Unprecedented phytoplankton blooms in autumn/winter in the southern Bohai Sea (China) due to high Yellow River discharge: Implications of extreme rainfall events.

The occurrence of abnormal phytoplankton blooms is one of the significant changes in coastal ecosystems due to climate change. However, the underlying mechanism of such blooms remains poorly understood due to the complexity of the system. In this study, the data from numerous observations was used to elucidate the unprecedented phytoplankton blooms in the autumn and winter of 2021 in Laizhou Bay, a typical aquaculture bay in the southern Bohai Sea of China. The abundance of phytoplankton cells increased by more than tenfold in the southern waters compared to that in the same period from 2019 to 2020. The phytoplankton bloom was first observed in winter in the Bohai Sea, with the cell abundance in the southern bay exceeding 108 cells L-1 in December 2021. The diversity and evenness of phytoplankton communities decreased in the southern area. Cerataulina pelagica was the dominant algae, comprising 69 % of the total phytoplankton in October and 99 % in December. In autumn 2021, the largest flood of the Yellow River in recent decades occurred. This was attributed to extreme rainfall events within the river basin. The input of substantial riverine nutrients played a significant role in promoting phytoplankton blooms. Correlation analysis indicated the important cumulative impact of the Yellow River on phytoplankton blooms rather than a direct short-term effect. Numerical modeling results indicated that exceptionally high Yellow River discharge in autumn could significantly affect the entire bay from autumn to the following spring. This study may contribute to understanding the abnormal phytoplankton blooms in coastal waters and provide valuable insights for environmental management in river basins and coastal waters.

Vibrio paucivorans sp. nov. and Vibrio qingdaonensis sp. nov., two marine bacteria.

Two Gram-stain-negative, facultatively anaerobic, motile, rod-shaped and flagellated marine bacteria, designated strains DBSS07T and ZSDZ65T, were isolated from the surface sediments of the Bohai sea and Qingdao coastal seawater, respectively. Phylogenetic analysis based on 16S rRNA genes, multilocus sequence analysis (MLSA), phylogenomic analysis of single-copy gene families and whole-genome data placed DBSS07T and ZSDZ65T within the genus Vibrio. DBSS07T was most closely related to Vibrio aestivus M22T, with 97.51 % sequence similarity, whereas ZSDZ65T was most closely related to Vibrio variabilis R-40492T with 97.58 % sequence similarity. DBSS07T grew with 1-7 % (w/v) NaCl (optimum 3 %), at 16-37 °C (optimum 28 °C) and at pH 6.0-9.0 (optimum pH 7.0); whereas ZSDZ65T grew with 1-5 % (w/v) NaCl (optimum 2 %), at 16-32 °C (optimum 28 °C) and at pH 6.0-9.0 (optimum pH 8.0). Both strains shared the same major fatty acid components (more than 10 % of total fatty acids) of summed feature 3 (C16 : 1ω7c or/and C16 : 1ω6c), with different proportions. The DNA G+C contents of DBSS07T and ZSDZ65T were 44.7 and 44.3 %, respectively. On the basis of the results of polyphasic analysis, DBSS07T and ZSDZ65T are considered to represent novel species within the genus Vibrio, for which the names V. paucivorans sp. nov. (type strain, DBSS07T = KCTC 82896T= MCCC 1K06284T) and V. qingdaonensis sp. nov. (type strain, ZSDZ65T = KCTC 82893T = MCCC 1K06289T) are proposed, respectively.

Brown tides linked to the unique nutrient profile in coastal waters of Qinhuangdao, China.

Brown tides caused by the pelagophyte Aureococcus anophagefferens have frequently occurred in the Bohai Sea since 2009 and have led to a dramatic collapse of the local scallop culture. To determine why brown tides occurred in the Bohai Sea rather than in other eutrophic coastal waters of China, phytoplankton communities and nutrients were evaluated and nutrient addition experiments were conducted in the Qinhuangdao coastal area. The concentration of dissolved organic nitrogen (DON) was nearly five times higher than that of dissolved inorganic nitrogen (DIN) during brown tides. High levels of phytoplankton biomass and nutrients were observed in the inshore waters, and the patterns of different nutrients were heterogeneous, which could be due to the uneven distribution of pelagophytes and non-brown tide phytoplankton populations (NBTP). The nutrient enrichment results indicated that the growth of the phytoplankton community was nitrogen-limited. Enrichment of DON, especially urea, could promote the growth of pelagophytes during the development stages of the brown tide. In brief, the results of this study imply that the unique nutrient profile (rich in DON but deficient in DIN) could support the outbreak of brown tides in the inshore waters of Qinhuangdao.

