International audience | In coastal ecosystems, top predators are exposed to a wide variety of nutrient and contaminant sources due to the diversity of trophic webs within coastal areas. Mercury contamination could represent an additional threat to shark populations that are declining worldwide. Here we measured total mercury, carbon and nitrogen isotopes as well as mercury isotopes in two co-occurring shark species (the bull shark Carcharhinus leucas and the tiger shark Galeocerdo cuvier) and their prey from a coastal ecosystem of the western Indian Ocean (La Réunion Island), to (i) determine their main trophic Hg source and (ii) better characterize their diet composition and foraging habitat. Hg isotope signatures (Δ199Hg and δ202Hg) of shark prey suggested that bull sharks were exposed to methylmercury (MeHg) produced in the water column while tiger sharks were exposed to mesopelagic MeHg with additional microbial transformation in slope sediments. Δ199Hg values efficiently traced the ecology of the two predators, demonstrating that bull sharks targeted coastal prey in shallow waters while tiger sharks were mainly foraging on mesopelagic species in the slope deeper waters. Unexpectedly, we found a positive shift in δ202Hg (>1‰) between sharks and their prey, leading to high δ202Hg values in the two shark species (e.g. 1.91 ± 0.52‰ in the bull shark). This large shift in δ202Hg indicates that sharks may display strong MeHg demethylation abilities, possibly reflecting evolutionary pathways for mitigating their MeHg contamination.

In coastal ecosystems, top predators are exposed to a wide variety of nutrient and contaminant sources due to the diversity of trophic webs within inshore marine habitats. Mercury contamination could represent an additional threat to shark populations that are declining worldwide. Here we measured total mercury, carbon and nitrogen isotopes, as well as mercury isotopes, in two co-occurring shark species (the bull shark Carcharhinus leucas and the tiger shark Galeocerdo cuvier) and their potential prey from a coastal ecosystem of the western Indian Ocean (La Réunion Island). Our primary goals were to (i) determine the main trophic Hg sources for sharks and (ii) better characterize their diet composition and foraging habitat. Hg isotope signatures (Δ¹⁹⁹Hg and δ²⁰²Hg) of shark prey suggested that bull sharks were exposed to methylmercury (MeHg) produced in offshore epipelagic waters, while tiger sharks were exposed to offshore mesopelagic MeHg with additional microbial transformation in slope sediments. Δ¹⁹⁹Hg values efficiently traced the ecology of the two predators, demonstrating that bull sharks targeted coastal prey in shallow waters while tiger sharks were mainly foraging on mesopelagic species in the deeper waters of the island slope. Unexpectedly, we found a positive shift in δ²⁰²Hg (>1‰) between sharks and their prey, leading to high δ²⁰²Hg values in the two shark species (e.g. 1.91 ± 0.52‰ in bull sharks). This large shift in δ²⁰²Hg indicates that sharks may display strong MeHg demethylation abilities, possibly reflecting evolutionary pathways for mitigating their MeHg contamination.

In coastal ecosystems, top predators are exposed to a wide variety of nutrient and contaminant sources due to the diversity of trophic webs within coastal areas. Mercury contamination could represent an additional threat to shark populations that are declining worldwide. Here we measured total mercury, carbon and nitrogen isotopes as well as mercury isotopes in two co-occurring shark species (the bull shark Carcharhinus leucas and the tiger shark Galeocerdo cuvier) and their prey from a coastal ecosystem of the western Indian Ocean (La Réunion Island), to (i) determine their main trophic Hg source and (ii) better characterize their diet composition and foraging habitat. Hg isotope signatures (Δ199Hg and δ202Hg) of shark prey suggested that bull sharks were exposed to methylmercury (MeHg) produced in the water column while tiger sharks were exposed to mesopelagic MeHg with additional microbial transformation in slope sediments. Δ199Hg values efficiently traced the ecology of the two predators, demonstrating that bull sharks targeted coastal prey in shallow waters while tiger sharks were mainly foraging on mesopelagic species in the slope deeper waters. Unexpectedly, we found a positive shift in δ202Hg (>1‰) between sharks and their prey, leading to high δ202Hg values in the two shark species (e.g. 1.91 ± 0.52‰ in the bull shark). This large shift in δ202Hg indicates that sharks may display strong MeHg demethylation abilities, possibly reflecting evolutionary pathways for mitigating their MeHg contamination.

