Modeling Habitat Suitability for Cerithidea rhizophorarum and Telescopium telescopium in Indo-West Pacific Mangroves.

Mangroves provide habitat for a diverse array of marine species, especially snails. We used a MaxEnt model to predict potential global suitable habitat for Cerithidea rhizophorarum and Telescopium telescopium in the family Potamididae. A total of 667 occurrence data were obtained from the Global Biodiversity Information Facility (GBIF) with the following sub-data set contribution, "iNaturalist Research Grade Observations" (85%), "International Barcode of Life project (iBOL)" (7%), "FBIP: SeaKeys_SANBI: Marine images iSpot_2013" (1%), "A dataset of marine macroinvertebrate diversity from Mozambique and São Tomé and Príncipe" (1%), occurrence data of some marine invertebrates and freshwater crabs housed in the natural history collection at the National Museums of Kenya (1%), and Natural History Museum Rotterdam-Specimens (1%). Our results showed that temperature with a contribution of above 80% in the present and future model is the most important driver of the distribution of mangrove snails. In the present and future models, the most potentially suitable habitats for C. rhizophorarum and T. telescopium were observed along coastal areas with a temperature between 20°C-21°C and 30°C, respectively. Our model predicts that by 2100, high-suitability areas will shrink as a result of global warming. The vulnerability of mangrove snails under future climate conditions is evident in our results. Our findings contribute significant insights into the intricate relationship between mangrove habitats and mangrove snails, offering a valuable foundation for conservation initiatives aimed at safeguarding the biodiversity and ecological functions of these crucial coastal ecosystems in the face of changing global environmental conditions.

Mangrove tree aerial root extract mediated green synthesis of Ag/Fe3O4/rGO nanocomposite and its application as a catalyst for one pot synthesis of 7-phenyl-6H,7H-benzo[4,5]imidazo[2,1-b]chromeno[4,3-d][1,3]thiazin-6-one derivatives.

In this study, we report the green preparation of magnetically separable Ag/Fe3O4/rGO nanocomposites using mangrove tree aerial root extract as a stabilising agent. The morphology, size, chemical composition, magnetic property and other characteristic parameters of synthesised Ag/Fe3O4/rGO nanocomposite were determined by analytical techniques like Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results proved that mangrove tree aerial root extract has the ability to reduce Ag+ ions, graphene oxide (GO) to Ag nanoparticle and reduced graphene oxide (rGO), respectively. The prepared Ag/Fe3O4/rGO nanocomposite was used successfully as a prompt catalyst for synthesis of 7-phenyl-6H,7H-benzo[4,5]imidazo[2,1-b]chromeno[4,3-d][1,3]thiazin-6-one derivatives by one-pot multi-component reaction of 4-hydroxycoumarin (10 mmol), 2-mercaptobenzimidazole (10 mmol) and different arylaldehyde (10 mmol) in the presence of ethanol (10 ml) as an eco-benign solvent at reflux condition. By utilising this protocol, we have constructed 7-phenyl-6H,7H-benzo[4,5]imidazo[2,1-b]chromeno[4,3-d][1,3]thiazin-6-one derivatives in good to excellent yield of 80-90%. This synthesis involves the formation of C-C, C-N and C-S bonds. The synthesised organic heterocyclic compounds were examined for the green matrix properties such as atom economy (AE), E-factor and product mass intensity (PMI). This green protocol is of big interest due to employing simple, non-toxic heterogeneous, separable, reusable Ag/Fe3O4/rGO as an eco-safe heterogeneous catalyst and environmentally benign ethanol as a green solvent without the use of any harmful mineral acid and toxic transition metal catalyst.

Stand age-related effects of mangrove on archaeal methanogenesis in sediments: Community assembly and co-occurrence patterns.