Evaluating the effectiveness of coastal environmental management policies in China: The case of Bohai Sea.

With marine pollution issues becoming serious and widespread, a series of coastal environmental managemental policies are being carried out worldwide, the effectiveness of which requires comprehensive evaluation. Taking the Bohai Sea (BS) of China as an example, which has been plagued by serious ecological and environmental issues for decades due to terrestrial pollution discharge, this study explored and quantified, for the first time to our best knowledge, the variability of water quality after initiating a dedicated 3-year pollution control action (Uphill Battle for Integrated Bohai Sea Management, UBIBM, 2018-2020) implemented by China's central government, with two water quality indexes of water color (Forel-Ule index, FUI) and transparency (Secchi disk depth, ZSD, m) from satellite observations. During the UBIBM, a significant improvement in water quality was detected, characterized by a clearer and bluer BS, with ZSD and FUI improved by 14.1% and 3.2%, respectively, compared with the baseline period (2011-2017). In addition, an abrupt drop in the long-term record (2011-2022) of the coverage area of highly turbid waters (ZSD≤2 m or FUI≥8) was found in 2018, which coincided with the start of the UBIBM, indicating that the water quality improvement may be attributed to the pollution alleviation of the UBIBM. Independent data of land-based pollution statistics also supported this deduction. (3) Compared with the previous two pollution control actions in the first decade of 21st century, UBIBM was proved to be the most successful one in terms of the achieved highest transparency and lowest FUI during the past two decades. Reasons for the achievement and implications to future pollution control are discussed for a more sustainable and balanced improvement in the coastal environment. This research provides a valuable example that satellite remote sensing can play a vital role in the management of coastal ecosystems by providing effective evaluation of pollution control actions.

Short-term changes in algal blooms and phytoplankton community after the passage of Super Typhoon Lekima in a temperate and inner sea (Bohai Sea) in China.

Extensive multi-species harmful algal blooms (HABs) were triggered by Super Typhoon Lekima in Laizhou Bay (Bohai Sea) in August 2019. After conducting two field cruises before and after the typhoon passage, we employed both high-performance liquid chromatography (HPLC)-pigment and microscopic methods to study the changes in the phytoplankton community and biomass. Following the passage of Lekima, the average surface salinity decreased, while dissolved inorganic nitrogen and dissolved silicate concentrations increased in the study area. The phytoplankton abundance and Chl a significantly increased after the typhoon event. Post-typhoon, the highest abundance values of Pseudo-nitzschia spp., Noctiluca scintillans, and Coscinodiscus spp. reached 106 cells/L and those of Bacillaria paxillifera, Ceratium spp., and Gymnodinium catenatum were in the order of 105 cells/L. HPLC-pigment CHEMTAX analysis showed that the biomass (Chl a) of dinoflagellates, diatoms, cryptophytes, chlorophytes, and haptophytes increased significantly after the typhoon. The increase in Chl a concentration was mainly attributable to large-sized phytoplankton, which are mostly diatoms and dinoflagellates. This study highlights that typhoons may cause HABs by introducing large amounts of freshwater and nutrients and change the phytoplankton community in a temperate and inner bay.

Long-term investigation of heavy metal variations in mollusks along the Chinese Bohai Sea.

Biomonitoring is an effective way to assess the effects of pollutants on marine ecosystems. As an important fishing region in China, the Chinese Bohai Sea has been contaminated with heavy metals, posing great risks to seafood safety and human health. Herein, the spatiotemporal variations in the concentrations of seven heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) in 11 species of mollusks (658 samples) collected from the Chinese Bohai Sea were studied during 2006-2016. The concentrations of Cr, As, Cd, and Pb in approximately 41%, 100%, 71%, and 18% of the sampled mollusks exceeded the maximum permissible levels in aquatic products set by China, indicating that the mollusks were contaminated with varied concentrations of heavy metals. Except for slight fluctuations, no significant temporal variations were observed during the sampling period, suggesting a relatively stable status of these metals. Cluster analysis showed that oyster had higher bioaccumulation potential for Zn and Cu, whereas Mactra veneriformis, Rapana venosa, Meretrix meretrix, Chlamys farreri, and Mya arenaria had higher bioaccumulation potentials for Cr, As, Ni, Cd, and Pb, respectively. These findings are useful for biomonitoring and developing guidelines for seafood consumption in coastal regions. Significant relationships were observed between heavy metal concentrations in mollusks and socioeconomic indices (gross domestic product, per capita gross domestic product, and population amount), suggesting the effects of anthropogenic activities on heavy metal contamination. Our study established a good model to evaluate the risks of heavy metals and provided a sound scientific basis for controlling seafood safety in coastal regions.

