Coastal environments, essential for about half of the world's population living near coastlines, face severe threats from human-induced activities such as intensified urbanization, aggressive development, and particularly, coastal sewage pollution. This type of pollution, comprising untreated sewage discharging nutrients, pathogens, heavy metals, microplastics, and organic compounds, significantly endangers these ecosystems. The issue of sewage in coastal areas is complex, influenced by factors like inadequate sewage systems, septic tanks, industrial and agricultural runoff, and natural processes like coastal erosion, further complicated by oceanic dynamics like tides and currents. A global statistic reveals that over 80 % of sewage enters the environment without treatment, contributing significantly to nitrogen pollution in coastal ecosystems. This pollution not only harms marine life and ecosystems through chemical contaminants and eutrophication, leading to hypoxic zones and biodiversity loss, but also affects human health through waterborne diseases and seafood contamination. Additionally, it has substantial economic repercussions, impacting tourism, recreation, and fisheries, and causing revenue and employment losses. Addressing this issue globally involves international agreements and national legislations, but their effectiveness is hindered by infrastructural disparities, particularly in developing countries. Thus, effective management requires a comprehensive approach including advanced treatment technologies, stringent regulations, regular monitoring, and international cooperation. The international scientific community plays a crucial role in fostering a collaborative and equitable response to this pressing environmental challenge.

This study addresses the pressing issue of plastic pollution in coastal and marine ecosystems, challenging the misconception that the entrapment of plastics can be considered as an ecosystem service. We differentiate between essential natural processes that sustain ecological balance and biodiversity and the detrimental accumulation of synthetic polymers. The pathways through which plastics enter these environments—from terrestrial to maritime sources—are examined, alongside their pervasive impacts on crucial ecosystem services such as habitat quality, the vitality of marine species, and nutrient cycling. Our findings highlight the paradox of resilience and vulnerability in these ecosystems: while capable of accumulating substantial amounts of plastic debris, they suffer long-lasting ecological, socio-economic, and health repercussions. We argue for a paradigm shift in management strategies aimed at reducing plastic production at the source, improving waste management practices, conducting targeted cleanup operations, and rehabilitating impacted ecosystems. Emphasizing a comprehensive understanding of plastic pollution is vital for framing effective solutions and necessitates a reevaluation of societal, industrial, and regulatory frameworks. This shift is imperative not only to address current pollution levels but also to safeguard and sustain the functionality of coastal ecosystems, ensuring their ability to continue providing essential services and supporting biodiversity.

Society's interest in rare earth elements (REEs) and their increasing use in many fields is leading to enrichments in aquatic environments, such as estuaries. This study of the Seine estuary assessed the distribution of REEs along the food web, including different species from 5 phyla representing different trophic levels. Total REE concentrations, which were higher in algae, mollusks, crustaceans and annelids (4.85–156; 1.59–4.08; 2.48 ± 1.80 and 0.14 ± 0.11 μg/g dw, respectively) than in vertebrates (0.03–0.15 μg/g dw), correlated with δ15N indicated a trophic dilution. REE contributions in the studied species were higher for light REEs than for heavy and medium REEs. Positives anomalies for Eu, Gd, Tb and Lu were highlighted particularly in vertebrates, possibly due to species-dependent bioaccumulation/detoxification or related to anthropogenic inputs. The calculated BAF and BSAF indicated an important partitioning of REEs in organisms compared to the dissolved phase and a limited transfer from sediment to organisms.

Spat collection of the pearl oyster Pinctada margaritifera in atoll lagoons of French Polynesia is the fundamental sustain of black pearl farming. Spat collection has always yielded variable results in space and time, but obvious signs of steady decreases, even collapses, have emerged in several lagoons. Spat collection materializes the ecological connectivity pathways between wild spawning populations and the location of artificial larval settlement substrates. To assess if oyster larval dispersal modelling could capture such pathways, we compared four six-week long spat collector deployment periods with dispersal simulations in two different lagoons. Spat collectors displayed wide spatial and temporal variations. Numerical modelling and field experiments were generally not in agreement. Although both methods have limitations, they can still approximate each other. But the accuracy of model simulations cannot be ascertained with spat collection data only. Using a SWOT (Strength-Weakness-Opportunities-Threats) analysis, we emphasize the complementarity of both approaches for management decisions.

