Fishing gears are conventionally made from non-biodegradable materials including polyamide (PA). When lost in the ocean, these gears have long-lasting impacts, including marine littering, microplastics production, leaching of chemicals, and an extended period of ghost fishing due to its durability. The use of biodegradable co-polyester material such as polybutylene succinate co-adipate-co-terephthalate (PBSAT) and polybutylene succinate-co-butylene adipate (PBSA) as fishing gear materials have been considered as a potential solution to reduce the associated impact. Ocean is a complex environment in which multiple degradation paths can occur for plastic materials, and decoupling of factors could aid in understanding the impact of each potential factor. In this study, the focus is on the impact of pure water hydrolysis phenomena on biodegradable co-polyester PBSAT and PBSA in comparison to PA monofilaments through accelerated aging at 40 °C, 60 °C, 70 °C and 80 °C. As a single factor accelerated aging process, the prediction of loss of mechanical strength over time was possible at other temperatures namely 2 °C, 10 °C, 15 °C, 20 °C and 30 °C. Different end-of-life criteria were used. This study concluded that solely through pure hydrolysis, a drastic reduction of the time to reach end-of-life criteria was observed by using biodegradable monofilaments instead of PA, but still longer than the expected service time. For example, at 2 °C, it would take approximately 10 years, 20 years and 1000 years for PBSAT, PBSA and PA to have lost 50 % of their initial stress at break respectively.

From the scientific viewpoint, the deepest ocean includes the least known regions on Earth. Advanced technologies, complex logistics and very specific expertise, requiring adequate funding, are needed for in situ observation of the deep sea. In this paper we present the results of the inspection of the floor of the deepest site in the Mediterranean Sea, the 5122 m in depth Calypso Deep in the Ionian Sea, with the Human Occupied Vehicle (HOV) Limiting Factor by Caladan Oceanic in 2020. The dive videos show the floor of the Calypso Deep littered by anthropogenic debris, with litter concentrations among the highest ever recorded in a deep sea environment. The dominant litter category by material type is plastics, accounting for 88 % of the identified litter items. No interactions have been found between litter and the rare life forms identified so far in the deep Ionian Sea. This illustrates that the deep sea is often a final sink for pollution and as such deserves more attention on associated processes and impacts. Harmonized monitoring and assessment should include the deep sea areas in order to enable efficient mitigation. Our findings provide a strong argument in favour of the urgent implementation at global scale of policy actions to reduce ocean littering thus easing the conservation of unique marine habitats, including the deepest on Earth. Our results also appeal to the society at large in terms of consumption habits, waste reduction, care of the environment and the pressing need for action to protect our ocean.

Driven by eutrophic conditions, AM (algal mat) proliferation is now ubiquitous in coastal areas generating significant ecological and economic impacts. The need to mitigate negative effects has prompted the exploration of removal methods, but neither the success nor the impacts on intertidal mudflats have been assessed. Limited success using a specially-adapted vessel, prompted a shift to manual removal by hand-rake at two UK (Portsmouth and Poole) and two French study sites (Brittany and Normandy). Significant reductions in AM biomass and percentage cover were only observed at one site (Portsmouth), in contrast to significant temporal effects throughout the 180 days at each site. Significant effects of removal on the benthos and birds were also limited to an increase in organic content at Brittany and a reduction in macrofaunal abundance at Poole but with all sites dominated by temporal effects. To assess if AM removal can be used to ameliorate excess nitrogen (N) we calculated the amount of N that could be removed from a site and its potential cost-effectiveness (price of N credit after subtraction of removal costs) within an NTS (Nutrient Trading Scheme). N export by AM removal is influenced by site and season, for example, 66 kg N ha−1 yr−1 (winter) to 95 kg N ha−1 yr−1 (summer) at Poole. N removal rates from some sites (Poole, all seasons; Brittany, autumn) are comparable to other Nature-Based Solutions (NBSs) such as clam aquaculture. However, a single annual AM harvest at these sites yields lower N removal rates compared to seaweed, mussel, and oyster aquaculture. Using a global mean N credit price, the removals at Poole and Portsmouth have medium/high cost-effectiveness across all seasons, potentially generating up to half a million pounds of N credits, which could be increased if post-harvesting value-chains were maximised e.g. biofuel production. Although, implementation at scale could rapidly reduce the many impacts of AMs and contribute to the blue-green bioeconomy revolution, to improve water quality, AM removal must be framed within a multifaceted management process. Previous article in issue