Temporal and spatial variation, input fluxes and risk assessment of cyclic methylsiloxanes in Rivers-Bohai Sea System.

In the present study, the total concentrations of three cyclic methylsiloxanes (ΣCMSs), including octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6), in surface water and sediment samples of five main rivers draining into the Bohai Sea were in the range of 1.62-1.39 × 103 ng/L and 1.92-1.69 × 103 ng/g dw, respectively. Riverine input had great influence on the coastal distribution of siloxanes in the Bohai Sea. The concentrations of ΣCMSs in coastal sediments farthest away (40-50 Km) from the estuaries were only 4-33% of those close to the estuaries. But surprisingly, compared with those in coastal sediments (1.03-1.44 × 103 ng/g dw), the concentrations of CMSs (1.56-2.67 × 103 ng/g dw) in some deep-sea sediments were higher, and certain positive correlation existed between sediment ΣCMSs in this area with the total petroleum hydrocarbons concentration (R2 = 0.92, p < 0.05) suggested offshore oil exploitation as one important emission source of siloxanes. Overall, calculated based on their sediment concentrations, D4-D6 had negligible ecological risks to the benthic organisms in river-Bohai Sea system, i.e. HQs < 1. However, sediment-accumulation of siloxanes should be paid attention, especially for some deep-sea sediments nearby drilling platforms, where it will take only less than 1 year for D4 to reach its threshold.

Decade-low aerosol levels over the Bohai and Yellow Seas amid the COVID-19 lockdown.

Coronavirus disease 2019 (COVID-19) has crucially influenced anthropogenic activities, which in turn impacts upon the environment. In this study, we investigated the variations on aerosol optical depth (AOD) at 550 nm over the Bohai Sea and Yellow Sea during the COVID-19 lockdown (from February to March in 2020) of China mainland based on Moderate-resolution Imaging Spectroradiometer (MODIS) observation by comparing with historical AOD records (2011-2019). Our results show that with the lockdown implementation, the decade-low AOD levels are achieved in February and March 2020 (0.39 ± 0.18 and 0.37 ± 0.19, respectively), which are 22% and 28% (p < 0.01) lower than the average AOD between 2011 and 2019 (0.50 ± 0.08 and 0.52 ± 0.05, respectively). After the lockdown restrictions were relaxed and industrial production gradually resumed, the AOD in April 2020 rebounded to the historical average level. Besides, compared with historical observations (2011-2019), the AOD temporal variability from February to April 2020 showed different pattern, with the decade-high increase from March to April (+0.11) and decade-low increase from February to March (-0.01). Independent observations and simulation, including fine particulate matter (PM2.5) from ground-based measurements, wind field from Cross-Calibrated Multi-Platform, satellite-derived aerosol type, and back trajectories calculation by Hybird Single Paricle Lagrangian Intergrated Trajectory (HYSPLIT) model, indicated that the above abnormal AOD variation can be attributed to reduction of anthropogenic emissions during the COVID-19 lockdown period. The results of this paper, therefore, indicate that aerosols over the Bohai and Yellow Seas are strongly influenced by human activities, and the public health events such as the epidemic may alter the intensity of human activities and thus the spatio-temporal pattern of aerosol over ocean. With the global spread of the epidemic and the corresponding significant changes in human behavior patterns (restrictions on human activities, etc.), more studies should be carried out in the future about the aerosol variability and its potential impact on the marine environment.

Analysis and Model Comparison of Carbon and Nitrogen Concentrations in Sediments of the Yellow Sea and Bohai Sea by Visible-Near Infrared Spectroscopy.

