Sanya Bay Research Articles

The emerging and legacy persistent organic contaminants in corals of the South China Sea

Seawater warming, ocean acidification and chemical pollution are the main threats to coral growth and even survival. The legacy persistent organic contaminants (POCs), such as polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs), and the emerging contaminants, including polybrominated diphenyl ethers (PBDEs), dechlorane plus (DPs) and novel brominated flame retardants (NBFRs) were studied in corals from Luhuitou fringing reef in Sanya Bay and Yongle atoll in Xisha Islands, the South China Sea (SCS). Total average concentrations of ∑16PAHs, ∑23OCPs, ∑34PCBs, ∑8PBDEs, ∑2DPs and ∑5NBFRs in 20 coral species (43 samples) from the SCS were 40.7 ± 34.6, 5.20 ± 5.10, 0.197 ± 0.159, 3.30 ± 3.70, 0.041 ± 0.042 and 36.4 ± 112 ng g−1 dw, respectively. PAHs and NBFRs were the most abundant compounds and they are likely to be dangerous pollutants for future coral growth. Compared to those found in other coral reef regions, these pollutants concentrations in corals were at low to median levels. Except for PBDEs, POCs in massive Porites were significantly higher than those in branch Acropora and Pocillopora (p < 0.01), as large, closely packed corals may be beneficial for retaining more pollutant. The current study contributes valuable data on POCs, particularly for halogenated flame retardants (HFRs, including PBDEs, DPs and NBFRs), in corals from the SCS, and will improve our knowledge of the occurrence and fate of these pollutants in coral reef ecosystems.

Nearshore Depth Estimation Using Fine-Resolution Remote Sensing of Ocean Surface Waves

In the field of water depth inversion using imagery, the commonly used methods are based on water reflectance and wave extraction. Among these methods, the Optical Bathymetry Method (OBM) is significantly influenced by bottom sediment and climate, while the wave method requires a specific study area. This study introduces a method combining the FFT and spatial profile measurement to invert the wavelength of the wave bathymetry method (WBM), which enhances accuracy and reduces workload. The method was applied to remote sensing images of Sanya Bay in China, obtained from the Worldview satellite. The average error of the inverted depth results after applying the wavelength inversion technique was 15.9%, demonstrating consistency with the depth measurements obtained through the OBM in clear water of the bay. The WBM has notable advantages over the OBM, as it is unaffected by water quality. In addition, the influence of wave period on the accuracy of water depth retrieval was theoretically evaluated, revealing that a larger wave period leads to a better depth measurement. The depth measurement from two images with different wave periods aligned with the theoretical analysis. These results showcase the applicability and potential of the WBM for accurately estimating water depth in various coastal environments.

Winter and Summer Variations in the Physiological Parameters of Two Scleractinian Corals in Sanya Bay

Coral reefs in Sanya Bay have been degrading in recent decades under climate change and human activities. To identify physiological changes of scleractinian corals and corresponding influencing factors, aquatic environmental factors and physiological parameters of Pocillopora damicornis, Porites pukoensis and their symbiotic zooxanthellae were examined in four Sanya Bay coral reef areas in December 2020 (winter) and July 2021 (summer). The density and chlorophyll a+c2 content of the symbiotic zooxanthellae were significantly high in winter and low in summer. Superoxide dismutase and caspase3 activities of corals and zooxanthellae were high in summer and low in winter, whereas catalase activity showed the opposite pattern. The variations were consistent for both coral symbionts. Water temperature and salinity were the main factors affecting the physiological variations of corals. Compared with winter, the high temperature/low salinity aquatic environment in summer reduced the density and chlorophyll a+c2 content of zooxanthellae, resulting in high superoxide dismutase and caspase3 activities in the corals and zooxanthellae. In addition, turbidity was an important factor affecting the physiological characteristics of coral–zooxanthellae symbionts among the four coral reef areas. Our results have important implications for understanding the changes in coral reef communities in Sanya Bay and coral reef protection.

Spatiotemporal variations and impact factors of nutrients in the Sanya Bay, northern South China Sea.

