Otolith morphogenesis during the early life stages of fish is temperature-dependent: Validation by experimental approach applied to European seabass (Dicentrarchus labrax).

Otolith shape is often used as a tool in fish stock identification. The goal of this study was to experimentally assess the influence of changing temperature and ontogenic evolution on the shape component of the European seabass (Dicentrarchus labrax) otolith during early-life stages. A total of 1079 individuals were reared in a water temperature of 16°C up to 232 days post hatch (dph). During this experiment, several specimens were transferred into tanks with a water temperature of 21°C to obtain at the end of this study four different temperature treatments, each with varying ratios between the number of days at 16 and 21°C. To evaluate the otolith morphogenesis, samples were examined at 43, 72, 86 and 100 dph. The evolution of normalized otolith shape from hatching up to 100 dph showed that there were two main successive changes. First, faster growth in the antero-posterior axis than in the dorso-ventral axis changed the circular-shaped otolith from that observed at hatching and, second, increasing the complexity relating to the area between the rostrum and the anti-rostrum. To test the effect of changing temperature, growing degree-day was used in three linear mixed-effect models. Otolith morphogenesis was positively correlated to growing degree-day, but was also dependent on temperature level. Otolith shape is influenced by environmental factors, particularly temperature, making it an efficient tool for fish stock identification.

Advancing environmental monitoring across the water continuum combining biomarker analysis in multiple sentinel species: A case study in the Seine-Normandie Basin (France).

Nowadays, biomarkers are recognized as valuable tools to complement chemical and ecological assessments in biomonitoring programs. They provide insights into the effects of contaminant exposures on individuals and establish connections between environmental pressure and biological response at higher levels. In the last decade, strong improvements in the design of experimental protocols and the result interpretation facilitated the use of biomarker across wide geographical areas, including aquatic continua. Notably, the statistical establishment of reference values and thresholds enabled the discrimination of contamination effects in environmental conditions, allowed interspecies comparisons, and eliminated the need of a reference site. The aim of this work was to study freshwater-estuarine-coastal water continua by applying biomarker measurements in multi-species caged organisms. During two campaigns, eight sentinel species, encompassing fish, mollusks, and crustaceans, were deployed to cover 25 sites from rivers to the sea. As much as possible, a common methodology was employed for biomarker measurements (DNA damage and phagocytosis efficiency) and data interpretation based on guidelines established using reference values and induction/inhibition thresholds (establishment of three effect levels). The methodology was successfully implemented and allowed us to assess the environmental quality. Employing multiple species per site enhances confidence in observed trends. The results highlight the feasibility of integrating biomarker-based environmental monitoring programs across a continuum scale. Biomarker results align with Water Framework Directive indicators in cases of poor site quality. Additionally, when discrepancies arise between chemical and ecological statuses, biomarker findings offer a comprehensive perspective to elucidate the disparities. Presented as a pilot project, this work contributes to gain insights into current biomonitoring needs, providing new questions and perspectives.

Harnessing Fishers' local knowledge and their perceptions: Opportunities to improve management of coastal fishing in Mediterranean marine protected areas.

To contribute to the sustainable management of the coastal fishing in the future Marine Protected Area (MPA) of "Taza" (Algeria, SW Mediterranean), the aim of this study was to evaluate the Local Knowledge (LK) of fishers operating near the forthcoming MPA and to understand their conservation-oriented attitudes. Data were collected through interviews and participatory mapping. To this end, 30 face-to-face semi-structured interviews were conducted between June and September 2017 with fishers, collecting socioeconomic, biological, and ecological information in the fishing harbor of Ziama (Jijel, NE Algeria). The case study focuses on both professional and recreational coastal fisheries. This fishing harbor is located in the eastern part of the Gulf of Béjaia, a Bay located within the area of this future MPA, but outside its boundaries. Based on fishers' LK, cartography of fishing grounds within the MPA perimeter was obtained, while the perceived healthy bottom habitats and polluted areas in the Gulf were mapped by the use of a hard copy map. The results show that fishers present detailed knowledge that is consistent with literature about different target species and their breeding seasons, showing awareness about the reserve effects 'spillover' in enhancing local fisheries. Overall, the fishers noted that the good management of the MPA relies on limiting trawling in coastal areas and avoiding land-based pollution within the Gulf. Some of such management measures are already included in the proposed zoning plan, but lack of enforcement is a perceived constraint. Given the gap observed between the two shores of the Mediterranean Sea in terms of both financial resources and MPA coverage, the use of local knowledge system (e.g., fishers' LK and their perceptions) can enable the implementation of a cost-effective method to encourage the creation of new MPAs in the Southern shore for more ecological representativeness systems of MPAs at a Mediterranean scale. Therefore, this work offers management opportunities that may be used for addressing the lack of scientific knowledge in managing coastal fishing and valuing MPAs in Southern Mediterranean low-income countries characterized by a data-poor context.