Visible-near infrared spectroscopy is considered an effective method for rapidly determining total carbon (TC) and total nitrogen (TN) in terrestrial soils. However, reports on measuring them by VNIR in marine sediments are limited. This article provides an analysis and spectral model comparison of TC and TN in marine sediments using VNIR. The best TC and TN spectral models were established when using the least square support vector machine algorithm with a wavelength, which extended from 226 nm to 975 nm. The prediction results of TN have a high coefficient of determination and residual predictive deviation, providing accurate quantitative predictions. The TC spectral model comes with a disadvantage might due to its usual high concentrations of organic carbon. Characteristic wavelength extraction may lead to the loss of identification information for the characteristics of TC and TN, and full wavelength spectrum contains more information helps more to the quantification.

Dynamics of bacterial communities during a seasonal hypoxia at the Bohai Sea: Coupling and response between abundant and rare populations.

Marine bacterial community plays a vital role in the formation of the hypoxia zone in coastal oceans. Yet, their dynamics in the seasonal hypoxia zone of the Bohai Sea (BHS) are barely studied. Here, the 16S rRNA gene-based high-throughput sequencing was used to explore the dynamics of their diversity, structure, and function as well as driving factors during the gradual deoxygenation process in the BHS. Our results evinced that the bacterial community was dominated by Proteobacteria, followed by Bacteroidetes, Firmicutes, Actinobacteria, and Cyanobacteria, etc. The abundant subcommunity dominated in the number of sequences (49%) while the rare subcommunity dominated in the number of species (99.61%). Although abundant subcommunity accounted for most sequences, rare subcommunity possessed higher diversity, richness and their population dramatically changed (higher turnover) during the hypoxia transition. Further, co-occurrence network analysis proved the vital role of rare subcommunity in the process of community assembly. Additionally, beta diversity partition revealed that both subcommunities possessed a higher turnover component than nestedness and/or richness component, implying species replacement could explain a considerable percentage of community variation. This variation might be governed by both environmental selection and stochastic processes, and further, it influenced the nitrogen cycle (PICRUSt-based prediction) of the hypoxia zone. Overall, this study provides insight into the spatial-temporal heterogeneity of bacterial and their vital role in biogeochemical cycles in the hypoxia zone of the BHS. These findings will extend our horizons about the stabilization mechanism, feedback regulation, and interactive model inside the bacterial community under oxygen-depleted ecosystems.

Decabromodiphenyl Ether versus Decabromodiphenyl Ethane: Source, Fate, and Influencing Factors in a Coastal Sea Nearing Source Region.

Both decabromodiphenyl ether (BDE 209) and decabromodiphenyl ethane (DBDPE) are still produced in large quantities in China, especially in the Shandong Province closed to the Bohai Sea (BS). This study conducted a comprehensive investigation of the distribution and budget of brominated flame retardants (BFRs) in the BS. BDE 209 was the predominant BFR in most of the investigated rivers flowing into the BS, although DBDPE exceeded BDE 209 in certain rivers as a result of the replacement of BDE 209 with DBDPE in North China. The spatial distributions of BFRs in the rivers were controlled by the proximity of the BFR manufacturing base and the extent of urbanization. BFRs' spatial distribution in the BS was influenced by a combination of land-based pollution sources, environmental parameters (e.g., suspended particulate matter, particulate organic carbon, and particulate black carbon), and hydrodynamic conditions. The spatial variation trend of BDE 209/DBDPE ratios in various environmental media provided useful information. Vertically, the BDE 209/DBDPE ratio decreased from the seawater surface layer to the sediment, indicating their differential transport in the BS. A multi-box mass balance model and analysis of BDE 209 showed that degradation was the primary sink of BFRs in seawater (∼68%) and surface sediment (∼72%) in the BS.

Potential threat of SARS-CoV-2 in coastal waters.

A novel coronavirus (SARS-CoV-2) has caused more than 150 million confirmed infections worldwide, while it is not clear whether it affects the coastal waters. This paper proposed a biophysical model based on 16 scenarios with different virus half-life parameters to assess potential viral contamination from 25 municipal sewage outfalls into the Bohai Sea. Viral concentration maps showing spatial and temporal changes are provided based on a biophysical model under multiple scenarios. Results demonstrate that adjacent sea areas can become exposed to SARS-CoV-2 via water-borne transport from outfalls, with a higher risk in winter, because SARS-CoV-2 can be highly stable at low temperature. As coastal waters are the ultimate sink for wastewater and the epidemic will last for long time, this work is of great importance to raise awareness, identify vulnerable areas for marine mammals, and avoid the risk of exposure of tourists at bathing beach.

