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In China, the invasion of Spartina alterniflora is an important driver for the decrease of mangrove area and ecological service functions related to this habitat. In the past few decades, S. alterniflora clearing and mangrove restoration projects have mainly focused on the areas where it is already changed but ignored the potential distribution areas. This study suggested that implementation of mangrove protection prior to the areas with the threat of S. alterniflora invasion could greatly improve protection efficiency and save costs. Thus, using Maximum Entropy Modeling (MaxEnt), we estimated the potential spatial distribution of both mangroves and S. alterniflora in China, considering the current distribution data, topographical, sediments, sea surface temperature and bioclimatic variables. What’s more, we identified and calculated the potential distributed areas in each province. We aimed to explore (i) the key factors determining the distribution of mangrove and Spartina alterniflora along the coastline and (ii) the hotspots of their competitive occurrence, including S. alterniflora invasion areas and mangroves degradation areas, in order to support mangrove conservation. The model showed that the distance to the coastline and the topography play important roles in the distribution of S. alterniflora, while mangroves were more sensitive to the range of the annual sea surface temperature. Our results furthermore confirm that S. alterniflora has a wider potential distribution area (~10,585 km2) than mangroves (~9124 km2) at the coastline of China; and predict the provinces Zhangzhou, Quanzhou, Zhanjiang, Beihai and Wenzhou as hotspots for the competition between mangroves and S. alterniflora. We propose that priority should be given to the protection or restoration of mangrove plants in those areas which are co-suitable for mangroves and S. alterniflora. In these areas, management measures should be conducted that hinder S. alterniflora invasions or clear existing S. alterniflora plants, firstly. This study provides guidance for the management of native species by preventing biological invasion.

The coastal zone of China has experienced large increases in population, economy and urbanization since the early 1980s. Many studies have reported the loss, degradation and fragmentation of coastal wetlands in China at local to regional scales. To date, at the national scale, our knowledge of the spatial distribution, inter-annual variation and multi-decadal trends of coastal wetlands in China remains very limited. Here we analysed ~62,000 Landsat-5, -7 and -8 images over the period 1984–2018 and generated maps of coastal wetlands for individual years in China at 30-m spatial resolution. We found that coastal wetland area significantly decreased between 1984 and 2011. We also found a substantial increase in saltmarsh area and a stable trend of tidal flat area since 2012, driven by reduced anthropogenic activities and increased conservation and restoration efforts. These coastal wetland maps for the period 1984–2018 are invaluable for improvement of coastal wetland management and sustainability in China. China’s coasts have become more populous and urbanized. This study finds a rebound in the area of coastal wetlands, reflecting recent conservation and restoration, with large losses between 1984 and 2011 followed by increases in saltmarsh area and stabilization of tidal flats.

Mangroves are prone to receive pollutants and act as a sink for antibiotic resistance genes (ARGs). However, knowledge of the human health risk of ARGs and its influencing factors in mangrove ecosystems is limited, particularly at large scales. Here, we applied a high-throughput sequencing technique combined with an ARG risk assessment framework to investigate the profiles of ARGs and their public health risks from mangrove wetlands across South China. We detected 456 ARG subtypes, and found 71 of them were identified as high-risk ARGs, accounting for 0.25 % of the total ARG abundance. Both ARGs and bacterial communities showed a distance-decay biogeography, but ARGs had a steeper slope. Linear regression analysis between features of co-occurrence network and high-risk ARG abundance implies that greater connections in the network would result in higher health risk. Structural equation models showed that geographic distance and MGEs were the most influential factors that affected ARG patterns, ARGs and MGEs contributed the most to the health risk profiles in mangrove ecosystems. This work provides a novel understanding of biogeographic patterns and health risk assessment of ARGs in mangrove ecosystems and can have profound significance for mangrove environment management with regard to ARG risk control.

Revealing planktonic fungal ecology under coastal eutrophication is crucial to our understanding of microbial community shift in marine pollution background. We investigated the diversity, putative interspecies interactions, assembly processes and environmental responses of abundant and rare planktonic fungal communities along a eutrophication gradient present in the Beibu Gulf. The results showed that Dothideomycetes and Agaricomycetes were the predominant classes of abundant and rare fungi, respectively. We found that eutrophication significantly altered the planktonic fungal communities and affected the abundant taxa more than the rare taxa. The abundant and rare taxa were keystone members in the co-occurrence networks, and their interaction was enhanced with increasing nutrient concentrations. Stochastic processes dominated the community assembly of both abundant and rare planktonic fungi across the eutrophication gradient. Heterogeneous selection affected abundant taxa more than rare taxa, whereas homogenizing dispersal had a greater influence on rare taxa. Influences of environmental factors involving selection processes were detected, we found that abundant fungi were mainly influenced by carbon compounds, whereas rare taxa were simultaneously affected by carbon, nitrogen and phosphorus compounds in the Beibu Gulf. Overall, these findings highlight the distinct ecological adaptations of abundant and rare fungal communities to marine eutrophication.

