The inputs of autochthonous organic carbon driven by mangroves reduce metal mobility and bioavailability in intertidal regions.

The significance of mangroves in carbon storage is widely acknowledged. However, the potential role of carbon enhancement driven by mangroves in mitigating the risk of metal exposure remains unclear. In this study, a natural mangrove reserve located in Futian was selected to investigate the potential role of autochthonous organic carbon on metal bioavailability. The presence of mangroves seemed to have little effect on the accumulations of Cu(II), Zn(II), Cr(VI/III), Pb(II), and Ni(II) in surface sediments. Metal mobility and bioavailability, however, were found to be directly influenced by the presence of mangroves. Compared with mudflat, mangrove sediments exhibited an obvious in the bioavailability of Cu(II), Zn(II), Cr(VI/III), Pb(II), and Ni(II) by 19-79 %, with the highest reduction occurring in the interior of mangroves dominated by K. obovata. Mangroves also significantly enhanced the accumulation of organic carbon in sediments, regardless of carbon components. Moreover, the results from random forest analysis further showed that autochthonous organic carbon was the most important carbon component that negatively related to metal bioavailability. In summary, this is the first study to provide a linkage between mangrove cover and increased autochthonous organic carbon input, which decreases metal bioavailability. The present data also suggest that mangroves are an efficient natural barrier to alleviate the risk of metal exposure in intertidal regions.

Insights into the spatial distributions of bacteria, archaea, ammonia-oxidizing bacteria and archaea communities in sediments of Daya Bay, northern South China Sea.

Microbe plays an important role in the biogeochemical cycles of the coastal waters. However, comprehensive information about the microbe in the gulf waters is lacking. This study employed high-throughput sequencing and quantitative PCR (qPCR) to investigate the distribution patterns of bacterial, archaeal, ammonia-oxidizing bacterial (AOB), and archaeal (AOA) communities in Daya Bay. Community compositions and principal coordinates analysis (PCoA) exhibited significant spatial characteristics in the diversity and distributions of bacteria, archaea, AOB, and AOA. Notably, various microbial taxa (bacterial, archaeal, AOB, and AOA) exhibited significant differences in different regions, playing crucial roles in nitrogen, sulfur metabolism, and organic carbon mineralization. Canonical correlation analysis (CCA) or redundancy analysis (RDA) indicated that environmental parameters such as temperature, salinity, nitrate, total nitrogen, silicate, and phosphate strongly influenced the distributions of bacterial, archaeal, AOB, and AOA. This study deepens the understanding of the composition and ecological function of prokaryotes in the bay.

Cloning and Expression of Class I Chitinase Genes from Four Mangrove Species under Heavy Metal Stress.

Chitinases are believed to act as defense proteins when plants are exposed to heavy metal stress. Typical Class I chitinase genes were cloned from Bruguiera gymnorrhiza, Rhizophora stylosa, Kandelia obovata, and Avicennia marina using the methods of reverse-transcription-polymerase chain reaction and rapid amplification of cDNA ends. All four cDNA sequences of chitinase from the mangrove plants were 1092 bp in length and consisted of an open reading frame of 831 bp, encoding 276 amino acids. However, there were differences in the sequences among the four mangrove species. Four gene proteins have a signal peptide, are located in the vacuole, and belong to the GH19 chitinase family. The sequence of chitinase was highly similar to the protein sequences of Camellia fraternal chitinases. A real-time polymerase chain reaction was used to analyze the chitinase expressions of the above four mangrove species exposed to different concentrations of heavy metal at different times. The gene expression of chitinase was higher in Bruguiera gymnorrhiza leaves than in other mangrove plant species. With an increase in heavy metal stress, the expression level of Bruguiera gymnorrhiza increased continuously. These results suggest that chitinase plays an important role in improving the heavy metal tolerance of mangrove plants.

