Coastal Waters Of Qinhuangdao Research Articles

Retrieval and spatiotemporal variation of total suspended matter concentration using a MODIS-derived hue angle in the coastal waters of Qinhuangdao, China

Retrieval and spatiotemporal variation of total suspended matter concentration using a MODIS-derived hue angle in the coastal waters of Qinhuangdao, China

Seasonal and anthropogenic influences on bacterioplankton communities: ecological impacts in the coastal waters of Qinhuangdao, Northern China.

Marine bacterioplankton play a crucial role in the cycling of carbon, nitrogen, and phosphorus in coastal waters. And the impact of environmental factors on bacterial community structure and ecological functions is a dynamic ongoing process. To systematically assess the relationship between environmental changes and bacterioplankton communities, this study delved into the spatiotemporal distribution and predicted metabolic characteristics of bacterioplankton communities at two estuarine beaches in Northern China. Coastal water samples were collected regularly in spring, summer, and autumn, and were analyzed in combination with environmental parameters and bacterioplankton community. Results indicated significant seasonal variations in bacterioplankton communities as Bacteroidetes and Actinobacteria were enriched in spring, Cyanobacteria proliferated in summer. While Pseudomonadota and microorganisms associated with organic matter decomposition prevailed in autumn, closely linked to seasonal variation of temperature, light and nutrients such as nitrogen and phosphorus. Particularly in summer, increased tourism activities and riverine inputs significantly raised nutrient levels, promoting the proliferation of specific photosynthetic microorganisms, potentially linked to the occurrence of phytoplankton blooms. Spearman correlation analysis further revealed significant correlations between bacterioplankton communities and environmental factors such as salinity, chlorophyll a, and total dissolved phosphorus (TDP). Additionally, the metabolic features of the spring bacterioplankton community were primarily characterized by enhanced activities in the prokaryotic carbon fixation pathways, reflecting rapid adaptation to increased light and temperature, as well as significant contributions to primary productivity. In summer, the bacterial communities were involved in enhanced glycolysis and biosynthetic pathways, reflecting high energy metabolism and responses to increased light and biomass. In autumn, microorganisms adapted to the accelerated decomposition of organic matter and the seasonal changes in environmental conditions through enhanced amino acid metabolism and material cycling pathways. These findings demonstrate that seasonal changes and human activities significantly influence the structure and function of bacterioplankton communities by altering nutrient dynamics and physical environmental conditions. This study provides important scientific insights into the marine biological responses under global change.

Succession of phytoplankton communities from macro-scale to micro-scale in coastal waters of Qinhuangdao, China

The coastal area of Qinhuangdao, particularly the Changli Gold Coast Nature Reserve, is experiencing ecological degradation and frequent Harmful Algal Blooms (HABs). This study focuses on the changing phytoplankton communities in these coastal waters, examining them from both a macroscopic and microscopic perspective. Utilizing microscopy, molecular techniques, and pigment analysis, seasonal shifts were observed, with diatoms predominating in June and July, and dinoflagellates in August. Our morphological examination enabled the classification of 89 species into four distinct groups. The species Paralia sulcata and Pseudo-nitzschia pungens were most abundant in early summer, while Tripos furca, a dinoflagellate, dominated in August. This indicates a shift in phytoplankton communities due to environmental factors such as phosphate deficiency and high nitrogen/phosphorus ratios. Additionally, the study notes the impact of reduced river runoff and reintroduction of scallop farming contributing to nitrogen-rich eutrophication in August. Molecular analysis revealed a disparity between microscopic observations and the prevalence of Teleaulax blooms during early summer. Elevated concentrations of TN and DOC, coupled with limited water exchange, emerged as primary factors contributing to their occurrence. Sediment analysis revealed a high diversity but low abundance of dinoflagellates in August, with a significant presence of harmful species. The study highlights the shift from diatoms to harmful dinoflagellate populations, exacerbated by eutrophication and pollution, leading to HABs. These findings provide a theoretical basis for understanding toxic algal blooms and are crucial for environmental agencies in developing strategies to protect and sustainably develop offshore environments.