Nutrients play a fundamental role in maintaining coastal ecosystem stability. Based on two cruise observations in the winter of 2020 and the summer of 2021, the spatiotemporal variations of dissolved inorganic nitrogen (DIN) and orthophosphate (PO43-) and their influencing factors in Sanya Bay were analyzed. Results show that the mean DIN concentrations in the bay are 2.36μmol/L in winter and 1.73μmol/L in summer, and the mean PO43- concentrations are 0.08μmol/L in winter and 0.04μmol/L in summer. The nutrient concentrations and composition are significantly affected by the Sanya River. The surface DIN concentrations at the Sanya River estuary are 15.80 and 5.25 times than those inside the bay in winter and summer, respectively. Meanwhile, a high proportion of NO3- (74%) and a low proportion of NH4+ (20%) in DIN appear near the river estuary, while a low proportion of NO3- (37%) and a high proportion of NH4+ (53%) occur away from the estuary. In addition, the thermocline promotes the accumulation of NH4+ at the bottom layer in summer. The high proportion of NO3- is likely not favorable for the survival of coral reefs in eastern bay. Compared with the previous nutrient concentrations, the DIN concentration in the bay has a decrease after 2014, which might benefit from the implementation of the environmental protection policy by government.

Chemistry, Chemo-Ecology, and Biological Activities of Uncommon and Structurally Diverse Sesquiterpenoids from the Sanya Bay Nudibranch Hexabranchus sanguineus.

A detailed chemical investigation of the Sanya Bay nudibranch Hexabranchus sanguineus yielded thirteen new sesquiterpenoids, namely sanyagunins A-H, sanyalides A-C, and sanyalactams A and B, along with eleven known related ones. Sanyalactams A and B feature an unprecedented hexahydrospiro[indene-2,3'-pyrrolidine] core. The structures of new compounds were established by a combination of extensive spectroscopic data analysis, quantum mechanical-nuclear magnetic resonance methods, the modified Mosher's method, and X-ray diffraction analysis. Based on analysis of NOESY correlations and the modified Mosher's method, the stereochemistry of two known furodysinane-type sesquiterpenoids were revised. A plausible biogenetic relationship between these sesquiterpenoids wasproposed and discussed, and a chemo-ecological relationship of the title animal and its possible sponge preys has been analyzed. In bioassays, sanyagunin B showed moderate antibacterial activity, whereas 4α-formamidogorgon-11-ene exhibited potent cytotoxicity with IC50 values ranging from 0.87 to 1.95 μM.

Structurally Diverse Diterpenoids from the Sanya Bay Nudibranch Hexabranchus sanguineus and Its Sponge-Prey Chelonaplysilla sp.

Investigation of the South China Sea nudibranch Hexabranchus sanguineus from Sanya Bay afforded, in addition to three known compounds, nine new diterpenoids of the 5,19-cycloclerodane- (sanyanolides A-D), clerodane- (sanyanolide E) and subersin- (sanyanolides F-I) type. Remarkably, six diterpenoids aforementioned from H. sanguineus were also isolated from the sponge Chelonaplysilla sp. from the same water region, suggesting a trophic relationship between H. sanguineus and Chelonaplysilla sp. The structure and absolute configuration of new compounds were established by a combination of spectroscopic data, X-ray diffraction analysis and/or time-dependent density functional theory/electronic circular dichroism calculations. A plausible biogenetic relationship between these diterpenoids, along with the chemo-ecological implications of their co-occurrence in the two organisms investigated, was proposed and discussed. In in vitro bioassays, echinoclerodane A exhibited a potent inhibitory effect (IC50 =2.81 μM) on LPS-induced inflammatory response in RAW 264.7 macrophage cells. In addition, echinoclerodane A and oculatolide showed considerable antibacterial activities with MIC values ranging from 1.0 to 8.0 μg/mL.

A guided-liquid-based hybrid triboelectric nanogenerator for omnidirectional and high-performance ocean wave energy harvesting

Ocean wave energy is a promising clean and renewable energy source to mitigate the global energy crisis and environmental issues. Here, a guided-liquid-based isotropic triboelectric–electromagnetic-hybrid nanogenerator (iTEHG) is developed for efficient and sustainable harvesting of omnidirectional ocean wave energy. The fully-enclosed iTEHG is based on a triboelectric nanogenerator (TENG) and electromagnetic generator (EMG), with the structure design of a unique concentric circular electrode pair built on a tilted satellite-dish-inspired plate for gravity-guided motion of the liquid. The newly-designed ocean wave harvester solves the wear and insufficient contact problems of mainstream solid–solid-interfaced TENGs, prolonging the device lifetime, and improves controllability of liquid compared with other solid–liquid-interfaced TENGs. This produces immediate power and current densities of 7.25 µW·cm–3 and 4.85 µA·cm–3 with undifferentiated 360° coverage. The iTEHG can charge a 0.1 F supercapacitor to 3.1 V and continuously drive a wireless thermometer for over 26 min. It exhibits superior performance for practical applications in real ocean environments, proven by continuously driving 320 high luminosity LEDs in Sanya Bay, China, even during quiet periods of ocean activity. The proposed design is expected to have a broad prospect for future blue energy harvesting and inspire development of self-sufficient ocean sensors.

