Iron oxides play a significant role in the global soil (sediment) organic carbon (OC) storage. Mangrove wetlands, receiving both terrestrial and marine inputs, provide a unique habitat for the preservation of organic carbon by reactive iron oxides (Fe_R). However, the impact of Fe_R in the surface sediments of mangroves on the preservation process of OC, as well as the selectivity of Fe_R towards different OC components, is still unclear. The surface sediments in the present work was collected in the natural mangrove areas around the estuaries of the Dafeng River and Maowei Sea in Guangxi, which are highly influenced by tides and rivers. The research was focused on the changes in the content and composition of iron-bound organic carbon (Fe-OC) in sediments. The results indicated that the average content of Fe-OC in surface sediments in the estuaries of Dafeng River and Maowei Sea was 0.16% ± 0.07% and 0.17% ± 0.07%, respectively. These values represented 16.2 ± 5.04% and 10.9 ± 5.63% of the total organic carbon (TOC) content in the respective sediments, which were primarily preserved through adsorption. Furthermore, the preservation of OC by Fe_R was influenced by the sediment particle size, the content and form of Fe_R, and the source and composition of TOC. TOC, Fe_R and Fe-OC were mainly distributed in the smaller grain size sediment fractions. The predominant form of iron in surface sediments was Fe³⁺, accounting for 87.42% of the total iron, and was relatively higher in high salinity sediments. Fe_R selectively preserved OC with higher δ¹³C (stable carbon isotope natural abundance) and aromatic OC. Compared with the Maowei Sea, the proportion of protein-like fluorescent components in Fe-OC of surface sediments from the Dafeng River estuary was higher and the proportion of protein-like fluorescent components increased as the molar ratio of Fe-OC∶Fe increased. This study helps to clarify the selective preservation mechanism of OC by Fe_R in mangrove surface sediments in Guangxi, and deepen our understanding of the preservation process of OC in land-sea interface sediments.

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.

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.

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 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.

In order to investigate the impact of climate change on the catch of bigeye tuna, we utilized the annual Pacific bigeye tuna catch data from 1960 to 2021, which was statistically compiled by the Western and Central Pacific Fisheries Commission. We also employed corresponding monthly climate indices, including Niño1+2, Niño3, Niño4, Niño3.4, Southern Oscillation Index (SOI), North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), North Pacific Index (NPI), and global sea-air temperature anomaly (dT). By using a BP neural network and variable sensitivity analysis, we examined the relationship between these low-frequency climate factors and bigeye tuna catch. Our findings revealed that Niño1+2, SOI, NAO, PDO, NPI, and dT are relatively independent climate factors that have an impact on bigeye tuna catch. The optimal lag orders for these climate factors were determined to be 8 years for Niño1+2, 2 years for SOI, 9 years for NAO, 0 years for PDO, 9 years for NPI, and 3 years for dT. Among these factors, Niño1+2, SOI, and NAO were identified as the key climate factors influencing bigeye tuna catch. We constructed an optimal BP neural network model with a structure of 6-8-1, and the ratio of the difference between the predicted and actual bigeye tuna catch to the actual catch has been maintained within 15% since 1971. Additionally, the trend of the predicted and actual catch was found to be basically consistent, indicating a satisfactory level of model fit.

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.

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.

Oil spill is one of the critical target of marine environmental monitoring. Synthetic Aperture Radar (SAR), thermal infrared remote sensing, and optical remote sensing for monitoring of marine oil spills have been elucidated, and it is crucial for marine environmental protection to utilize the features and advantages of multi-source remote sensing to achieve accurate monitoring and quantitative assessment of marine oil spills. On April 27, 2021, the collision between the Panamanian vessel Sea Justice and the Liberian oil tanker A Symphony resulted in an estimated 9400 t of cargo oil seeping into the yellow sea. Here, we used multi-source satellite remote sensing data to monitor and analyze the coverage of oil spill and the distribution of emulsified oil in this accident. Based on the response mechanism and characteristics of oil spill multi-source remote sensing, the processing of multi-source data is optimized to realize the identification of oil spills and the classification of multiple oil types. The findings indicate that from May 1 to May 22, 2021, the cumulative pixel area of oil spills from A Symphony tanker was 2368.7 km², of which the emulsified oil pixel area was 1019.3 km², accounting for 43.0%. The maximum daily oil spill pixel area reached 734 km². The results of multi-remote sensing monitoring validated each other, and optical remote sensing is more capable of identifying different oil types, in which the emulsified oil represents the key of pollution hazards. It improves the accuracy of monitoring and assessment of marine oil spills, and provides reliable technical and methodological references for the hazard assessment and refined monitoring of oil pollution events.

Based on analyses of solid-phase and porewater chemistry of sediment cores at four sites collected from Laizhou Bay of the Bohai Sea, we revealed diagenetic cycles of iron, manganese and sulfur and their responses to terrestrial inputs and anthropogenic perturbations. Results suggest that water eutrophication of the bay has not given rise to organic carbon (OC) enrichment in the sediments. Actually, contents and lability of sediment OC are generally low, largely due to the inputs of terrestrial refractory OC and intense sediment resuspension induced by natural processes and anthropogenic perturbations in the river-dominated area. This feature greatly dampens sulfate reduction, resulting in low accumulation of total reduced inorganic sulfide (0.28−88 μmol/g). Porewater Mn²⁺ is mainly from reductive dissolution of amorphous and poorly crystalline Mn oxides, while precipitation of MnCO₃ is mainly responsible for Mn²⁺ consumption in sediment below 10 cm depth. Intense sediment resuspension and refractory nature of sediment OC encourage dissimilatory iron reduction, with relative contribution of this pathway to total anaerobic OC mineralization of about 51%, on average. At the site (S6) heavily influenced by the Huanghe River input, dynamic depositional regime facilitates reductive dissolution of manganese oxides, but dampens reduction of iron oxides and sulfate to some extent. Upward diffusive fluxes of porewater Mn²⁺ and Fe²⁺ in the sediments are at the lower end for sediments of other areas dominated by major river inputs, which is attributable to overall low lability of sediment OC.