CMWs (coal mine wastes) as the waste products of coal exploitation or washing plants are a source of pollution that generates waste management problems, especially those that are very old and without a known owner. CMW chemical composition indicates that it contains SiO2-Al2O3-Fe2O3 in such percentages that it can be used in the production of Portland cement clinker, which can lead to potential savings in clinker production, not only in raw material but also in fuels if the CMW has a minimum calorific value and has not suffered self-combustion. After characterization of different CMWs from mining sites located in the north of Spain, six types of CMW have been selected and different raw meal formulations have been designed by software, maximizing the substitution rate of CMW and ensuring a correct raw meal chemical parameters. Along with a reference raw meal, all CMW clinkers were sintered, ground with gypsum, and tested determining the setting time, compressive strength, and soundness. The results of the physico-mechanical tests show that the mechanical performance of the CMW cements was consistent with the European requirements for a CEM Type I cement. CMW, especially those with a residual energetic content, can be utilized in clinker raw meal due to its availability in large quantities at low cost with the further significant benefits for waste management and environmental practices in mining and in cement production processes.

CMWs (coal mine wastes) as the waste products of coal exploitation or washing plants are a source of pollution that generates waste management problems, especially those that are very old and without a known owner. CMW chemical composition indicates that it contains SiO₂-Al₂O₃-Fe₂O₃ in such percentages that it can be used in the production of Portland cement clinker, which can lead to potential savings in clinker production, not only in raw material but also in fuels if the CMW has a minimum calorific value and has not suffered self-combustion. After characterization of different CMWs from mining sites located in the north of Spain, six types of CMW have been selected and different raw meal formulations have been designed by software, maximizing the substitution rate of CMW and ensuring a correct raw meal chemical parameters. Along with a reference raw meal, all CMW clinkers were sintered, ground with gypsum, and tested determining the setting time, compressive strength, and soundness. The results of the physico-mechanical tests show that the mechanical performance of the CMW cements was consistent with the European requirements for a CEM Type I cement. CMW, especially those with a residual energetic content, can be utilized in clinker raw meal due to its availability in large quantities at low cost with the further significant benefits for waste management and environmental practices in mining and in cement production processes.

peer reviewed

The endocrine system of crustaceans regulates the molt cycle with ecdysteroid hormones, mainly the 20-hydroxyecdysone (20-HE). Moreover, the molt process requires the action of chitinolytic enzymes (e.g., chitinase, chitobiase) to break down the old cuticle. However, endocrine disrupting compounds (EDC) are capable of altering their normal functioning. Glyphosate-based herbicides (GBH), such as Roundup®, the most widely used herbicides, are found in freshwater environments and have been considered EDC for many aquatic organisms. Therefore, this study examined the effects of environmentally relevant GBH concentrations (0.0065, 0.065, and 0.28 mg L⁻¹) on the 20-HE concentration and chitobiase activity in the decapod prawn Macrobrachium potiuna exposed for 14 days. Additionally, lipid peroxidation, a biomarker of membrane lipid degradation, was evaluated in hepatopancreas to assess cellular damage. Results showed that GBH decreased the 20-HE concentration in females at the two highest concentrations tested, while an increase was observed in males exposed to the highest GBH concentration. In addition, GBH also decreased chitobiase activity in males (all concentrations) and females (the two highest concentrations). Finally, GBH caused increased lipid peroxidation in males, indicating cellular damage in the hepatopancreas. In conclusion, this work suggests that GBH is an EDC for crustaceans by disrupting molting, which could lead to altered reproduction and thus population dynamics. Graphical abstract Decrease in the 20-HE concentration and chitobiase activity in muscle of males and females of the freshwater prawn Macrobrachium potiuna exposed to the herbicide Roundup® for 14 days