An Aquaporin Gene (KoPIP2;1) Isolated from Mangrove Plant Kandelia obovata Had Enhanced Cold Tolerance of Transgenic Arabidopsis thaliana.

Aquaporins (AQPs) are essential channel proteins that play central roles in maintaining water homeostasis. Here, a novel aquaporin gene, named KoPIP2;1, was cloned from the mangrove plant Kandelia obovata by RACE technology. The KoPIP2;1 gene was 1404 bp in length with an open reading frame (ORF) of 852 bp, encoded with 283 amino acids. Database comparisons revealed that KoPIP2;1 protein shared the highest identity (91.26%) with the aquaporin HbPIP2;2, which was isolated from Hevea brasiliensis. Gene expression analysis revealed that the KoPIP2;1 gene was induced higher in leaves than in stems and roots of K. obovata under cold stress. Transient expression of KoPIP2;1 in Nicotiana benthamiana epidermal cells revealed that the KoPIP2;1 protein was localized to the plasma membrane. Overexpressing KoPIP2;1 in Arabidopsis significantly enhanced the lateral root number of the transgenic lines. KoPIP2;1 transgenic Arabidopsis demonstrated better growth, elevated proline content, increased superoxide dismutase (SOD) and peroxidase (POD) activities, and reduced malondialdehyde (MDA) content compared with the wild-type Arabidopsis when exposed to cold stress. The findings suggest that overexpression of KoPIP2;1 probably conferred cold tolerance of transgenic Arabidopsis by enhancing osmoregulation and antioxidant capacity. This present data presents a valuable gene resource that contributes to the advancement of our understanding of aquaporins and their potential application in enhancing plant stress tolerance.

Polymeric carbohydrates utilization separates microbiomes into niches: insights into the diversity of microbial carbohydrate-active enzymes in the inner shelf of the Pearl River Estuary, China.

Polymeric carbohydrates are abundant and their recycling by microbes is a key process of the ocean carbon cycle. A deeper analysis of carbohydrate-active enzymes (CAZymes) can offer a window into the mechanisms of microbial communities to degrade carbohydrates in the ocean. In this study, metagenomic genes encoding microbial CAZymes and sugar transporter systems were predicted to assess the microbial glycan niches and functional potentials of glycan utilization in the inner shelf of the Pearl River Estuary (PRE). The CAZymes gene compositions were significantly different between in free-living (0.2-3 µm, FL) and particle-associated (>3 µm, PA) bacteria of the water column and between water and surface sediments, reflecting glycan niche separation on size fraction and selective degradation in depth. Proteobacteria and Bacteroidota had the highest abundance and glycan niche width of CAZymes genes, respectively. At the genus level, Alteromonas (Gammaproteobacteria) exhibited the greatest abundance and glycan niche width of CAZymes genes and were marked by a high abundance of periplasmic transporter protein TonB and members of the major facilitator superfamily (MFS). The increasing contribution of genes encoding CAZymes and transporters for Alteromonas in bottom water contrasted to surface water and their metabolism are tightly related with particulate carbohydrates (pectin, alginate, starch, lignin-cellulose, chitin, and peptidoglycan) rather than on the utilization of ambient-water DOC. Candidatus Pelagibacter (Alphaproteobacteria) had a narrow glycan niche and was primarily preferred for nitrogen-containing carbohydrates, while their abundant sugar ABC (ATP binding cassette) transporter supported the scavenging mode for carbohydrate assimilation. Planctomycetota, Verrucomicrobiota, and Bacteroidota had similar potential glycan niches in the consumption of the main component of transparent exopolymer particles (sulfated fucose and rhamnose containing polysaccharide and sulfated-N-glycan), developing considerable niche overlap among these taxa. The most abundant CAZymes and transporter genes as well as the widest glycan niche in the abundant bacterial taxa implied their potential key roles on the organic carbon utilization, and the high degree of glycan niches separation and polysaccharide composition importantly influenced bacterial communities in the coastal waters of PRE. These findings expand the current understanding of the organic carbon biotransformation, underlying the size-fractionated glycan niche separation near the estuarine system.

