Guangxi Mangrove Research Center

Chemical sequential extraction and high-resolution diffusive gradients in thin-film (DGT) techniques were employed to study the mobilization behavior and underlying mechanisms of phosphorus (P) in estuarine sediments. This study focused on two contrasting subtropical estuaries in the Maowei Sea, northern Beibu Gulf: the Maoling River Estuary (MLRE, dominated by natural processes) and the Qin River Estuary (QRE, influenced by coastal shrimp pond effluent). Sediment samples were collected in December 2020 (winter) and July 2021 (summer). Overall, the contents of inorganic P, organic P (OP), and DGT-labile P in core sediments of the QRE were significantly higher than those in the MLRE. Notably, the average concentration of DGT-labile P in the QRE sediments (7.82 ± 4.94 µmol L−1) was approximately 4.6 times greater than that in the MLRE sediments (1.69 ± 0.96 µmol L−1). During the investigation, the QRE sediments consistently acted as a net source of P to the overlying water. In contrast, the MLRE sediments functioned as a source of P in winter but transitioned to a weak sink in summer. Sedimentary P release was driven by dissimilatory sulfate reduction and dissimilatory Fe (III) reduction, regulated mainly by the content and speciation of sedimentary P and sedimentary organic matter (SOM). In the MLRE, where sedimentary P and SOM contents were relatively low, P release was governed by the migration and transformation of multiple P forms, including exchangeable P (Ex-P), Fe-bound P (Fe–P), OP and authigenic apatite P (Ca–P). In comparison, due to shrimp pond effluent inputs, the QRE exhibited higher sedimentary P and SOM contents, and P release was primarily controlled by Fe–P mobilization. These results highlight that coastal shrimp aquaculture can supply substantial amounts of high-quality SOM and P to estuarine sediments, significantly altering sedimentary P cycling.

We studied the relationships between functional traits of Halophila beccarii (shoot density, seed bank density, number of blades, above-ground biomass, below-ground biomass, leaf length, leaf width, and petiole length) and environmental factors (pH, salinity, temperature, physical disturbance by humans, and algal coverage) in eight populations along the coast of China. There were statistically significant differences in the functional traits of H . beccarii between tropical and subtropical regions. Traits such as shoot density, seed bank density, and biomass were notably higher in tropical populations, whereas leaf dimensions showed greater variability across regions. Further analysis using a linear mixed-effects model revealed that water temperature and salinity positively influenced shoot density, seed bank density, and biomass. Conversely, salinity negatively impacted traits such as leaf length, leaf width, and petiole length. Additionally, physical disturbance by humans and algal coverage demonstrated statistically significant negative correlations with shoot density and biomass. These findings provide insights into the environmental adaptability and conservation needs of this vulnerable seagrass species.

Nutrients function as essential biological substrates for coastal phytoplankton growth and serve as pivotal indicators in marine environmental monitoring. The intensification of land-based nutrient sources inputs has exacerbated eutrophication in Chinese coastal water, while mechanistic understanding of differential self-purification processes among distinct land-based source nutrients (river source, domestic source, aquaculture source, and industrial source) remains limited, constraining accurate assessment of bay’s self-purification capacity. This study conducted incubation experiments in Tieshan Bay (TSB) during Summer (June 2023) and winter (January 2024), systematically analyzing the self-purification process of nutrients and associated environmental drivers. Distinct source-specific patterns emerged: river inputs exhibited maximal dissolved inorganic nitrogen (DIN) 1.390 ± 0.74 mg/L, whereas industrial discharges showed peak dissolved inorganic phosphorus (DIP) 4.88 ± 1.45 mg/L. Chlorophyll a (Chl-a) concentrations varied markedly across sources, ranging from 34.97 ± 23.37 μg/L (domestic source) to 86.63 ± 77.08 μg/L (river source). First-order kinetics demonstrated significant source differentiation (p < 0.05). River-derived DIN exhibited the highest attenuation coefficient (−0.3244 ± 0.17 d−1), contrasting with industrial-sourced DIP showing maximum depletion (−0.4332 ± 0.20 d−1). Correlation analysis indicated that summer was significantly associated with the impacts of three key control factors pH, dissolved oxygen, and turbidity on nutrient dynamics (p < 0.05), whereas winter exhibited a stronger dependence on salinity. These parameters collectively may modulate microbial degradation pathways and particulate matter adsorption capacities. These findings establish quantitative thresholds for coastal nutrient buffering mechanisms, highlighting the necessity for source-specific eutrophication mitigation frameworks. The differential self-purification efficiencies underscore the importance of calibrating pollution control strategies according to both anthropogenic discharge characteristics and regional hydrochemical resilience, which is of key importance for ensuring the traceability and control of land-based sources of pollution into the sea and the scientific utilization of the self-purification capacity of the bay water body.