International audience | Monitoring Floating Marine Macro Litter (FMML) is a global priority, stressed within international programs, and regulated for the European Seas by the Marine Strategy Framework Directive. Although some well-defined common protocols exist for the assessment of beach litter and ingested litter, methodologies for FMML monitoring still vary, leading to some inconsistent results and hampering the global assessment of this threat. Within the MEDSEALITTER project (2016–2019), field experiments were implemented to define optimal monitoring parameters for FMML visual monitoring at different spatial scales, by assessing the influence of platform speed, strip width, observers experience, weather conditions, and litter size on its detectability. Along with the results of these experiments, we present the FMML density ranges detected across the over 20,000 km surveyed, highlighting a decreasing gradient from river mouths to coastal areas and the open sea, and providing a valuable contribution to the assessment of FMML in the Mediterranean Sea.

Monitoring Floating Marine Macro Litter (FMML) is a global priority, stressed within international programs, and regulated for the European Seas by the Marine Strategy Framework Directive. Although some well-defined common protocols exist for the assessment of beach litter and ingested litter, methodologies for FMML monitoring still vary, leading to some inconsistent results and hampering the global assessment of this threat. Within the MEDSEALITTER project (2016–2019), field experiments were implemented to define optimal monitoring parameters for FMML visual monitoring at different spatial scales, by assessing the influence of platform speed, strip width, observers experience, weather conditions, and litter size on its detectability. Along with the results of these experiments, we present the FMML density ranges detected across the over 20,000 km surveyed, highlighting a decreasing gradient from river mouths to coastal areas and the open sea, and providing a valuable contribution to the assessment of FMML in the Mediterranean Sea.

peer reviewed | The persistence of pathogenic Agrobacterium strains as soil-associated saprophytes may cause an inconsistency in the efficacy of the biocontrol inoculants under field condition. The study of the interaction occurring in the rhizosphere between the beneficial and the pathogenic microbes is thus interesting for the development of effective biopesticides for the management of crown gall disease. However, very little is still known about the influence of these complex interactions on the biocontrol determinants of beneficial bacteria, especially Bacillus strains. This study aimed to evaluate the effect of the soil borne pathogen Agrobacterium tumefaciens C58 on root colonization and lipopeptide production by Bacillus velezensis strain 32a during interaction with tomato plants. Results show that the presence of A. tumefaciens C58 positively impacted the root colonization level of the Bacillus strain. However, negative impact on surfactin production was observed in Agrobacterium-treated seedling, compared with control. Further investigation suggests that these modulations are due to a modified tomato root exudate composition during the tripartite interaction. Thus, this work contributes to enhance the knowledge on the impact of interspecies interaction on the ecological fitness of Bacillus cells living in the rhizosphere. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.

The persistence of pathogenic Agrobacterium strains as soil-associated saprophytes may cause an inconsistency in the efficacy of the biocontrol inoculants under field condition. The study of the interaction occurring in the rhizosphere between the beneficial and the pathogenic microbes is thus interesting for the development of effective biopesticides for the management of crown gall disease. However, very little is still known about the influence of these complex interactions on the biocontrol determinants of beneficial bacteria, especially Bacillus strains. This study aimed to evaluate the effect of the soil borne pathogen Agrobacterium tumefaciens C58 on root colonization and lipopeptide production by Bacillus velezensis strain 32a during interaction with tomato plants. Results show that the presence of A. tumefaciens C58 positively impacted the root colonization level of the Bacillus strain. However, negative impact on surfactin production was observed in Agrobacterium-treated seedling, compared with control. Further investigation suggests that these modulations are due to a modified tomato root exudate composition during the tripartite interaction. Thus, this work contributes to enhance the knowledge on the impact of interspecies interaction on the ecological fitness of Bacillus cells living in the rhizosphere.

