French Research Institute for Exploitation of the Sea
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Technical note: Euclidean Distance Score (EDS) for algorithm performance assessment in aquatic remote sensing
No full textIn the absence of community consensus, there remains a gap in standardized, consistent performance assessment of remote-sensing algorithms for water-quality retrieval. Although the use of multiple metrics is common, whether reported individually or combined into scoring systems, approaches are often constrained by statistical limitations, redundancy, and dataset- and context-dependent normalizations, leading to subjective or inconsistent interpretations. To address this, we propose the Euclidean Distance Score (EDS), which integrates five statistically appropriate and complementary metrics into a composite score. Capturing three core aspects of performance (regression fit, retrieval error, and robustness), EDS is computed as the Euclidean distance from an idealized point of perfect performance, providing a standardized and interpretable measure. We demonstrate the applicability of EDS in three scenarios: assessing a single algorithm for different retrieved variables, comparing two algorithms on shared retrievals, and evaluating performance across contrasting trophic conditions. By offering an objective framework, EDS supports consistent validation of aquatic remote sensing algorithms and transparent comparisons in varied contexts
Capturing dense shelf water cascading with a high-resolution ocean reanalysis
No full textDense shelf water cascading (DSWC) is an oceanographic process that occurs when dense shelf water overflows over the shelf edge downslope toward the deep sea. Monitored in the northwestern Mediterranean by moorings since 1993 in the Lacaze-Duthiers Canyon and since 2005 in the Cap de Creus Canyon, numerical modeling with reanalysis extends this timeline further into the past. This study investigates a regional reanalysis (1987–2021) validated against mooring observations at 750–1000 m depth. The reanalysis successfully reproduces observed intense DSWC (IDSWC) events from 1999, 2000, 2005, 2006, 2012, 2013, and 2018 while identifying one previously unreported event in 1987 and detecting no IDSWC between 1988 and 1998. The reanalysis effectively matches 84 % of observed IDSWC days within the same week and 56 % on the exact date. Instead of assimilating IDSWC events from mooring observations to resolve the cascading process, the model relies solely on the seawater density on the shelf and revealed the seawater properties along the canyon that caused IDSWC. This work highlights the importance of high-resolution reanalyses in investigating the impacts of mesoscale processes on larger scales in the deep ocean
Larval Adaptation to Salinity Shock in Cane Toads (Rhinella marina) From Coastal French Guiana
No full textMany habitats not only differ in mean conditions but also in the degree to which these conditions fluctuate through time. Therefore, local adaptation to both mean abiotic conditions and habitat variability can enhance organismal viability. Within their native range in French Guiana, cane toads (Rhinella marina) inhabit both coastal beach and inland rainforest habitats. We surveyed breeding pools to quantify abiotic conditions. Breeding pools in coastal habitats exhibited high salinity levels and intermittent seawater inflow with rapid increases in salinity. Breeding pools in inland habitats had low, stable salinity levels. Salinity shock only caused mortality within coastal environments. To determine whether larvae were locally adapted to salinity conditions, we raised the offspring of toads collected from 14 inland and coastal sites under a range of salinity levels. We also mimicked seawater inflow by exposing larvae from 15 clutches to sudden increases in salinity to measure their tolerance to salinity shock. Although coastal and inland tadpoles performed similarly under constant salinity, tadpoles from coastal habitats survived a rapid increase in salinity better than did conspecifics from inland habitats. The capacity to tolerate variable environments and adapt to local conditions may have contributed to the cane toad's translocation success
Do offspring characteristics reflect parental migration variation?