Mangrove sediment is a key source of methane emissions; however, archaea community structure dynamics and methanogenesis activities during long-term mangrove restoration remain unclear. In this study, microcosm incubations revealed a substantial reduction in microbial-mediated methane production potential from mangrove sediments with increasing stand age; methane production rates decreased from 0.42 ng g-1 d-1 in 6-year-old stands to 0.23 ng g-1 d-1 in 64-year-old stands. High-throughput sequencing revealed a reduction in community diversity because of specific microorganism colonization and species loss, notably a decline in the relative abundance of Bathyarchaeia in sediments of 64-year-old stands. In addition, mangrove sediments, especially those in older stands (20- and 64-year-old), had more complex and stable co-occurrence microbial networks than mudflats. Furthermore, archaea community assembly in older stands was dominated by stochastic processes wherein dispersal limitation was prominent, and that in younger stands (6- and 12-year-old) was driven by deterministic processes. The proportion of dispersal limitation of Bathyarchaeia and traditional methanogens in sediment decreased with an increase in stand age. Quantitative polymerase chain reaction analysis confirmed a decrease in Bathyarchaeia (from 3.50 to 0.54 copies g-1) and mcrA gene (from 3.83 to 0.25 copies g-1) abundance in mangrove sediments with an increase in stand age. These findings demonstrate the critical role of Bathyarchaeia in methanogenesis; the decline in microbial interactions and abundance, and the reduced proportion of dispersal limitation of Bathyarchaeia and traditional methanogens collectively contributed to the mitigation of microbial-mediated methane production potential in older mangrove stands.

Identifying toxic elements in water, sediments, and roots of mangrove forest (Avicennia marina) in Chabahar Bay, Sea of Oman.

Mangroves play a crucial role in filtering pollutants from water and sediments. However, excessive accumulation of potentially toxic elements (PTEs) has harmful effects on marine organisms. This article investigates the concentration and distribution of PTEs in water, sediment, and the roots of endangered mangrove species in Chabahar Bay, a subtropical coastal wetland. The relationship between PTE absorption and accumulation rates with flow rate, mangrove extent, and sedimentation was also explored. Water, sediments, and aerial roots samples were taken at four stations along the wetland from upstream fresh water toward outfall. According to the results, Cd had more distribution in sediment and water samples and plants did not play as adsorbent in the study area. The lowest and highest PTEs concentrations were detected in water and sediment media, respectively. The average concentrations of PTEs in the sediments in the Chabahar Bay were Fe > Cr > Zn > Ni > Cu > Pb > Co > As > Cd while in aerial roots of the mangroves were Fe > Zn > Ni > Cr > Cu > Co > As > Pb > Cd. Except Zn, As, and Cd, there was a good correlation between increasing PTEs content in the sediments with decreasing flow velocity and increasing vegetation density along stations 3 to 4. In addition, the amount of PTEs uptake by the mangroves was less than that of global wetlands. The results also demonstrated a greater uptake in aerial roots in saline water for Cr, Ni and Co. Since the absorption rate of PTEs by the aerial roots of pneumatophores is slower than that in sediments, elevated concentrations of PTEs in the sediment can disrupt the entire ecosystem, leading to a potential decline in biodiversity. These toxins can enter the food chain, affecting not only organisms directly interacting with the sediment but also higher trophic levels, such as fish and birds.

Two new polyketone derivatives from the mangrove endophytic fungus Aspergillus sp. GXNU TH4b.

Two new polyketones, exserone B (1) and cytosporone F (2), along with three known metabolites, were isolated from the mangrove endophytic fungus Aspergillus TH4b. The structures of 1 and 2 were determined by detailed NMR, and MS spectroscopic data. The absolute configurations of 1 and 2 were determined by single crystal X-ray diffraction analysis and the combination of experimental ECD and computational ECD, respectively. Compounds 1-2 have strong inhibitory activity against citrus Psyllid (Diaphorina citri) with 95.4% and 93.7% lethal at 1000 mg/kg.

Temporal enrichment of comammox Nitrospira and Ca. Nitrosocosmicus in a coastal plastisphere.