Molecular identification and nutritional analysis of green tide algae in the coastal waters of Qinhuangdao, China

Since 2015, the coastal waters of Qinhuangdao in Hebei province, China have experienced green tide disasters for consecutive years. Resource utilization is an important measure for preventing and controlling green tides. To comprehensively utilize green tide algae, this study first identified theses green tide algae and then assessed their nutritional value. Based on analysis of the internal transcribed spacer (ITS), 5S spacer regions (5S) and the mitochondrial cytochrome C oxidase I (COI), the dominant species were Ulva prolifera, Bryopsis plumose, Ulva australis, and Gracilariopsis lemaneiformis. The basic nutritional components, i.e., chlorophyll, amino acids, mineral elements, and heavy metal contents, of these four algae were measured and analyzed, and the four dominant species were shown to be high-nutrient-value marine foods with complete and reasonable protein, amino acid, and mineral compositions. This indicates that there is value in further research and development towards their utilization as nutrient sources. This study provides a basis for the comprehensive development and utilization of green tide algae resources in the coastal waters of Qinhuangdao.

Occurrence and spatial distribution of paralytic shellfish toxins in seawater and marine organisms in the coastal waters of Qinhuangdao, China

In recent years, paralytic shellfish toxins (PSTs) have been prevalent in the coastal waters of Qinhuangdao, the west coast of the Bohai Sea, China. The content of PSTs in shellfish often exceeded the regulatory limit of 800 μg STX equivalent (eq.) kg−1, which poses a serious threat to human health. In this study, two surveys were conducted in May 2021 and May 2022 to investigate the distribution of PSTs in the coastal waters of Qinhuangdao. Seawater, surface sediment, phytoplankton, zooplankton, and other marine organism samples were collected, and the composition and concentration of PSTs were analyzed by liquid chromatography with tandem mass spectrometry (LC-MS/MS). Results showed that multiple PST components were detected in all seawater samples collected at different depths, mainly including GTX1/4, GTX2/3, dcGTX2, STX and C1/2, and the highest concentration of PSTs reached 244 ng STX eq. L−1. The sediment samples also contained low levels of C1/2 and GTX2/3. Trace amounts of C1/2 and GTX1-4 were detected in phytoplankton and zooplankton. Moreover, all bivalve shellfish samples were found to contain PSTs, and the scallop Azumapecten farreri and the ark clam Anadara kagoshimensis showed relatively high concentrations of 607 and 497 μg STX eq. kg−1, respectively. In addition, low levels of PSTs were also found in some non-traditional PST vectors, including whelk Rapana venosa, octopus Amphioctopus ovulum, goby Ctenotrypauchen chinensis, and greenling Hexagrammos agrammus. Results of this study improve the understanding of the distribution of PSTs in seawater and marine organisms and the potential risk of persistent PSTs in seawater to marine ecosystems and human health.

Evaluation of seven atmospheric correction algorithms for OLCI images over the coastal waters of Qinhuangdao in Bohai Sea

Atmospheric correction (AC) over coastal waters is always critical in ocean color remote sensing. The performance of the AC algorithms determines the reliability of the retrieval of the water-leaving radiance and subsequent bio-optical parameters. In this study, the seven AC algorithms for the Ocean and Land Color Instrument (OLCI) were evaluated with an in situ dataset over the coastal waters of Qinhuangdao in the Bohai Sea, China: the Baseline Atmospheric Correction (BAC), the Case 2 Regional Coast Color Atmospheric Correction (C2RCC) and its alternative version (C2RCC-AltNets), the Management Unit Mathematical Models (MUMM), the polynomial-based algorithm applied to MERIS (POLYMER), the image correction for atmospheric effects (iCOR), and ACOLITE for Dark Spectrum Fitting (ACOLITE-DSF). For OLCI-derived remote sensing reflectance, Rrs(λ), where λ is light wavelength, on the respective match-ups, all algorithms except ACOLITE-DSF had higher accuracy in the wavelength range from 490 nm to 560 nm, with the absolute percentage difference (APD) < 43%. On the common match-ups of all algorithms, the performance of seven AC algorithms was better than that of the respective match-ups. POLYMER obtained the best performance in visible bands, with APD less than 24.04% and 17.13% for respective and common match-ups, respectively. In terms of blue/green band ratios, Rrs(490)/Rrs(560) obtained by all algorithms except C2RCC performed better than Rrs(442)/Rrs(560). POLYMER performed best in blue/green band ratios, with the APD of 10.38% and 5.51% for Rrs(442)/Rrs(560) and Rrs(490)/Rrs(560), respectively. Using a scoring scheme based on all statistical parameters, POLYMER scored the highest. ACOLITE-DSF represented the worst accuracy for all evaluations over our in situ dataset.