BackgroundThe mangrove ecosystem has been severely threatened by the invasive species Spartina alterniflora for a long time. The macrobenthos diversity, as a biological indicator for assessing ecosystem sensitivity, can respond sensitively to the removal of the invasive S. alterniflora. Traditional morphological method has been commonly used to study macrobenthos diversity. However, it is difficult to comprehensively and accurately assess using traditional morphological method alone. Few studies have systematically assessed the effectiveness of environmental DNA in monitoring the diversity of macrobenthos in mangrove ecosystems.MethodsTraditional morphological method and eDNA metabarcoding (using COI primers) were combined to analyze changes in macrobenthos diversity in September (before S. alterniflora removal), October (after S. alterniflora removal but before mangrove planting), and December (after S. alterniflora removal and mangrove planting) of 2022 at the Quanzhou Bay Mangrove Wetland Nature Reserve, Fujian Province, China.ResultsThe results showed that 26 species were identified using traditional morphological method, while 212 species were identified through eDNA metabarcoding, especially more Arthropod were detected. However, no species were found to be common between the two methods at the species level. In terms of abundance, Arthropods and Annelids were the dominant groups for two methods, both 28.38% in the traditional morphological method and 38.38% and 32.94% in the eDNA metabarcoding, respectively. Additionally, the traditional morphological method indicated that following the removal of S. alterniflora, species richness, density, biomass, and diversity indices of macrobenthos initially declined, but subsequently showed a consistent recovery trend.DiscussionOur study suggests that eDNA metabarcoding has tremendous potential to monitor macrobenthos diversity, but shows low consistency in species with traditional method. For broader application in macrobenthos diversity using eDNA metabarcoding, further optimization is needed. Additionally, the results suggested that after the removal of S. alterniflora, macrobenthos diversity initially declined but gradually recovered, and long-term monitoring is warranted in order to better understand the changes in macrobenthos diversity with planting of mangroves.

Mangroves not only provide ecosystem and cultural services but also contribute to the mitigation of global warming. Mangrove dynamics and their environmental responses in the past can inform mangrove conservation and restoration. However, our understanding of mangrove dynamics over the past century and the impact of human activities on these ecosystems remains limited. Using the quantified mangrove-derived organic carbon (MOC) contributions of seven sediment cores, we reconstructed the historical mangrove development in Yingluo Bay and the Maowei Sea in tropical China since 1900. The results indicated that the natural undisturbed mangroves in Yingluo Bay gradually flourished in response to rising temperatures. In contrast, the significantly human-disturbed mangroves in Maowei Sea experienced a marked decline. Although both areas share similar natural conditions, the intense anthropogenic disturbance reversed the natural potential for mangrove growth in Maowei Sea. To verify the global prevalence of this phenomenon, we compiled data on mangrove pollen, δ13Corg, MOC, and mangrove area from over 40 sites/regions worldwide. The data enabled us to reconstruct the natural and human-disturbed mangrove changes over the past century. Our findings indicated that, owing to the global warming and rising temperatures, natural undisturbed mangroves have gradually flourished, while human-disturbed mangroves exhibited three changing patterns: (1) continuous degradation, (2) flourishing-degradation, and (3) degradation-regeneration. Unreasonable anthropogenic activities, such as seawall construction, aquaculture activity, agricultural expansion, logging, and urbanization, have significantly reversed the natural progression of mangroves such that any typological description used for mangroves globally likely need disturbance modifiers for accuracy.

BackgroundHalophila beccarii is one of the oldest two generations of seagrass plants and one of the 10 species of seagrass currently at risk of extinction worldwide. Therefore, how to effectively protect the H. beccarii resources from extinction is a huge challenge. Molecular biology research can provide a scientific basis for species conservation. So far, there has been no detailed analysis of the mitochondrial genome of the genus Halophila.ResultsThe mitochondrial genome of H. beccarii was assembled into 28 circular chromosomes, ranging in length from 41,738 bp to 104,744 bp, with a total length of 1,964,072 bp and a GC content of 46.71%. It contains 39 genes, including 26 protein coding genes, 10 tRNA genes, and 3 rRNA genes. Repeat sequence analysis and prediction of RNA editing sites revealed a total of 850 dispersed repeats, 1,205 simple repeats, 61 tandem repeats, and 120 RNA editing sites. Analysis of codon usage indicates that codons ending in A/U are preferred. Gene migration between the mitochondrial genome and the chloroplast genome was observed through homologous fragment detection. In addition, Ka/Ks analysis showed that most protein coding genes in the mitochondrial genome experienced negative selection, while only the nad3 gene experienced potential positive selection in most Alismatales. Nucleotide polymorphism analysis revealed variations in each gene, with rpl10 being the most significant. In addition, comparative analysis shows that the GC content is conserved, but there are significant differences in the size and structure of mitochondrial genomes among different species of Alismatales. The phylogenetic analysis based on the mitochondrial genome reflects the exact evolutionary and taxonomic status of H. beccarii.ConclusionIn this study, we sequenced and annotated the mitochondrial genome of H. beccarii, and compared it with the mitochondrial genomes of other plants in Alismatales. Our findings enrich the mitogenome database of seagrass plants and highlight the potential for mitochondrial genes to help decipher plant evolutionary history.