Aliphatic and polycyclic aromatic hydrocarbons (AHs and PAHs, respectively) were analyzed in the dissolved fraction (<0.7 μm) of surface water and in various particulate/planktonic size fractions (0.7–60, 60–200, 200–500 and 500–1000 μm) collected at the deep chlorophyll maximum, along a North-South transect in the Mediterranean Sea in spring 2019 (MERITE-HIPPOCAMPE campaign). Suspended particulate matter, biomass, total chlorophyll a, particulate organic carbon, C and N isotopic ratios, and lipid biomarkers were also determined to help characterizing the size-fractionated plankton and highlight the potential link with the content in AHs and PAHs in these size fractions. Ʃ28AH concentrations ranged 18–489 ng L−1 for water, 3.9–72 μg g−1 dry weight (dw) for the size fraction 0.7–60 μm, and 3.4–55 μg g−1 dw for the fractions 60–200, 200–500 and 500–1000 μm. AH molecular profiles revealed that they were mainly of biogenic origin. Ʃ14PAH concentrations were 0.9–16 ng L−1 for water, and Ʃ27PAH concentrations were 53–220 ng g−1 dw for the fraction 0.7–60 μm and 35–255 ng g−1 dw for the three higher fractions, phenanthrene being the most abundant compound in planktonic compartment. Two processes were evidenced concerning the PAH patterns, the bioreduction, i.e., the decrease in concentrations from the small size fractions (0.7–60 and 60–200 μm) to the higher ones (200–500 μm and 500–1000 μm), and the biodilution, i.e., the decrease in concentrations in plankton at higher suspended matter or biomass, especially for the 0.7–60 and 60–200-μm size fractions. We estimated the biological pump fluxes of Ʃ27PAHs below 100-m depth in the Western Mediterranean Sea at 15 ± 10 ng m−2 day−1, which is comparable to those previously reported in the South Pacific and Indian Ocean.

Plankton plays a prominent role in the bioaccumulation of mercury (Hg). The MERITE-HIPPOCAMPE campaign was carried out in spring 2019 along a north-south transect including coastal and offshore areas of the Mediterranean Sea. Sampling of sea water and plankton by pumping and nets was carried out in the chlorophyll maximum layer. Two size-fractions of phytoplankton (0.7–2.7 and 2.7–20 μm) and five of zooplankton (between 60 and >2000 μm) were separated, and their total mercury (THg) and monomethylmercury (MMHg) contents were measured. Bioconcentration of THg was significantly higher in the smallest phytoplankton size-fraction dominated by Synechococcus spp. The bioaccumulation and biomagnification of MMHg in zooplankton was influenced by size, food sources, biochemical composition and trophic level. MMHg was biomagnified in the plankton food web, while THg decreased toward higher trophic levels. Higher MMHg concentrations were measured in oligotrophic areas. Plankton communities in the Southern Mediterranean Sea had lower MMHg concentrations than those in the Northern Mediterranean Sea. These results highlighted the influence of environmental conditions and trophodynamics on the transfer of Hg in Mediterranean plankton food webs, with implications for higher trophic level consumers.

Macroplastics are ubiquitous in aquaculture ecosystems. However, to date the potential role of plastics as a support for bacterial biofilm that can include potential human pathogenic bacteria (PHPB) and antibiotic-resistant bacteria (ARB) has been largely overlooked. In this study, we used a combination of metabarcoding and standard antibiotic susceptibility testing to study the pathobiome and resistome of macroplastics, fish guts and the environment in a marine aquaculture farm in Mauritius. Aquaculture macroplastics were found to be higher in PHPB, dominated by the Vibrionaceae family (0.34 % of the total community), compared with environmental samples. Moreover, isolates from aquaculture plastics showed higher significant multiple antibiotic resistance (MAR) compared to non-plastic samples of seawater, sediment and fish guts. These results suggest that plastics act as a reservoir and fomite of PHPB and ARB in aquaculture, potentially threatening the health of farmed fish and human consumers.

Structurally complex habitats, such as mangrove forests, allow for rich assemblages of species that benefit from the provided space, volume and substrate. Changes in habitat complexity can affect species abundance, diversity and resilience. In this study, we explored the effects of habitat complexity on food web networks in four developmental stages of mangrove forests with differing structural complexities: climax > degrading > colonizing > bare, by analyzing food web structure, stable isotopes and habitat complexity. We found that food webs became gradually more biodiverse (species richness: +119 %), complex (link density: +39 %), and robust (connectance: −35 %) in climax versus bare stages with increasing complexity of the mangrove forest (i.e., number of trees, leaf cover, and pneumatophore densities). This study shows that habitat complexity drives food web network structure in dynamic mangrove forests. We recommend restoration practitioners to use this food web network approach to quantify habitat restoration successes complementary to traditional biodiversity metrics.

Multirotor drones can be efficiently used to monitor macro-litter in coastal and riverine environments. Litter on beaches, dunes and riverbanks, along with floating litter on coastal and river waters, can be spotted and mapped from aerial drone images. Items detection and classification are prone to image resolution, which is expressed in terms of Ground Sampling Distance (GSD). The GSD is determined by drone flight altitude and camera properties. This paper investigates what is a suitable GSD value for litter survey. Drone flight altitude and camera setup should be chosen to obtain a GSD between 0.5 cm/px and 1.25 cm/px. Within this range, the lowest GSD allows litter categorization and classification, whereas the highest value should be adopted for a coarser litter census. In the vision of drawing up a global protocol for drone-based litter surveys, this work sets the ground for homogenizing data collection and litter assessments.