No full textSea trout, Salmo trutta, display a wide range of migratory behaviours, and one aspect of variation comes from freshwater migration distance. The overall aim of this study was to determine if offspring of long‐ and short‐distance migrants exhibited phenotypic differences relating to parental migration distance. For that purpose, we conducted several behavioural tests (dyadic contest, boldness scoring and open field test) and morphological analysis (relative pectoral‐fin length) in multiple freshwater systems across the distribution range of the target species in Europe. It was expected that offspring of long‐distance migrants would be more active, bold and dominant than those of short‐distance migrants and would have longer pectoral fins relative to body length. Additionally, we investigated if boldness varied in relation to latitude. We showed that offspring of long‐distance migrants were more dominant in two cases and more active in one case than those of short‐distance migrants; however, there was no difference in swimming distance or velocity. Boldness and relative pectoral‐fin length were significantly related to site of origin; however, the direction of this relationship differed between systems. Generally, we detected a decrease in boldness with declining latitude. In summary, we have detected variation among juveniles related to location within a stream; however, the drivers and processes behind these are likely more complex than purely parental migratory strategy. Our results can inform suitable management and conservation efforts directed to anadromous Salmo trutta. For example, habitat restoration and removal of migration barriers can increase the possible range of migration distances helping maintain the phenotypic diversity of offspring
Avis de l'Ifremer concernant le dossier de demande d'autorisation environnementale relatif aux opérations de dragage d'entretien des fonds portuaires des ports de plaisance et de commerce de Vannes
No full textRanking the cytotoxic potency of Ostreopsis cf. ovata, Ostreopsis cf. siamensis (O. sp. 9), and purified ovatoxins in human keratinocytes
No full textOvatoxins (OVTXs), a family of marine polyketides structurally similar to palytoxin (PLTX), are suspected to cause respiratory symptoms and skin irritation among coastal users during blooms of the dinoflagellate Ostreopsis cf. ovata. To investigate their role in cutaneous toxicity, crude extracts from six O. cf. ovata strains (OVTX(+) and OVTX(−)) and three O. cf. siamensis (O. sp. 9) strains (OVTX(−)), along with six purified OVTX analogs, were tested for cytotoxicity (MTT assay) and cell death phenotypes (microscopy) in human keratinocyte models. Interestingly, cytotoxicity was driven by OVTX content, while OVTX(−) extracts were, on average, 150-fold and >1,000-fold less potent for O. cf. siamensis and O. cf. ovata, respectively. Nevertheless, the latter two induced PLTX-like cell death, suggesting the presence of unidentified PLTX-like toxins. Purified OVTXs exhibited sub-nanomolar cytotoxicity, 3.5- to 12.5-fold lower than PLTX (IC50 = 0.036-0.642 nM vs. 0.011-0.049 nM), ranking in potency: PLTX > OVTX-d > OVTX-b > OVTX-a > OVTX-c > OVTX-e >>> OVTX-h (non-toxic, likely due to ring-opening). This study demonstrates the high toxic potency of OVTXs, close to that of PLTX, while providing a comprehensive cytotoxicity assessment of OVTX analogs, which could be useful for assessing the risks of human exposure
Environmental Variables Influence on Spatial Distribution of Bacterial Communities Across the English Channel in Two Main Productive Seasons
No full textThe English Channel features a wide range of ecological habitats that host numerous biodiversity resources and are submitted to natural and/or anthropogenic pressures. During the ‘EcoPel’ oceanographic campaigns (spring and summer 2018) in French waters of the English Channel and North Sea, a variety of coastal pelagic habitats were sampled for analysing environmental variables and bacterial communities. Results of PCA suggest that main environmental variables were SPM, POM, PIM, salinity and NO2−/NO3+ in spring and salinity, SPM, Si and Chl‐a in summer. The Shannon index suggested summer alpha diversity had higher richness and equitability compared to spring. A clear seasonality in the bacterial community structure was also revealed by hierarchical cluster analysis. Most of the spring communities had a higher proportion of Bacteroidetes while most of the summer communities had a higher proportion of Proteobacteria, Actinobacteria, Verrucomicrobia and Planctomycetes. Based on distance correlations and statistical significance, the spring taxonomic composition was correlated with Chl‐a, PO4, POM, SPM and PIM, while the summer composition was correlated with salinity. According to hierarchical cluster analyses, both environmental variables and bacterial communities seem to be clustered in parallel with the coast, evidencing the main influence of coastal‐offshore gradients and implying possible links with river inputs and phytoplankton/algae dynamics