While substantial progress has been made in evaluating the ecological carrying capacity (ECC) for fish farming in temperate regions, studies in tropical environment remain scarce, and benthic ecological thresholds are still lacking. This study combines spatial measurements of waste deposition (quantified with sediment traps and depositional modelling approaches), with measurements of sediment physical and biogeochemical properties and macrobenthic community structure at a shallow, non-dispersive site in Martinique. Despite minimal changes in sediment physical and biogeochemical properties, pronounced effects were observed on macrobenthic communities structure. At farm sites, benthic communities were highly perturbed (extremely low diversity and abundance of individuals) and dominated by few individuals of second-order opportunistic species. At sites located between 25 and 150 m from the farm, benthic communities were similar and characterised by higher diversity and abundance, with the presence of sensitive species to OM enrichment. The benthic response was strongly driven by organic waste deposition, which was elevated directly beneath and adjacent to the fish cages. The benthic response to depositional fluxes was best described by M-AMBI index. Notably, the transition from ‘Moderate’ to ‘Poor’ ecological status occurred within a depositional range of 1.2–3.0 kg m−2 year−1 for POM and 0.6–1.1 kg m−2 year−1 for TOC, with model predictions suggesting that these effects may extend up to 30 m from the farm. This study represents a step forward in defining benthic ecological thresholds for tropical fish farming and will help decision makers in fostering the sustainable development of aquaculture in these regions.

The consequences of the progressive intrusion of anthropogenic noise into natural oceanic soundscapes are largely unknown despite the fact that most metazoans utilize sound or vibration for intra- and interspecific interactions as well as orientation. Coastal ecosystems in particular can be characterized by a high level of human activity and thus anthropogenic noise sources. Here, we studied the impact of such noise on marine mesograzers, small invertebrates that play crucial ecological roles by controlling macrophyte growth while serving as key food sources for higher trophic levels in algae-dominated coastal ecosystems. The effect of added continuous low-frequency noise on the habitat choice, feeding rate, and metabolic enzyme activities of the amphipod mesograzer Marinogammarus marinus was tested in a controlled laboratory setting. While habitat choice appeared unaffected by the added noise, exposed animals exhibited reduced feeding performance as well as altered metabolic enzyme activities. If sustained, the physiological homeostasis of M. marinus and their role in the ecosystem may be jeopardized. The ever-rising sound levels in the oceans may thus have consequences for algae-dominated animal communities in coastal areas.

Plastic pollution is increasingly affecting the South Pacific, including remote islands and coastal regions of Small Island Developing States (SIDS), yet data remain sparse in many areas. This baseline study presents original data on beach macrolitter and microplastics in surface waters and sediments across six islands of French Polynesia (Moorea, Bora Bora, Tahaa) and the Cook Islands (Aitutaki, Rarotonga), collected during an opportunistic cruise in 2024.Beach surveys revealed high plastic contamination on most sites, with macroplastics (size > 2.5 cm) densities ranging from 18 to 58 items/100 m, exceeding European threshold values (e.g. 22 items/100m) on majority of sampled beaches. Single-use plastics and plastic fragments dominated the debris, with local sources such as tourism and coastal activities clearly identifiable.Surface microplastics (315 µm–5 mm) were found at low densities, ranging from 0 to 4668 particles/km2, confirming relatively low contamination in surface waters. Only 17 particles were detected from 8 manta net tows. Sediment and beach microplastic analysis yielded very limited results, with microplastics found at only two sites (Huahine and Rarotonga), dominated by fragments and colored fibers. These results suggest localized contamination linked to urbanization and tourism rather than widespread oceanic inputs.Despite methodological limitations due to the cruise format, this study contributes rare data from under-sampled regions, supporting long-term monitoring efforts and informing future policy and mitigation actions. The results underline the need to improve regional waste management, which will be beneficial for local societies largely based on tourism.

The increasing contamination of coastal environments by Rare Earth Elements (REEs) necessitates a thorough understanding of the dynamics of these elements in ecosystems under anthropogenic pressure. Sedimentary bodies influenced by large rivers, such as the West Gironde Mud Patch (WGMP), are among these pressured ecosystems. REE analyses in seven benthic marine species and ambient media (i.e., dissolved fraction of bottom water, sediments) of this mud patch has provided REE signatures (i.e., REE concentrations and shape of normalized patterns) using one concentration descriptor (i.e., ∑REE) and six descriptors of pattern shapes (i.e., La/La*; Ce/Ce*; Eu/Eu*; Pr/Lu; Pr/Gd; Gd/Lu). A robust procedure of multivariate analyses (i.e., PERMDISP, PERMANOVAs, PCO) was applied to study the controlling factors of REE signatures in these species. Assessment of the within- and between-species variability suggests that differences in REE concentrations and shapes of normalized patterns between species were related to the ambient media's geochemical processes and the fauna's ecological and biological traits. REE concentrations in the fauna document trophic dilution, reflected by elevated concentrations in pure microphages and reduced concentrations in pure carnivores. The predominance of calcareous skeletons in bivalves and brittle stars results in a dilution effect on REE concentrations at the whole-organism level. The chitinous exoskeleton of crabs and shrimps is subject to adsorption processes for REEs present in the sediment.

This study presents the first assessment of Technological Critical Elements (TCE), specifically platinum (Pt) and rare earth elements (REE), in coastal sediments along the French western Mediterranean Sea. These trace elements, increasingly used in advanced technologies, raise particular concerns due to their potential environmental impact. Surface sediment samples were collected from 21 stations along the French Mediterranean coast (from Spain border to Italy including Corsica Island) to evaluate TCE concentrations and identify potential sources. Most of the REE concentrations fell within expected natural levels and were mainly influenced by the geological characteristics of local watersheds, indicating a dominant geogenic origin. When normalized to European Shale, REE distribution patterns exhibited convex shapes, typical of coastal environments. In contrast, localized Pt enrichment were detected at specific sites, particularly in port areas, which could be linked to anthropogenic emissions from vehicular catalytic converters. These results highlight platinum as a relevant emerging contaminant in urban coastal environments. However, unexpected REE and Pt concentrations at the mouth of the Hérault river call for further investigation. This study highlights the importance of integrating geological background and anthropogenic pressures in coastal sediment quality assessments and supports the inclusion of TCE in long -term environmental monitoring programs in the Mediterranean Sea.