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.

Formation mechanism and environmental drivers of Alexandrium catenella bloom events in the coastal waters of Qinhuangdao, China

In the last 5 years, paralytic shellfish toxins (PSTs) have been recurrently detected in mollusks farmed in the mussel culture area of Qinhuangdao city, along with the occurrence of toxic outbreaks linked to dinoflagellate species of the Alexandrium genus. To understand the formation mechanism and variation of these events, continuous and comprehensive PSTs monitoring was carried out between 2017 and 2020. Through the analysis of both phytoplankton and cysts via light microscopy and quantitative polymerase chain reaction, it was shown that Alexandrium catenella was responsible for the production of PSTs, which consisted mainly of gonyautoxins 1,4 (GTX1/4, 87%) and GTX2/3 (13%). During bloom events in 2019, mussels accumulated the highest PSTs value (929 μg STX di-HCl eq·kg−1) in conjunction with the peak of cell abundances, and toxin profiles were consistent with high distributions of GTX1/4, GTX2/3, and Neosaxitoxin. Toxin metabolites vary in different substances and mainly transferred to a stable proportion of α-epimer: β-epimers 3:1. The environmental drivers of Alexandrium blooms included the continuous rise of water temperature (>4 °C) and calm weather with low wind speed and no significant precipitation. By comparing toxin profiles and method sensitivity, it was found that dissolved toxins in seawater are more useful for early warning. These results have important implications for the effective monitoring and management of paralytic shellfish poisoning outbreaks.

Tempo-spatial distribution and species composition of green algae micro-propagules in the coastal waters of Qinhuangdao after green tides bloom in 2020

Since 2015, the coastal waters of Qinhuangdao have been experiencing bloomed of green tides from April to September, with Jinmenghaiwan bath being the main affected area. Previous studies have shown that micro-propagules play an important role in the formation of green tides. In this study, we aimed to assess the temporal and spatial distribution of green algae micro-propagules in the coastal waters of Qinhuangdao after the green tides bloom in 2020. We found that the number of green algae micro-propagules in Jinmenghaiwan bath was significantly higher than that of the other surveyed areas. In addition, these micro-propagules of green algae presented a distribution trend of “high near the shore and low away from the shore” pattern. Compared to the period from October 2016 to April 2017, both the number of green algae micro-propagules and the proportion of Ulva prolifera micro-propagules in the coastal waters of Jinmenghaiwan bath decreased considerably in the period from October 2020 to April 2021. This may also be the reason why the green tides scale in 2021 was significantly lower than that in 2017. The results of this study will provide a theoretical basis for early warning and control of green tides in Qinhuangdao.

A Simple Model for a Fast Forewarning System of Brown Tide in the Coastal Waters of Qinhuangdao in the Bohai Sea, China

Qinhuangdao, a famous coastal resort city in northeastern China, has been affected by the rapid growth of harmful algae. The brown tide induced by Aureococcus anophagefferens (A. anophagefferens) first occurred along Qinhuangdao’s coastline in 2009, and it then developed into a harmful alga for the Bohai Sea. Based on MIKE 21, we construct a 2D coupled hydrodynamic and transport model to study the variation and distribution of total nitrogen (TN), and establish the relationship between A. anophagefferens, dissolved organic nitrogen (DON), and TN to provide a fast forewarning system for brown tide in Qinhuangdao. This model considers the decay, diffusion, and settling of TN, and the model results are in good agreement with the measured tidal level, current, and TN, indicating that the model is capable of capturing the observed TN distribution during the brown tide period. The transfer function relating TN to A. anophagefferens leads to a reliable fast forewarning and monitoring system. Moreover, the transferred A. anophagefferens cell density can be used to forecast the regional risk level of brown tide with a specific color indicator. The implementation of national policy relating to marine ecosystems decreases the nearshore concentration of N, P, and other nutrients, and therefore decreases harmful algal blooms. The fast routine assessment of brown tide by the present warning system provides robust guidance for the government to take action.