Molecular Cloning and Expression Analysis of the Typical Class III Chitinase Genes from Three Mangrove Species under Heavy Metal Stress.

Chitinases are considered to act as defense proteins when plants are exposed to heavy metal stresses. Typical class III chitinase genes were cloned from Kandelia obovate, Bruguiera gymnorrhiza, and Rhizophora stylosa by using RT-PCR and RACE and named KoCHI III, BgCHI III, and RsCHI III. Bioinformatics analysis revealed that the three genes encoding proteins were all typical class III chitinases with the characteristic catalytic structure belonging to the family GH18 and located outside the cell. In addition, there are heavy metal binding sites in the three-dimensional spatial structure of the type III chitinase gene. Phylogenetic tree analysis indicated that CHI had the closest relationship with chitinase in Rhizophora apiculata. In mangrove plants, the balance of the oxidative system in the body is disrupted under heavy metal stress, resulting in increased H2O2 content. Real-time PCR illustrated that the expression level under heavy metal stress was significantly higher than that in the control group. Expression levels of CHI III were higher in K. obovate than in B. gymnorrhiza and R. stylosa. With the increase in heavy metal stress time, the expression level increased continuously. These results suggest that chitinase plays an important role in improving the heavy metal tolerance of mangrove plants.

Combined effect of microplastic and triphenyltin: Insights from the gut-brain axis.

Microplastics (MPs), an emerging group of pollutants, not only have direct toxic effects on aquatic organisms but also cause combined toxicity by absorbing other pollutants. Triphenyltin (TPT), one of the most widely used organotin compounds, has adverse effects on aquatic organisms. However, little is known about the combined toxicity of MPs and TPT to aquatic organisms. To investigate the individual and combined toxicity of MPs and TPT, we selected the common carp (Cyprinus carpio) for a 42-day exposure experiment. Based on the environmental concentrations in a heavily polluted area, the experimental concentrations of MPs and TPT were set at 0.5 mg L-1 and 1 µg L-1, respectively. The effects of MPs combined with TPT on the carp gut-brain axis were evaluated by detecting gut physiology and biochemical parameters, gut microbial 16S rRNA, and brain transcriptome sequencing. Our results suggest that a single TPT caused lipid metabolism disorder and a single MP induced immunosuppression in carp. When MPs were combined with TPT, the involvement of TPT amplified the immunotoxic effect induced by MPs. In this study, we also explored the gut-brain axis relationship of carp immunosuppression, providing new insights for assessing the combined toxicity of MPs and TPT. At the same time, our study provides a theoretical basis for evaluating the coexistence risk of MPs and TPT in the aquatic environment.

Assessing the ecotoxicity of combined exposure to triphenyltin and norfloxacin at environmental levels: A case study of immunotoxicity and metabolic regulation in carp (Cyprinus carpio).

This paper evaluates the coexistence risks of triphenyltin (TPT) and norfloxacin (NOR) to aquatic organisms in the aquatic environment. Carp (Cyprinus carpio) was used as the test organism, the control and exposure groups (1 µg/L TPT), 1 mg/L (NOR), 1 µg/LTPT+1 mg/LNOR (TPT_NOR)) were set up according to the environmental concentration in the severely polluted area for 42 days. The single/combined toxic effects of TPT and NOR on aquatic organisms were evaluated by analyzing carp brain transcriptome sequencing, gut microbiota structure, and detection of biochemical indicators and RT-qPCR. Our results show that TPT and NOR induce lipid metabolism disorder in carp brain tissue, affecting the metabolism of cytochrome P450 to exogenous substances, and NOR also induces immunosuppression in carp. Long-term exposure to TPT combined with NOR amplifies the monotoxicity of TPT or NOR on lipid metabolism and immunosuppression in carp, induces immune dysfunction in brain tissue and changes in gut microbiota structure. However, TPT_NOR has no obvious neurotoxicity on the brain, but it can inhibit the level of intestinal MDA. This highlights that co-exposure of TPT and NOR amplifies metabolic disorders and immunosuppressive functions in carp.

