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To assist the researches of toxic and harmful algae and provide government workers with judgment basis for decision-making related events, we established a biological information management system for toxic and harmful algae in China's offshore to assist relevant research. In this study, Karenia mikimotoi was studied as a typical toxic and harmful algae species, and the basic biological information and biogeographic distribution information of K. mikimotoi were systematically studied and collected. In the part of basic biological information, the name, toxin, and molecular characteristic sequence of K. mikimotoi were sorted out by literature searching and website browsing. Through experimental means, the relevant information of morphological identification, pigment composition, and lipid composition were obtained. In the part of biogeographic distribution information, this study sorted out the information of K. mikimotoi, analyzed the characteristics of its occurrence, and completed the standardized construction of biogeographic distribution information. Through the collation of basic biological information and biogeographic distribution information of K. mikimotoi, the standardization of related information was completed, which provided template and method reference for information collection of other toxic and harmful algae species, which was beneficial to the database analysis and design. [ABSTRACT FROM AUTHOR]

The "harmful algae and algal toxins in coastal waters of China: investigation and database" project (HAATC) is funded (US$2.3 million) by the Ministry of Science and Technology of China for 60 months starting on the 1st Jan 2019. Since the 1990s, national projects and other related work have greatly improved harmful algal bloom (HAB) research in China. However, the existing research on HABs is often limited to specific sea areas or specific algal bloom disasters, which is insufficient for understanding the long-term evolution of HAB occurrence under the influence of intensified human activity and global change. The HAATC project intends to determine the overall distribution of marine harmful microalgae and macroalgae, and marine algal toxins (in phytoplankton and shellfish) through a large-scale investigation in the coastal waters of China and continuous investigation in key sea areas. It also aims to observe biotic and abiotic processes during harmful red tides and green tides, and establish an open database and query platform of HABs in China. The research consortium, led by chief scientist Prof. Tian YAN, includes approximately 100 scientists and students. More than 2 years of work have shown the increased distribution of HAB species (including cysts) and algal toxins in China's coastal waters, the increased occurrence of macroalgae blooms (mainly by Ulva prolifera and Sargassum horneri) in the Southern Yellow Sea, increased amount of causative species being identified due to the use of molecular technologies in taxonomy, and new records of algal toxins such as azaspiracid, cycloimines and neurotoxins β-N-methylamino-l-alanine have been detected, which complicates the research in algal toxins and toxicology. Eventually, the project will provide systematic basic data and techniques for the rapid and accurate identification of harmful algae species to support the research, monitoring, and control of harmful algal blooms, as well as seafood safety management in China. [ABSTRACT FROM AUTHOR]