Small chromophytic phytoplankton (SCP) are anticipated to be more important for a significant proportion of primary production in estuarine-coastal ecosystems. However, responses of SCP community to coastal eutrophication are still unclear. In this study, we investigated diversity, co-occurrence and assembly features of SCP communities, as well as their relationship with environmental factors in the subtropical Beibu Gulf. The results exhibited that the alpha diversity (ANOVA, p < 0.001) and beta diversity (ANOSIM, p < 0.001) of SCP communities were significantly different among eutrophic states. Co-occurrence network analysis revealed a complex interaction between SCP community and environmental factors. Most ASVs in modules of the network were specific to trophic states. Further, phylogenetic based β-nearest taxon distance analyses revealed that stochastic processes mainly provided 69.26% contribution to SCP community assembly, whereas deterministic processes dominated community assembly in a heavy eutrophic state. Importantly, increased environmental disturbances, such as nitrogen and phosphorus nutrients, could alter SCP community structure and disrupt ecological processes. Overall, our findings elucidate the mechanism of diversity and assembly in marine SCP community and promote the understanding of SCP ecology related to subtropical coastal eutrophication.

Small chromophytic phytoplankton (SCP) are anticipated to be more important for a significant proportion of primary production in estuarine-coastal ecosystems. However, responses of SCP community to coastal eutrophication are still unclear. In this study, we investigated diversity, co-occurrence and assembly features of SCP communities, as well as relationship with environmental factors in subtropical Beibu Gulf. The results exhibited that the alpha diversity and beta diversity of SCP communities were significantly different among eutrophic states. Co-occurrence network revealed a complex interaction that most amplicon sequence variants (ASVs) in modules of the network were specific to trophic states. Further, phylogenetic based β-nearest taxon distance analyses revealed that stochastic processes mainly provided 69.26% contribution to SCP community assembly, whereas deterministic processes dominated community assembly in heavy eutrophic state. Overall, our findings elucidate the mechanism of diversity and assembly in SCP community and promote the understanding of SCP ecology related to subtropical coastal eutrophication.

Due to rapid losses of mangrove forests caused by anthropogenic disturbances and climate change, accurate and contemporary maps of mangrove forests are needed to understand how mangrove ecosystems are changing and establish plans for sustainable management. In this study, a new classification algorithm was developed using the biophysical characteristics of mangrove forests in China. More specifically, these forests were mapped by identifying: (1) greenness, canopy coverage, and tidal inundation from time series Landsat data, and (2) elevation, slope, and intersection-with-sea criterion. The annual mean Normalized Difference Vegetation Index (NDVI) was found to be a key variable in determining the classification thresholds of greenness, canopy coverage, and tidal inundation of mangrove forests, which are greatly affected by tide dynamics. In addition, the integration of Sentinel-1A VH band and modified Normalized Difference Water Index (mNDWI) shows great potential in identifying yearlong tidal and fresh water bodies, which is related to mangrove forests. This algorithm was developed using 6 typical Regions of Interest (ROIs) as algorithm training and was run on the Google Earth Engine (GEE) cloud computing platform to process 1941 Landsat images (25 Path/Row) and 586 Sentinel-1A images circa 2015. The resultant mangrove forest map of China at 30 m spatial resolution has an overall/users/producer’s accuracy greater than 95% when validated with ground reference data. In 2015, China’s mangrove forests had a total area of 20,303 ha, about 92% of which was in the Guangxi Zhuang Autonomous Region, Guangdong, and Hainan Provinces. This study has demonstrated the potential of using the GEE platform, time series Landsat and Sentine-1A SAR images to identify and map mangrove forests along the coastal zones. The resultant mangrove forest maps are likely to be useful for the sustainable management and ecological assessments of mangrove forests in China.