Vertical distribution of microplastics in a river water column using an innovative sampling method.

Due to limitations of sampling methods, subsurface water is usually a less well-investigated compartment of the water column when scientists assess microplastic contamination. In this study, microplastic (MP) contamination was assessed in a freshwater river both in surface and subsurface using an innovative sampling method. Microplastic contamination in the lower part of the water column, i.e., near-bottom water and in sediments, was also studied. Three sampling campaigns were carried out during different weather conditions: stormy, rainy, and dry in order to observe their influence on the microplastics vertical distribution. No significant difference was observed between the abundance and types of MPs in surface and subsurface water. The proportion of polymer with theoretical density < 1 (polypropylene d = 0.9, polyethylene d = 0.91-0.95) and polystyrene (d = 0.1-1.06) in the surface and subsurface samples was 73.5%, and this proportion drops to 40.8% for the samples located in the near-bottom water and the sediments. Our results indicate that the MP concentration of the different compartments analyzed can be significantly influenced by rainfall during and prior to the sampling day. This study highlights that in shallow rivers, surface water sampling is representative of the water column MP contamination, but that sampling without taking environmental conditions into account may lead to erroneous estimation of MPs concentration and flux entering the marine environment.

Optimization, performance, and application of a pyrolysis-GC/MS method for the identification of microplastics.

Plastics are found to be major debris composing marine litter; microplastics (MP, < 5 mm) are found in all marine compartments. The amount of MPs tends to increase with decreasing size leading to a potential misidentification when only visual identification is performed. These last years, pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS) has been used to get information on the composition of polymers with some applications on MP identification. The purpose of this work was to optimize and then validate a Py-GC/MS method, determine limit of detection (LOD) for eight common polymers, and apply this method on environmental MP. Optimization on multiple GC parameters was carried out using polyethylene (PE) and polystyrene (PS) microspheres. The optimized Py-GC/MS method require a pyrolysis temperature of 700 °C, a split ratio of 5 and 300 °C as injector temperature. Performance assessment was accomplished by performing repeatability and intermediate precision tests and calculating limit of detection (LOD) for common polymers. LODs were all below 1 µg. For performance assessment, identification remains accurate despite a decrease in signal over time. A comparison between identifications performed with Raman micro spectroscopy and with Py-GC/MS was assessed. Finally, the optimized method was applied to environmental samples, including plastics isolated from sea water surface, beach sediments, and organisms collected in the marine environment. The present method is complementary to µ-Raman spectroscopy as Py-GC/MS identified pigment containing particles as plastic. Moreover, some fibers and all particles from sediment and sea surface were identified as plastic. Graphical abstract ᅟ.

Nematodes parasitizing Trachurus trachurus (L.) and Boops boops (L.) from Algeria.

A total of 455 Boops boops (Linnaeus, 1758) and 953 Trachurus trachurus Linnaeus, 1758 from the east coast of Algeria were examined for their parasitic Nematoda. Two hundred ninety-five specimens of larval stages L3 and L4 were collected from the peritoneal cavity of these two examined fishes. Photonic and scanning electronic microscopy (SEM) studies were performed on these larvae specimens in order to characterize their morphology. Two different species of Nematoda (Anisikidae) were identified: Anisakis simplex (Rudolphi, 1809) and Hysterothylacium aduncum (Rudolphi, 1802). These two parasitic species were reported for the first time on T. trachurus and B. boops from the eastern coast of Algeria. These parasites were attached on different organs in the abdominal cavity (particularly on ovaries and testes). The infestation rate changed according to the month and the host size. The parasitism did not show a significant negative impact on the condition of the examined fishes.

