Three separate mangrove ecosystems in Kerala's Kannur district were examined for trace metal build-up in sediment and two polychaete species, Marphysa gravelyi and Dendronereis aestuarina. By classifying the areas according to the intensity of anthropogenic activity, metal deposition in polychaete tissue was investigated. ICP-MS was used to assess the heavy metal load and the accumulation of metals in sediment in the range of, Zn 24.37-59 mg/kg, Ni 23.67- 59.25 mg/kg, Cu 11.27- 38.6 mg/kg, Pb 4.5- 16.4 mg/kg, Cd 0.1-1.8 mg/kg, Fe 1.25- 3.67 %, and Al 0.65-2.43 %. The soil sample's Zn concentration was at its highest and heavy metals accumulated in the pattern Zn˃Ni˃Cu˃Pb˃Cd. By just switching the concentrations of Ni and Cu, polychaetes' trace metal concentrations follow the same pattern as those found in soil, however, M. gravelyi was discovered to have larger amounts of accumulation when compared to D. aestuarina, mostly for metals like Zn and Pb. Based on data compiled from all stations, the average concentration of accumulation for Zn was 62.34 mg/kg & 43.45 mg/kg, and for Pb, it was 6.59 mg/kg & 1.86 mg/kg in M. gravelyi and D. aestuarina, respectively. Most metal buildup is found in mangrove soil, which has higher levels of organic carbon and clay particles. The findings imply that D. aestuarina is an organism that is sensitive to pollution and that M. gravelyi is a species that is extremely tolerant of pollution, suggesting that the species can be used to anticipate the state of its surrounding environment.

International audience | Mangroves are threatened ecosystems that provide numerous ecosystem services, especially through their wide biodiversity, and their bioremediation capacity is a challenging question in tropical areas. In a mangrove in Mayotte, we studied the potential role of microbial biofilm communities in removing nutrient loads from pre-treated wastewater. Microbial community samples were collected from tree roots, sediments, water, and from a colonization device, and their structure and dynamics were compared in two areas: one exposed to sewage and the other not. The samples from the colonization devices accurately reflected the natural communities in terms of diversity. Communities in the zone exposed to sewage were characterized by more green algae and diatoms, higher bacteria densities, as well as different compositions. In the area exposed to sewage, the higher cell densities associated with specific diversity patterns highlighted adapted communities that may play a significant role in the fate of nutrients.

International audience | Mangroves are threatened ecosystems that provide numerous ecosystem services, especially through their wide biodiversity, and their bioremediation capacity is a challenging question in tropical areas. In a mangrove in Mayotte, we studied the potential role of microbial biofilm communities in removing nutrient loads from pre-treated wastewater. Microbial community samples were collected from tree roots, sediments, water, and from a colonization device, and their structure and dynamics were compared in two areas: one exposed to sewage and the other not. The samples from the colonization devices accurately reflected the natural communities in terms of diversity. Communities in the zone exposed to sewage were characterized by more green algae and diatoms, higher bacteria densities, as well as different compositions. In the area exposed to sewage, the higher cell densities associated with specific diversity patterns highlighted adapted communities that may play a significant role in the fate of nutrients.

To assess the severity of oil spills on mangroves, diagnosis of the vegetation health is crucial. Some aspects of photosynthesis such as photochemical efficiency and leaf pigment composition together with the level of oxidative stress may constitute reliable indicators for vegetation health. To test this approach 14 month old Laguncularia racemosa were contaminated with 5 L m−2 of the marine fuel oil MF-380 and treated with an oil degrading bacterial consortium in microcosms. Contamination resulted in a 20% decrease in shoot dry weight after 128 days. Photochemical efficiency, pigment content, catalase and ascorbate peroxidase remained unchanged. Multivariate ordination of DGGE microbial community fingerprints revealed a pronounced separation between the oil contaminated and the non-contaminated samples. Further studies are necessary before physiological parameters can be recommended as indicators for plant's health in oil polluted mangroves.

Laboratory studies demonstrated that the mussels were good model organisms in revealing microplastics (MPs) uptake and toxicity. However, only limited field study data on the MPs in benthic marine mesoherbivores collected from mangrove forests are currently available. In this study, the MPs in the snails (Ellobium chinense) organs, rather than the shell, from a mangrove forest were dominant fraction (maximum reaching to 60%). Unexpectedly, no significant linear relationships were found between the levels of MPs in the organs of the snails and the levels in the sediment/tidal water. Further studies were done to explore the sources of the MPs in snail organs. MPs in snail organs at both the landward (interior) and seaward (exterior) zones mainly origin from the pore water. Moreover, the MPs found in the snails showed no relevance to the particulate matter (PM) collected from pore water. The findings reported here imply that both the MPs and PM in pore water affect the extent of MPs enter into the organs of benthic marine mesoherbivores collected from mangrove forest.

