017. Since then, the index has declined. The rfb-rule was applied for the second time. The advice was reduced by 19.7% compared to the 2024-2025 advice. For ling in Division 5b the recruitment has been very low since 2018 causing the spawning stock to go below Blim in 2024 and the same can be expected in foreseeable future. The fishing mortal-ity is high, as well as the catch, but are expected to decrease for the coming years. ICES issued a zero advice for 2024 and 2025 and chances are high that this will be reiterated for 2026. The rfb rule was applied for the second time for the ling stock in subareas 3, 4, 6-9, 12 and 14. The standardized CPUE series from the Norwegian longline fleet operating in subareas 4 and 6 and Division 3.a where the bulk of the catches are taken was used as a biomass index and length distribution from international commercial catches from 2022 to 2024 was used as Length-Based Indicator (LBI). Since 2022, the CPUE follows a downward trend and LBI indicators are sugges-tive that ling may have been subject to over-exploitation. It should, however, be noted that the biomass stock size index is estimated to be above the proxy reference point Itrigger. Moreover, since the advice is provided for a wide area ICES provides additional information for other areas than those covered by the CPUE index based on the Norwegian longline reference fleet. The Spanish Porcupine survey and an exploratory analysis of biomass index based on IBTS surveys (1990-2024), covering the most of the stock area, are also indicative of a declining trend in the biomass index. Advice for roughhead grenadier was last provided in 2020 for the period 2021-2025. The availa-ble information is insufficient to evaluate stock status or trends. Historical landings are not con-sidered reliable due to suspected species misidentification (i.e. potential confusion in logbooks data between roughhead and roundnose grenadier). Discarding is also known to have taken place in the past, but WGDEEP cannot quantify the corresponding catch. The majority of land-ings of roughhead grenadier are reported from ICES divisions 2.a and 14.b and there are no re-ported catches in the NEAFC regulatory areas in the period between 2020 and 2024. Considering the uncertainty over the status of the stock and vulnerable nature of grenadiers to exploitation, WGDEEP considers that should be no directed fisheries for roughhead grenadier. There are no reported catches of roughsnout grenadier across the Northeast Atlantic and Arctic oceans since 2008. There is very limited data available for this species, and some of the reported historical landings data are considered to be species misreporting. Since the adoption of the Landing Obligation, the misreporting is no longer considered to take place. It is currently not possible to provide quantified advice on fishing opportunities for roughsnout grenadier. For Blackspot seabream in Subarea 10 (Azores grounds), the Category 2 stock assessment was conducted using the SPiCT model for the first time. Model fitting was further improved based on the benchmark recommendations. According to the assessment results, the stock appears to be in a state of potential recovery, as fishing pressure is above FMSY and below Flim, and the ex-ploitable stock biomass is above MSY Btrigger and Blim. For tusk in subareas 1 and 2, the biomass index based on the targeted fishery by the Norwegian longliners increased steadily, from 2004 and peaked in 2017. Since then, the index has been rela-tively stable. The rfb-rule was applied for the second time. The advice was increased by 8.4% compared to the 2024-2025 advice. For tusk in subareas 4 and 7–9. and in divisions 3.a. 5.b, 6.a, and 12.b, the biomass index based on the targeted fishery by the Norwegian longliners increased steadily from 2004 and peaked in 2019. Since then, the index has been declining. The rfb-rule was applied for the second time. The advice was reduced by 23% compared to the 2024-2025 advice
The DeepSea' Nnovation Project: Innovative Sensing and Sampling for Breakthrough Deep-Sea Marine Sciences
No full textThe France 2030 DeepSea'Nnovation project (ANR-21-ESRE-0042, 2021–2029) is dedicated to the development and scientific use of 15 innovative devices for the deep-sea vehicles of the French Oceanographic Fleet operated by Ifremer (IR* FOF). These devices enable in-situ multidisciplinary investigation and exploration of the marine realm from sea-surface to oceanic seafloor. Here, we present the scientific approaches for selecting these new developments which improve the perception and spatial analysis of the environment, increase measurement precision and performance and extend in-situ sampling capacity from metric to micro metric spatial scale. The methodology section provides a detailed overview of the technological approaches required to carry out system integration and scientific validation at sea. Then we describe the 15 instruments developed and integrated on the deepsea underwater vehicles. At last, we provide an overview of scientific outcomes that can be achieved by association of multi-disciplinary devices, thus delivering breakthrough and innovative scientific datasets
Impact of deep learning and post-processing algorithms performances on biodiversity metrics assessed on videos