Former uranium mine-induced effects in caged roach: a multiparametric approach for the evaluation of in situ metal toxicity.

To characterize environmental risks linked to former uranium mines in the Limousin region of France, a study was conducted on fish health effects from uranium releases. Two private ponds were compared in this study, one with uranium contamination and one background site, upstream of the mining zone. Roach, Rutilus rutilus, were caged for 28 days in both ponds. Physico-chemical parameters of water and sediments and bioaccumulation of metals in several organs were determined. After 14 and 28 days of caging, immune, oxidative stress, biotransformation, neurotoxicity and physiological parameters were measured. Iron and aluminium were quantified in the water of both sites; however, barium and manganese were only present in the water of the uranium contaminated site. Uranium was present in both sites but at very different concentrations. The sediments from the uranium contaminated site contained high levels of radioactive elements coming from the disintegration chain of uranium. Results of biological parameters indicated stimulation of immune parameters and of oxidative stress and a decrease of AChE in fish caged in the uranium contaminated pond compared to the uranium-free pond. Overall, the results determined roach health status in the context of pollution from poly-metallic mining. The data strengthen our knowledge of the environmental risk assessment associated with radioactive substances in the environment.

Harbour porpoises (Phocoena phocoena) stranded along the southern North Sea: an assessment through metallic contamination.

Throughout the last few years, the southern North Sea has witnessed an increase in the number of stranded marine mammals, particularly the harbour porpoise (Phocoena phocoena). This species is subject to several potential threats such as exposure to contaminants, changes in food supply, marine traffic and fishery by-catch. The aims of this study were to investigate potential associations between contaminants and health status and to analyze spatial and temporal trends of metal concentrations in harbour porpoises. Selected trace elements (As, Cd, Cr, Cu, Hg, Mn, Se, V and Zn) were measured in kidneys and livers of 105 harbour porpoises stranded along the southern North Sea (French and Belgian coasts from 2006 to 2013) and 27 stranded along the Bay of Biscay (French coast from 2009 to 2012). Porpoises that died from infectious disease displayed significant higher hepatic concentrations of Cd, Hg, Se and Zn compared to healthy porpoises that died from physical trauma. Adult porpoises displayed significant higher concentrations of Cd, Cr, Hg, Se and V in livers compared to juveniles. No spatial or temporal trends in metal concentrations were detected in our study. The results of the present study suggested that chemical contamination may represent one of many threats encountered by harbour porpoises, but it cannot explain alone the increase in the number of stranded individuals.

A scanning electron microscopy study of Argulus vittatus (Rafinesque-Schmaltz, 1814) (Crustacea: Branchiura) from Algerian coast.

A study of the Algerian Branchiura, Argulus vittatus (Rafinesque-Schmaltz, 1814) was conducted using the scanning electron microscopy (SEM). New morphological features are reported for the first time (mouth con, first maxilla, second maxilla, structures and ornamentation of thoracic segments, structure of semen papillae, etc.). The morphology of small and large female specimens was compared. Two new hosts, Pagellus erythrinus L. and Sparus aurata L., are reported for this species. Until now, six host species were reported for A. vittatus, and stenoxenic specificity for Sparid fishes was observed for Algerian specimens. The biogeographical distribution of this species seems to be restricted to the eastern coast of Algeria. Additional information about the host specificity, ecology, and life cycle of this parasitic species were given.

To what extent is blue mussels caging representative of microplastics in the natural environment?

Bivalves have gained prominence in active biomonitoring of microplastics (MPs) pollution. Nevertheless, critical questions persist regarding blue mussels' selectivity and representativeness of the presence of microplastics in the natural environments. In this current study, we explored short- and long-term exposure durations for caged mussels, aiming to establish the minimum period required for them to attain a steady-state in microplastics retention and investigate their selectivity in a real-world context. Various deployment periods (1, 2, and 5 weeks) were tested, with concurrent collection of MPs from the surrounding water each week. The results revealed a significant increase in ingested MPs, reaching a threshold of approximately 1.4 MPs per gram of wet weight during the fifth week of caging. The characteristics of MPs found in mussels exhibited some differences from those collected in the surrounding waters and were less temporally variable. Notably, the collected caged mussels demonstrated a tendency to retain smaller particles (<80 µm). This study underscores complex processes governing MPs selection in natural environments and the need for further research to gain a more comprehensive understanding of the conditions and suitability of mussels as bioindicators for assessing MPs pollution.

