Mangroves are essential ecosystems for coastal protection, carbon sequestration, biodiversity, and food production. In particular, mud crabs, with an annual global landing of over 100,000 metric tons, are crucial for the economic livelihoods and food security of millions of small-scale fishers in Southeast Asia. Here, we review the impact of pollutants on mud crab populations in mangrove ecosystems, with emphasis on pollutant sources, toxic effects on crabs, and remediation using microbes and biochar. Pollutants include microplastics, per- and polyfluoroalkyl substances, pesticides, polycyclic aromatic hydrocarbons, and heavy metals. Pollution originates from agricultural runoff, industrial discharges, mining activities, urbanization, and domestic waste. We present the use of biochar for pollutant remediation and enhancing carbon sequestration. We observe that heavy metals, pesticides, and microplastics induce oxidative stress, disrupt antioxidant defense mechanisms, and impair the growth, reproduction, and survival rates of mud crabs. Microbial bioremediation can remove more than 90% of polycyclic aromatic hydrocarbons. Biochar application reduces by 87% the bioavailability of heavy metal in contaminated soils.

Mangrove forests are vital for flood reduction, yet their failure mechanisms during storms are poorly known, hampering their integration into engineered coastal protection. In this paper, we aimed to unravel the relationship between the resistance of mangrove trees to overturning and root distribution and the properties of the soil, while avoiding damage to natural mangrove forests. We therefore (i) tested the stability of 3D-printed tree mimics that imitate typical shallow mangrove root systems, mimicking both damaged and intact root systems, in sediments representing the soil properties of contrasting mangrove sites, and subsequently (ii) tested if the existing stability models for terrestrial trees are applicable for mangrove tree species, which have unique shallow root systems to survive waterlogged soils. Root systems of different complexities were modeled after Avicennia alba, Avicennia germinans, and Rhizophora stylosa, and printed at a 1:100 scale using material densities matching those of natural tree roots, to ensure the geometric scaling of overturning moments. The mimic stability increased with the soil shear strength and root plate surface area. The optimal root configuration for mimic stability depended on the sediment properties: spreading root systems performed better in softer sediments, while concentrating root biomass near the trunk improved stability in stronger sediments. An adapted terrestrial tree resistance model reproduced our measurements well, suggesting that such models could be adapted to predict the stability of shallow-rooted mangroves living in waterlogged soils. Field tree-pulling experiments are needed to further confirm our conclusions with real-world data, examine complicating factors like root intertwining, and consider mangrove tree properties like aerial roots. Overall, this work establishes a foundation for incorporating mangrove storm damage into hybrid coastal protection systems.

Vegetated blue carbon environments have the potential to sequester large amounts of carbon due to their high productivity and typically saturated, anaerobic soils that promote carbon accumulation. Despite this, and the coupling of Fe-S-C cycling processes, the influence of iron (Fe) in acid sulfate soils (ASSs) on carbon sequestration in blue carbon environments has yet to be systematically explored. To address this knowledge gap, this review provides an overview linking the current state of blue carbon studies with the influence of Fe on soil organic carbon (SOC), as well as the potential influence ASSs have on carbon sequestration. A systematic literature review on SOC stock in blue carbon studies using the Web of Science database yielded 1477 results. Studies that investigated the drivers of carbon accumulation in blue carbon studies were restricted to vegetation species/structure and geomorphic setting, and few focused on soil properties and type. Iron both protects and enhances SOC decomposition depending on its redox state. Under oxic conditions, Fe oxyhydroxides can protect SOC via adsorption, co-precipitation and by acting as a cement in soil aggregates. Iron can also increase SOC decomposition under oxic conditions due to Fenton reactions. However, under anoxic conditions, SOC mineralisation can also occur as Fe acts as an electron transporter in dissimilatory reductions. ASSs contain a range of Fe minerals, but the oxidation of Fe sulfides can result in soil acidification (pH < 4) and subsequent impacts, such as a decline in vegetation health, poor water quality and infrastructure damage. Therefore, potential SOC protection by Fe under oxic conditions may come at the cost of soil acidification in ASSs, while maintaining anoxic conditions prevents acidification but may enhance SOC decomposition. Future studies on the influence of ASSs on Fe-S-C cycling and carbon sequestration in blue carbon environments are important, particularly for 'hotspots' such as Australia.

