Qiongzhou Strait Research Articles

Numerical study of the circulation and water transport in Beibu Gulf: A short communication

The Beibu Gulf, located in the northwestern South China Sea, is rich in oceanic energy and biological resources. Based on the FVCOM model, a three-dimensional numerical model was adopted in the study, which was validated with the observation data. The results show that Beibu Gulf is a typical diurnal tidal area. The K1 and O1 tide have an amphidromic point near Hue, Vietnam, forming a rotary tidal system. From the amphidromic point, the amplitudes increase gradually, eventually reaching more than 80 cm and 100 cm, respectively. The maximum amplitudes of M2 and S2 tide are about 70 cm and 10 cm, respectively. Meanwhile the tidal current presents a typical rectilinear flow in Beibu Gulf, with strong the diurnal tidal currents. Seasonal changes in the circulation structure of Beibu Gulf are obvious. The Beibu Gulf is generally controlled by a non-closed anticlockwise circulation in winter. In summer, there are two counterclockwise eddies. The tidal residual current flowing through Qiongzhou Strait goes west all year round, with the largest average flow flux of 0.07 Sv in winter. Based on DYE module from FVCOM, pollutants from the Pearl River Estuary pass through Qiongzhou Strait, and reach Weizhou Island after 109 days. This is of great significance to the monitoring and control of red tide, and the protection of marine ecological environment in Beibu Gulf.

A dynamic adaptive grating algorithm for AIS-based ship trajectory compression

AbstractAutomatic identification system (AIS)-based ship trajectory data are important for analysing maritime activities. As the data accumulate over time, trajectory compression is needed to alleviate the pressure of data storage, migration and usage. The grating algorithm, as a vector data compression algorithm with high compression performance and low computation complexity, has been considered as a very promising approach for ship trajectory compression. This algorithm needs the threshold to be set for each trajectory which limits the applicability over a large number of different trajectories. To solve this problem, a dynamic adaptive threshold grating compression algorithm is developed. In this algorithm, the threshold for each trajectory is dynamically generated using an effective approaching strategy. The developed algorithm is tested with a complex trajectory dataset from the Qiongzhou Strait, China. In comparison with the traditional grating method, our algorithm has improved advantages in the ease of use, the applicability to different trajectories and compression performance, all of which can better support relevant applications, such as ship trajectory data storage and rapid cartographic display.

Occurrence, source apportionment and risk assessment of antibiotics in water and sediment from the subtropical Beibu Gulf, South China

The widespread use of antibiotics has raised global concerns, but scarce information on antibiotics in the subtropical marine environment is available. In the present study, seawater and sediment samples were collected to investigate the occurrence, spatial distribution, source, and ecological risks of 22 antibiotics in the Beibu Gulf. The total concentrations of target antibiotics (∑antibiotics) were in the range of 1.74 ng/L to 23.83 ng/L for seawater and 1.33 ng/g to 8.55 ng/g dry weight (dw) for sediment. Spatially, a decreasing trend of antibiotic levels from coast to offshore area was observed, with relatively high levels at the sites close to the Qinzhou Bay and Qiongzhou Strait. Sulfamethoxazole (SMX), trimethoprim (TMP), and norfloxacin (NOX) were predominant in seawater, while NOX, enoxacin (ENX), and enrofloxacin (ENR) were the most abundant antibiotics in sediment. In general, the sediment-water partitioning coefficients (Kd) were positively correlated with log molecular weight (MW). Salinity, particle size, and pH of water were predicted to be vital factors influencing the partition of sulfadiazine (SDZ), CIX, and ENR (p < 0.05). Livestock and aquaculture were identified as dominant sources of antibiotics in the Beibu Gulf based on PCA-MLR and Unmix model. Risk assessment revealed that SMX, CIX could pose medium risks to algae in the Beibu Gulf. Overall, our results provided paramount insights into understanding the fate and transport behaviors of antibiotics in the subtropical marine environment.

Phylogeographic structure of the dwarf snakehead (Channa gachua) around Gulf of Tonkin: Historical biogeography and pronounced effects of sea-level changes.

