In November 2020, sediment samples were collected from the Yalong Bay Qingmei Port mangrove nature reserve and the Sanya River mangrove nature reserve in Hainan Province. The present study focused on the community characteristics of marine nematodes and their influencing factors in these two mangroves. The results of the present study showed that the average abundance of marine nematodes was (80.4 ± 40.3) ind./cm² in the Qingmei Port mangrove, while it was (96.7 ± 55.6) ind./cm² in the Sanya River mangrove. In this study, the average abundance of marine nematodes in the two study mangrove wetlands was (88.5 ± 47.1) ind./cm². There were significant differences in the abundance of marine nematodes between the two mangrove wetlands. A total of 77 species of marine nematodes were identified, belonging to 56 genera, 21 families and 7 orders. The dominant genera in the Qingmei Port mangrove were Neochromadora, Terschellingia, Paramonohystera, Daptonema and Desmodora, and epigrowth feeders were the dominant feeding type. The dominant genera in the Sanya River mangrove were Terschellingia, Sabatieria, Eleutherolaimus, Parodontophora and Ptycholaimellus, and the selective deposit feeders dominated. Terschellingia dominated in both mangroves. There were spatial differences in the community structure of marine nematodes in study mangroves. Although the marine nematode communities differentiated between the two mangroves, the difference was not significant. Organic matter content and phaeophorbide content in sediments were important factors affecting the abundance and community structure of marine nematodes in Sanya River mangrove. The differences in mangrove vegetation types may affect the abundance and community structure of marine nematodes in Qingmei Port mangrove to some extent. The differences of sediment granularity characteristics, seawater pH and salinity could explain the differentiation of marine nematode communities at selected sites of the two mangrove. In addition, there are sewage project, port construction and tourism development in Qingmei Port mangrove. And there are felling, dike construction, salt pan development and wastewater discharge from shrimp ponds in Sanya River mangrove. The different pollution status in these two mangroves may also be the reason for the differences in the abundance and community structure of marine nematodes in this study.

The distribution of wave energy in enclosure aquaculture areas not only significantly influences nutrient transport but also constitutes a critical hydrological factor in validating the design of structures in inner aquaculture area. Investigating the changes in wave field energy influenced by these structures is crucial. The FUNWAVE 2.0 numerical model was employed to simulate irregular wave propagation in aquaculture areas with varying pile-net enclosure structures. The effects of pile spacing and incident wave angles in the evolution of wave energy was examined. The results indicate that if the internal facilities are positioned close to the outer pile-net enclosure structure, the pile spacing should be less than 10 m, provided that structural stability is ensured. Conversely, if the internal facilities are located farther from the outer pile-net enclosure, a pile spacing greater than 10 m should be selected. Additionally, oblique wave incidents may pose greater structural challenges at certain locations compared to normally incident waves, which should also be considered during design.

In response to contingencies that arise during the underwater coverage missions of multiple autonomous underwater vehicles (AUVs), this study addresses the problem of coverage path replanning for multiple AUVs. A multi-robot multi-regional coverage path planning (M²CPP) method is proposed to reassign uncovered areas to available AUVs and plan their coverage paths. Initially, the lawnmower algorithm is employed to determine the internal paths and candidate entry points within each region. Subsequently, a coevolutionary approach is utilized to solve for the optimal region allocation, region sequence, and the best entry points for each region. Three populations coevolve collaboratively to determine the complete paths for all AUVs, ensuring population diversity and preventing convergence into local optima. Simulation results demonstrate that the proposed method not only replans shorter paths for multiple AUVs based on their initial positions and remaining energy but also optimizes the path structure to ensure a balanced workload among the AUVs, effectively resolving the replanning issue under such scenarios.

Seagrass meadows play a vital role in protecting marine biodiversity, mitigating ocean acidification, and preventing soil erosion in the coastal ecosystem. However, global climate change and human activities seriously affect the life of seagrass, which cause the widespread degradation of the seagrass and threaten the safety of coastal ecosystems. Recently, the vital value of microorganisms in promoting the energy flow of seagrass meadows and their growth and development has gradually gained attention. Plant growth-promoting microorganisms(PGPM) will play their value in seedling cultivation, plant transplantation, seed planting and other techniques of seagrass meadow restoration. This paper reviewed the research on how microorganisms interacts with seagrass to promote the growth of plants and increase the resistance to abiotic stress. We introduced the mechanism of PGPM to enhance plant stress tolerance under high temperature, high salt, and low light. We propsoed that modern molecular biological technique should be used to screen seagrass PGPM, clarify the colonization site of PGPM, and explore the molecular interaction mechanism between PGPM and seagrass in different environmental conditions. This paper is some advice for promoting the application of PGPM in seagrass meadow restoration and seagrass protection.