Plastic marine debris is known to harbor a unique microbiome (termed the "plastisphere") that can be important in marine biogeochemical cycles. However, the temporal dynamics in the plastisphere and their implications for marine biogeochemistry remain poorly understood. Here, we characterized the temporal dynamics of nitrifying communities in the plastisphere of plastic ropes exposed to a mangrove intertidal zone. The 39-month colonization experiment revealed that the relative abundances of Nitrospira and Candidatus Nitrosocosmicus representatives increased over time according to 16S rRNA gene amplicon sequencing analysis. The relative abundances of amoA genes in metagenomes implied that comammox Nitrospira were the dominant ammonia oxidizers in the plastisphere, and their dominance increased over time. The relative abundances of two metagenome-assembled genomes of comammox Nitrospira also increased with time and positively correlated with extracellular polymeric substances content of the plastisphere but negatively correlated with NH4+ concentration in seawater, indicating the long-term succession of these two parameters significantly influenced the ammonia-oxidizing community in the coastal plastisphere. At the end of the colonization experiment, the plastisphere exhibited high nitrification activity, leading to the release of N2O (2.52 ng N2O N g-1) in a 3-day nitrification experiment. The predicted relative contribution of comammox Nitrospira to N2O production (17.9%) was higher than that of ammonia-oxidizing bacteria (4.8%) but lower than that of ammonia-oxidizing archaea (21.4%). These results provide evidence that from a long-term perspective, some coastal plastispheres will become dominated by comammox Nitrospira and thereby act as hotspots of ammonia oxidation and N2O production.

Growth, Morphology and Respiratory Cost Responses to Salinity in the Mangrove Plant Rhizophora Stylosa Depend on Growth Temperature.

Mangrove plants, which have evolved to inhabit tidal flats, may adjust their physiological and morphological traits to optimize their growth in saline habitats. Furthermore, the confined distribution of mangroves within warm regions suggests that warm temperature is advantageous to their growth in saline environments. We analyzed growth, morphology and respiratory responses to moderate salinity and temperature in a mangrove species, Rhizophora stylosa. The growth of R. stylosa was accelerated in moderate salinity compared with its growth in fresh water. Under warm conditions, the increased growth is accompanied by increased specific leaf area (SLA) and specific root length. Low temperature resulted in a low relative growth rate due to a low leaf area ratio and small SLA, regardless of salinity. Salinity lowered the ratio of the amounts of alternative oxidase to cytochrome c oxidase in the mitochondrial respiratory chain in leaves. Salinity enhanced the leaf respiration rate for maintenance, but under warm conditions this enhancement was compensated by a low leaf respiration rate for growth. In contrast, salinity enhanced overall leaf respiration rates at low temperature. Our results indicate that under moderate saline conditions R. stylosa leaves require warm temperatures to grow with a high rate of resource acquisition without enhancing respiratory cost.

Hydrogeochemical dynamics under saltwater-freshwater mixing in a mangrove wetland over tidal cycles.