Do tidal fluctuations affect microplastics distribution and composition in coastal waters?

The hydro-meteorological conditions in marine environments are recognized to have a major impact on the transport and dispersion of microplastics (MP), although their precise effects remain poorly understood. This study investigates the effects of tidal fluctuations on MP abundance and composition in a megatidal coastal water. Waters samples were collected every ninety minutes over the course of two complete tidal cycles - one during spring tide and another during neap tide. There were no significant disparities in term of abondance, size, and composition of MPs between the samples collected during the two tidal cycles. Nevertheless, MP abundance and characteristics (morphology, size and polymer types) can be influenced over the course of a complete tidal cycle due to the impact of tidal currents and water height. This study highlights the need to consider the fluctuations of the tidal cycle when planning in-situ surveys to better assess MP pollution in coastal environments.

Microplastic inputs to the Mediterranean Sea during wet and dry seasons: The case of two Lebanese coastal outlets.

Few studies have highlighted the impact of urbanization and meteorological events on the quantity of microplastics (MPs) discharged into the sea through rivers. To evaluate this issue in the Mediterranean Basin, surface water samples were collected from two more or less urbanized Lebanese Rivers: the Nahr Ibrahim (S1) and the Nahr Antelias (S2), during dry and wet periods. A significant higher abundance of 14.02 ± 9.8 particles/L was reported in the most industrialized river S2 compared to 1.73 ± 1.38 particles/L at S1. A correlation was found between particle contamination and the season at each site. Our results indicate that the MP concentrations were highest on the first sampling day of the wet season and tended to decrease progressively with increasing cumulative precipitation. Some polymers were identified only during one season. Meteorological events should be taken more specifically into account in order to define the influx of plastic pollution into coastal waters more accurately.

Relevance of flounder caging and proteomics to explore the impact of a major industrial accident caused by fire on the Seine estuarine water quality.

On September 26th 2019, a major fire occurred in the Lubrizol factory located near the Seine estuary, in Rouen-France. Juvenile flounders were captured in the Canche estuary (a reference system) and caged one month in the Canche and in the Seine downstream the accident site. No significant increases of PAHs, PCBs and PFAS was detected in Seine vs Canche sediments after the accident, but a significant increase of dioxins and furans was observed in water and sewage sludge in the Rouen wastewater treatment plant. The proteomics approach highlighted a dysregulation of proteins associated with cholesterol synthesis and lipid metabolism, in fish caged in the Seine. The overall results suggested that the fire produced air borne dioxins and furans that got deposited on soil and subsequently entered in the Seine estuarine waters via runoff; thus contaminating fish preys and caged flounders in the Seine estuary.

An innovative approach for microplastic sampling in all surface water bodies using an aquatic drone.

The lack of one standardized method to evaluate microplastic pollution in different aquatic environments worldwide represent a gap to fill for the scientist's community. To help overcome this challenge, we adapted an aquatic drone, named Jellyfishbot®, to sample microplastics. The aquatic drone has been compared with the actual most used method for sampling MPs in surface waters: the Manta net. In order to test the reliability of the aquatic drone in different environments, samples were collected in a river and coastal waters sites. The results obtained with the two methods were similar in term of MPs abundances, shapes and colors. It provides also a better reproducibility and more accurate sampling of MPs located in the surface waters mainly the lighter and smaller ones. This sampling method has the advantage of combining the benefits of Manta net sampling (i.e. a representative surface water sampling method that covers a large sampling area and volume (several tens m3) with those of pump filtration and grab sampling (easy access to confined and hard-to-reach areas). This new sampling method could be applied in different aquatic environments making it possible to compare the data and hence become a new standardized approach to evaluate microplastic pollution levels.

Spatio-temporal contamination of microplastics in shellfish farming regions: A case study.