Carbon storage in mangroves is considered a natural solution to mitigate climate change as an essential coastal blue carbon ecosystem service for climate change. The magnitude of carbon storage in soils depends on the carbon metabolic activities of the microbial community, and these dynamics are subject to the influence of climate conditions, including seasonal changes. Despite mangroves being one of the world's highest in soil carbon density and carbon sequestration rates, our understanding of this aspect remains limited. Here, we investigated the seasonal changes in the carbon metabolic profile of microbial communities in mangrove soils along the seashore of the whole Hainan Island (with the highest diversity of mangrove species in China). There was a clear season dependence in the metabolic activity and functional diversity of mangrove soil microbial community on Hainan Island, showing the trend of the rainy season > the dry season. The carbon metabolic activity in the rainy season is three times higher than in the dry season. The season plays a critical role in shaping the carbon functional diversity of microbial communities, which that by changing biotic interactions and soil properties, particularly soil TN, NO2 -N, plant richness and mean DBH. This study provides important insights into comprehend the carbon metabolic functional diversity of microbial communities in mangrove soils and provides basic data support for predicting the blue carbon feedback of mangrove ecosystems to global climate change.

Aeluropus lagopoides, a dominant palatable species in various sabkha and coastal regions of Saudi Arabia, can withstand harsh saline environments through phenotypic plasticity. When subjected to grazing, how A. lagopoides adapt phenotypically is currently unknown. There is a breakage in the chain of study on the spatial and temporal expansion strategy of A. lagopoides plants when subjected to different grazing stresses in different saline soil habitats. A grazing experiment was conducted to investigate the phenotypic plasticity and resource allocation pattern response of A. lagopoides in different saline soils. Individual A. lagopoides rhizomes from five saline regions were grown and exposed to varied grazing treatments in the form of clipping, viz; light, moderate, and heavy grazing, as compared to a grazing exclusion control. Our results showed that heavy grazing/clipping significantly decreased the shoot system and above-ground biomass in high-saline region plants in the early season. Plant length, root length, root and shoot biomass, the number of stolons, average stolon length, leaf area, and SLA of A. lagopiodes responded significantly to grazing intensities. A. lagopoides from the Qareenah, Qaseem, and Jizan regions were more tolerant to light grazing than A. lagopoides from the Salwa and Jouf regions. Light grazing showed significantly good re-growth, especially during the late season. Light grazing decreased the synthesis of chlorophyll content. Also, A. lagopiodes reduced the risk caused by reactive oxygen species via the increased accumulation of proline content. Overall, plants adapted to different morphological and physiological strategies to tolerate different levels of grazing intensities by adapting their morphological attributes. Though heavy grazing damages the plant, light and moderate grazing can be allowed to maintain the productivity and economic benefits of sabka habitats where soil conditions are moderately saline.

Environmental pollution and climate change have been reported to severely affect the growth and productivity of mangroves. However, it is still unclear how the mangroves will fare if stressed by these adverse conditions, and how the mangroves might fare if these conditions improve. In this study, the trends of mangrove forests in the Thi Vai catchment (Vietnam) were assessed using mathematical models, addressing the polluted environment under climate change conditions. This simulated study was conducted based on the analysis of different types of data. Data on 18 elements' concentrations accumulated in mangrove tissues in this catchment were analyzed in relation to the states of tree growth rates. Data on the economic productivity and water quality of the Thi Vai River in the five years from 2017 to 2021 were analyzed to detect the main sources of pollution that induced damage to mangrove forests. The results achieved from data analysis are the linear and nonlinear interactions between the concentrations of tissue-accumulated substances and the growth rates of trees. Concentrations of P, Mg, and Sr in mangrove leaves have a linear relationship with plant growth while Cr, Cu, and Ni accumulated in roots have a nonlinear relationship. The mining industry and accommodation and food services are the main contributing sources of Cr and Cu, which affect mangrove health. Information supplied from the data analysis helped in designing the scenarios of different combined environmental conditions for model simulations. Our previously developed mangrove dynamics model was applied to predict the trajectory of the mangrove forest in this area under a total of 16 combined environmental condition scenarios.