Geological events, landscape features, and climate fluctuations have shaped the distribution of genetic diversity and evolutionary history in freshwater fish, but little attention has been paid to that around the Gulf of Tonkin; therefore, we investigated the phylogeographic structure of the dwarf snakehead (Channa gachua) on Hainan Island and mainland China, as well as two populations in Vietnam. We attempted to elucidate the origins of freshwater fish in South Hainan by incorporating genetic data from DNA markers on both the mitochondrial cytochrome b gene (cyt b) and the nuclear recombination‐activating gene 1 (RAG‐1). Mitochondrial phylogenetic analysis identified two major lineages (lineages A and B), which may represent separate species. Divergence data suggested that C. gachua populations diverged between 0.516 and 2.376 myr. The divergence of the two cryptic species is congruent with sea‐level rise, which subsequently isolated Hainan from the mainland. During the Pleistocene glaciations, the entire region of the Gulf of Tonkin and the Qiongzhou Strait became part of the coastal plain of the Asian continent, which might have resulted in the current distribution patterns and dispersal routes of C. gachua populations. The formation of three sublineages in lineage A indicated that the Gulf of Tonkin was a geographical barrier between Hainan Island and mainland China but not between Vietnam and Hainan Island. The results of this study may help to elucidate the origins of freshwater fish in South Hainan and the phylogeographic structure of C. gachua.

Observation of Internal Tides in the Qiongzhou Strait by Coastal Acoustic Tomography

Observation of Internal Tides in the Qiongzhou Strait by Coastal Acoustic Tomography

Genetic Structure and Diversity of the Yellowbelly Threadfin Bream Nemipterus bathybius in the Northern South China Sea

The genetic structure and demography of the yellowbelly threadfin bream, Nemipterus bathybius, in the northern South China Sea were examined using the mitochondrial DNA cytochrome b gene (1141 bp). High levels of haplotype and nucleotide diversities (0.98 and 5.26 × 10−3, respectively) showed that all populations exhibited a high level of genetic diversity. Analysis of molecular variance (AMOVA), FST statistics, and haplotype networks suggested the absence of significant genetic differentiation along the coast of the northern South China Sea. Although the results suggested that the lack of differentiation within the population structure of N. bathybius was shaped by ocean currents, our results also showed that the Qiongzhou Strait limited their migration between Beibu Gulf and the northern South China Sea. Neutrality tests and mismatch distributions indicated population expansion, but the Bayesian skyline plots and approximate Bayesian computation approaches suggested that the population sizes recently contracted. The diversification of multiple stocks, which were induced by two ocean current systems, contributed to these discordant results. Although these analyses of demographic history revealed no evidence for recent population bottlenecks, the population demography needs to be evaluated further.

Time domain nonlinear kinematic seismic response of composite caisson-piles foundation for bridge in deep water

As a new type of bridge foundation in deep water, the composite caisson-piles foundation (CCPF) is inevitability suffered from multiple hazards such as earthquake, scouring and erosion, especially for sea-crossing bridges in ocean environment. In this study, a simplified method in time domain is proposed for predicting the nonlinear kinematic seismic response of CCPF and the effect of scouring on the seismic response is investigated. The proposed method is verified by the results of centrifuge shaking-table tests. It is found that compared with frequency domain method, the proposed time domain method can give good estimations of the acceleration and the displacement of the CCPF, especially at high frequencies. Moreover, the kinematic seismic response of CCPF designed for the Qiongzhou Strait Bridge is analyzed. The results indicate that the proposed model can effectively simulate the soil nonlinearity, and the soil nonlinearity significantly affects the kinematic seismic response of CCPF, especially the acceleration and displacement time histories. Finally, the scouring effect is considered by an analytical model and the performance of the CCPF under combined earthquake and scouring is investigated.