The dinoflagellate Alexandrium catenella producing only carbamate toxins may account for the seafood poisonings in Qinhuangdao, China

An outbreak of paralytic shellfish poisoning, recorded in April 2016 in Qinhuangdao China, was suspected to be caused by a toxic species in genus Alexandrium. Shortly after the poisoning outbreak, shellfish and net-concentrated phytoplankton samples were collected from the Bohai Sea, and analysed using high performance liquid chromatography coupled with fluorescence detection. Paralytic shellfish toxins (PSTs) were detected in both phytoplankton and shellfish samples, with similar toxin profiles dominated by carbamate toxins. High throughput sequencing data for phytoplankton samples collected previously in the coastal waters of Qinhuangdao were then analysed, and 8 operational taxonomic units (OTUs) were assigned to Alexandrium affine, A. andersonii/A. ostenfeldii, A. catenella, A. fraterculus, A. hiranoi/A. pseudogonyaulax, A. margalefii, A. pacificum and A. pohangense, among which A. catenella, A. pacificum and A. ostenfeldii could be potential producers of PSTs. During a cruise in 2019, three isolates of Alexandrium were established by cyst germination, and identified as A. catenella based on the sequences of the 28S ribosomal RNA gene (28S rDNA) D1−D2 region. Interestingly, all the three strains had the same toxin profile consisting of gonyautoxins 1, 3, 4 (GTX1, 3, 4) and neosaxitoxin (NEO). The toxin profile is similar to those of phytoplankton samples collected previously in the coastal waters of Qinhuangdao, but remarkably different from the general toxin profile of A. catenella dominated by N-sulfocarbamoyl toxins C1−2 in the Bohai Sea and the Yellow Sea. The results suggest that A. catenella is most likely to be the causative species of the poisoning outbreak in Qinhuangdao. As far as we know, this is the first report of A. catenella in the Bohai Sea producing PSTs dominated by high potent gonyautoxins GTX1−4. Occurrence of the highly toxic A. catenella will increase the risk of paralytic shellfish poisoning, which necessitates in-depth mechanism studies and increasing monitoring efforts.

Distribution and source identification of nitrogen and phosphorus in aerosols in the Qinhuangdao coast, north China

Abstract Nitrogen and phosphorus in aerosols is an important source of nutrients in the coastal waters. To study all forms of composition and potential source of nitrogen and phosphorus in atmospheric particulates in the coastal waters of Qinhuangdao, 135 atmospheric aerosol samples were collected from August 2015 to August 2016. The result showed that the nitrogen in aerosols in the Qinhuangdao coastal area was more soluble (accounting for 91.7%), while phosphorus was more insoluble (62.3%). The same seasonal variation of nitrogen and phosphorus components was discovered, with the highest concentration in winter and the lowest in summer. Frequent dust and haze weather processes have a significant impact on the nitrogen and phosphorus species in aerosols. The concentrations of soluble nitrogen and phosphorus increased more significantly in haze days, while insoluble nitrogen and phosphorus increased more significantly in dust days. Both weather processes may aggravate the phosphorus limitation in the coastal waters of Qinhuangdao. Quantitative analysis of potential sources area indicated that Beijing–Tianjin–Hebei, Mongolia, Inner Mongolia contributed the most to the atmospheric nitrogen and phosphorus in Qinhuangdao coastal area. The total contribution of these three regions to atmospheric nitrogen and phosphorus pollution of Qinhuangdao were about 70%, which indicated that most of the atmospheric nitrogen and phosphorus in Qinhuangdao offshore come from the atmospheric pollutant transport channel in the northwest.