Rayon fibres are well-known materials that were primarily utilised as reinforcement in tyres. Today these materials are perceived as a promising substitute for synthetic fibres, exhibiting good mechanical characteristics and biodegradation in many environments. This paper investigates their potential use for marine structures. It first describes the tensile properties of the fibres and their derived yarns and ropes. These properties are then monitored during seawater ageing and the ultimate biodegradation is characterised by respirometry tests. Both material scales demonstrate rapid degradation rates under biotic conditions (90 % strength reduction after 2 weeks for yarns and 6 months for small ropes) and a relative stability in abiotic conditions. Additionally, the fibres show rapid bio-assimilation rates. The rope construction is demonstrated to have a significant impact on the degradation kinetics, suggesting possible strategies to enhance durability. The results indicate that these rayon fibre ropes may offer an attractive alternative to synthetic fibre ropes to reduce impact where there is a high risk of rope loss at sea.

Human sewage is the main source of contamination of environmental waters with human enteric viruses, that can contaminate food such as shellfish. Metagenomic represents a new way of analyzing viral diversity through an a priori massive parallel sequencing approach. However, the precise identification of enteric viruses in sewage or shellfish matrices, is still challenging due to the low viral load, large diversity of viral genera and the large amounts of matrix masking viral sequences. This work compared three commercial kits using capture-based enrichment during the library preparation, for the diversity of detected enteric viruses and for the identification of viral strains in sewage and shellfish samples, focusing on four families impacting human health. Triplicate libraries were prepared for each sample and each kit. All three kits allowed the characterization of a variety of viral genera. In sewage samples, a large number of long contigs was obtained allowing a precise identification of more than 35 strains. In shellfish samples, long contigs were rarer but allowed the identification of one human astrovirus and one norovirus strains. Of the tested kits, one displayed lower variation between replicates, allowed to sequence a higher diversity of viruses from the four families of interest and yielded a higher number of nearly-whole genomes.

Offshore wind energy may offer many advantages: next to the aim of renewable energy production, offshore wind farms (OWFs) enable multi-purpose opportunities with nature conservation and aquaculture. OWFs may also affect the marine ecosystem. The environmental impact of OWFs is starting to be investigated regarding the effect of novel habitat introduction, underwater noise, electromagnetic fields, or exclusion of fisheries. However, the impact of chemical emissions from OWFs remains largely unknown. It is essential to account for these emissions at an early stage, to comprehensively assess the environmental impact with the objective of developing a future fit-for-purpose regulatory framework to protect the marine environment. This review compiled a literature-based list of potential OWF-related chemical emissions containing >200 organic and inorganic contaminants, including polymers. Compounds are categorised according to data source and emission type. Major gaps in assessing the impact of the compounds are identified, including challenges in environmental monitoring, numerical modelling and assessing the toxicity of individual and mixtures of chemical contaminants on marine organisms and humans consuming potential OWF aquaculture products. A risk-based prioritisation is essential to target the compounds of higher concern and overcome costs linked to assessing a wide variety of chemical contaminants. Although some countries have regulations to reduce OWF chemical emissions, standardized impact assessments or monitoring requirements for OWF-based chemical contaminants have not been established. This stresses the importance of providing more detailed information on occurrence, distribution and impact of OWF chemical emissions as an essential step towards sound ecosystem-based management of OWF installations.

The New Caledonian archipelago is an important hotspot of marine biodiversity. Due to mining activities, urbanization, and industrialization, significant amounts of contaminants are discharged into the lagoon. This study analysed the concentrations, spatial distribution, and potential drivers of 14 metallic compounds and trace elements (MTEs) and 22 persistent organic pollutants (POPs) in ~400 coral reef fish sampled from various sites around New Caledonia, across a gradient from mining centers to remote, uninhabited locations. Boosted regression trees modelling explained between 61 and 86 % of the global variation in MTEs and POPs concentration. Fish body size emerged as the most important correlate of MTEs and POPs concentrations in coral reef fish. Monthly rainfalls were the second most important variable for POPs, whereas the reef area was the second variable explaining MTE concentrations. Our modelling approach allowed us to predict and map the distribution of concentrations at the fish community level for 17 contaminants (9 MTEs and 8 POPs). Predicted concentrations ranged from ~1.5 ng.g−1 (β-endosulfan) to ~11.5 μg.g−1 (Ni), and revealed a widespread contamination throughout the lagoon, from the coast to the barrier reef. Contamination by mining-related elements (Ni, Cr…) were clearly influenced by the surface area of mining registry and to lithology to a lesser extent, whereas Hg contamination strongly depended on biological variables. Our study is the largest of its kind at the archipelago scale, combining data on 36 contaminants in ~400 fish samples with a modelling framework offering insights into underlying processes and spatial data for policy use.