A new perspective on endocrine disrupting effects of triphenyltin on marine medaka: From brain transcriptome, gut content metabolome and behavior.

Triphenyltin (TPT) is an endocrine contaminant that is often detected in the environment. However, the mechanism of the effects of TPT on biological systems is not fully understood. Here we exposed marine medaka (Oryzias melastigma) to TPT for 21 days. Brain transcriptome, intestinal content metabolism group, and behavior analysis were carried out. Through the comprehensive analysis of multiomics for the in-depth understanding of the ways related to health improvement, we determined that the glycine-serine-threonine metabolic axis was most perturbed by TPT. Through behavioral analysis, it was found that there was behavioral hyperactivity in the exposed group; behavioral hyperactivity may be caused by the interference of TPT with the neuroendocrine system. In order to gain a full understanding of the impacts of TPT on human health, transcriptomic screening of differential genes and an impartial attitude based on bioinformatics were used. Gene-disease interaction analysis using the Comparative Toxicogenomics Database (CTD) revealed the possible effects of TPT on human health. Finally, based on these findings, the relevant adverse outcome pathway (AOP), which is the "epigenetic modification of PPARG leading to adipogenesis," was identified from AOP Wiki. Further research is required to validate the potential AOP of TPT.

Mangrove restoration promotes the anti-scouribility of the sediments by modifying inherent microbial community and extracellular polymeric substance.

Coastal erosion will aggravate the loss of shorelines and threaten the safety of coastal engineering facilities. Mangrove is often considered as an efficient coastal guard; however the mechanisms involved in anti-scouribility ascribed to mangrove are still poorly understood. Thus, two artificial mangrove forests (including exotic Sonneratia apetala and native Kandelia obovata) and an unvegetated mudflat control were selected to explore the potential function of microbial extracellular polymeric substance (EPS) on the anti-scouribility of the sediments. A cohesive strength meter was used for the analysis of anti-scouribility, while a sequential extraction and 16S high-throughput sequencing were employed to evaluate the changes in EPS and microbial community driven by mangrove restoration. Principal component, redundancy, and two-matrix correlation heatmap analyses were performed for the analyses of the correlations among shear stress, EPS, microbes, and soil properties. The results showed an obvious enhancement of anti-scouribility after mangrove restoration. Compared to those of unvegetated mudflat, shear stress increased from 1.94 N/m2 to 3.26 and 4.93 N/m2 in the sediments of S. apetala and K. obovata stands, respectively. Mangrove restoration also promoted EPS content in the sediments, irrespective of EPS components and sub-fractions. Both extracellular protein and polysaccharide were found to be positively correlated with anti-scouribility. Coinciding with increased anti-scouribility and EPS, increased bacterial abundances were also detected in the sediments after mangrove restoration (especially K. obovata), whereas Proteobacteria and Bacteroides may be important and influential for EPS secretion and anti-scouribility promotion. Nevertheless, increased total organic carbon, total nitrogen and total phosphorus induced by mangrove restoration may also partially contribute to improvement of anti-scouribility. In conclusion, this is the first study to provide evidence for a link between mangrove restoration and increased EPS which improve resistance to scouring. The present study provides a novel perspective on the revealing of the function of mangrove on erosion mitigation.

Comparative physiological and proteomic analyses of mangrove plant Kandelia obovata under cold stress.