Study on Local Sediment Scour and Stress State of Submarine Cables in Offshore Wind Farms

The laying of submarine cables will destroy the local seabed topography, leading to changes in the submarine hydrodynamic boundary, which will cause the local unbalanced sediment transport phenomenon when the submarine cable is buried. When the submarine cable begins to be exposed or the topography changes greatly, the scour phenomenon will be more severe. This article starts from the safety and stability of the submarine cable during the operation and maintenance of the 200MW offshore wind farm in Xuwen Wailuo, Guangdong Province, China and refers to the partial scour of the submarine cable in the “Southern Main Grid and Hainan Power Grid Second Interconnection Project” near the site near the Qiongzhou Strait. In this case, the measured ocean hydrological data at the site is used as the input condition, and Fluent is used to establish a refined hydrodynamic model of the submarine cable scour, to simulate the development process of the submarine cable scour of the wind farm under real sea conditions, and to perform the force analysis after the submarine cable is exposed. These will provide a certain scientific basis for ensuring the safe and stable operation of submarine cables during wind farm operation and maintenance.

A fluid-solid coupled modeling on water seepage through gasketed joint of segmented tunnels

The water leakage at segment joints of underwater shield tunnels has always been the major concern and trouble to be dealt with in tunneling practices, not only for its threat to the durability and safe operation of tunnels but also for its difficulty to check the leaking process directly in the joints either on-site or in the laboratory test. In order to explore the water leakage mechanism of the segmented tunnel, a Coupled Eulerian-Lagrangian based model considering water flow and large deformation of rubber gasket was developed to simulate the whole process of water seepage through the gasketed joint. A series of numerical modelings were conducted to investigate the seepage pattern and the stress variation during the seepage process, and the dynamic waterproof performance of gasket was investigated. Then, the numerical modeling results were verified against the laboratory test data to prove the reliability of the proposed numerical method. Finally, a formula quantifying the relationship between the waterproof capacity and joint deformations was established, and the critical joint deformation sets were derived from the formula. It was found that the water has an impact effect on the gasket during seepage, which is up to 4 times the initial contact stress. The pressurized water must overcome a cluster of seepage stress barriers to form a seepage path through the gasketed joint. And therefore, the waterproof performance over the length of the gasket-gasket interface is changing and fluctuating with the seepage process, with higher values at both ends of the interface and lower values in the middle. Based on a comprehensive analysis, the critical joint deformation sets (joint opening, joint offset) are recommended for the design and construction of Qiongzhou Strait Tunnel (a planned deep-water shield tunnel in Hainan Province, China) to meet the long-term waterproof capacity of 2 MPa. It is suggested that the assembly accuracy of the segments and gaskets as well as the adhesion of gaskets to joint groove should be strongly guaranteed during the construction process.

Genetic diversity of &amp;lt;italic&amp;gt;Platycephalus&amp;lt;/italic&amp;gt; sp.1 in coastal waters of China based on mtDNA &amp;lt;italic&amp;gt;cox&amp;lt;/italic&amp;gt;1 sequence