No full textAssessing the escalating biodiversity crisis, driven by climate change, habitat destruction, and exploitation, necessitates efficient monitoring strategies to assess species presence and abundance across diverse habitats. Video-based surveys using remote cameras are a promising, non-invasive way to collect valuable data in various environments. Yet, the analysis of recorded videos remains challenging due to time and expertise constraints. Recent advances in deep learning models have enhanced image processing capabilities in both object detection and classification. However, the impacts on models' performances and usage on assessment of biodiversity metrics on videos is yet to be assessed. This study evaluates the impacts of video processing rates, detection and identification model performance, and post-processing algorithms on the accuracy of biodiversity metrics, using simulated remote videos of fish communities and 14,406 simulated automated processing pipelines. We found that a processing rate of one image per second minimizes errors while ensuring detection of all species. However, even near-perfect detection (both recall and precision of 0.99) and identification (accuracy of 0.99) models resulted in overestimation of total abundance, species richness and species diversity due to false positives. We reveal that post-processing model outputs using a confidence threshold approach (i.e., to discard most erroneous predictions while also discarding a smaller proportion of correct predictions) is the most efficient method to accurately estimate biodiversity from videos
Regulation of coral assemblages: Spatial and temporal variation in the abundance of recruits, juveniles, and adults
No full textUnderstanding the processes that maintain coral assemblages is of crucial importance given increasing rates of coral mortality on reefs globally. Here, we compared relationships among distribution patterns of recruit, juvenile, and adult corals with distinct life history traits to determine the contribution of early life stages to the structure of adult assemblages at Toliara, southwest Madagascar. Results highlighted a marked spatio-temporal variability in the abundance of all life stages within and between major reef habitats. Indications of stock-recruitment relationships (where the adults drive the abundance of early life stages) were found for Acroporidae, whereas Poritidae and its dominant genus Porites were likely regulated by recruitment-limitation mechanisms (where early life stages drive the abundance of adults), with significant correlations between the abundance of juveniles and those of adults of the subsequent years. We found stronger links between all life stages for Pocilloporidae, indicative of both recruitment-limitation and stock-recruitment relationships. In contrast, no significant correlations were recorded for the category of ‘other’ families, which is likely the result of mixing taxa with different life history traits. In fact, positive correlations between juveniles and adults were found for Galaxea, Cycloseris, and Pavona genera, which made up the ‘other’ category. The discrepancies of regulation processes among coral taxa highlighted here suggest implementing conservation actions that benefit all life stages. Maintaining the biomass of herbivorous fishes and invertebrates to control algal biomass can benefit coral recruitment and decrease mortality of early life stages and adult colonies. Our results also suggest that sites on the outer slope and on patch reefs, which show higher recruitment rates and abundance of adult colonies, could be considered as recruitment hotspots
Assessing the effectiveness of no-take zones on fish populations in the Marine Natural Park of Cap Corse and Agriate, Northwestern Mediterranean Sea
No full textNo-take zones (NTZs) are expected to rebuild exploited fish populations, yet their performance is rarely assessed with species-level indicators. We quantified the reserve effect of the Nonza–San Fiurenzu NTZ (24.2 km2) inside the Marine Natural Park of Cap Corse and Agriate (north-western Mediterranean) and simultaneously compared the effectiveness of two underwater visual census (UVC). Using 488 underwater visual-census transects (2018–2022) we monitored densities, size structure and biomass of three emblematic predators—the common dentex Dentex dentex, dusky grouper Epinephelus marginatus and brown meagre Sciaena umbra—and compared trends with neighbouring fished sectors. Gaussian GLMs related log-transformed density and biomass to protection status, season, year, sea-surface temperature (SST) and chlorophyll-a. Protection was the dominant predictor for E. marginatus and S. umbra: mean densities inside the NTZ were 3–4 times higher than outside, and biomass was enriched by factors of six and four, respectively. For the mobile D. dentex densities did not differ, but biomass was greater in the NTZ, indicating size-selective benefits. SST showed a negative effect on D. dentex and S. umbra; chlorophyll-a had no detectable influence. Cross-transect surveys (two divers) yielded density estimates comparable to—or higher than—the logistically intensive comb protocol (four to eight divers), suggesting that simpler designs can suffice for long-term monitoring. Our results demonstrate that a well-enforced NTZ embedded in a moderately protected park can rapidly enhance biomass and restore size structure of vulnerable Mediterranean predators
Presentation, calibration and testing of the DCESS II Earth system model of intermediate complexity (version 1.0)