The present study aimed to determine metal accumulation levels in tissue and biomineralisation in shells of 20 species of molluscs (13 gastropods and 7 bivalves) from Palk Bay, India. In most cases, metal concentrations in the tissues were higher than in the shells of the same species collected from same location, meaning that in many cases biomineralisation factors of metal ratios were <1. The highest biomineralisation factor for Cd was detected in Melampus sincaporensis (3.72 ± 0.1) from the Thondi mangrove, for Pb in Cerithidea cingulata (2.51 ± 0.17) from the Vattanam mangrove, for Cu in Melampus sincaporensis (0.88 ± 0.2) from the Thondi mangrove, and for Zn in Cerithidea cingulata (0.93 ± 0.3) from the Devipattinam mangrove. In most cases, metal concentrations were higher than reported in previous studies but were within the maximum limits stated by national and international regulatory agencies. Variations in the biomineralisation factor of metal ratios among the molluscan species likely stems from variations in bioaccumulation efficiency, selectivity of individual organisms, and availability of metals in the mangrove and coastal environments.

Mangrove environments are important for maintaining biodiversity and carbon cycling. However, these systems are being degraded at alarming rates around the world, particularly in rapidly developing regions. Here, we examine a sediment profile from a mangrove forest near a large port complex at Suape, northeast Brazil, in order to assess the impact of rapid urbanization and industrialization. We find that total organic carbon (TOC) and total nitrogen (TN) accumulation rates have increased in the estuary since the 1980's, directly related to rapid urban development. The TN and heavy δ¹⁵N values in the sediment column suggest increasing anthropogenic influences. In contrast, heavy metal fluxes did not increase during these transitions. The increase in TOC and TN accumulation rates during the past four decades highlight the significant role mangrove areas play as sinks for anthropogenically enhanced nutrients in poorly-understood tropical areas.

An investigation of microplastic abundance and its characteristics was conducted in Muara Angke Wildlife Reserve, a relic mangrove forest in the Jakarta metropolitan, to contribute to marine microplastics' national data inventory. Microplastics were found in all the stations, with an average of 28.09 ± 10.28 particles per kg of dry sediment (n kg⁻¹). Sediments in the outside mangrove area contained more microplastics than the inside area. Foam form was the most dominant in all the samples and was found more abundant on the outside. More than half of microplastics were of size <1000 μm, and nearly 50% were polystyrenes. This polymer is widely used for food packaging, which is prone to be fragmented. Polypropylene and polyethylene form another 50% of microplastics, which are widely used for textiles and fishing gears. As Jakarta is the largest city in Indonesia, this microplastic dataset may be the benchmark for other mangroves around the country.

Thirty cores to maximum depth of 3.7 m were taken in 2018 to investigate sedimentary characteristics and hydrocarbon penetration within mangrove sediments in Bodo (southeastern Niger Delta), an area contaminated by numerous ongoing oil spills but most significantly in 2008. Sediments were dominated by organically rich (Chikoko) mud underlain by clay with sandier sediments at deeper core depths and adjacent to shorelines. Analysis of 202 samples showed high median hydrocarbon concentrations at the surface (39,000 mg/kg) and shallow subsurface (10–25 cm, 25,000 mg/kg), decreasing with depth: 430 mg/kg at 40–70 cm; 157 mg/kg at 75–120 cm, and <30 mg/kg at depths ≥150 cm. Most (85%) EPA-16 priority polycyclic aromatic hydrocarbons and all monoaromatics were below detection limit. Shallow subsurface oil penetration was aided by crab burrows and presence of mangrove remnants and was inhibited from deeper depths by groundwater at ~25 cm and increased sediment compaction.

We evaluated the status of anthropogenic marine debris (AMD) in two natural mangrove forests on Mauritius, one of which in proximity to human settlement (Mahebourg) and the other more remote (Ferney). AMD was collected monthly from October to December 2018 in 1500 m² at both sites and classified into material composition and their potential sources. In all, 2127 items (150.07 kg) was sampled at Mahebourg and 1098 items (43.71 kg) at Ferney. In line with global studies, plastic made up most of the debris in terms of both count (42.92%, 43.66%) and total weight (40.65%, 32.08%) at Mahebourg and Ferney respectively. Most debris originated from shoreline and recreational activities. This work sets a baseline to assess impacts of AMD on mangroves, public awareness required and future strategies for waste monitoring and management in mangroves that may be applied both locally and on other small islands.