Impact of Sea Ice on the Hydrodynamics and Suspended Sediment Concentration in the Coastal Waters of Qinhuangdao, China

The influence of sea ice on the hydrodynamics, sediment resuspension, and suspended sediment concentration (SSC) in the coastal area of Qinhuangdao was systematically investigated using 45-day in situ measurements at two stations (with ice at station M1 and without ice at station M2) in the Bohai Sea in the winter of 2018. It was found that the daily fluctuations of temperature and salinity at M1 are more significant than those at M2. During a typical seawater icing event on January 28, the temperature and salinity of the bottom water at M1 were decreased by 1.77 °C and increased by 0.4 psu, respectively. Moreover, due to the shielding effect of the sea ice, the residual current was much less affected by the wind at M1 than at M2. For the vertical distribution of current velocity, it changed from a traditional logarithmic type under ice-free conditions to parabolic type under ice-covered conditions due to the larger drag coefficient of the water body on the solid ice surface. For the SSC and turbidity at the bottom layer, the average values were 4.9 μL/L and 8.6 NTU at M1, respectively, approximately half of those at M2. The smaller SSC and turbidity at M1 can be attributed to the lower near-bottom turbulent kinetic energy (TKE). At M2, however, the larger SSC is closely related to the strong wind forcing, which could induce higher TKE without sea ice cover, and hence stronger turbulent resuspension. The seabed sediment analysis results showed that in the study area, fine sand is most likely to resuspend, while cohesive particles would resuspend only under strong hydrodynamic conditions.

Development of a sensitive qPCR method for the detection of pelagophyte Aureococcus anophagefferens

AbstractBrown tides of pelagophyte Aureococcus anophagefferens have been recorded in the coastal waters of Qinhuangdao in the Bohai Sea (BS) since 2009. Current understandings on the dynamics and mechanisms of brown tides in the BS, however, are still quite limited due to the lack of accurate methods for detecting low‐abundance of A. anophagefferens cells. In this study, a Taqman qPCR method was developed, which targeted 28S rDNA D1‐D2 domain of A. anophagefferens. The specificity of the qPCR method was tested using 25 strains of microalgae commonly present in the coastal waters, and the targeted species A. anophagefferens was the only species that had reliable positive signal. The method was highly sensitive and reproducible, and the lower detection limit could reach 0.3 cells of A. anophagefferens. A calibration curve was established for A. anophagefferens using the DNA template extracted from different number of cells, and the lower and upper limits of detection for the qPCR assay is 0.3 cells and 1.2 × 105 cells, respectively. A high recovery rate ranged from 96.5% to 107% was achieved for A. anophagefferens at different cell densities. The qPCR assay has been successfully applied to the study on spatial and temporal variations of A. anophagefferens in the coastal waters of Qinhuangdao in 2014.

Amplicon-Based Illumina Sequencing and Quantitative PCR Reveals Nanoplankton Diversity and Biomass in Surface Water of Qinhuangdao Coastal Area, China

Aureococcus anophagefferens caused brown tides for three consecutive years from2009 to2011 in the coastal waters of Qinhuangdao, China, with numerous, widespread ecological and economic impact on ecosystems. To understand the population dynamics of nanoplankton during the brown tides, sequences of the V9 region of the 18S rDNA gene, used as a marker, were analyzed by Illumina sequencing to assess nanoplankton biomass, and real-time fluorescence quantitative PCR was performed to analyze spatial variation in the 18S rDNA copy concentrations of nanoplankton off the Qinhuangdao coast in July,2011. The results showed that A. anophagefferens and Minutocellus polymorphus were the dominant species in the local phytoplankton community during the brown tide in July2011. The highest 18S rDNA copy concentrations of A. anophagefferens and M. polymorphus were detected at stations SHG and FN, respectively. The central area most strongly affected by the brown tide migrated southward from2011 to2013. Redundancy analysis (RDA) showed that the decreasing NOx concentration might provide suitable nutrient conditions for the A. anophagefferens outbreak. During the brown tide caused by A. anophagefferens, other phytoplankton, such as diatoms, cryptophytes, chlorophytes, dinoflagellates and other flagellates, could co-occur with it. For zooplankton, due to less selective feeding behavior, Amoebozoa was the most abundant zooplankton at station SHG, while Ciliophora was the most abundant zooplankton at other stations for its more selective feeding.