Salt marshes are important natural carbon sinks with a large capacity to absorb exogenous nutrient inputs. The effects of nutrients on biogeographic productivity patterns, however, have been poorly explored in salt marshes. We conducted field surveys to examine how complex environments affect productivity of two common salt marsh plants, invasive Spartina alterniflora and native Phragmites australis, along an 18,000-km latitudinal gradient on the Chinese coastline. We harvested peak aboveground biomass as a proxy for productivity, and measured leaf functional traits (e.g., leaf area, specific leaf area [SLA], leaf nitrogen [N] and phosphorus [P]), soil nutrients (dissolved inorganic N [DIN] and available P [AP]), and salinity. We compiled data on mean annual temperature (MAT) and exogenous nutrients (both N and P). Then, we examined how these abiotic factors affect salt marsh productivity using both linear mixed effect models and structural equation modeling. Using a trait-based approach, we also examined how salt marsh productivity responds to changing environments across latitude. Exogenous nutrients (both N and P), compared with temperature and other variables (e.g., DIN, AP, salinity), were the dominant factors in explaining the biogeographic productivity patterns of both S. alterniflora and P. australis. Leaf size-related traits (e.g., leaf area), rather than leaf economic traits (e.g., SLA, leaf N and P), can be used to indicate the positive effects of exogenous nutrients on the productivity of these two species. Our results demonstrated that human eutrophication surpassed temperature as the major driver of biogeographic salt marsh productivity pattern, challenging current models in which biogeographic productivity pattern is primarily controlled by temperature. Our findings have potential broad implications for the management of S. alterniflora, which is a global invader, as it has benefited from coastal eutrophication. Furthermore, exogenous nutrient availability and leaf size need to be integrated into earth system models that are used to predict global plant productivity in salt marshes.

Seagrass research in China is still in its infancy. Even though there has been progress recently, there is still a great deal of research needed to gain a better understanding of seagrass. In this article we review and discuss the advances in seagrass research in China from two aspects: (1) seagrass species and their distribution; (2) seagrass research in China, including studies on their taxonomy, ecology, photosynthesis, applications in aquaculture, salt-tolerance mechanisms and other research topics. A total of 18 seagrass species belonging to 8 genera are distributed in nine provinces and regions in China (including Hong Kong and Taiwan), as well as the Xisha and Nansha Archipelagos. They can be divided into two groups: a North China Group and a South China Group. Based on the seagrass distribution, the Chinese mainland coast can be divided into three sections: North China Seagrass Coast, Middle China Seagrass Coast, and South China Seagrass Coast. Ecological studies include research on seagrass communities, nutrient cycling in seagrass ecosystems, genetic diversity, pollution ecology and research in the key regions of Shandong, Guangdong, Guangxi, and Hainan. Seagrass species and their locations, community structure, ecological evaluation, epiphytes, ecological functions and threats in the key regions are also summarized. Other studies have focused on remote sensing of seagrass, threatened seagrass species of China, and pollen morphology of Halophila ovalis.

In this study, we present the complete mitochondrial DNA sequences of Epinephelus areolatus for the first time, which is 16,893 bp in length and contains 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and a putative control region. The overall base composition of the H-strand is 27.0% T, 28.0% C, 28.6% A, and 16.3% G. The CO1 gene is initiated by GTG codon and ATP6 gene is initiated by TTG codon. The tRNA-Ser2 cannot be folded into the typical cloverleaf secondary structure because its dihydrouridine arm is replaced by a simple loop. A long-tandem repeat motif (76 bp), repeated six times, is found in the control region.

The complete mitochondrial genome of the peacock sole Pardachirus pavoninus was firstly determined in this study. It is 16,537 bp in length, consisting of 13 protein-coding genes, two rRNA genes, 22 tRNA genes and one control region with the typical gene order in vertebrates. There are 26 bp overlaps and 28 bp short intergenic spaces located in 7 and 11 gene junctions, respectively. The overall nucleotide composition of the L-strand is 29.1% A, 29.5% C, 16.4% G and 25.0% T. The 22 tRNAs range from 65 bp (tRNA-Cys) to 74 bp (tRNA-Val, tRNA-Leu1, tRNA-Lys and tRNA-Thr) in length. Two start codons (ATG and GTG) and two stop codons (AGG and TAA/T) were found in 13 protein-coding genes.

The wavyband sole Pseudaesopia japonica is the only known member of the genus Pseudaesopia. In this study, we firstly determined the complete mitochondrial genome of P. japonica. It is 16,789 bp in length and contains two rRNA genes, 22 tRNA genes, 13 protein-coding genes and one putative control region with the typical gene order and transcriptional direction in vertebrates. The overall base composition of mitogenome in P. japonica is 28.4% A, 30.3% C, 15.6% G and 25.7% T. Two start codons (ATG and GTG) and four stop codons (AGA, AGG, TAG and TAA) were found in 13 protein-coding genes. The 22 tRNAs range from 67 bp (tRNA-Cys and tRNA-Tyr) to 75 bp (tRNA-Lys) in length. The control region is 1120 bp in length, representing a higher proportion of A + T (65.3%) while lower of G (12.0%).