Microplastic Pollution in Nearshore Sediment from the Bohai Sea Coastline.

Microplastics are recognized as an emerging global issue in marine environments. In this study, microplastic pollution in subtidal sediments from nine typical stations in the Bohai Sea was investigated. The mean concentration was 458.6 ± 150.0 items/kg of dry weight, varying from 280.0 to 773.4 items/kg. All of the microplastics were categorized according to shape, color and size. Among these microplastics, fiber (77.1%), white/blue/black (85.0%) and small microplastics (< 1500 µm) (82.9%) were the most abundant types. Seven polymer types were identified and were, in decreasing order of abundance, rayon > PE > PS > PP > PET > ABS > PA. The microplastics abundance was of the same order of magnitude as that of other similar areas. The microplastic characteristics suggest that tourism, maritime activities and sewage discharge are possible sources. Our results provide useful information for performing an environmental risk assessment of microplastic pollution in this area.

Geosynchronous Satellite GF-4 Observations of Chlorophyll-a Distribution Details in the Bohai Sea, China.

We analyzed the distribution of chlorophyll-a (Chla) in the Bohai Sea area based on data from the geosynchronous orbit optical satellite Gaofen-4 (GF-4), which was launched in 2015, carrying a panchromatic multispectral sensor (PMS). This is the first time the geosynchronous orbit optical satellite GF-4 remote-sensing data has been used in China to detect the Chla change details in the Bohai Sea. A new GF-4 retrieved model was established based on the relationship between in situ Chla value and the reflectance combination of 2 and 4 bands, with the R2 of 0.9685 and the total average relative error of 37.42%. Twenty PMS images obtained from 2017 to 2019 were applied to analyze Chla in Bohai sea. The results show that: (1) the new built Chla inversion model PMS-1 for the GF-4 PMS sensor can extract Chla distribution details in the Bohai Sea well. The high Chla content in the Bohai Sea is mainly located in coastal areas, such as the top of Laizhou Bay, Bohai Bay and Liaodong Bay, with the value being around 13 µg/L. The concentration of Chla in the Bohai Strait and northern Yellow Sea is relatively low with the value being around 5 µg/L. (2). Taking full advantage of the continuous observation of geostationary orbit satellite, GF-4 with a high-resolution sensor PMS of 50 m can effectively detect short-term change (changes within 10 min) in Chla concentration. The changes mainly appear at the southwest and northeast costal area as well as in the center of Bohai Sea with the change value of around 3 µg/L. (3) The change of Chla concentration in the Bohai sea is related to the environmental factors such as seawater temperature, salinity, illumination and nutrient salts, as well as the dynamic factors such as wind, flow field and tidal current.

Corallincola luteus sp. nov., a marine bacterium isolated from surface sediment of Bohai Sea of China.

A novel Gram-stain negative, strictly aerobic, rod-shaped motile bacterium with a single flagellum, designated strain DASS28T, was isolated from surface sediment of Bohai Sea in China. Growth occurred in the presence of 1.0-4.0% NaCl (w/v, optimum 2.0%), at 10-37 °C (optimum 20 °C) on the Marine agar 2216E and pH 6.0-10.0 (optimum pH 8.0). The major fatty acids (> 10% of total fatty acids) were summed feature 3 (C16:1ω7c and/or iso-C15:0 2-OH), C16:0 and C18:1ω7c. The polar lipids were phosphatidylglycerol, phosphatidylethanolamine, an unidentified phospholipid, an unidentified aminolipid and two unidentified polar lipids. The major respiratory quinone was ubiquinone-8 (Q-8). The genomic DNA G + C content calculated from the genome sequence of strain DASS28T was 48.8 mol%. Phylogenetic analysis based on 16S rRNA gene sequence indicated that strain DASS28T belongs to the genus Corallincola and shows high 16S rRNA gene sequence similarity of 96.7% to Corallincola platygyrae JLT 2006T (= JCM18796T = CGMCC 1.10992T). On the basis of the polyphasic evidence, strain DASS28T is considered to represent a novel species in the genus Corallincola, for which the name Corallincola luteus sp. nov. is proposed. The type strain is DASS28T (= KCTC 52376T = MCCC 1K03208T).