Seawater and groundwater interactions shape the hydrogeochemical profile of mangrove aquifers, revealing how biogeochemical processes adapt to saline-freshwater mixing via the fluctuating patterns of key hydrochemical indicators and primary biogenic elements. This study, utilizing a multi-level monitoring profile spanning the entire submerged aquifer within a mangrove wetland, analyzed the spatiotemporal dynamics of DO, ORP, pH, alkalinity and biogenic elements (C, N, S). The results revealed that among the basic hydrochemical parameters, total alkalinity showed the most stable spatiotemporal distribution and was positively correlated with salinity. pH demonstrated a significant negative correlation with salinity, whereas the correlations of ORP and DO with salinity were not substantial. The discharge of terrestrial freshwater into the mangrove wetland is marked by hydrogeochemical reactions favoring the input of Mg2+ and DIC, with potential iron mineral precipitation within the aquifer. Spatial distribution of biogenic elements in the groundwater showed no apparent pattern across sampling periods. DOC concentrations ranged from 0.3 to 1.3 mmol/L. Three components of dissolved organic matter were identified using three-dimensional fluorescence spectroscopy, with high molecular weight components (C1 + C2) accounting for an average of 47 to 73 %. Both elevated DOC concentrations and high molecular weight component ratios were primarily found in shallow layers of dense mangrove areas, decreasing with depth. Concentrations of ammonia, nitrite, and nitrate varied dynamically, reflecting active biochemical processes in the shallow to mid-layers of the aquifer. Furthermore, sulfate and sulfide concentrations, ranging from 0 to 26 mmol/L and 0.4 to 576.8 µmol/L, respectively, underscore the interplay of biogeochemical reactions, especially sulfate reduction. These findings highlight valuable insights into the complex biogeochemical processes within mangrove aquifers and provide theoretical guidance for protecting the ecological health of mangrove wetlands.

Comparison of organelle genomes between endangered mangrove plant Dolichandrone spathacea to terrestrial relative provides insights into its origin and adaptative evolution.

Dolichandrone spathacea is a mangrove associate with high medicinal and ecological values. However, due to the dual-pressure of climate change and human activities, D. spathacea has become endangered in China. Moreover, misidentification between D. spathacea and its terrestrial relative D. cauda-felina poses further challenges to field protection and proper medicinal usage of D. spathacea. Thus, to address these problems, we sequenced and assembled mitochondrial (mt) and chloroplast (cp) genomes for both D. spathacea and D. cauda-felina. Comparative analysis revealed apparently different size and scaffold number between the two mt genomes, but a high similarity between the cp genomes. Eight regions with high sequence divergence were identified between the two cp genomes, which might be used for developing candidate DNA markers for distinguishing the two species. The splitting between D. spathacea and D. cauda-felina was inferred to occur at ~6.8 - 7.7 million years ago (Mya), which may be driven by the environment fluctuations in late Miocene. In the cp genome, 12 genes related to the expression of photosynthesis-associated proteins were detected with signatures of positive selection, which may contribute to the origin and evolutionary adaptation of Dolichandrone mangrove species. These new findings do not only enrich organelle genomic resources of Dolichandrone species, but also provide important genetic clues for improving the conservation and proper usage of endangered mangrove associate D. spathacea.

Genomic convergence in terrestrial root plants through tandem duplication in response to soil microbial pressures.

Despite increasing reports of convergent adaptation, evidence for genomic convergence across diverse species worldwide is lacking. Here, our study of 205 Archaeplastida genomes reveals evidence of genomic convergence through tandem duplication (TD) across different lineages of root plants despite their genomic diversity. TD-derived genes, notably prevalent in trees with developed root systems embedded in soil, are enriched in enzymatic catalysis and biotic stress responses, suggesting adaptations to environmental pressures. Correlation analyses suggest that many factors, particularly those related to soil microbial pressures, are significantly associated with TD dynamics. Conversely, flora transitioned to aquatic, parasitic, halophytic, or carnivorous lifestyles-reducing their interaction with soil microbes-exhibit a consistent decline in TD frequency. This trend is further corroborated in mangroves that independently adapted to hypersaline intertidal soils, characterized by diminished microbial activity. Our findings propose TD-driven genomic convergence as a widespread adaptation to soil microbial pressures among terrestrial root plants.

Comprehensive stomata image dataset of Sundarbans Mangrove and Ratargul Swamp forest tree species in Bangladesh.