<italic>Platycephalus</italic> sp.1 is a commercially important trawling fish species widely distributed in the northwestern Pacific. For better protection and sustainable exploitation of this valuable fishery resource, sequences of partial mitochondrial <italic>cox</italic>1 gene of 155 individuals from 7 populations were determined to analyze genetic diversity of <italic>Platycephalus</italic> sp.1 in coastal waters of China. In total, 28 variable sites in the aligned 652 bp sequences determined 28 haplotypes, indicating low haplotype diversity (<italic>H</italic>_d = 0.428) and low nucleotide diversity (π=0.001 02). Fangchenggang, Lianyungang and Fuzhou population possessed the highest (<italic>H</italic>_d = 0.864), the second (<italic>H</italic>_d = 0.489) and the lowest (<italic>H</italic>_d = 0.298) haplotype diversity, while Fangchenggang, Lianyungang and Nantong population had the the highest (π=0.003 02), the second (π=0.001 24) and the lowest (π=0.000 61) nucleotide diversity respectively. Significant genetic differentiation existed between Fangchenggang population and other populations (east of Qiongzhou Strait population, composed of Dalian, Weifang, Lianyungang, Nantong, Fuzhou and Jieyang). The pairwise <italic>F</italic>_st between Fangchenggang population and east of Qiongzhou Strait population were significantly different, ranging from median to high level(0.088 61-0.189 29). Meanwhile, the result of AMOVA showed that molecular variation between Fangchenggang population and east of Qiongzhou Strait population explained 24.19 % of variance within the whole population. A star-like haplotype network indicated weak phylogenetic lineage and a possible recent fast population expansion. Furthermore, negative neutrality test result (<italic>D</italic> = -1.024, <italic>P</italic> = 0.152; <italic>F</italic>_s =-2.60, <italic>P</italic>=0.015) and unimodal mismatch distribution curve indicated a possible population expansion in Fangchengguang population around 167-56 Ka B.P. in the last interglacial period. Significant negative neutrality test result (<italic>D</italic>=-2.468, <italic>P</italic>= 0.000; <italic>F</italic>_s = - 34.02, <italic>P</italic>=0.000) and the nearly Z-shaped Bayesian skyline plot suggested a population expansion in east of Qiongzhou Srait population around 25-30 Ka B.P. in the late last glacial period. It is hypothesized that ancient <italic>Platycephulas</italic> sp.1 population had expanded in the last interglacial period, then returned to refuge in the last glacial period because of sea level drop. In the late last glacial period, it spreaded out in coastal waters of China with rising sea level and achieved population expansion. Simultaneously, Fangchenggang population gradually adapted to its environment and differentiated from east of Qiongzhou Strait population because Qiongzhou Strait had separated each other and restricted their exchange of eggs, larvae and juveniles via currents. By contrast, east of Qiongzhou Strait population was more homogeneous under the influence of current cycle and possible reproductive migration. Due to significant genetic differentiation on either side of Qiongzhou Strait, Fangchenggang population and east of Qiongzhou Strait population should be set as two independent management units respectively. As Fangchenggang population owned the highest genetic diversity, it should be protected in priority for exploitation. It is also recommended to protect Dalian population and to take measures to avoid the decrease of genetic diversity of Nantong population since they owned the highest and the lowest nucleotide diversity in east of Qiongzhou Strait population respectively.

The forensic landscape and the population genetic analyses of Hainan Li based on massively parallel sequencing DNA profiling.

Due to the formation of the Qiongzhou Strait by climate change and marine transition, Hainan island was isolated from the mainland southern China during the Last Glacial Maximum. Hainan island, located at the southernmost part of China and separated from the Leizhou Peninsula by the Qiongzhou Strait, laid on one of the modern human northward migration routes from Southeast Asia to East Asia. The Hlai language-speaking Li minority, the second largest population after Han Chinese in Hainan island, is the direct descendants of the initial migrants in Hainan island and has unique ethnic properties and derived characteristics; however, the forensic-associated studies on Hainan Li population are still insufficient. Hence, 136 Hainan Li individuals were genotyped in this study using the MPS-based ForenSeq™ DNA Signature Prep Kit (DNA Primer Set A, DPMA) to characterize the forensic genetic polymorphism landscape, and DNA profiles were obtained from 152 different molecular genetic markers (27 autosomal STRs, 24 Y-STRs, 7 X-STRs, and 94 iiSNPs). A total of 419 distinct length variants and 586 repeat sequence sub-variants, with 31 novel alleles (at 17 loci), were identified across the 58 STR loci from the DNA profiles of Hainan Li population. We evaluated the forensic characteristics and efficiencies of DPMA, demonstrating that the STRs and iiSNPs in DPMA were highly polymorphic in Hainan Li population and could be employed in forensic applications. In addition, we set up three datasets, which included the genetic data of (i) iiSNPs (27 populations, 2640 individuals), (ii) Y-STRs (42 populations, 8281 individuals), and (iii) Y haplogroups (123 populations, 4837 individuals) along with the population ancestries and language families, to perform population genetic analyses separately from different perspectives. In conclusion, the phylogenetic analyses indicated that Hainan Li, with a southern East Asia origin and Tai-Kadai language-speaking language, is an isolated population relatively. But the genetic pool of Hainan Li influenced by the limited gene flows from other Tai-Kadai populations and Hainan populations. Furthermore, the establishment of isolated population models will be beneficial to clarify the exquisite population structures and develop specific genetic markers for subpopulations in forensic genetic fields.

Whistle signal variations among three Indo-Pacific humpback dolphin populations in the South China Sea: a combinedeffectof the Qiongzhou Strait's geographical barrier function and local ambient noise?