Succession of the Nanoplankton Community during a Brown Tide in a Scallop Culture Area in China

Brown tides caused by Aureococcus anophagefferens have occurred frequently in the coastal waters of Qinhuangdao since 2009. The Changli coast is the area most strongly affected by the brown tides, which result in significant economic losses and serious ecological harm. To understand the effects of brown tides on nanoplankton diversity and biomass, samples were collected from May to July in 2012 at station XKK, which is approximately 0.2 nautical miles off the Changli coast. The V9 region of the 18S rDNA gene was used as a marker and was analyzed by Illumina sequencing to assess the nanoplankton diversity and biomass, and real-time fluorescence quantitative PCR was performed to analyze the temporal variations in the copy concentrations of the 18S rDNA of nanoplankton. The results showed that nanoplankton diversity, as determined by the Shannon index, decreased from May to June and increased in July. Illumina sequencing analysis revealed that the plankton community differed among the samples from May to July, and over this period, the dominant phytoplankton groups changed from pelagophytes to chlorophytes. Sufficient nutrients and low grazing pressure by zooplankton and scallops accelerated the growth of small-celled phytoplankton. A. anophagefferens was the most dominant phytoplankton species, with an 18S rDNA maximum copy concentration detected on 26 June, followed by Micromonas sp. and Bathycoccus prasinos, with maximum copy concentrations observed on 3 July. Ciliophora, Arthropoda and Cercozoa were the dominant taxa of the local zooplankton community. The Ciliophora and Arthropoda biomasses decreased, and the Cercozoa biomass increased when the copy concentration of A. anophagefferens peaked on 26 June. We suspect that A. anophagefferens had a significantly negative effect on the growth of Ciliophora and Arthropoda and could be ingested by Cercozoa to promote its proliferation. The small and low-abundance plankton that are likely missed in microscopic and clone library analyses could be detected using Illumina sequencing and qPCR, which provide an effective method for a comprehensive analysis of the plankton community.

Spatial-temporal variation of Aureococcus anophagefferens blooms in relation to environmental factors in the coastal waters of Qinhuangdao, China

The brown tides occurring in the coastal scallop cultivation area of Qinhuangdao, China, in recent years are caused by Aureococcus anophagefferens and significantly impact the scallop industry and the marine ecosystem in this region. Long-term investigations of phytoplankton and hydrological variables in the Qinhuangdao sea area were conducted in this study to understand the spatial-temporal variations of A. anophagefferens in relation to environmental factors. Samples were collected during twelve cruises from July 2011 to December 2013 and were analyzed for the temperature, salinity, dissolved oxygen (DO), nutrients and phytoplankton pigments. All diagnostic pigments of A. anophagefferens, such as chlorophyll c3 (Chl c3), Chl c2, 19′-butanoyloxyfucoxanthin (But-fuco), fucoxanthin (Fuco), and diadinoxanthin (Diad), were detected in the surface water by using high-performance liquid chromatography (HPLC). The highest concentrations of But-fuco (5.64 μg L−1), Fuco (37.94 μg L−1) and chlorophyll a (Chl a, 17.25 μg L−1) occurred in different seasons and sampling sites. The A. anophagefferens bloom (as indicated by But-fuco) usually expanded from the south to the north of the Qinhuangdao sea area, close to scallop-culturing regions. The bloom unusually starts in May, reaches its peak in June and almost disappears in August, with the temperature ranging from ca. 19 °C to 23 °C. The redundancy analysis (RDA) indicated that relatively high salinity (>29) and low inorganic nutrients were suitable for the development of the A. anophagefferens bloom. The ratios of diagnostic pigments to Chl a were not constant during different cruises and generally obeyed two different linear relationships, thus indicating the co-occurrence of the blooms of A. anophagefferens and other species, such as Minutocellus polymorphus. In summary, our work reports the long-term variation of A. anophagefferens blooms based on diagnostic pigments and environmental controls, which may provide more insights into the formation mechanisms of the brown tide in this region.

Understanding the nitrogen uptake and assimilation of the Chinese strain of Aureococcus anophagefferens (Pelagophyceae)