Plants' leaf stomata are crucial for various scientific research, including identifying species, studying ecology, conserving ecosystems, improving agriculture, and advancing the field of deep learning. This dataset, containing 1083 images, encompasses 11 species from two distinct locations in Bangladesh: nine from the Sundarbans mangrove forest and two from the Ratargul Swamp Forest. It is a valuable tool for refining machine learning algorithms that specialize in detecting stomata and categorizing species accurately. Researchers can explore a deeper understanding of plant physiology, adaptation mechanisms, and environmental interactions by employing pattern recognition, deep learning, and feature extraction techniques. Additionally, this dataset could be a potential tool for enhancing research in macroscopic metamaterials, extending its impact beyond traditional biological studies into interdisciplinary fields of technology and material science.

Occurrence, Source Apportionment, and Risk Assessment of Antibiotics in Mangrove Sediments from the Lianzhou Bay, China.

In recent years, the widespread application of antibiotics has raised global concerns, posing a severe threat to ecological health. In this study, the occurrence, source, and ecological risks of 39 antibiotics belonging to 5 classes in mangrove sediments from Lianzhou Bay, China, were assessed. The total concentrations of the antibiotics (∑39 antibiotics) ranged from 65.45 to 202.24 ng/g dry weight (dw), with an average of 142.73 ± 36.76 ng/g dw. The concentrations of these five classes of antibiotics were as follows: Sulfonamides (SAs) > Tetracyclines (TCs) > Fluoroquinolones (QUs) > Penicillin (PCs) > Macrolides (MLs). The spatial distribution of antibiotics varied as high tidal zone > middle tidal zone > low tidal zone. The total organic carbon (TOC), pH, nitrate (NO3--N), and nitrite (NO2--N) of the sediment significantly influenced the distribution of antibiotics (p < 0.05). A source analysis identified untreated sewage from aquaculture as the primary source of antibiotics in the local mangrove. A risk assessment revealed that ciprofloxacin, norfloxacin, ofloxacin of QUs, and tetracycline of TCs exhibited medium risks to algae in certain sampling sites, while other antibiotics exhibited low or no risks to all organisms. Nevertheless, the total risk of all the detected antibiotics to algae was medium in 95% of the sites. The overall ecological risk level of antibiotics in the middle tidal zone was slightly lower than in the high tidal zone and the lowest in the low tidal zone. In summary, the experimental results provided insights into the fate and transport behaviors of antibiotics in mangrove sediments from Lianzhou Bay.

Unveiling a New Antimicrobial Peptide with Efficacy against P. aeruginosa and K. pneumoniae from Mangrove-Derived Paenibacillus thiaminolyticus NNS5-6 and Genomic Analysis.

This study focused on the discovery of the antimicrobial peptide (AMP) derived from mangrove bacteria. The most promising isolate, NNS5-6, showed the closest taxonomic relation to Paenibacillus thiaminolyticus, with the highest similarity of 74.9%. The AMP produced by Paenibacillus thiaminolyticus NNS5-6 exhibited antibacterial activity against various Gram-negative pathogens, especially Pseudomonas aeruginosa and Klebsiella pneumoniae. The peptide sequence consisted of 13 amino acids and was elucidated as Val-Lys-Gly-Asp-Gly-Gly-Pro-Gly-Thr-Val-Tyr-Thr-Met. The AMP mainly exhibited random coil and antiparallel beta-sheet structures. The stability study indicated that this AMP was tolerant of various conditions, including proteolytic enzymes, pH (1.2-14), surfactants, and temperatures up to 40 °C for 12 h. The AMP demonstrated 4 µg/mL of MIC and 4-8 µg/mL of MBC against both pathogens. Time-kill kinetics showed that the AMP acted in a time- and concentration-dependent manner. A cell permeability assay and scanning electron microscopy revealed that the AMP exerted the mode of action by disrupting bacterial membranes. Additionally, nineteen biosynthetic gene clusters of secondary metabolites were identified in the genome. NNS5-6 was susceptible to various commonly used antibiotics supporting the primary safety requirement. The findings of this research could pave the way for new therapeutic approaches in combating antibiotic-resistant pathogens.

Two C23-Steroids and a New Isocoumarin Metabolite from Mangrove Sediment-Derived Fungus Penicillium sp. SCSIO 41429.

