Despite their ecological and socioeconomic importance, mangroves are among the most threatened tropical environments in the world. In the past two decades, the world's mangrove degradation and loss were estimated to lie between an 35% and >80%. However, appropriate bioindicators for assessing the impact of external factors, and for differentiating polluted from unpolluted areas are still scarce. Here, we determine the physicochemical profiles of the soils of two mangroves, one exposed to and one not exposed to anthropogenic factors. By metagenomic analysis based on 16S rRNA, we generated the bacterial diversity profiles of the soils and estimated their functional profiles. Our results showed that the two examined mangrove forests differed significantly in the physicochemical properties of the soils, especially regarding organic carbon, phosphorus and metal content, as well as in their microbial communities, which was likely caused by anthropogenic pollution. The physicochemical differences between the soils explained 76% of the differential bacterial composition, and 64% depended solely on gradients of phosphorus, metal ions and potassium. We found two genera JL-ETNP-Z39 and TA06 exclusively in polluted and non-polluted mangroves, respectively. Additionally, the polluted mangrove was enriched in Gemmatimonadetes, Cyanobacteria, Chloroflexi, Firmicutes, Acidobacteria, and Nitrospirae. A total of 77 genera were affected by anthropic contamination, of which we propose 33 as bioindicators; 26 enriched, and 7 depleted upon pollution.

To verify weather mangroves act as sinks for marine litter, we surveyed through visual census 20 forests along the Red Sea and the Arabian Gulf, both in inhabited and remote locations. Anthropogenic debris items were counted and classified along transects, and the influence of main drivers of distribution were considered (i.e. land-based and ocean-based sources, density of the forest and properties of the object). We confirmed that distance to major maritime traffic routes significantly affects the density of anthropogenic debris in Red Sea mangrove forests, while this was independent of land-based activities. This suggests ocean-based activities combined with surface currents as major drivers of litter in this basin. Additionally, litter was more abundant where the mangrove density was higher, and object distribution through the mangrove stand often depended on their shape and dimension. We particularly show that pneumatophores act as a sieve retaining large plastic objects, leading to higher plastic mass estimates in mangroves compared to those of beaches previously surveyed in the Red Sea.

The effect of different sewage concentrations (0, 20, 60 and 100%), vegetation (Bare, Avicennia marina or Rhizophora mucronata) and immersion periods (immersion/emersion period of 12/12 h or 3/3 days just for 100%) conditions were studied for 6 months on survival and growth rates of Terebralia palustris (Linnaeus, 1767). Gastropods' activity and ecosystem engineering preformed at bare and A. marina planted cells and 3 sewage conditions (0, 20 and 60%) were determined. Survival rates were higher than 70% in all treatments. Growth rate decreased significantly with increasing sewage concentrations (mainly at unplanted conditions) and longer immersion periods. A complete shift (from immersion to emersion periods) and a significant decrease in mobility and consequently its engineer potential, due to sewage contamination, lead to a 3–4 fold decrease in the amount of sediment disturbed. Sewage contamination, primary producers' abundance and environmental conditions may have influenced the gastropods survival, growth and its ecosystem engineering potential. Terebralia palustris high ecosystem engineering potential in constructed mangrove wetlands.

The distribution of polycyclic aromatic hydrocarbons (PAHs) in the surface water and sediments in five regions of the Indian Sundarbans was assessed. The capability of microbial biofilm communities to sequester PAHs in a biofilm-promoting vessel was evaluated. The total PAH concentration of water and sediments ranged from undetectable to 125 ng ml⁻¹ and 4880 to 2 × 10⁴ ng g⁻¹ dry weight respectively. The total PAHs concentration of sediments exceeded the Effects Range–Low value and the recommended Effects Range-Median values, implying the PAHs might adversely affect the biota of the Sundarbans. Pyrogenic and petrogenic sources of PAH contamination were identified in most of the sampling sites. Indigenous biofilms were cultivated in a patented biofilm-promoting culture vessel containing liquid media spiked with 16 priority PAHs. Biofilm-mediated 97–100% removal efficiency of 16 PAHs was attained in all media. There was no significant difference between the mean residual PAH from the liquid media collected from hydrophobic and hydrophilic flasks. Residual amounts of acenaphthene (Ace), anthracene (Ant), benzo(b)fluoranthene [B(b)F], benzo(a)pyrene [B(a)P] and benzo(g,h,i)perylene [B(g,h,i)P] showed differences when cultivated in hydrophobic and hydrophilic flasks. The mean residual amounts of total PAHs extracted from biofilm biomasses were variable. A biofilm obtained from a specific sampling site cultured in the hydrophobic flask showed higher PAH sequestration when compared to the removal attained in the hydrophilic flask. Relative abundances of different microbial communities in PAH-sequestering biofilms revealed bacterial phyla including Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, Chloroflexi and Planctomycetes as well as members of Ascomycota phylum of fungi. The dominance of Candida tropicalis, Clostridium butyricum, Sphingobacterium multivorum and Paecilomyces fulvus were established.

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.

Mangroves are often exposed to heavy metals that accumulate in the food chain, generate toxicity to mangrove plants and affect microbial diversity. This study determined the abundance of genes associated with resistance and tolerance to heavy metals in the rhizosphere microbiome of Avicennia germinans from a semi-arid mangrove of La Guajira-Colombia by metagenomics and genomics approach. Twenty-eight genes associated with tolerance and 49 genes related to resistance to heavy metals were detected. Genes associated with tolerance and resistance to Cu, especially cusA and copA, were the most abundant. The highest number of genes for tolerance and resistance were for Zn and Co, respectively. The isolate Vibrio fluvialis showed the ability to tolerate Cu, Ni, Zn, and Cd. This work used a complementary approach of metagenomics and genomics to characterize the potential of mangrove microorganisms to tolerate and resist heavy metals and the influence of salinity on their abundance.

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.

Mangrove has been destroyed and reforestation is often undertaken, but whether a regenerated forest could restore its ecological function is not clear. This study compares microbial community structure and function in sediment of the 17-years old natural regenerated mangrove forest (Y17) with the original forest (Y74). No significant differences in phospholipid fatty acid (PLFA) profiles and microbial metabolism of most carbon substrates were found between these two forests. However, activities of dehydrogenase, protease, cellulase and phosphatase were lower in Y17 than Y74, and some specific microbial functions were also different. Both forests exhibited significant seasonal differences in enzyme activities and microbial characteristics, but such difference was larger in Y17 than Y74, indicating the regenerated forest was more sensitive to season. Correspondence analysis based on PLFA profiles and enzyme activities revealed the microbial community in Y17 was comparable to Y74, suggesting sediment microbial characteristics in natural regenerated mangroves could be restored.

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.

Accumulation of microplastics (MPs) data on a global scale is key to supporting plastic waste management for protecting ecosystems. To respond this call, a sampling campaign was conducted in the summer and winter seasons of 2018 to collect beach and mangrove sediment samples from 32 sites along the coastline of South China. The MPs concentrations in the intertidal zone along the coast of South China were comparable to those in other regions around the world. Polystyrene foams and fibers were the most abundant debris in the 0.2–5 mm and 0.02–2 mm MPs, respectively. Principal component and correlation analyses indicated that the abundances of MPs were related to wind direction, wastewater discharge amount, and tourist and fishing activities. Risk assessments suggested that potential ecological risks induced by MPs on beaches and mangrove forest along the coast of South China should not be overlooked.