International audience

[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples | Oxythermal window drastically constraints the survival and development of European sturgeon early life phases

European sturgeon Acipenser sturio is an anadromous fish species being classified “critically endangered” with only one remaining population in the Gironde-Garonne-Dordogne basin (France). In the global warming context, this paper aims to determine the sensitivity of A. sturio early life phases to temperature and oxygen saturation. Embryos were experimentally exposed to a combination of temperature (12 to 30 °C) and oxygen (30 to 90% O₂ saturation) conditions. Lethal and sublethal effects were evaluated using embryonic mortality, hatching success, malformation rate, yolk sac resorption, tissue development and swimming speed. Embryonic survival peaked at 20 °C and no survival was recorded at 30 °C regardless of the associated oxygen saturation. No hatching occurred at 50% O₂ sat or below regardless of temperature. Malformation frequency appeared to be minimum at 20 °C and 90% O₂ sat. Swimming speed peaked at 16 °C. The temperature optimum of early life phases of A. sturio was determined to be close to 20 °C. Its upper tolerance limit is between 26 and 30 °C and its lower tolerance limit is below 12 °C. Oxygen depletion induces sublethal effects at 70% O₂ sat and lethal effects at 50% O₂ sat. Within the spawning period in the Gironde-Garonne-Dordogne basin, we identified yearly favourable oxythermal windows. Consequences of climate change would depend of the phenological adaptation of the species for its spawning period.

International audience | Due to the dramatic quantity of plastic debris released into our environment, one of the biggest challenges of the next decades is to trace and quantify microplastics (MPs) in our environments, especially to better evaluate their capacity to transport other contaminants such as trace metals. In this study, trace elements (Fe, Cu, Zn, As, Cd, Sn, Sb, Pb, and U) were analyzed in the microplastic subsurface (200 μm) using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Microplastics subjected to the marine environment were collected on beaches (Guadeloupe) exposed to the north Atlantic gyre. We established a strategy to discriminate sorbed contaminants from additives based on the metal concentration profiles in MP subsurface using qualitative and quantitative approaches. A spatiotemporal correlation of the sorption pattern was proposed to compare MPs in terms of relative exposure time and time-weighted average concentrations in the exposure media.

Due to the dramatic quantity of plastic debris released into our environment, one of the biggest challenges of the next decades is to trace and quantify microplastics (MPs) in our environments, especially to better evaluate their capacity to transport other contaminants such as trace metals. In this study, trace elements (Fe, Cu, Zn, As, Cd, Sn, Sb, Pb, and U) were analyzed in the microplastic subsurface (200 μm) using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Microplastics subjected to the marine environment were collected on beaches (Guadeloupe) exposed to the north Atlantic gyre. We established a strategy to discriminate sorbed contaminants from additives based on the metal concentration profiles in MP subsurface using qualitative and quantitative approaches. A spatiotemporal correlation of the sorption pattern was proposed to compare MPs in terms of relative exposure time and time-weighted average concentrations in the exposure media.

International audience | Due to the dramatic quantity of plastic debris released into our environment, one of the biggest challenges of the next decades is to trace and quantify microplastics (MPs) in our environments, especially to better evaluate their capacity to transport other contaminants such as trace metals. In this study, trace elements (Fe, Cu, Zn, As, Cd, Sn, Sb, Pb, and U) were analyzed in the microplastic subsurface (200 μm) using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Microplastics subjected to the marine environment were collected on beaches (Guadeloupe) exposed to the north Atlantic gyre. We established a strategy to discriminate sorbed contaminants from additives based on the metal concentration profiles in MP subsurface using qualitative and quantitative approaches. A spatiotemporal correlation of the sorption pattern was proposed to compare MPs in terms of relative exposure time and time-weighted average concentrations in the exposure media.