Presence and environmental risk assessment of selected antibiotics in coastal water adjacent to mariculture areas in the Bohai Sea.

The presence and concentrations of 25 antibiotics in Dalian coastal water of the Bohai Sea were investigated using solid-phase extraction coupled with high-performance liquid chromatography tandem mass spectrometry. Results showed that antibiotics were widely detected in this region with total concentration ranging from 22.6 to 2402.4 ng/L. Enrofloxacin and trimethoprim were 100% detected followed by sulfamethoxazole with a detection rate of 90.9%. No significant correlations were found between antibiotics concentrations and sample parameters such as dissolved organic carbon, salinity, and distance from the coast, suggesting that concentrations and distributions of the antibiotics in this area were source-dependent. Antibiotic concentration in the sample from an offshore cage-culture area was the highest. Based on composition profiles, mariculture was supposed to be an important source of antibiotics. According to the assessment, individual antibiotic posed low to moderate risk, while the antibiotic mixture presented high risk. Enrofloxacin, clarithromycin and sulfamethoxazole, the top three contributors to the mixture risk quotients for each site, need priority control in this area. Besides, levels of enrofloxacin were high enough to exert a selective pressure on bacteria that may lead to an increase in the prevalence of resistance.

Vertical distributions of mercury in marine sediment cores from central and southern part of Bohai Sea, China.

In past decades, China has experienced substantial economic growth and industrialization. However, the effects of vast development of China on Hg input to the nearby oceans are still unclear. In this study, four representative 210Pb-dated sediment cores were collected in the central and southern part of Bohai sea to investigate vertical changes of Hg contents and explore the relationship between the Hg deposition and pollution history in this region utilizing a large amount of information available. The results indicated that Hg median concentrations of sediment core B62, B66, JQ17 and HZ24 were 0.043 mg/kg, 0.054 mg/kg, 0.033 mg/kg and 0.018 mg/kg respectively, among which, B66 in Yellow river estuary and B62 in central part of Bohai Sea had higher concentrations and HZ24 in Bohai Strait had a lower concentration. 210Pb profile appeared as a three segments model in the core B62, but as many steps of decay with depth in B66. For HZ24, 210Pb activity only fluctuated with depth without any discernible trend. Sedimentary rates of these cores decreased as follows: B66＞B62＞JQ17＞HZ24. Vertical distributions of Hg concentrations in sediment cores were totally different from each other. Hg concentrations in sediment core B62 experienced an initial fluctuation followed by a decreasing trend, while sediment core HZ24 almost showed the uniform decreasing trends from the surface to the bottom. There were three segments of variation in sediment cores JQ17: initial fluctuation followed by an obviously decreasing tendency and then a converted variation from surface to bottom. Hg contents changes in core B62 might reflect the additive effects from atmospheric deposition at a larger scale and the river-delivered sediment accumulation, while Hg vertical changes in B66 mainly had a close relationship with the input of Yellow river. The converted variation at the bottom section in sediment cores JQ17 was inferred to have some relationship with the Chengbei platform construction in the corresponding periods.

Distribution of dissolved gaseous mercury (DGM) and its controlling factors in the Yellow Sea and Bohai Sea.

Elemental mercury (Hg0) is the major form of mercury (Hg) emitted into the environment via anthropogenic activities, resulting in the distribution of Hg worldwide via atmospheric transport. Hg0 in oceans plays an important role in global Hg cycling, mainly by affecting the oceanic-atmospheric exchange of Hg. Due to the large amounts of Hg that are released into Chinese coastal seas from rivers and other sources, Chinese coastal seas are thought to be important sources of Hg in open oceans and in the atmosphere. There have been some studies on the distribution of dissolved gaseous mercury (DGM) in Chinses coastal seas and their controlling factors. However, most of these studies were focused on the surface seawater. There is still a lack of comprehensive study on the DGM through the entire water column in Chinese coastal seas. In this study, two cruises were conducted in August 2017 and in December 2017 to January 2018 to identify the distribution of DGM and its controlling factors in the Yellow Sea (YS) and the Bohai Sea (BS). The concentrations of DGM were higher in summer (167.5 ±â€¯121.4 pg/L) than in winter (41.5 ±â€¯25.5 pg/L), reflecting a significant seasonal variation in DGM. DGM concentrations in the BS and the YS were higher than in open oceans and lower than in some coastal regions. DGM concentrations were generally highest in the BS, followed by the northern YS and the southern YS in summer, whereas the reverse trend was observed in winter. DGM in seawater presented a complicated spatial distribution pattern, with high DGM concentration areas present both nearshore and offshore areas. This result indicates that both terrestrial input and in situ production may play important roles in controlling the DGM distribution. Correlation and multiple regression analyses suggested that temperature (T) and wind speed may be important factors affecting the seasonal variation in DGM in the YS and the BS, and reactive Hg (RHg), dissolved Hg (DHg), dissolved oxygen (DO) and suspended particulate matter (SPM) play important roles in controlling the spatial distribution of DGM.