Cold events had broadly affected the survival and geographic distribution of mangrove plants. Kandelia obovata, has an excellent cold tolerance as a true halophyte and widespread mangrove species. In this study, physiological characters and comparative proteomics of leaves of K. obovata were performed under cold treatment. The physiological analysis showed that K. obovata could alleviate its cold-stress injuries through increasing the levels of antioxidants, the activities of related enzymes, as well as osmotic regulation substances (proline). It was detected 184 differentially expressed protein spots, and of 129 (70.11%) spots were identified. These proteins have been involved in several pathways such as the stress and defense, photosynthesis and photorespiration, signal transduction, transcription factors, protein biosynthesis and degradation, molecular chaperones, ATP synthesis, the tricarboxylic acid (TCA) cycle and primary metabolisms. The protein post-translational modification may be a common phenomenon and plays a key role in cold-response process in K. obovata. According to our precious work, a schematic diagram was drawn for the resistance or adaptation strategy of mangrove plants under cold stress. This study provided valuable information to understand the mechanism of cold tolerance of K. obovata.

Triphenyltin exposure causes changes in health-associated gut microbiome and metabolites in marine medaka.

Triphenyltin (TPT), an organic compound with a wide range of applications, is often detected in water bodies and aquatic animals. However, the mechanism underlying the biological metabolic health problems caused by long-term exposure to environment concentrations of TPT remains unclear. The morphology and gene expression in the gut and liver were investigated; and 16SrRNA gene amplification sequencing and non-targeted LC-MS/MS metabonomics were investigated after marine medaka (Oryzias melastigma) was treated with 1, 10, and 100 ng/L TPT for 21 days. During prolonged exposure to TPT, the adaptation mechanism maximized the energy of absorption, increased the length of intestinal microvilli, reduced the number of rough endoplasmic reticulum in the liver, and caused loss of weight. TPT exposure significantly changed the intestinal microbiome of marine medaka, thereby resulting in a significant decrease in microbial diversity. Following exposure to 100 ng/L TPT, the metabolic profiles were significantly changed and the altered metabolites were mainly concentrated in the lipid metabolic pathway. Finally, based on comprehensive network analysis, the association between the significantly changed bacteria and metabolites contributed further to the prediction of the impact of TPT on the host. This study provides a novel insight into the underlying mechanisms of host metabolic diseases caused by TPT and emphasizes the importance of monitoring pollutants in the environment.

Bacterial community variations in the South China Sea driven by different chemical conditions.

In this study, Illumina MiSeq sequencing of the 16 S rRNA gene was used to describe the bacterial communities in the South China Sea (SCS) during the southwest monsoon period. We targeted different regions in the SCS and showed that bacterial community was driven by the effects of the river, upwelling, and mesoscale eddy through changing the environmental factors (salinity, temperature, and nutrients). Distinct bacterial communities were observed among different chemical conditions, especially between the estuary and the open sea. The abundance of Burkholderiales, Frankiales, Flavobacteriales, and Rhodobacterales dominated the estuary and its adjacent waters. Bacteria in cyclonic eddy were dominated by Methylophilales and Pseudomonadales, whereas Prochlorococcus, SAR11 clade, and Oceanospirillales had relatively high abundance in the anticyclonic eddy. Overall, the abundance of specific phylotypes significantly varied among samples with different chemical conditions. Chemical conditions probably act as a driver that shapes and controls the diversity of bacteria in the SCS. This study suggests that the interaction between microbial and environmental conditions needs to be further considered to fully understand the diversity and function of marine microbes.

Assessing ecological health of mangrove ecosystems along South China Coast by the pressure-state-response (PSR) model.

The pressure-state-response (PSR) model was applied to establish a mangrove ecosystem health evaluation system combined with analytical hierarchy process (AHP) in this paper. The mangrove wetlands are divided into five ecological levels: excellent health, good health, health, sub-health and morbidity, which is based on the comprehensive health index (CHI) value. Twelve representative sites were selected for sampling to assess the ecological health condition of mangroves. As a result, the ecological health level of Gaoqiao mangrove area is excellent health; the ecological health level of Taiping mangrove area is good health; the ecological health level of Huguang and Qi'ao mangrove area is health; the ecological health level of Techeng and He'an mangrove area is sub-health; the ecological health level of Huidong mangrove area is morbidity. These results will give some advises for ecological protection and biological resource sustainable development of mangrove ecosystem in China.