The coast of Hainan Island is dominated by embayed beaches, which is an important coastal tourist destination in China and also has a high incidence of drowning accidents caused by rip currents. To investigate the distribution characteristics of rip currents on embayed beaches, the occurrence and distribution characteristics of rip currents are interpreted from the satellite images of 54 embayed beaches around Hainan Island over the past 20 years, and compared with the field survey results. The results show that, in terms of regional distribution, the occurrence probability of rip currents on the eastern and southern coasts is significantly higher than that on the western and northern coasts of Hainan Island. In terms of location distribution, the number of rip currents in the middle of the headland bays is higher than that on the two sides. In terms of geometric characteristics, the average rip length was positively correlated with the average rip width, and the average rip spacing. The distribution density of rip currents is negatively correlated with significant wave height, average wave period, incident wave power, and wave energy. The scale of the headland has a significant effect on the number of rips, which is positively correlated with the bay width, the maximum bay indentation, and length of the headland, but the curvature of the shoreline has no significant correlation with the average number of rips. The results of satellite image interpretation for the occurrence of rips are consistent with the results of the field survey and the evaluation of the Ω-RTR model. These conclusions can provide useful references for the beach safety management and rip current warning work on Hainan Island.

In order to understand the long−term variations in the nutritional environment and the key influencing factors of Bohai Bay, sediment cores from the mouth of the bay (BH15) and the outer area of the bay (BH47) were collected in April and June 2018 separately. The contents of total organic carbon (TOC), total nitrogen (TN), phosphorus (P), biogenic silica (BSi), and stable isotopes of carbon and nitrogen (δ¹³C, δ¹⁵N) were analyzed, and the causes of the changes of the above parameters were discussed in combination with the changes of climate and surrounding human activities. The results showed that the TN content in both sediment cores exhibited an increasing trend since the 1980s, which is consistent with the long-term variations in dissolved inorganic nitrogen (DIN) in the sea water. Sewage discharge, fertilizer application and mariculture are the main sources of nitrogen in the Bohai Bay, among which the input of agricultural fertilizer has decreased since 2007, while the discharge of mariculture and domestic sewage into the sea has shown a continuous upward trend. Inorganic Phosphorus (IP) was the main form of phosphorus in sediments. The IP in BH15 in the bay has shown a decreasing trend since the mid-1990s, while the IP in BH47 from the mouth of the bay has shown a decreasing trend after 1970s and a slow increasing trend since 1990s. All of them show obvious terrigenous input characteristics. The results of TOC/TN ratio、δ¹³C value and δ¹³C two-endmember mixing model indicated that the sediment organic matter in the mouth of Bohai Bay and adjacent sea area was influenced by both terrestrial input and marine autochthonous sources, with marine organic matter being the dominant source, the contribution of marine organic matter has decreased Since the 1990s. Compared with the BH47 core from the mouth of the bay, the BH15 core is closer to the coastal area, more significantly affected by terrestrial input, with higher TN content and contribution of terrestrial organic matter. This study shows that in order to effectively manage the water environment of Bohai Bay, it is necessary to strengthen the control of mariculture and domestic sewage discharge into the sea while controlling the use of agricultural fertilizers in the future.

Against the backdrop of global warming, the Arctic has experienced a series of changes, including permafrost degradation, reduced summer sea ice, increased land runoff, and intensified coastal erosion. With global warming, organic carbon (OC) stored in permafrost is accelerating its migration and release to the sea, which will affect the pattern of carbon cycling in the Arctic Ocean. However, there is currently little evidence to directly confirm this inference. This article analyzes the lignin and carbon isotopes of two hundred year scale sedimentary cores in the Chukchi Sea, and discusses the sources and profile changes of the buried organic matter. The results showed that the organic carbon in the columnar sediments of the Chukchi Sea came from a mixed contribution of herbaceous tissue of terrestrial C3 plants and marine source production. The absolute content of lignin Σ8 in sediment shows an overall upward trend, indicating that with global warming, more terrestrial materials are being transported to the Chukchi Sea. This study indicates that global warming caused by human activities has indeed increased the migration of organic carbon from permafrost to the sea, and the increase in lignin content due to enhanced terrestrial inputs is direct evidence of the enhanced melting of permafrost caused by global warming on a century scale.