Cyanobacterial Harmful Algae Blooms (CyanoHABs) in the eutrophic lakes have become a global environmental and ecological problem. In this study, a CNN-LSTM integrated model for predicting the CyanoHABs area was proposed and applied to the prediction of the CyanoHABs area in Taihu Lake. Firstly, the time-series data of the CyanoHABs area in Taihu Lake for 20 years were accurately obtained using MODIS images from 2000 to 2019 based on the FAI method. Then, a principal component analysis was performed on the daily meteorological data for the month before the outbreak of CyanoHABs in Taihu Lake from 2000 to 2019 to determine the meteorological factors closely related to the outbreak of CyanoHABs. Finally, the features of CyanoHABs area and meteorological data were extracted by Convolutional Neural Networks (CNN) model and used as the input of Long Short Term Memory Network (LSTM). An integrated CNN-LSTM model approach was constructed for predicting the CyanoHABs area. The results show that high R 2 (0.91) and low mean relative error (17.42%) verified the validity of the FAI index to extract the CyanoHABs area in Taihu Lake; the meteorological factors closely related to the CyanoHABs outbreak in Taihu Lake are mainly temperature, relative humidity, wind speed, and precipitation; the CNN-LSTM integrated model has better prediction effect for both training and test sets compared with the CNN and LSTM models. This study provides an effective method for predicting temporal changes in the CyanoHABs area and offers new ideas for scientific and effective regulation of inland water safety., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Simultaneous ocean warming and acidification will alter marine ecosystem structure and directly affect marine organisms. The alga Phaeocystis globosa commonly causes harmful algal blooms in coastal areas of eastern China. P. globosa often outcompetes other species due to its heterotypic life cycle, primarily including colonies and various types of solitary cells. However, little is known about the adaptive response of P. globosa to ocean warming and acidification. This study aimed to reveal the global molecular regulatory networks implicated in the response of P. globosa to simultaneous warming and acidification. After exposure to warming and acidification, the phosphatidylinositol (PI) and mitogen-activated protein kinase (MAPK) signaling pathways of P. globosa were activated to regulate other molecular pathways in the cell, while the light harvesting complex (LHC) genes were downregulated to decrease photosynthesis. Exposure to warming and acidification also altered the intracellular energy flow, with more energy allocated to the TCA cycle rather than to the biosynthesis of fatty acids and hemolytic substances. The upregulation of genes associated with glycosaminoglycan (GAG) degradation prevented the accumulation of polysaccharides, which led to a reduction in colony formation. Finally, the upregulation of the Mre11 and Rad50 genes in response to warming and acidification implied an increase in meiosis, which may be used by P. globosa to increase the number of solitary cells. The increase in genetic diversity through sexual reproduction may be a strategy of P. globosa that supports rapid response to complex environments. Thus, the life cycle of P. globosa underwent a transition from colonies to solitary cells in response to warming and acidification, suggesting that this species may be able to rapidly adapt to future climate changes through life cycle transitions. [Display omitted] • Life cycle of Phaeocystis globosa to adapt to ocean warming and acidification. • Energy allocated to biosynthesis of fatty acid and hemolytic substances was decreased. • Meiosis is key to rapid adaptation to climate change. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) and the invasion of smooth cordgrass (Spartina alterniflora) have become important environmental problems in intertidal zones of China, which caused serious damage on the coastal ecological systems. By using S. alterniflora as algaecide, this helps to utilize this invasive plant, in addition, is expected to help to control the expansion of S. alterniflora. The potential of S. alterniflora in HABs mitigation was investigated on controlling Phaeocystis globosa (haptophyceae) and Prorocentrum donghaiense (dinophyceae). The growth of both HABs species was significantly inhibited at high concentrations, and P. globosa was more sensitive than P. donghaiense. Furthermore, the extracts of S. alterniflora reduced the effective quantum yield, photosynthetic efficiency, and relative maximal electron transport rate of both algal species at high concentrations, which implies a disruption on their photosynthetic system. Flavonoids, which were previously known as antialgal chemicals, were found to be abundant in the extracts of S. alterniflora by UPLC-MS detection. Our results revealed that the potential of S. alterniflora as a novel antialgal agent for controlling HABs, simultaneously, resource utilization possibility for the invasive plant S. alterniflora., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Highlights • A new indicator (DCCPI) is proposed for the prediction of harmful algal blooms (HABs). • The DCCPI predicts a HAB using nutrients and environmental data. • The DCCPI yields accurate predictions by using limited amount of data. • HABs are predicted based on the difference between normal and critical DCCPI values. • The date of a HAB is predicted using the data from the previously available date. Abstract Harmful algae blooms (HABs) may occur in lakes and reservoirs, causing serious water quality problems. The occurrence of HABs is related to many water environmental indices. Hence, it is of great importance to develop new indices to predict HABs. In this study, a novel HABs prediction index named DCCPI (Discriminant of Cusp Catastrophe as the Prediction Index) was proposed based on the catastrophe theory. The DCCPI was calibrated and validated using a three-year dataset of observations of algae biomass, nutrients and environmental variables from the WS1 Reservoir in Northern China. The index was trained using the first two years and verified using the third year of observations. The index could accurately predict a HAB every year. The main advantage of this index is its ability to yield accurate predictions without the need for large training datasets. Thus, it can be especially suitable for areas with limited monitoring data. The DCCPI could serve as an effective tool for water managers to ensure the quality of water in lakes and reservoirs. [ABSTRACT FROM AUTHOR]