Distribution and characteristics of microplastics in the tidal flats of Sanya Bay, China

Microplastics are plastic particles with a diameter of less than 5 mm that originate from human activities and are widely present in marine environments, resulting in serious impacts on marine organisms and ecosystems. In this study, 10 sampling sites were set in the tidal flats of Sanya Bay based on functional and depth differences. The samples were collected using the coring sampling method and then statistically analyzed using a stereo microscope. The spatial distribution, size range, color , shape characteristics of the microplastics and pollution level were analyzed. The results revealed that the abundance of microplastics in the tidal flats of Sanya Bay was about 16�51.3 pcs/kg. Vertically, the highest abundance of microplastics occurred in the subtidal zone. Horizontally, the highest abundance of microplastics occurred in the hotel resort area, while the lowest was in the transition zone. The distribution of microplastic abundance was influenced by the tide and by tourist activities. The size of the microplastics ranged primarily from 0.1 to 2 mm, with the highest proportion in the 1�2 mm range. The predominant colors were black, blue, and white; black microplastics accounted for the highest proportion. The shape of the microplastics was predominantly fibrous. The pollution level of microplastics in the tidal flats of Sanya Bay is not high, but the impact of tourism waste cannot be ignored. To address microplastic pollution, it is necessary to strengthen pollution source management and control and to promote environmental awareness. Governments and relevant organizations can take measures to encourage the development and use of sustainable materials and products as alternatives to plastics in order to reduce plastic consumption.

Analysis of hydrodynamic influence before and after the demolition of Fenghuang Two Island

In this paper, the hydrodynamic survey data around Fenghuang Island in March 2018 and April 2022 were collected to analyze the impact of the demolition of Fenghuang 2 Island on the hydrodynamic of Sanya Bay. The results show that the tidal pattern of the Sanya Bay is irregular diurnal. The current velocity outside the mouth of the Sanya River is slightly lower than that in Hanoi. The mean current velocity near the shore gradually increases to the open sea, and the mean current velocity in Hanoi and the mouth is significantly lower than that in other sea areas. Before the demolition of Fenghuang II Island, due to the weakening of the shield effect of Fenghuang II Island on the southbound waves, the northwest coastal sand transport capacity was enhanced, resulting in the change of the sand content of the surrounding stations of Fenghuang II Island.

A tube-shaped solid–liquid-interfaced triboelectric–electromagnetic hybrid nanogenerator for efficient ocean wave energy harvesting

Ocean waves, the most widely distributed energy source within the marine environment, promise renewable energy for next-generation self-sufficient ocean exploration and monitoring instrumentation. Triboelectric nanogenerator (TENG) technology has shown the potential in harvesting ocean wave energy. However, most TENG designs suffer from challenges such as relatively low contact intimacy and energy power density, limiting their practical application. This paper proposes a solid–liquid-interfaced, tube-shaped triboelectric–electromagnetic hybrid nanogenerator (TTEHG) to efficiently capture wave energy. Owing to the solid–liquid interface in conjunction with the coupled TENG and the electromagnetic generator (EMG) design, the TTEHG features a reduced frictional loss and broadened range of harvestable wave energy. At a frequency of 1 Hz, the instantaneous power density and current density of the TTEHG are 0.25 mW·cm–3 and 5 mA·cm–3, respectively. Even at an ultra-low operational frequency of 0.2 Hz, the TTEHG exhibits an excellent output performance with a peak current of nearly 15 mA, and is able to power various functional electronic devices, such as temperature and humidity sensors, to monitor the marine environment. The TTEHG was deployed in Sanya Bay, China, to demonstrate its practical application in harsh ocean environments.