Geographic variations in the dolphin whistles could be useful in assessing association and isolation among populations. Whistle of free-ranging Indo-Pacific humpback dolphins (Sousa chinensis) among the Pearl River Estuary (PRE), Leizhou Bei (LZB) and Sanniang Bay (SNB) populations were investigated. A total of 2850 whistles with legible fundamental contour were extracted and 15 acoustic parameters were measured. Contrary to SNB, PRE and LZB had the same relative proportion of tonal type compositions with flat and sine representing the most frequent types. The generalized linear model analysis showed significant acoustic difference among populations and tonal types. All frequency parameters in SNB were significantly higher than those in PRE and LZB, where no significant variation was observed in most of the parameters either at the population level or within each tonal type. Canonical discriminant functions analysis showed a smaller difference between PRE and LZB than between PRE and SNB and between LZB and SNB. Compared with previous recordings, recent recordings demonstrated a consistent pattern of becoming higher in whistle frequency parameters in both LZB and SNB populations, suggesting that noise pollution in LZB and SNB increasing with time according to the acoustic niche hypothesis. Dolphin whistle's geographic variations could be shaped by the combined function of the geographical barrier function of the Qiongzhou strait and local ambient noise. Considering the isolated condition and the relatively smaller population size of the humpback dolphin in the SNB, more effective and proactive conservation actions should be taken to prevent the extinction of small populations.

Risk Cloud Model for Evaluating Nautical Navigational Environments

Uncertainty makes the risk evaluation of complex water transportation systems (WTSs) a difficult task. To achieve reasonable results while accounting for uncertainty, the risk evaluation of nautical navigational environments (NNEts) is often based on classical cloud model theory. This study proposes the concept of a risk cloud model (RCM) for NNEt evaluation and uses a fuzzy statistics-based computational approach to obtain the RCM parameters. As a case study, the proposed RCM method was applied to the risk evaluation of the Qiongzhou Strait. The performance of the proposed method was compared to those of a fuzzy theory-based method and an earlier proposed simplified algorithm. The results of the case study demonstrated the effectiveness of the proposed method along with several key advantages. First, the method could deal with uncertainty, take advantage of multichannel information, and evaluate risk features. Second, the RCM droplets intuitively displayed the qualitative and quantitative characteristics of risk levels, which facilitated understanding and analysis. Third, it showed a good sensitivity to ensure the refinement of evaluation results. The proposed method offered an improved approach to NNEt risk evaluation under uncertain conditions.

Characteristics of Organic Matter and Biomarkers in Core Sediments From the Offshore Area of Leizhou Peninsula, South China Sea

Total organic carbon (TOC), total nitrogen (TN) and multi-biomarker indexes were analyzed for two sediment cores from the eastern coastal area of the Beibu Gulf (core 45, AMS 14C dated) and Qiongzhou Strait (core 29), South China Sea. The results showed that the TOC and TN content of the samples studied were 0.32–0.62% and 0.02–0.07%, respectively. The hydrocarbons in offshore sediments of Leizhou Peninsula were consisted of biogenic hydrocarbons and petrogenic hydrocarbons. The Core 29 sediments contain more terrigenous organic matter than that of sediments in core 45 due to the difference in hydrodynamic conditions. The composition and distribution of various lipid biomarkers indicate the presence of petrogenic hydrocarbons in the sediments of the whole profile of two sediment cores. There are multiple natural sources of hydrocarbons that could potentially contribute to the petroleum background through oil seeps and erosion of carbon-rich rock outcrops or bitumen deposits. Deep sourced hydrocarbon inputs from the submarine hydrocarbon seepage cannot be excluded. Further study is needed to resolve the specific sources for the petrogenic hydrocarbons and may be significant to petroleum exploration in the study area.