No full textA new Earth system model of intermediate complexity, DCESS II, is presented that builds upon, improves and extends the Danish Center for Earth System Science (DCESS) Earth system model (DCESS I). DCESS II has considerably greater spatial resolution than DCESS I while retaining the fine, 100 m vertical resolution in the ocean. It contains modules for the atmosphere, ocean, ocean sediment, land biosphere and lithosphere and is designed to deal with global change simulations on scales of years to millions of years while using limited computational resources. Tracers of the atmospheric module are temperature, nitrous oxide, methane (12,13C isotopes), carbon dioxide (12,13,14C isotopes) and atmospheric oxygen. For the ocean module, tracers are conservative temperature, absolute salinity, water 18O, phosphate, dissolved inorganic carbon (12,13,14C isotopes), alkalinity and dissolved oxygen. Furthermore, the ocean module considers simplified dynamical schemes for large-scale meridional circulation and sea ice dynamics, stratification-dependent vertical diffusion, a gravity current approach to the formation of Antarctic Bottom Water, and improvements in ocean biogeochemistry. DCESS II has two hemispheres with six zonally averaged atmospheric boxes and 12 ocean sectors distributed across the Indian-Pacific, the Atlantic, the Arctic and the Southern oceans. A new extended land biosphere scheme is implemented that considers three different vegetation types whereby net primary production depends on sunlight and atmospheric carbon dioxide. The ocean sediment and lithosphere model formulations are adopted from DCESS I but now applied to the multiple ocean and land regions of the new model.Model calibration was carried out for the pre-industrial climate, and model steady-state solutions were compared against available modern-day observations. For the most part, calibration results agree well with observed data, including excellent agreement with ocean carbon species. This serves to demonstrate model utility for dealing with the global carbon cycle. Finally, two idealized experiments were carried out in order to explore model performance. First, we forced the model by varying Ekman transport out of the model Southern Ocean, mimicking the effect of Southern Hemisphere westerly wind variations, and second, we imposed freshwater melting pulses from the Antarctic ice sheet on the model Southern Ocean shelf. Changes in ocean circulation and in the global carbon cycle found in these experiments are in line with results from much more complex models. Thus, we find DCESS II to be a useful and computationally friendly tool for simulations of past climates as well as for future Earth system projections
Emerging Climate Signals in Oxygen Minimum Zones
No full textThe ocean is losing oxygen due to anthropogenic climate change. This loss is particularly worrying when it occurs in naturally low-oxygen regions, such as the Oxygen Minimum Zones (OMZs) found at mid-depth in tropical oceans, because the expansion of OMZs reduces habitable space for marine life and threatens oxygen-dependent ecosystems. However, detecting the emergence of climate-driven signals is challenging due to internal variability. Here, we isolate externally forced signals of OMZ volume change and regional deoxygenation, and determine their time of emergence using the IPSL-CM6A-LR Large Ensemble. We apply time of emergence analysis to identify when climate-driven signals become statistically distinguishable from natural variability. Our results show that OMZ edges consistently expand, with emergence occurring in the second half of the 20th century, which is in phase with regional mean deoxygenation in the tropical Pacific and tropical Atlantic. In contrast, we reveal a marked spatial asymmetry in the emergence of OMZ core and hypoxic volumes between the northern and southern parts of OMZs. While OMZ core volumes in the tropical North Pacific and hypoxic volumes in the tropical North Atlantic expand, their southern counterparts contract due to a sudden, ventilation-driven oxygen increase from the Southern Ocean at the start of the 21st century. Uncertainties in emergence timing range from 20 to 30 years across ensemble members, and increase substantially in regions influenced by abrupt changes in OMZ ventilation. By linking the emergence of regional deoxygenation to that of OMZ volume changes, climate-driven expansions of OMZ volumes are likely already beginning to emerge, with distinct dynamics between northern and southern tropical oceans
Distinct Microbial Communities Within and On Seep Carbonates Support Long-term Anaerobic Oxidation of Methane and Divergent pMMO Diversity
No full textAt methane seeps worldwide, syntrophic anaerobic methane-oxidizing archaea and sulfate-reducing bacteria promote carbonate precipitation and rock formation, acting as methane and carbon sinks. Although maintenance of anaerobic oxidation of methane (AOM) within seep carbonates has been documented, its reactivation upon methane exposure remains uncertain. Surface-associated microbes may metabolize sulfide from AOM, maintain carbonate anoxia, contribute to carbonate dissolution, and support higher trophic levels; however, these communities are poorly described. We provide insights into microbial diversity, metabolism, activity, and resiliency within and on seep carbonates through amplicon and metagenomic sequencing, incubations, and non-canonical amino acid tagging combined with fluorescence in situ hybridization (BONCAT-FISH). Ca. Methanophaga (ANME-1) dominated the carbonate interiors in active and low activity seeps, co-occurring with Ca. Desulfaltia as main sulfate reducer, potentially a new syntrophic partner in AOM. Single-cell BONCAT-FISH revealed variability in ANME-1 activity, suggesting potential dormancy in carbonates from low activity seep sites. However, incubations with carbonates from low activity seeps (≥24 months) showed exponential AOM reactivation (~44-day doubling), suggesting these carbonates retain the potential as long-term methane sinks under dynamic seepage conditions. Surface-associated microbial communities were heterogeneous and distinct from the carbonate interior and other seep habitats. Anaerobic methane-oxidizing biofilms and sulfide-oxidizing mats were associated with carbonates with high and intermediate AOM rates potentially influencing carbonate precipitation/dissolution. Shared aerobic methanotrophs between carbonate surfaces and invertebrates indicated carbonate surfaces may represent animal epibiont reservoirs. Recovered particulate methane monooxygenases included both aerobic methanotrophs and divergent forms associated with the Methylophagaceae, suggesting a new function in this group