Applying a Set of Potential Methods for the Integrated Assessment of the Marine Eco-Environmental Carrying Capacity in Coastal Areas

The accelerated socioeconomic development has placed the coastal ecosystems under stress, which influences the sustainable development of coastal areas. Marine eco-environmental carrying capacity assessment (MECCA) can provide a scientific basis for coordinating coastal socioeconomic development and eco-environmental protection, ensuring a more effective marine ecosystem-based management approach toward sustainability. However, accurate assessment methods are still in the exploratory stage, as there has been a lack of systematic research and applications combining integrated MECCA with a unified method to underpin coastal management processes. In light of this issue, this study applied the marine eco-environmental carrying capacity in coastal waters (MECCCW) conceptual framework to support the establishment of an assessment indicator system for MECCA and used the regularization method and entropy method to determine weights. This study also applied the simplified state space model to comprehensively evaluate and analyze the marine eco-environmental carrying capacity (MECC) of coastal areas. Focusing on the coastal area of Sanya Bay, southern China, as the study area, we assessed the MECC for the period from 2015 to 2020. The state of the MECC was divided into three grades: load capacity, full-load capacity, and overload capacity. The results showed that (1) the MECCA indicator system in Sanya Bay included a total of three criteria and eight assessment indicators and (2) the weights of the environmental carrying capacity (ECC) and human activities (HA) were both relatively higher than that of ecological resilience (ER). The latter result indicates that either ECC or HA could play a more predominant role in the changes of the MECC state in Sanya Bay. The results also indicated that (3) for each criterion, ECC, ER, and HA were at load capacity from 2015 to 2020. In this instance, ECC and HA presented similar change trends in relation to the MECC state of Sanya Bay. Finally, (4) the overall Sanya Bay’s MECC was also at load capacity and weakened, fluctuating between 2015 and 2020. These findings indicate that the coastal area of Sanya Bay is capable of sustainable development, but that there is a need for further eco-environmental improvement. The results of this study can serve as a reference when decisions have to be made about coastal management from an environmental and ecological perspective. Furthermore, this method may provide a feasible approach for integrated MECCA in other coastal areas.

Evaluation of coral skeletal δ88Sr as a paleoclimate proxy in the northern South China Sea

The climate and environmental significance of the stable strontium isotope composition (δ88Sr) in coral skeletons deserves further investigation. To improve our understanding of stable strontium isotope fractionation during the biomineralization process, correlations between monthly coral skeletal δ88Sr values and climatic and environmental variables (along with their corresponding geochemical proxies) between 2008 and 2009 were studied using a massive zooxanthellae Porites coral head from Sanya Bay on the south coast of Hainan Island in the northern South China Sea. Sea surface temperature and its corresponding geochemical proxies (Sr/Ca and δ18O), pH and its proxy δ11B, and precipitation (representing river runoff) show clear annual cycles, but their correlations with coral δ88Sr were not significant during 2008 and 2009. However, both total solar irradiance (TSI) and coral δ88Sr values followed a gradually increasing trend over the study period and showed a statistically significant correlation. These results indicate that the fractionation associated with coral skeleton δ88Sr is not temperature-dependent, but TSI may play a major role in controlling coral δ88Sr values at our study site. The underlying mechanism of TSI-induced 88Sr/86Sr fractionation in coral skeletons may be similar to that associated with coral δ13C. That is, symbiotic zooxanthellae preferentially uptakes 86Sr during photosynthesis leaving the internal strontium reservoirs enriched in 88Sr; consequently, increased uptake of 88Sr by the coral skeleton occurs when photosynthetic rates increase. However, the correlation between coral δ88Sr and δ13C values may be masked by the carbon input from terrestrial river runoff and the kinetic isotope fractionation effect during the calcification process.

Uncommon eunicellin-based diterpenoid and 9, 11-secosteroid from the Sanya soft coral Cladiella krempfi: Structure and stereochemistry

Two new compounds, namely an uncommon eunicellin-based diterpenoid (clakrefielin A, 2) and a 9, 11-secosteroid (cladiellasterol A, 4), along with a known carotenoid (all-trans-peridinin, 7), were isolated from the Ximao Island, Sanya Bay soft coral Cladiella krempfi. The structures of these compounds were established on the basis of extensive spectroscopic analysis, X-ray diffraction analysis, chemical transformations, as well as the comparison with the reported data in the literature. The biological activities of these compounds were investigated, and compound 7 was found to be a new protein tyrosine phosphatase 1B (PTP1B) inhibitor (IC50 = 7.2 μM).