Two new C23-steroids derivatives, cyclocitrinoic acid A (1) and cyclocitrinoic acid B (2), and a new isocoumarin metabolite, (3R,4S)-6,8-dihydroxy-3,4,5-trimethyl-7-carboxamidelisocoumarin (10), together with 12 known compounds (3-9, 11-15) were isolated from the mangrove-sediment fungus Penicillium sp. SCSIO 41429. The structures of the new compounds were comprehensively characterized by 1D and 2D NMR, HRESIMS and ECD calculation. All isolates were evaluated for pancreatic lipase (PL) inhibitory and antioxidant activities. The biological evaluation results revealed that compounds 2, 14 and 15 displayed weak or moderate inhibition against PL, with IC50 values of 32.77, 5.15 and 2.42 µM, respectively. In addition, compounds 7, 12 and 13 showed radical scavenging activities against DPPH, with IC50 values of 64.70, 48.13, and 75.54 µM, respectively. In addition, molecular docking results indicated that these compounds had potential for PL inhibitory and antioxidant activities, which provided screening candidates for antioxidants and a reduction in obesity.

New Sesquiterpenoids from the Mangrove-Derived Fungus Talaromyces sp. as Modulators of Nuclear Receptors.

Four new sesquiterpenoids, talaroterpenes A-D (1-4), were isolated from the mangrove-derived fungus Talaromyces sp. SCSIO 41412. The structures of compounds 1-4 were elucidated through comprehensive NMR and MS spectroscopic analyses. The absolute configurations of 1-4 were assigned based on single-crystal X-ray diffraction and calculated electronic circular dichroism analysis. Talaroterpenes A-D (1-4) were evaluated with their regulatory activities on nuclear receptors in HepG2 cells. Under the concentrations of 200 µM, 1, 3 and 4 exhibited varying degrees of activation on ABCA1 and PPARα, while 4 showed the strongest activities. Furthermore, 4 induced significant alterations in the expression of downstream target genes CLOCK and BMAL1 of RORα, and the in silico molecular docking analysis supported the direct binding interactions of 4 with RORα protein. This study revealed that talaroterpene D (4) was a new potential non-toxic modulator of nuclear receptors.

The Cytochalasins and Polyketides from a Mangrove Endophytic Fungus Xylaria arbuscula QYF.

Twelve compounds, including four undescribed cytochalasins, xylariachalasins A-D (1-4), four undescribed polyketides (5-8), and four known cytochalasins (9-12), were isolated from the mangrove endophytic fungus Xylaria arbuscula QYF. Their structures and absolute configurations were established by extensive spectroscopic analyses (1D and 2D NMR, HRESIMS), electronic circular dichroism (ECD) calculations, 13C NMR calculation and DP4+ analysis, single-crystal X-ray diffraction, and the modified Mosher ester method. Compounds 1 and 2 are rare cytochalasin hydroperoxides. In bioactivity assays, Compound 2 exhibited moderate antimicrobial activities against Staphylococcus aureus and Candida albicans with MIC values of 12.5 µM for both Compound 10 exhibited significant cytotoxic activity against MDA-MB-435 with an IC50 value of 3.61 ± 1.60 µM.

Methods Using Marine Aquatic Photoautotrophs along the Qatari Coastline to Remediate Oil and Gas Industrial Water.