Dynamics of radial oxygen loss in mangroves subjected to waterlogging.

Tidal flooding can directly result in oxygen (O2) shortage, however the functions of root aeration in flooding tolerance and O2 dynamics within mangroves are still poorly understood. Thus, in this study, the correlations among waterlogging tolerance, root porosity and O2 movement within the plants were investigated using two mangrove species (Aegiceras corniculatum and Bruguiera gymnorrhiza) and a semi-mangrove Heritiera littoralis. Based on the present data, the species A. corniculatum and B. gymnorrhiza, which possessed higher root porosity, exhibited higher waterlogging tolerance, while H. littoralis is intolerant. Increased root porosity, leaf stoma, and total ROL were observed in the roots of A. corniculatum and B. gymnorrhiza growing in stagnant solution when compared to respective aerated controls. As for ROL spatial pattern along roots, external anaerobic condition could promote ROL from apical root regions but reduce ROL from basal roots, leading to a 'tighter barrier'. In summary, the present study indicated that the plants (e.g., A. corniculatum and B. gymnorrhiza) prioritized to ensure O2 diffusion towards root tips under waterlogging by increasing aerenchyma formation and reducing O2 leakage at basal root regions.

Isolation and expression analysis of two novel C-repeat binding factor (CBF) genes involved in plant growth and abiotic stress response in mangrove Kandelia obovata.

Kandelia obovata is one of the cold tolerant mangrove plants along the China coast. To reveal the cold tolerant mechanism of K. obovata, the present work isolated two CBF/DREB1 genes (designated KoCBF1 and KoCBF3) from cold-stressed K. obovata and characterized their expression profiles in various organs and in response to multiple abiotic stresses. The deduced proteins of KoCBF1 and 3 all contain specific features of CBFs, and show high similarity to AmCBF1 and 3 from Avicennia marina, respectively. Different expression patterns of the two CBF orthologous under various abiotic stresses and exogenous hormone suggested that they may have different regulators and be involved in different regulatory pathway. The high basal and cold induced expression of the two genes indicated that they may all play important roles in growth and cold resistance of plants. The significant induction of KoCBF3 after salt and lead (Pb2+) treatments suggested that this CBF gene may also participate in response to salinity and heavy metal stresses. This study will provide a better understanding of CBF-regulated stress-resistant mechanism, which may be benefit in mangrove biotechnological breeding, high-latitude transplanting, and bioremediation of heavy metal pollutions.

Isolation and expression analysis of a CBF transcriptional factor gene from the mangrove Bruguiera gymnorrhiza.

The present work isolated a CBF/DREB1 gene from mangrove Bruguiera gymnorrhiza (BgCBF1) and compared its expression levels in various tissues under normal condition and cold stress, and in leaves exposed to various environmental stimuli. Results showed that the BgCBF1 deduced protein showed almost 100% similarities to that of AcCBF1 from Aegiceras corniculatum and AmCBF1 from Avicennia marina. Real-time quantitative PCR analysis showed that BgCBF1 gene displayed constitute expression in leaf, stem and root samples of plantlets under normal condition, but with different expression levels and tissue preference. When exposed to cold, BgCBF1 could be rapidly, slightly and transiently induced in all tissues. Furthermore, the BgCBF1 gene in leaves displayed a transient and small induction after salt and drought (PEG) exposure, while exhibited relatively high up-regulated expression after the phytohormone abscisic acid (ABA) treatment. These results suggest that the BgCBF1 gene may participate in the ABA mediated development and protection of plant against cold and drought. Further studies on its promoters and downstream genes will be needed to better understand its functions.

Distribution patterns and source identification for heavy metals in Mirs Bay of Hong Kong in China.