Human activities and climate change have negatively affected the world's oceans, leading to a decline of 30 to 60 % in coastal ecosystems' biodiversity and habitats. The projected increase in the human population to 9.7 billion by 2050 raises concerns about the sustainability of marine ecosystem conservation and exploitation. Marine turtles, as sentinel species, accumulate contaminants, including trace elements, due to their extensive migration and long-life span. However, there is a lack of data on the degree of contamination and their effects on marine turtles' health. This study focuses on assessing in-situ inorganic contamination in juvenile green sea turtles from La Réunion Island and its short-term impact on individual health, using conventional biomarkers and proteomics. The goals include examining contamination patterns in different tissues and identifying potential new biomarkers for long-term monitoring and conservation efforts. The study identified differential metal contamination between blood and scute samples, which could help illuminate temporal exposure to trace elements in turtle individuals. We also found that some conventional biomarkers were related to trace element exposure, while the proteome responded differently to various contaminant mixtures. Immune processes, cellular organization, and metabolism were impacted, indicating that contaminant mixtures in the wild would have an effect on turtle's health. Fifteen biomarker candidates associated with strong molecular responses of sea turtle to trace element contamination are proposed for future long-term monitoring. The findings emphasize the importance of using proteomic approaches to detect subtle physiological responses to contaminants in the wild and support the need for non-targeted analysis of trace elements in the biomonitoring of sea turtle health.

The application of plant protection products (PPPs) may have delayed and long-term non-intentional impacts on aquatic invertebrates inhabiting agricultural landscapes. Such effects may induce population responses based on developmental and transgenerational plasticity, selection of genetic resistance, as well as increased extirpation risks associated with random genetic drift. While the current knowledge on such effects of PPPs is still scarce in non-target aquatic invertebrate species, evidences are accumulating that support the need for consideration of evolutionary components of the population response to PPPs in standard procedures of risk assessment. This mini-review, as part of a contribution to the collective scientific assessment on PPP impacts on biodiversity and ecosystem services performed in the period 2020–2022, presents a brief survey of the current results published on the subject, mainly in freshwater crustaceans, and proposes some research avenues and strategies that we feel relevant to fill this gap.

Green tides occurrence has increased in coral reefs, yet few reference values have been documented to support bloom management in these ecosystems. Here, we took advantage of recent Ulva green tides that occurred in New Caledonia to (i) identify the elements limiting the growth of Ulva spp. during these blooms; and (ii) validate the use of isotopic markers for identifying sources of nutrients that generated blooms. N/P ratios highlighted a stronger limitation of algae by phosphorus than by nitrogen on sites under oceanic influence, while the proportions of N and P were optimal for algal growth at sites where green tides occurred. Macroalgae highly exposed to sewage water was characterized by higher δ15N than macroalgae collected in areas exposed to synthetic inorganic fertilizers. From these results, we established a new set of threshold values for using δ15N in Ulva species as an indicator of nitrogen source type in coral reefs.

Natural ecological restoration is a cornerstone of modern conservation science and managers need more documented “success stories” to lead the way. In French mediterranean sea, we monitored Posidonia oceanica lower limit using acoustic telemetry and photogrammetry and investigated the descriptors driving its variations, at a national scale and over more than a decade. We showed significant effects of environmental descriptors (region, sea surface temperature and bottom temperature) but also of wastewater treatment plant (WWTP) effluents proxies (size of WWTP, time since conformity, and distance to the closest effluent) on the meadows lower limit progression. This work indicates a possible positive response of P. oceanica meadows to improvements in wastewater treatment and a negative effect of high temperatures. While more data is needed, the example of French wastewater policy should inspire stakeholders and coastal managers in their efforts to limit anthropogenic pressures on vulnerable ecosystems.