Dynamic Monitoring and Analysis of Ecological Environment in the Coastal Tourist Destinations of Sanya City, Hainan

Taking the Sanya Bay as the study area, based on the remote sensing images of Gaofen-2 in 2015, 2017, 2019 and 2020, this paper extracted 7 land use types of Sanya Bay. The main objectives of this paper includes: (1) Applying the theory of landscape ecology to calculate the landscape fragmentation and disturbance intensity in order to indicate the ecological changes in the study area; (2) Analysing the impact of landscape changes on the surroundings areas driven by the diversity of land use and perform the “Dynamic Monitoring and Analysis Technology for the Ecological Environment of Coastal Tourism Regions”. In which to monitor the dynamics of the ecological environment in the area of research. The results showed that the quality of the ecological environment in the study area changed dynamically with the construction of tourism sites: from year 2015 to 2017, due to a large number of construction, the ecological environment deteriorated to a certain extent; From 2017 to 2020, with the suspension of construction and environment restoration work, the quality of the ecological environment in the study area improved. Technology established in this paper provides a reference for the dynamic monitoring of the ecological environment in the coastal tourist area.

Beach erosion and nourishment in the east section of Sanya Bay, China

Beach erosion and nourishment in the east section of Sanya Bay, China

Abundance and Characteristics of Microplastics in Seawater and Corals From Reef Region of Sanya Bay, China

Microplastics (MPs) contamination is widespread in the coral reef ecosystems leading to the exposure of both corals and other biotas. Knowledge gaps still exist concerning patterns in MPs abundance spatially. This work quantified the MPs abundance and characteristics in the seawater and corals in the Sanya Bay, Hainan Island. MPs abundance was detected in the seawater and coral samples ranging from 15.50 to 22.14 items L–1, and 0.01 to 3.60 items polyp–1, respectively. We found the predominant size and type of MPs in seawater and corals were smaller than 2 mm and fiber. Further analysis revealed that the characteristics of MPs in the corals were significantly different from those in the seawater environment, indicating that the MPs are selectively enriched in corals. Furthermore, the MPs particles ingested and retained in coral tissue may be related to the polyp size. This study shows that MPs are present in the whole coral reef region and the coral community structure would be potentially harmed by these contaminants.

An Improved Adaptive Subsurface Phytoplankton Layer Detection Method for Ocean Lidar Data

Phytoplankton, as the foundation of primary production, is of great significant for the marine ecosystem. The vertical distribution of phytoplankton contains key information about marine ecology and the optical properties of water bodies related to remote sensing.The common methods to detect subsurface phytoplankton biomass are often in situ measurements and passive remote sensing; however, the bio-argo measurement is discrete and costly, and the passive remote sensing measurement is limited to obtain the vertical information. As a component of active remote sensing, lidar technology has been proved as an effective method for mapping the vertical distribution of phytoplankton. In the past years, there have been few studies on the phytoplankton layer extraction method for lidar data. The existing subsurface layer extraction algorithms are often non-automatic, which need manual intervention or empirical parameters to set the layer extraction threshold. Hence, an improved adaptive subsurface phytoplankton layer detection method was proposed, which incorporates a curve fitting method and a robust estimation method to determine the depth and thickness of subsurface phytoplankton scattering layer. The combination of robust estimation method can realize automatic calculation of layer detection threshold according to the characteristic of each lidar signal, instead of an empirical fixed value used in previous works. In addition, the noise jamming signal can also be effectively detected and removed. Lidar data and in situ spatio-temporal matching Chlorophyll-a profile data obtained in Sanya Bay in 2018 was used for algorithm verification. The example result of step-by-step process illustrates that the improved method is available for adaptive threshold determination for layer detection and redundant noise signals elimination. Correlation analysis and statistical hypothesis testing shows the retrieved subsurface phytoplankton maximum depth by the improved method and in situ measurement is highly relevant. The absolute difference of layer maximum depth between lidar data and in situ data for all stations is less than 0.75 m, and mean absolute difference of layer thickness difference is about 1.74 m. At last, the improved method was also applied to the lidar data obtained near Wuzhizhou Island seawater, which proves that the method is feasiable and robust for various sea areas.