Distribution of perfluorinated alkyl substances in marine shellfish along the Chinese Bohai Sea coast.

Perfluorinated alkyl substances (PFASs) are emerging persistent organic pollutants, which pose a threat to human health primarily by dietary exposure, especially through seafood. Bohai Sea (a semi-closed sea located north of China) is an important shellfish aquaculture area that is possibly highly-polluted with PFASs. In this study, we first evaluated contamination by PFASs in a total of 230 samples of marine shellfish from the Bohai Sea. Samples included five important shellfish species, collected from important aquaculture spots distributed around the Bohai Sea. Samples were analyzed by an ultra-fast liquid chromatography-tandem mass spectrometry method, which could simultaneously detect 23 PFASs in shellfish. Our research verified that PFASs have become a threat to the safety of shellfish products in this area. Furthermore, contamination by PFASs in shellfish changed depending on the components of PFASs, the species of shellfish, and the sampling sites. Many of the 23 target compounds contributed to the high detection ratio (>50%) as follows: perfluorooctanoic acid (PFOA) > perfluorononanoic acid > perfluorodecanesulfonic acid > perfluorooctanesulfonic acid (PFOS). Compared with other dominant components, PFOA not only had the highest detection percentage in shellfish samples (98.3%), but its detection level contributed to 87.2% of total PFASs concentrations, indicating that PFOA is the major threat to the safety of shellfish products. The highest level of PFAS was found in clams (62.5 ng g-1 wet weight of PFOA). The concentration of total PFAS in different shellfish species showed the following trend: clams > mussels > scallops > whelks > oysters. The maximum concentration of total PFAS or PFOA was found in Shouguang. The total concentration of PFOS and its precursor were highest in Cangzhou, possibly due to local industrial activities. The results presented in this paper provide new data on the contamination of marine shellfish along the Bohai Sea coasts in China, and constitute a reference for future monitoring of contamination by emerging contaminants in Bohai coast.

Marinobacter bohaiensis sp. nov., a moderate halophile isolated from benthic sediment of the Bohai Sea.

A Gram-stain-negative, motile, aerobic and rod-shaped bacterial strain, designated T17T, was isolated from benthic sediment sampled at Jiaozhou Bay, Bohai Sea, China, and its taxonomic position was investigated. The 16S rRNA gene sequence of strain T17T exhibited the highest similarity values to those of the type strain Marinobacter lacisalsi FP2.5 (96.2 %) and Marinobacter koreensis DD-M3T (96.2 %). Strain T17T grew optimally at 35 °C, pH 7.0-8.0 and in the presence of 6.0-10.0 % (w/v) NaCl. The predominant ubiquinone in strain T17T was identified as Q-9. The major fatty acids of strain T17T were C12 : 0, C16 : 0 and C16 : 0 10-CH3. The major polar lipids of strain T17T were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidglycerol, an unidentified aminolipid and an unidentified phospholipid. The DNA G+C content of strain T17T was 63.0 mol%. The draft genome sequence of strain T17T includes 4 755 891 bp in total (N50=2 856 325 bp) with a medium read coverage of 100.0x and 11 scaffolds. In silico DNA-DNA hybridization with the three type strains showed 20.3, 19.7 and 19.9 % relatedness to Marinobacter santoriniensis NKSG1T, Marinobacter segnicrescens SS11B1-4T and Marinobacter daqiaonensis CGMCC 1.9167T, respectively. On the basis of the phenotypic, phylogenetic, genomic and chemotaxonomic properties, strain T17T is considered to represent a novel species within the genus Marinobacter, for which the name Marinobacterbohaiensis sp. nov. is proposed. The type strain is T17T (=KCTC 52710T=MCCC 1K03282T).