Brown tides caused by Aureococcus anophagefferens have occurred annually and severely impacted on the local ecology and economy in the coastal waters of Qinhuangdao, China since 2009. The uptake preference, pigment composition and growth responses of the Chinese strain of A. anophagefferens to different nitrogen substrates were studied in the laboratory to better understand its nitrogen (N) strategies and compare the findings with those from the other strains in the U.S.A. Our results indicated that A. anophagefferens had a high absolute uptake rate (ρmax) for NH4+ and low half-saturation constants (Ks) for NO3− and urea. It grew faster on the organic substrates (urea and glutamic acid) than that on the inorganic substrates (NO3− and NH4+). A. anophagefferens had higher contents of cellular pigments for both photosynthesis (chlorophyll a, chlorophyll c2, 19′-butanoyloxyfucoxanthin and fucoxanthin) and photoprotection (β-Carotene and diadinoxanthin) on urea than did on NO3− and NH4+, suggesting a stronger capability for photosynthesis on urea. A. anophagefferens had higher contents of cellular carbon, N and proteins on urea than did on NO3− and NH4+, suggesting a stronger capability for the acclimation and storage of C and N on urea. A. anophagefferens produced more β-carotene rather than chlorophyll a on glutamic acid and thus inhibited photosynthesis and carbon fixation. We found in this study that urea was the best N substrate for the growth of A. anophagefferens. A. anophagefferens might have a competitive advantage over other phytoplankton in waters enriched with DON, particularly with urea.

Relationship between phytoplankton community succession and environmental parameters in Qinhuangdao coastal areas, China: A region with recurrent brown tide outbreaks

The picoplanktonic pelagophyte Aureococcus anophagefferens could trigger harmful algal blooms (HABs) to discolor water in brown, known as brown tide. Since 2009, large-scale brown tides, caused by A. anophagefferens, had been occurred in early summer for three consecutive years in the coastal waters of Qinhuangdao, China and resulted considerable deleterious effects on the scallop mariculture industry. The causes for the occurrence of brown tides were not fully understood. Therefore, we conducted a one-year survey from June 2013 to May 2014 to study the seasonal succession of the phytoplankton community, including A. anophagefferens and its relationship with environmental variables in the area. The results revealed that the population dynamics of the phytoplankton community were significant variation with seasonal succession, in which A. anophagefferens played an important role during the entire year. The trend of the whole diversity index indicated that the community structure became more stable in winter. The results of principle component analysis (PCA) applied to the environmental factors indicated four major seasonal groups in the environmental variables. The water temperature, silicate and total nitrogen were contributed to the environment in summer, autumn and spring, respectively. In addition, a few another environmental factors commonly contributed to the winter waterbody, indicated that the aquatic environment is more complex in the cold season. The result revealed that the phytoplankton community structure and its variation were mainly affected by the hydrological factors, by using the redundancy analysis (RDA) for the relationship between dominant species and the environment. Furthermore, we inferred Chaetoceros decipiens as a potential species for the breakout of harmful algae blooms (HABs) by RDA ordination. We concluded that the key factor for the seasonal variations in the dynamics of phytoplankton community could be the hydrological parameters in Qinghuangdao coastal area. This research may provide more insight into the occurrence mechanism of brown tide.

Significant activities of extracellular enzymes from a brown tide in the coastal waters of Qinhuangdao, China

Brown tides of Aureococcus anophagefferens have occurred annually in the coastal waters of Qinhuangdao since 2009. High levels of dissolved organic matter (DOM) are always measured during bloom periods. Study focusing on the effect of DOM on the occurrences of brown tides in this area is scare by far. To analyze the efficiency of DOM hydrolysis by different groups of microorganisms and the possible influence of DOM on the formation of brown tides, extracellular enzymes such as α, β-glucosidases (α, β-GLUs), leucine aminopeptidase (LAP) and alkaline phosphatase (AP) as well as other environmental parameters were analyzed during a pre-bloom period of A. anophagefferens in June 2014. Dissolved organic nitrogen (DON) and phosphorus (DOP) contributed more than half of the total dissolved nutrient pools. Approximately 60–70% of the enzyme activities were associated with phytoplankton of size >5 μm. The hydrolysis rates of LAP were approximately 5 to 20 fold higher than those of AP and α, β-GLUs. The ratios of β-GLU activities: LAP activities indicated the hydrolysis potential related to proteins rather than polysaccharides. The differences in turnover time among the enzymes suggested that DOP was firstly hydrolyzed and recycled in the water in the early minutes, followed by the hydrolysis of DON and dissolved organic carbon (DOC)(in hours). Results suggest that the hydrolysis of DOM, in particular DOP, might significantly contribute to the occurrences of brown tides in the coastal waters of Qinhuangdao, China.