The present study was carried out at 22 stations located on the fringing reefs of the island of Mayotte inside the perimeter of the Marine Natural Park of Mayotte (PNMM). The average assessment of the number of samples of marine litter (ML) collected at these stations was 3.9 ± 1.3 ML per 500 m² in winter and 3.8 ± 1.1 ML per 500 m² in summer. Plastic ML was dominant, representing approximately 92% of the litter collected at the stations for the two seasons. The majority was plastic ML from fishing gear (lines, nets etc.). Station 18 presented remarkable average densities of 39 ± 4.2 ML per 500 m² for the two seasons and differed from the other stations in that the ML came solely from the catchment areas, with a majority of aluminium ML (56%). Approximately half the coral colonies coming into contact with ML presented an impact dominated by the category of “Broken or abraded colonies”, with 25% of the colonies being impacted. The colonies most severely impacted by ML were branch or table corals, with the greatest majority for the present study being of the genus Acropora.

It was hypothesized that mangroves, tropical wetlands, could be used for the finishing treatment of domestic wastewaters. Our aim was to determine if a nutrient-stressed mangrove could tolerate long-term discharges of pretreated wastewater (PW). Since 2008, in an in situ experimental system set up in Mayotte Island (Indian Ocean), domestic PW are discharged into two impacted areas (675 m2) dominated by different species of mangrove trees. Anthropogenic inputs during > 4.5 years led to an increase in vegetation growth associated with an increase in leaf pigment content, leaf surface and tree productivity. A marked increase in tree mortality was observed. There was no effect on crabs and meiofauna densities, but significant modifications of community structures. These effects may be directly linked to PW inputs, or indirectly to the modifications of the environment associated with higher tree growth. However, our results indicate that there was no major dysfunction the ecosystem.

Mangrove crabs are ecosystem engineers through their bioturbation activity. On Mayotte Island, the abundance of Neosarmatium africanum decreased in wastewater-impacted areas. Previous analyses showed that global crab metabolism is impacted by wastewater, with a burst in O₂ consumption that may be caused by osmo-respiratory trade-offs since gill functioning was impacted. As the hepatopancreas is a key metabolic organ, the purpose of this study was to investigate the physiological effects of wastewater and ammonia-N 5-h exposure on crabs to better understand the potential trade-offs underlying the global metabolic state. Catalase, superoxide dismutase, glutathione S-transferase, total digestive protease, and serine protease (trypsin and chymotrypsin) activities were assessed. Histological analyses were performed to determine structural modifications. No effect of short-term wastewater and ammonia-N exposure was found in antioxidant defenses or digestive enzyme activity. However, histological changes of B-cells indicate an increase in intracellular digestive activity through higher vacuolization processes and tubule dilation in wastewater-exposed crabs.

To collect a complete dataset regarding the occurrence of organic substances in groundwater, this study presents the examination of 66 organic contaminants in the groundwater of overseas departments, including pesticides, pharmaceutical compounds, hormones and some industrial substances. The selective and sensitive analytical methods are described. These techniques begin with solid-phase extraction (SPE) followed by analysis using liquid chromatography–tandem mass spectrometry (LC-MS/MS) and gas chromatography–mass spectrometry (GC-ToF-MS). The paper summarises the analytical results from 40 sampling points collected during two campaigns in Guadeloupe, Martinique, Reunion, Mayotte and Guiana, representing 80 samples. Of the 66 target substances, 36 were determined at least once. Among the most frequently detected are bisphenol A (frequency, 96 %; max., 7,400 ng/L), caffeine (frequency, 91 %; max., 1,240 ng/L), pentachlorophenol (frequency, 55 %; max., 418 ng/L), and carbamazepine (frequency, 56 %; max., 22 ng/L). The results do not put in evidence that the origin of the sample or climatic characteristics of these regions influence the dilution and release of micropollutants.