Qatar and other Gulf States have a diverse range of marine vegetation that is adapted to the stressful environmental conditions of seawater. The industrial wastewater produced by oil and gas activities adds further detrimental conditions for marine aquatic photosynthetic organisms on the Qatari coastlines. Thus, these organisms experience severe stress from both seawater and industrial wastewater. This review discusses the biodiversity in seawater around Qatar, as well as remediation methods and metabolic pathways to reduce the negative impacts of heavy metals and petroleum hydrocarbons produced during these activities. The role of microorganisms that are adjacent to or associated with these aquatic marine organisms is discussed. Exudates that are released by plant roots enhance the role of microorganisms to degrade organic pollutants and immobilize heavy metals. Seaweeds may have other roles such as biosorption and nutrient uptake of extra essential elements to avoid or reduce eutrophication in marine environments. Special attention is paid to mangrove forests and their roles in remediating shores polluted by industrial wastewater. Seagrasses (Halodule uninervis, Halophila ovalis, and Thalassia hemprichii) can be used as promising candidates for phytoremediation or bioindicators for pollution status. Some genera among seaweeds that have proven efficient in accumulating the most common heavy metals found in gas activities and biodegradation of petroleum hydrocarbons are discussed.

Chemical constituents from the endophytic fungus Aspergillus sp. S3 of Hibiscus tiliaceus.

A new sterol, aspersterol E (1), a newly discovered alkaloid, asperginine A (2), and five known compounds (3-7) were obtained from the endophytic fungus Aspergillus sp. S3 of Hibiscus tiliaceus Linn. The compounds were extracted from their fermentation products using silica gel, ODS C18, and semi-preparative HPLC. The structure of each compound was determined through spectroscopic analysis. All the obtained compounds (1-7) were evaluated for their cytotoxic activity against the mouse pre-gastric cancer cell line MFC by using the MTT assay. The IC50 values of compounds 1, 2, 3, and 5 were found to be 153.43 µM, 61.25 µM, 73.19 µM, and 181.69 µM respectively.

Impact of geochemistry and microbes on the methylmercury production in mangrove sediments.

Unraveling the geochemical and microbial controls on methylmercury (MeHg) dynamics in mangrove sediments is important, as MeHg can potentially pose risks to marine biota and people that rely on these ecosystems. While the important role of sulfate-reducing bacteria in MeHg formation has been examined in this ecologically important habitat, the contribution of non-Hg methylating communities on MeHg production remains particularly unclear. Here, we collected sediment samples from 13 mangrove forests in south China and examined the geochemical parameters and microbial communities related to the Hg methylation. MeHg concentrations were significantly correlated to the OM-related parameters such as organic carbon content, total nitrogen, and dissolved organic carbon concentrations, suggesting the importance of OM in the MeHg production. Sulfate-reducing bacteria were the major Hg-methylators in mangrove sediments. Desulfobacteraceae and Desulfobulbaceae dominated the Hg-methylating microbes. Classification random forest analysis detected strong co-occurrence between Hg methylators and putative non-Hg methylators, thus suggesting that both types of microorganisms contribute to the MeHg dynamics in the sediments. Our study provides an overview of MeHg contamination in south China and advances our understanding of Hg methylation in mangrove ecosystems.

Cadmium contamination in sediments from a mangrove wetland: Insights from lead isotopes.

Cadmium (Cd) pollution has gained significant attention in mangrove sediments due to its high toxicity and mobility. However, the sources of Cd and the factors influencing its accumulation in these sediments have remained elusive. In this study, we utilized lead (Pb) isotopic signatures for the first time to assess Cd contamination in mangrove sediments from the northern region of the Beibu Gulf. A strong correlation was observed between Cd and Pb concentrations in the mangrove sediments, suggesting a shared source that can be estimated using Pb isotopic signatures. By employing a Bayesian mixing model, we determined that 70.1 ± 8.2 % of Cd originated from natural sources, while 12.9 ± 4.9 %, 9.8 ± 3.7 %, and 7.1 ± 3.4 % were attributed to agricultural activities, non-ferrous metal smelting, and coal combustion, respectively. Our study clearly suggests that natural Cd could also dominate the high Cd content. Agricultural activities were the most important anthropogenic Cd sources, and the increased anthropogenic Cd accumulation in mangrove sediment was related to organic matter. This study introduces a novel approach for assessing Cd contamination in mangrove sediment, providing useful insights into Cd pollution in coastal wetlands.