Sediment quality caused by heavy metals was investigated in the Mirs Bay and Tolo Harbor, Hong Kong, China. Samples were collected in January and July, 2010. One-way analysis of variance showed that sediment quality variables (Fe, Zn, Mn, Pb, V, Cu, Cr, Ba, Ni and As) were significantly different (p < 0.05) among the sampling areas, whereas the average concentration of V, Eh and Ba exhibited the significant seasonal variations (p < 0.05) between January and July. The spatial pattern of heavy metals (Pb, Zn and Cu) can probably be attributed to anthropogenic and tidal flushing influence in the harbor. Both geo-accumulation index (Igeo) and enrichment factor (EF) were used to identify the metal pollution level and its related source. Pb, Zn, and Cu are considered as "polluted metal" in Tolo Harbor. Cluster analysis (CA) identified three distinct clusters with the Tolo Habor and Shatou Jiao, the inner bay and the south part of the bay. Principal component analysis (PCA) identified the spatial patterns and their affected parameters in the studying area. Results showed metals distribution in Mirs Bay and its adjacent area is principally affected by human activities such as marineculture, dumping, located mostly in Tolo Harbor and Shatou Jiao, where was closely related with anthropogenic influence. While the monitoring stations including MS13-MS16 and MS8 locating in the south part of the studying area might be corresponded to natural influence.

Phytoplankton community, structure and succession delineated by partial least square regression in Daya Bay, South China Sea.

Daya Bay is facing the influence of human activities and nature changes, which result in phytoplankton adjusting to the changing environment. The data about environmental changes and phytoplankton were obtained from four seasonal cruises in 2013 in the bay. It is helpful to explore seasonal succession of phytoplankton driven by the determining environmental factors in this bay. Temperature is a significant indicator of season change. The limiting factor of phytoplankton growth totally changed from P (PO4-P) limiting during the southwest monsoon to Si (SiO3-Si) limiting during northeast monsoon. The order of diatoms and dinoflagellates was the dominant phytoplankton groups in Daya Bay. The dominant species included chain-forming diatoms (Skeletonema, Pseudo-nitzschia, Thalassionema, Chaetoceros and Rhizosolenia) were found all the year round and filamentous cyanobacteria (Trichodesmium) in spring and autumn. Partial least square regression (PLS) found that salinity, temperature and nutrients were important driving force for phytoplankton seasonal succession.

Effect of temperature on the accumulation of marine biogenic gels in the surface microlayer near the outlet of nuclear power plants and adjacent areas in the Daya Bay, China.

The surface microlayer (SML) in marine systems is often characterized by an enrichment of biogenic, gel-like particles, such as the polysaccharide-containing transparent exopolymer particles (TEP) and the protein-containing Coomassie stainable particles (CSP). This study investigated the distribution of TEP and CSP, in the SML and underlying water, as well as their bio-physical controlling factors in Daya Bay, an area impacted by warm discharge from two Nuclear power plants (Npp's) and aquaculture during a research cruise in July 2014. The SML had higher proportions of cyanobacteria and of pico-size Chl a contrast to the underlayer water, particularly at the nearest outlet station characterized by higher temperature. Diatoms, dinoflagellates and chlorophyll a were depleted in the SML. Both CSP and TEP abundance and total area were enriched in the SML relative to the underlying water, with enrichment factors (EFs) of 1.5-3.4 for CSP numbers and 1.32-3.2 for TEP numbers. Although TEP and CSP showed highest concentration in the region where high productivity and high nutrient concertation were observed, EFs of gels and of dissolved organic carbon (DOC) and dissolved acidic polysaccharide (> 1 kDa), exhibited higher values near the outlet of the Npp's than in the adjacent waters. The positive relation between EF's of gels and temperature and the enrichment of cyanobacteria in the SML may be indicative of future conditions in a warmer ocean, suggesting potential effects on adjusting phytoplankton community, biogenic element cycling and air-sea exchange processes.