The seasonal pattern of microplastics (MPs) contamination of the French littoral area of the Pertuis Charentais, one of the main French shellfish production regions, was assessed for the first time, between May 2019 and May 2020 at four different sites. The reference site was located at "Ile de Ré" and the other sites were located in the estuaries of the Sèvre Niortaise, Charente and Seudre rivers. Both blue mussels (Mytilus edulis) and Pacific oysters (Magallana gigas), that are considered sentinel species for the quality of the marine environment were analysed, along with sediment and seawater samples. MPs were extracted from each sample, counted, measured and sorted by colour and type. Micro-Raman spectroscopy was used to determine the proportion of confirmed MPs and the polymer types. The results showed that the contamination of mussels by fibres and fragments (1.9 ± 2.1 MPs/g ww) was significantly higher than for oysters (0.4 ± 0.4 MPs/g ww). Specifically, the contamination by fibres in both species was significantly greater than the contamination by fragments. Significant variations of MPs contamination were observed across the seasons and sites in bivalves, and depended on the species and the type of MPs (fibres or fragments). Mean concentrations of MPs measured in water and sediment were 0.007 MPs/L and 210 MPs/kg dw, respectively. Finally, blue was the dominant colour for fibres (79 %) and fragments (81 %). Blue fragments were mainly made of PS (70 %) followed by PC (18 %) and PP, PA or PLA (3 %) whereas blue fibres were mainly made of PA (80 %) followed by PET (13 %) or PP (7 %). This rare environmental case study of long-term chronic exposure of farming areas to MPs provides new knowledge on in situ variations of plastic fibres and fragments contamination throughout the seasons.

Role of estuarine habitats for the feeding ecology of the European eel (Anguilla anguilla L.).

This study aims to characterize and compare the feeding ecology of the European eels (Anguilla anguilla L.) during the continental phase (i.e. yellow and silver) along a salinity gradient (i.e. lower, middle and upper) in six northern France estuaries (i.e. brackish water). The diet and stable isotopic (i.e. δ15N and δ13C values) compositions of eels collected with a fyke net in six estuaries (Slack, Wimereux, Liane, Canche, Authie and Somme estuaries) located along the French coast of the eastern English Channel per season over a year were described by combining gut content and stable isotope analyses. Eel guts were dominated by typical BW prey, Malacostraca and Actinopterygii (54% and 40%, respectively), with the gammare Gammarus zaddachi and the green crab Carcinus maenas (38% and 14%, respectively), and smaller yellow eels of A. anguilla and juvenile European flounder, Platichthys flesus (19% and 14%, respectively) being the most frequently found in their guts. The δ13C values of a majority of eels confirmed the sea- and brackish water-specific carbon resources. Dietary and isotopic niche revealed no clear change between total length, silvering stages and seasons, but a significant difference between salinity gradients and estuaries. Eels δ13C values showed significant enrichment from upper to lower along the estuaries while the δ15N values showed an inverse effect, with the lowest values in the lower part and highest in the upper part. Higher variability in δ13C values in larger estuaries suggested that eels feed on a wide range of food sources than in smaller estuaries. While eels in the smaller estuaries fed mainly on Actinopterygii prey, eels in the larger ones had a lower trophic level (i.e. δ15N values) and fed mainly on Malacostraca prey. This spatial difference in dietary and isotopic niche is discussed in relation to biological structure of eel and environmental variables.

Bioaccumulation of trace metal elements and biomarker responses in caged juvenile flounder at a polluted site: Effects of fish density and time exposure.

This study investigates the effect of fish density and exposure duration on trace metal elements (TME) bioaccumulation and several biomarkers response. Juvenile flounders were caged at low, medium and high densities and exposed during 15 or 30 days in the Seine estuary. The concentrations of the TME measured in the muscle of the caged fish were all in agreement with their bioavailability percentage in the sediments. Higher concentrations of TME were found in flounders' muscle exposed for 15 days compared with those caged for 30 days. For the same exposure time, the density of fish had no effect on the accumulation of the TME in the flounders' muscle. Biomarkers responses varied according to density and duration of exposure. Special care should be taken in their interpretation. We underline that for an optimal assessment of TME pollution in the field, 15 days with low densities of fish per cage are sufficient.

Impacts of chemical stress, season, and climate change on the flounder population of the highly anthropised Seine estuary (France).