The complete mitochondrial genome of the brown guitarfish Rhinobatos schlegelii is presented for the first time in this study. It is 16,780 bp in length, consisting 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and 1 putative control region with the typical gene order and direction of transcription in vertebrates. The overall base composition is 32.1% A, 26.3% C, 13.2% G and 28.3% T. Two start codon (GTG and ATG) and two stop codon patterns (TAG and TAA/T) were found in protein-coding genes. The 22 tRNA genes ranged from 67 (tRNA-Ser2) to 75 (tRNA-Leu1) bp in length. The origin of L-strand replication (OL) was between tRNA-Asn and tRNA-Cys genes within the WANCY region. The tRNA-Ser2 could not be fold into the typical cloverleaf secondary structure because of the replacement of its dihydrouridine arm by a simple loop. The control region was 1089 bp in length with high A + T content (64.0%).

The complete mitochondrial genome of the striped grouper Epinephelus latifasciatus is first presented in this study. The total length of E. latifasciatus is 16,389 bp, consisting of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and an A+T-rich control region. The gene order and transcriptional orientation are identical to those of most vertebrates. The total base composition is 28.6% A, 29.1% C, 26.4% T, and 16.0% G, with a slight A+T bias of 55.0%. The dihydrouridine arm of tRNA-Ser2 is replaced with one loop, because of which it cannot be folded into typical cloverleaf secondary structure. The termination-associated sequences and conserved sequence blocks (CSB1-3) are found in the control region.

The complete mitochondrial genome of the Freshwater Whipray Himantura dalyensis is presented in this study. It is 17,693 bp in length and contains 37 genes in typical gene order and transcriptional orientation observed in vertebrates. There were a total of 86 bp short intergenic spacers and 22 bp overlaps in the genome. The overall base composition was 31.4% A, 25.5% C, 13.2% G and 29.9% T. Two start codons (GTG and ATG) and two stop codons (TAG and TAA/T) were found in 13 protein-coding genes. The length of 22 tRNA genes ranged from 68 (tRNA-Cys and tRNA-Ser2) to 75 bp (tRNA-Leu1). The origin of L-strand replication (OL) was found between the tRNA-Asn and tRNA-Cys genes. The base composition of the control region (1940 bp) was similar to the whole mitogenome.

The complete mitochondrial genome of the oriental sole Brachirus orientalis was presented in this study. It is 16,600 bp in length, contains 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and 1 control region. A total of 28 bp short overlaps and 23 bp non-coding intergenic spacers were found in the mitogenome. The overall base composition of the L-strand is 30.5% A, 28.7% C, 15.2% G and 25.6% T. Two start codons (ATG and GTG) and three stop codons (AGG, TAG and TAA/T) were found in the protein-coding genes. Twenty-two tRNA genes ranged from 66 bp to 75 bp. Since the tRNA-Ser2 lacks the dihydrouridine arm it can not fold into a typical cloverleaf structure. The control region demonstrates the highest A+T content (66.4%) and the lowest G content (11.8%) in the mitogenome.

The whale shark Rhincodon typus (Pisces: Chondrichthyes, Orectolobiformes, Rhincodontidae) is the largest living fish on Earth. In this study, we presented its complete mitogenome. It is 16,928 bp in length, contains 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and one control region with the typical gene order and transcriptional direction in the vertebrates. Overall base composition of the R. typus mitogenome is 33.5% A, 24.3% C, 12.8% G and 29.5% T. Two start codon (GTG and ATG) and two stop codon patterns (TAG and TAA/T) were found in protein-coding genes. The tRNA-Ser2 could not be folded into the typical cloverleaf secondary structure because of the replacement of its dihydrouridine arm by a simple loop. A termination associated sequences (TAS) and three conserved sequence blocks (CSB1-3) were identified in the control region.

The complete mitochondrial genome of Mustelus griseus was first determined in this study. It is 16,754 bp in length, consisting of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and 1 control region with the typical gene order in vertebrates. Overall nucleotide base composition of the mitogenome is 30.7% A, 24.9% C, 14.0% G and 30.3% T. After aligning, it comes to us that the mitogenomic portions of M. griseus are very similar to those of Mustelus manazo, ranging from 86.92% (control region) to 100% (tRNA-His and tRNA-Leu2). The origin of L-strand replication (OL) is identified between tRNA-Asn and tRNA-Cys genes. The control region is located between the tRNA-Pro and tRNA-Phe genes, containing one termination-associated sequence (TAS) and three short conserved sequences (CSB 1-3).