Spatiotemporal variation, speciation, and transport flux of TDP in Leizhou Peninsula coastal waters, South China Sea

Phosphorus (P) plays key role in phytoplankton primary production in coastal water. In this study, seawater samples collected within China's Leizhou Peninsula coastal waters from October 2017 to July 2018 were examined to determine the seasonal variation, speciation, and transport flux of total dissolved phosphorus (TDP) linked to hydrographic features. TDP concentration and speciation had significant seasonal variations (P < 0.01), and the annual mean TDP concentration was 0.42 ± 0.25 μmol·L−1. High concentrations of TDP occurred in coastal waters adjacent to Zhanjiang Bay and Jianjiang River estuary, whereas low TDP concentrations were found across large offshore areas. Dissolved inorganic and organic P were the main TDP bulk species in different seasons, comprising up to 55.5 ± 7.9% and 46.5 ± 22.6%, respectively. The Beibu Gulf was annually subjected to 3.5 × 109 mol flux of TDP through the Qiongzhou Strait. Coastal currents, river plumes, and human activities were responsible for the dynamic variations in P species.

Environmental Effects on the Spatiotemporal Variability of Fish Larvae in the Western Guangdong Waters, China

Spawning grounds occupy an important position in the survival and reproduction of aquatic life, which plays an important role in the replenishment of fishery resources, especially in the China coasts where fishery resources are depleting. This study investigated environmental effects on the spatiotemporal variability of fish larvae in the western Guangdong waters (WGWs), on the basis of generalized additive models (GAMs) and center of gravity (CoG). Satellite data including sea surface salinity (SSS), sea surface temperature (SST), and in situ observations for fish larvae from April to June in 2014–2015 were used. Results showed that 40.3% of the total variation in fish larvae density was explained. SST, SSS, and depth showed positive effects in 23–24 °C and 27–30 °C, 24–32 PSU, and 0–60 m, and showed negative effects in 24–27 °C, 32–34.2 PSU, 60–80 m. Based on the stepwise GAMs, the most important factor was month, with a contribution of 10.6%, followed by longitude, offshore distance, depth, and latitude, with contributions of 7.0%, 7.0%, 6.3%, 4.2%, 3.9%, and 1.3%, respectively. Fish larvae CoG shifted northward by 0.6° N and eastwards by 0.13° E from April to June. The distribution of fish larvae in the WGWs was affected by complex submarine topography in the Qiongzhou Strait, coastal upwelling in the WGWs, and runoff from the Pearl River.

MtDNA &amp;lt;italic&amp;gt;COⅠ&amp;lt;/italic&amp;gt; sequence diversity of &amp;lt;italic&amp;gt;Gerres limbatus&amp;lt;/italic&amp;gt; in coastal waters of China

In order to contribute information on genetic background of <italic>Gerres limbatus</italic> in coastal waters of China, 652 bp mtDNA <italic>COⅠ</italic> sequences of 140 individuals from 9 geographic populations were analyzed. 14 mutation sites were found and 13 haplotypes were identified, of which 9 were unique haplotypes and 4 were shared haplotypes. The overall haplotype and nucleotide diversity were low ( <italic>H</italic>_d=0.276±0.050, π =0.000 5±0.000 1 ), of which genetic diversity of populations from the east part of the Qiongzhou Strait ( <italic>H</italic>_d = 0.338-0.456, π = 0.000 6-0.001 1 ) was higher than those in the western Beibu Gulf ( <italic>H</italic>_d =0-0.295, π =0-0.000 5 ). Haplotype network diagrams did not show obvious genealogical and geographic structure. Genetic differentiation coefficicent(<italic>F</italic>_st) showed that there was indistinctively low-middle genetic differentiation between Naozhou population and other populations ( <italic>F</italic>_st= 0.0773-0.1696). No obvious differentiation was found among other populations ( <italic>F</italic>_st=-0.041 5-0.061 2). AMOVA analysis also showed that 95% population variation originated from within the group. The negative overall value of the neutrality test (Tajima’s <italic>D</italic>=-2.254 9; Fu’s <italic>F</italic>_s=-16.472 5 ) and a significant single peak in the nucleotide mismatch distribution were consistent with demographic expansion in the past, and deduced expansion time ranged from about 0.130 4 to 0.043 5 million years ago. Since the overall genetic diversity of the population was less than 0.5 and nucleotide diversity was less than 0.005, it was speculated that <italic>Gerres limbatus</italic> population in coastal waters of China had recently encountered a severe bottleneck effect. The nucleotide diversity of the Ningde and Naozhou populations was relatively high and had a conservation priority. As genetic diversity of populations in the Beibu Gulf was extremely low, measures should be taken to avoid further decline in genetic diversity.