The main objective of this study was to improve our knowledge on the responses of fish populations to multistress (diffuse pollution and warming waters) in estuaries. Adult flounders were caught in two estuaries in the Eastern English Channel: the heavily polluted Seine estuary vs the moderately contaminated Canche estuary. Fish samplings were conducted in January just before the reproduction period, and in July when gonads were at rest. The overall rise in coastal winter water temperatures detected over the Channel impairs the flounder's phenology of reproduction in the two estuaries, inducing a delay of maturation process and probably also spawning. The higher liver histopathology index in Seine vs Canche could be the consequence of the fish exposition to a complex cocktail of contaminants in a strongly industrialized estuary. Higher levels of neurotoxicity, gill lipid peroxidation, and liver EROD activity were observed in Seine vs Canche. Furthermore, a possible impairment in mitochondrial metabolism was suggested in the Seine flounder population. We confirmed in this study the potential role of two membrane lipids (sphingomyelin and phosphatidylserine) in the resistance towards oxidative stress in Seine and Canche. Finally, we suggest that the Seine flounder population (and possibly the connected Eastern English Channel flounder populations over the French Coast) could be seriously impacted in the future by multistress: higher winter temperatures and chemical contamination.

Is blue mussel caging an efficient method for monitoring environmental microplastics pollution?

The effectiveness of mussel caging for active microplastics (MPs) biomonitoring was investigated for the first time by comparing abundance and characteristics (shape, size, color and type of polymers) of MPs ingested by caged depurated blue mussels with those ingested by native mussels collected at the same sites and with those found in their surrounding environment (surface water and sediments). Mussels were exposed along a pollution gradient originating from a wastewater treatment plant discharge and near an abandoned coastal landfill. After 6 weeks of deployment, the majority (93%) of clean transplanted mussels had ingested MPs with a mean number of items ranging from 0.61 to 1.67 items/g. The occurrence, abundance and properties of MPs ingested by caged mussels were similar to those found in native mussels. Among the debris items detected in caged and native mussels, fragments were the most predominant type, consistent with the MPs found in their surrounding environment. MPs sizes were very similar whether in the water, sediments and both caged and native mussels, with a dominance of items <150 µm. Although some polymers were under-represented or totally absent in the caged mussels compared to overlying seawater or surrounding sediment, there was a good overlap in polymer types proportion being found between caged mussels and sediments (Morisita's index of similarity = 0.93) or seawater (0.86). Polystyrene dominated all samples in all the different matrices. Our study suggests that blue mussels caging may be a promising tool for MPs biomonitoring making monitoring more reliable with an accurate assessment of the biological effects of MPs over a predetermined exposure period. However, further methodological improvements should be considered to define a uniform protocol for blue mussels caging to allow spatial and temporal microplastics active biomonitoring.

Seasonal and Spatial Variability of Trace Elements in Livers and Muscles of Three Fish Species from the Eastern Mediterranean.

Levels of 20 trace elements (Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Ag, Cd, Sn, Sb, Ba, Hg, Pb, and U) were assessed in livers and muscles of two demersal fish species (Siganus rivulatus and Lithognathus mormyrus) and one pelagic species (Etrumeus teres) from the Lebanese coast located in the Eastern Mediterranean. The samples were collected from three sites along the Lebanese coast during the wet and dry seasons in 2017. The trace elements were more concentrated in livers than in muscles and interspecific differences were also found. The herbivorous species S. rivulatus showed the highest levels for most trace elements, while the carnivorous species L. mormyrus showed the least contamination. Elemental seasonal differences were species dependent and were observed for Ti, Cr, Mn, Fe, Ni, As, and Hg, with higher values during the wet season. Multivariate analysis showed spatial differences mainly during the wet season, while being closely related to species that reflected different accumulation patterns in each site. Levels of most trace metals in livers were higher than those reported in other Mediterranean regions (up to 2 to 3 folds). Nevertheless, the levels of Cd, Pb, and Hg in fish muscle were below the maximum levels set by the European Commission indicating that the consumption of these fish species is not likely to have adverse effect on human health. However, exposure depends on dietary habits of the population and a continuous exposure to these elements may result in adverse effects.