Multifactorial studies assessing the cumulative effects of natural and anthropogenic stressors on individual stress response are crucial to understand how organisms and populations cope with environmental change. We tested direct and indirect causal pathways through which environmental stressors affect the stress response of wild gilthead seabream in Mediterranean costal lagoons using an integrative PLS-PM approach. We integrated information on 10 environmental variables and 36 physiological variables into seven latent variables reflecting lagoons features and fish health. These variables concerned fish lipid reserves, somatic structure, inorganic contaminant loads, and individual trophic and stress response levels. This modelling approach allowed explaining 30 % of the variance within these 46 variables considered. More importantly, 54 % of fish stress response was explained by the dependent lagoon features, fish age, fish diet, fish reserve, fish structure and fish contaminant load latent variables included in our model. This integrative study sheds light on how individuals deal with contrasting environments and multiple ecological pressures.

Plastics in rivers and lakes have direct local impact, and may also reach the world's oceans. Monitoring river plastic pollution is therefore key to quantify, understand and reduce plastics in all aquatic ecosystems. The lack of harmonization between ongoing monitoring efforts compromises the direct comparison and combination of available data. The United Nations Environment Programme (UNEP) launched guidelines on freshwater plastic monitoring, to provide a starting point for practitioners and scientists towards harmonized data collection, analysis, and reporting. We developed a five-step workflow to support to design effective plastic monitoring strategies. The workflow was applied to three rivers (Rhine, Mekong and Odaw) across relevant gradients, including geography, hydrology, and plastic pollution levels. We show that despite the simplicity of the selected methods and the limited duration of the data collection, our harmonized approach provides crucial insights in the state of plastic pollution in very different river basins globally.

International audience | Soil contamination by trace elements like copper (Cu) can affect soil functioning. Environmental policies with guidelines and soil survey measurements still refer to the total content of Cu in soils. However, Cu content in soil solution or free Cu content have been shown to be better proxies of risks of Cu mobility or (bio-)availability for soil organisms. Several empirical equations have been defined at the local scale to predict the amount of Cu in soil solution based on both total soil Cu content and main soil parameters involved in the soil/solution partitioning. Nevertheless, despite the relevance for risk assessment, these equations are not applied at a large spatial scale due to difficulties to perform changes from local to regional. To progress in this challenge, we collected several empirical equations from literature and selected those allowing estimation of the amount of Cu in solution, used as a proxy of available Cu, from the knowledge of both total soil Cu content and soil parameters. We did the same for the estimation of free Cu in solution, used as a proxy of bio-available Cu. These equations were used to provide European maps of (bio-)available Cu based on the one of total soil Cu over Europe. Results allowed comparing the maps of available and bio-available Cu at the European scale. This was done with respective median values of each form of Cu to identify specific areas of risks linked to these two proxies. Higher discrepancies were highlighted between the map of bio-available Cu and the map of soil total Cu compared to the Cu available map. Such results can be used to assess environmental-related issues for land use planning.

International audience | Heterostructured nanomaterials exhibit pronounced potential in environmental science, including the water purification, pollutant monitoring, and environmental remediation. Especially, their application through advanced oxidation processes has been found capable and adaptable in waste water treatment. In semiconductor photocatalysts, metal sulfides are the leading materials. However, for further modifications, the progresses on specific materials need to be overviewed. Among metal sulfides, nickel sulfides are the emerging semiconductors due to relatively narrow band gaps, high thermal and chemical stability, and cost effectiveness. The aim of the present review is to conduct a thorough analysis and summary of recent progress in the application of nickel sulfide-based heterostructures in water decontamination. Initially, the review introduces the emerging needs of the materials for environment following the characteristics features of metal sulfides with emphasis on nickel sulfides. Subsequently, synthesis strategies and structural properties of nickel sulfide (NiS and NiS2)-based photocatalysts are discussed. Herein, controlled synthesis procedures to influence their active structure, compositions, shape, and size for the enhanced photocatalytic performances are also considered. Furthermore, there is discussion on heterostructures formed by metal modification, metal oxides, and carbon hybridized nanocomposites. In the continuation, the modified characteristics are investigated which favors the photocatalytic processes for degradation of organic contami-nations in water. The overall study highlights significant improvements in degradation efficiency of hetero-interfaced NiS and NiS2 photocatalysts towards organics that are comparable to expensive noble-metal photocatalysts. Finally, we also added a little on prospects for future advancement of nickel sulfide-based photocatalysts for applications in sustainable environmental remediation.

The Millennium Coral Reef Mapping Project (MCRMP) aimed to map coral reefs worldwide at geomorphological thematic scales using Landsat satellite images at 30 m spatial resolution. The 5-level hierarchical classification scheme implemented by MCRMP identified at Level 2 ‘Atolls’ as one of the main types of coral reef complexes. In this review, the qualitative criteria used by MCRMP to identify atolls are presented. Then, we report on the global census of atolls, from which a consistent geomorphologic GIS database is provided. A total of 598 atolls are identified and mapped. The quantitative database provides surface areas for all geomorphologic units at Level 4 and 5 of the MCRMP classification scheme. It allows further work on atoll and coral reef classifications, regionally and globally, in order to identify geomorphic trends and outliers. It is also a convenient database to use in multivariate analyses with ancillary biodiversity, fishery, socio-economic or climate data.