Genetic diversity and population structure of cutlassfish (Lepturacanthus savala) along the coast of mainland China, as inferred by mitochondrial and microsatellite DNA markers

Cutlassfish (Lepturacanthus savala) is a commercially important fish species that is distributed in the tropical coastal area throughout the Indo-West Pacific Oceans. However, there have been few genetic studies on this species. Therefore, based on mitochondrial COI gene and thirteen microsatellite DNA markers that have been successfully developed by predecessors, the objective of this study is to assess the genetic diversity and structure of L savala for the first time, using 172 individuals collected from six locations along the coast of mainland China during 2019. High levels of haplotype diversity (0.94) in mitochondrial DNA and the average number of alleles among the six populations ranged from 10.3 to 14.0 in microsatellite DNA data, which showed that all population exhibited a high level of genetic diversity. Analysis of molecular variance (AMOVA) showed that did not indicate any significant genetic differentiation among groups with no relation to the geographic area. The significant genetic differentiation was found in LYG and BH populations revealed that the prevention of gene flow caused by the Yangtze River and the Qiongzhou Strait. The results of STRUCTURE suggested that all populations were admixtures of two clusters, which could be explained only by the high migratory ability of L. savala resulting in extensive gene flow. Analysis of demographic history revealed that L. savala undergo historical lineage diversification and admixture due to the secondary contact based on ABC analysis, and no evidence for recent population bottlenecks were detected. Such study is both practical and theoretical value for genetic improvement, conservation, management, and sustainable resource utilization.

Marine Environmental Regionalization for the Beibu Gulf Based on a Physical-Biological Model

A physical–biological ocean model was employed to investigate characteristics of the Beibu Gulf in the northwest South China Sea (SCS) from 2011 to 2015. We adopted the spatially constrained multivariate clustering method to determine the refined marine environmental regionalization using 10 variables from the model output, and compared regionalization differences in ENSO (El Niño–Southern Oscillation) years. The simulated physical and biochemical variables display a wide spectrum of patterns in space and time. The regionalization maps indicated that the Qiongzhou Strait and its adjacent area can be classified as a separate region, characterized by the rich presence of nutrients, phytoplankton, zooplankton, and detritus, owing to the water invasion from the western Guangdong estuary. As a result of the invasive progression of the SCS, the northern and southern gulf show distinct features over a boundary near 20° N. In the La Niña year (2011), the classified boundary of the Qiongzhou Strait-northeastern gulf moved southwards due to enhanced phytoplankton growth. In the El Niño year (2015), the current collision from the northern gulf and SCS resulted in the boundary of the northern and southern gulf moving to approximately 19° N. These results provide useful guidance on subregional marine management and subregional studies for the gulf.

Research on the Tourism Cooperation Between Zhanjiang and Hainan

On April 13, 2018, Hainan and Guangdong jointly put forward the idea of accelerating the construction of Qiongzhou Strait economic belt and realizing integrated and coordinated development. As the southernmost city in the mainland of China, Zhanjiang is only one sea away from Hainan, they are close to each other in culture, geography, rich in tourism resources and distinctive product features. Both of them have good conditions for developing coastal tourism and winter vacation tourism. It is the common wish of both sides to promote the regional tourism integration of Qiongzhou Strait and build a tourism destination of Qiongzhou Strait. In recent years, under the guidance of the two governments, the two sides have carried out a lot of tourism cooperation, and the basic cooperation mechanism has been established. But at the same time, it also faces the problems of imperfect tourism infrastructure, homogenization of tourism products, imperfect tourism cooperation mechanism and so on. Therefore starting from Zhanjiang, this paper hopes to use Hainan free trade port, international tourism island and other policies to explore how to better explores the appropriate path for the integrated development of tourism between Zhanjiang and Hainan, thus enhancing the popularity and competitiveness of Qiongzhou Strait Tourism at home and abroad.