Tidal‐Driven Submarine Groundwater Discharge and Its Influences on the Carbonate System of a Coastal Coral Reef in the Northern South China Sea

AbstractThe driving mechanisms of submarine groundwater discharge (SGD) in Sanya Bay in the northern South China Sea were investigated using a combination of time‐series observation and modeling, as well as the influences of SGD on the carbonate system of a coastal coral reef. SGD flux, characterized by high variability on flood‐ebb and spring‐neap tidal cycles, was found to be mainly driven by tidal pumping. SGD posed more significant impacts on coastal water at the ebb phase during the spring tide (higher SGD flux and extended offshore reach of SGD impact), with nearshore water to be more heavily affected. Under the influence of SGD, the diurnal ranges of the carbonate variables observed in the coral reef system were 124 – 313 μmol kg−1 for dissolved inorganic carbon, 29 – 101 μmol kg−1 for total alkalinity, 179 – 717 μatm for partial pressure of CO2, and 0.20 – 0.45 for pH. The variations of the CO2 system were dominated by the enhanced SGD input during the spring tide, while biological metabolism of coral reef played a predominant role during the neap tide. The intensified SGD input resulted in higher diurnal variations of the carbonate variables, enhanced acidification, and oceanic CO2 emission during the spring tide. The SGD‐associated inorganic carbon flux is an additional stressor influencing coastal acidification in the context of rising atmospheric carbon dioxide.

Vertical distribution of subsurface phytoplankton layer in South China Sea using airborne lidar

The vertical distribution of subsurface phytoplankton in the ocean contains key information about not only ocean ecology but also water column optical properties relevant to remote sensing. The existing methods for measuring this vertical distribution are mainly field bio-optical and biogeochemical observations, which are time- and labor-intensive and do not provide sufficient spatial coverage. Passive satellite remote sensing provides global observations of phytoplankton but offers no information on subsurface vertical structure. In this study, we made the first quantitative measurements of vertical distribution of the subsurface phytoplankton layer (SPL) in the South China Sea (SCS) using airborne lidar. A total of five lidar flight experiments were conducted between 2017 and 2019 in the SCS, and approximately 2.5 terabytes of data were obtained. A hybrid retrieval method combining the Klett method for klidar and the perturbation method forβπ was developed. The lidar-retrieved chlorophyll-a concentrations and in situ data show good agreement (R2 greater than 0.8). The mean absolute percentage error for the lidar-retrieved chlorophyll-a concentrations is less than 15%. SPLs were observed both in Sanya Bay and in the open sea near Lingshui city, Hainan Province, China. The SPLs were observed at depths between 50 and 70 m in the open sea near Lingshui city, and between 5 and 30 m in Sanya Bay. The SPL depths have spatiotemporal variability, and we analyzed the possible factors (monsoon, seafloor depth, and sea surface temperature) that influence this spatiotemporal variability. The results show that lidar technology has a great potential for wide-range and long-term monitoring of SPLs, and is a good complement for discrete in situ observations and passive satellite remote sensing.

The distribution characteristics of β-propeller phytase genes in rhizosphere sediment provide insight into species specialty from phytic mineralization in subtropical and tropical seagrass ecosystems.

Seagrass meadows have seriously deteriorated in recent years. Seagrass associated phytate-mineralizing rhizobacteria potentially have functions related to seagrass nutrition, health and sustainable growth. The β-propeller phytases (BPPs) are the only phytase family in aquatic environments, but there are few studies on the BPP community structure of seagrass. In this study, clone libraries and quantitative PCR (qPCR) assays were used to compare the diversity and abundances of the BPP communities of Halodule endl, Halophila ovalis and Thalassia hemprichii in Xisha and Sanya, and to investigate the distribution characteristics of BPP genes in the rhizosphere sediment, which provedes insight into species specialty from phytic mineralization in subtropical and tropical seagrass ecosystems. The highest diversity of BPP genes was found for Thalassia hemprichii in Sanya Bay. Thalassia hemprichii in Sanya had higher abundances of BPPs, which were linked to Gammaproteobacteria. The BPP community diversity and OTUs of Thalassia hemprichii in Sanya were much higher than those of Thalassia hemprichii on Yongxing Island and Stone Island. The seagrass BPP communities had higher diversity and evenness from sampling sites with more human activity. The qPCR results showed that the abundance of phytate acid-degradating bacteria was approximately three times larger in Thalassia hemprichii rhizosphere sediment samples than in Halodule endl and Halophila ovalis rhizosphere sediment samples. This study highlighted that the diversity and abundances of bacteria genetically encoding BPP in the rhizosphere of Thalassia hemprichii were clearly higher than those of Halodule endl and Halophila ovalis. Further study of microbial phosphorus cycling will provide new insights into seagrass meadow ecosystems.