Phosphonates in the ocean are a kind of potential phosphorus (P) source which could be utilized by phytoplankton. Although dinoflagellates cannot directly utilize phosphonates themselves, their symbiotic bacteria have the capability to degrade phosphonates into phosphate, thereby promoting the growth of algal cells. However, no studies focusing on a specific bacteria strain have been conducted thus far. In this study, Prorocentrum donghaiense was cultured under conditions with 2-Aminoethylphosphonic acid (2-AEP) as the sole P source. Isolation and purification of the symbiotic bacteria from the culture was conducted and five kinds of bacteria were obtained. Genome sequencing results revealed the presence of two types of C-P lyase pathways in the bacterial strain designated as Yoonia sp. PD-AEP-1. The function of the bacteira strain was verified through the co-culture of bacteria and algal cells. The results demonstrated that after the algal cells were treated to phosphorus-starved condition, when 2-AEP and the bacteria suspension were added together, as compared to conditions which only 2-AEP or the bacterial suspension of PD-AEP-1 was introduced, both the growth rate of algal cells and the phosphate concentration in the cultures showed a significant increase. Meanwhile, alkaline phosphatase activity and non-photochemical quenching of the algal cells decreased significantly, indicating that PD-AEP-1 has the ability to degrade 2-AEP into phosphate, thereby alleviating phosphorus limitation for P. donghaiense cells and effectively promoting the growth of algal cells. The study suggests that symbiotic bacteria of P. donghaiense might play a part in providing P sources to the algal cells through the degradation of phosphonates. This process could probably contribute to the outbreak of P. donghaiense bloom, highlighting the importance of algae-bacteira interactions in marine ecosystems.

In order to investigate the characteristics and spatial-temporal variations of the phytoplankton community in artificial reef areas, as well as to elucidate the relationship between phytoplankton abundance and environmental factors associated with artificial reef construction, four surveys were conducted in 2021 (May, August, November) and 2022 (January) at two artificial reef areas and a control area in Xiangyun Bay. A total of 70 phytoplankton taxa belonging to 39 genera and 3 classes were identified in this study. The annual average abundance of phytoplankton in the artificial reef areas was recorded as 313.5 × 10⁴ cells/m³, which were 1.4 times higher than that observed in the control area. Except in spring, the richness index, diversity index and evenness index of phytoplankton in the artificial reef areas were higher than those in the control area. The succession rate of dominant species from spring to summer and from summer to autumu in the reef areas were lower than that in the control area, suggesting greater stability of community structure within artificial reef areas compared to the control area. The biological increment index for each phytoplankton taxon ranged from 0.9 to 3.6; notably, Bacillariophyta displayed an average biological increment index value of 1.8. Pearson correlation analysis revealed that phytoplankton abundance was primarily influenced by TP, TN, NH₄-N, NO₃-N and DIP; significant seasonal differences were observed among these variables. These findings demonstrate that artificial reef construction has a positive conservation effect on phytoplankton communities closely related to temporal and spatial changes in nutrient availability.

Benthic harpacticoid copepods are widely distributed in marine ecosystem, which is particularly abundant in the epilithic algal matrix(EAM) of coral reefs. Due to its unique habitat, there is currently limited research on its developmental process and cultivation methods. In this study, we collected epilithic algal matrix from the coral reef of Luhuitou, Sanya, Hainan in the summer of 2023, from which we isolated one species of Harpacticoida, which was belonging to the genus Robertgurneya based on morphological characteristics. The effects of mono-and mixed-algal cultures on the developmental dynamics of Robertgurneya sp. were observed and recorded. The results showed that the adult body length of the Robertgurneya sp. was 0.5−0.7 mm, with an average life cycle of about 61−68 days. There were no significant differences in egg number per female each time, brood number, reproductive cycle, and life cycle between different feed cultivation techniques. However, under mixed algae culture, the average egg diameter, larval survival rate, and maximum body length of nauplii stage VI in the embryonic development stage of the Robertgurneya sp. were significantly higher than those in the mono-algae culture group (p < 0.05). Moreover, the embryonic development time and cumulative copepodid development time were significantly shorter under mixed-algal culture (p < 0.05). The results indicate that Robertgurneya sp. in EAM have a short life cycle and strong reproductive ability. Considering the abundant benthic microalgae and organic debris in the mats, harpacticoida may be able to provide huge potential food resources for predators such as small fish in coral reefs. Therefore, it may play an important role in the material cycle and energy flow of coral reef ecosystems.