Littoral environments represent the main entry point for pollutants into the sea. Microplastics (MPs) are a growing concern, especially for the Mediterranean basin characterized by densely populated coasts and a semi-enclosed morphology. This article targets MPs associated with a unique coastal habitat - the largest bioconstruction in the Mediterranean (Torre Mileto, Southern Adriatic Sea) built by the reef-building polychaete Sabellaria spinulosa (anellida). We assessed MPs abundance in samples from both bioconstruction and surrounding sediments using stereomicroscopy with UV light and micro-Raman spectroscopy. MPs distribution was analyzed according to substrate (reef vs. sediment), longshore drift (west vs. east side), and reef morphology (hummock vs. platform). Results showed a significantly higher MPs abundance in samples from the western side of the site, potentially related to a longshore drift influence on pollutant distribution. By contrast, no significant differences in MPs abundances were observed in substrates (reefs vs. surrounding sediments) and in reef morphologies (hummock vs. platform), which suggest no direct control of reef-building activity in accumulating MPs. The passive accumulation of MPs, primarily driven by wave action, is likely the main factor explaining the MPs distribution. Micro-Raman Spectroscopy analysis revealed polyethylene terephthalate as the dominant polymer, and fibers as the most abundant morphology; prevalent MPs colors were colorless and black. Data provided here indicate that polychaete reefs temporarily trap MPs, retaining such pollutant in the littoral environment. The mechanism of MPs passive accumulation observed in this study raises questions about the growing risk for this bio-engineered benthic habitats.

The French Mediterranean coast has a long history of anthropogenic metal contamination, yet current contamination levels remain largely unquantified. This study aims to provide a comprehensive overview of metal accumulation along the coastline by establishing natural background levels, identifying spatial contamination patterns, and assessing associated ecological risks. Major elements (Al, Fe) and trace metals (Mn, Pb, Zn, Cd, Cu) were measured in surface sediments from 74 sites and in three sediment cores using ICP-MS, while mercury (Hg) was analyzed using an AMA instrument. Natural background concentrations were determined based on the depth layers of three sediment cores that predate the year 1917. This timeframe has been recognized as the pre-industrial period by applying multivariate change point analysis. Approximately 60 % of sediment samples exhibited a Pollution Load Index (PLI) above 1, indicating significant anthropogenic enrichment across the coast. The Mean Effects Range Median Quotient (m-ERM-Q) exceeded 1 only at Cortiou and Toulon, suggesting a localized ecological risk. At Cortiou, Cd (2.85 mg/kg) and Cu (212.0 mg/kg) were between Effect Range-Low (ERL) and Effect Range-Median (ERM) thresholds, while Pb (264.0 mg/kg), Hg (6.73 mg/kg), and Zn (654.0 mg/kg) were above ERM, due to wastewater discharge. In Toulon Bay, Pb (79.34 mg/kg) and Cu (50,00 mg/kg) were between the ERL and ERM, while Hg (5.57 mg/kg) exceeded the ERM, linked with long-term naval and industrial activities. These findings demonstrate pervasive metal enrichment and ecological risks driven by different sources and highlight the urgent need for targeted mitigation strategies.

Coralligenous reefs are among the most diverse Mediterranean ecosystems, particularly in the circalittoral zone. Shaped by calcified red algae, sponges, cnidarians, and bryozoans, they create a complex three-dimensional structure providing shelter for diverse fauna. These reefs develop either on steep rocky walls or as bioherms when calcified algae are the dominant organisms. Their structure and composition vary with location, depth, substrate, and environmental conditions. Assessing the status of such a complex ecosystem poses significant challenges. Ecosystem-based quality indices (EBQI) have already been applied successfully to various coastal Mediterranean habitats. Using a similar methodology, a new index, the Coralligenous Ecosystem-Based Quality Index (Cor-EBQI), was developed to assess the ecological status of the coralligenous ecosystem. The index incorporates the main functional compartments of these reefs, with each compartment weighted according to its importance in ecosystem functioning. Suitable descriptors were then selected to define five status classes for each compartment. A confidence index was also created to estimate data quality based on criteria such as methodology and expert judgement. Data from 63 sites along the French Mediterranean coast, including the Gulf of Lions, Provence, the French Riviera, Corsica, and Monaco, were analyzed. The ecological status ranged from bad to high, influenced by environmental conditions, geomorphology, anthropogenic pressures, and management practices. The Cor-EBQI is designed to meet the objectives of both the Habitats and Marine Strategy Framework Directives of the European Union. As such, it offers a practical tool for future monitoring networks across the Mediterranean Sea.