Ipomoea cairica (L.) Sweet is an invasive plant that cause serious invasion and damage in South China. Phaeocystis globosa is a common harmful algal bloom species on the southeast coast of China. Both species cause great environmental disturbances and serious economic damage to the localregion. This study explored the potential inhibitory effects of I. cairica leaf extracts on P. globosa. The results showed that solitary cells growth was inhibited at extract concentrations higher than 0.25 % (v/v). Although the colony diameter did not change, and the colony number increased rapidly in the first 36 h, we found that cells in the colonies had been damaged using scanning electron microscope and SYTOX-Green staining at 48 h. In addition, the rapid light-response curve of cells treated with extracts decreased, along with down-regulation of photosynthesis-related genes (psbA, psbD, and rbcL), suggesting damage to the photosynthetic system. Finally, the activities of antioxidant enzymes including superoxide dismutase, peroxidase, and catalase increased with increasing treatment time, indicating that cells activate antioxidant enzyme defense systems to alleviate the production of reactive oxygen species (ROS). Increased ROS levels disrupt cell membranes, alter cellular ultrastructures, and ultimately lead to cell death. This study not only achieved the reuse of invasive plant resources, but also demonstrated that I. cairica leaf extract has potential value as an algaecide. • I. cairica extract effectively inhibited the growth of solitary cells and colonies. • I. cairica extract inhibited photosynthesis and the expression of related genes • Elevated ROS levels cause disrupt cell membranes, alter cell surface ultrastructure, and ultimately lead to cell death. [ABSTRACT FROM AUTHOR]

A series of gramine modified montmorillonites (gramine-MMTs) were prepared and characterized by thermogravimetric analysis, X-ray diffraction and zeta potential measurements. These modified clays with various amounts of gramine all exhibited higher removal efficiencies of both Chattonella marina and Alexandrium tamarense than did natural clay. With the augmentation of gramine content in the modified clays, the removal efficiency increased. The 24 h LC50 values of gramine-MMT with 12.68 % of gramine on C. marina and A. tamarense were 9.16 and 10.21 mg L(-1), respectively. These data suggest gramine-MMT might be a promising material to remediate harmful algal blooms.

The fluxes of dissolved nutrients at sediment-water interface were investigated at 4 stations in the HAB area of East China Sea in May 2001 and May 2002. The benthic fluxes of nutrients were determined by incubating the sediment core samples with bottom seawater bubbled with air or nitrogen. The transfer of nutrients was more active under anoxic condition. The fluxes of dissolved nutrients were generally high at the stations close to the coast. The sediment was the source of SiO3(2-), which accounted for 6% of primary production. For DIN and PO4(3-), the sediment was the sink. DIN and PO4(3-) adsorbed by sediment accounted for 5.9% and 67% of the riverine DIN and PO4(3-) inputs, respectively, and the inputs of SiO3(2-) accounted for 7.8%.

The paralytic shellfish poisoning (PSP) toxicity levels of shellfish collected from shellfish growing zones in Zhoushan areas of East China Sea and Shenzhen areas of South China Sea during January-November 2002 were determined with AOAC bioassay method. The results showed that the toxicity levels of shellfish from Zhoushan were very low, and few shellfish samples could be detected the PSP toxicities. The same levels appeared in the shellfish from Shenzhen, but the percentage of shellfish samples contaminated PSP was up to 30%, and the scallop Chalmys nobilis was dominated in the contaminated shellfish species. Analyses on the toxic profiles of digest gland and edible tissue extraction of scallop from Shenzhen showed that a similar suite of toxins presented in the gland and edible tissues. The high potency neoSTX and low potency GTX5 had a high proportions, up to 60.8% and 11.4%, respectively in the tissue, and the high potency GTX1 + 2 and GTX5 were the dominant toxins, up to 38.9% and 20%, respectively in the gland. Most of the toxin were accumulated in ingested gland of scallop, and the toxic content in gland was about 8 folds more than that in the edible tissues.

Abstract  In order to test the use of lectins as a tool for the differentiation of harmful algal species, 13 species and 23 strains of algae were tested with 14 fluorescein isothiocyanate (FITC)-conjugated lectins, and the results examined using flow cytometry (FCM), epifluorescence microscopy (EFM) and spectrofluorometry (SFM). The lectin probes SBA, WGA, GSL I, DBA and PHA-E could distinguish between morphologically similar Gymnodinium-like species, such as Karenia mikimotoi (GMDH01), Takayama pulchellum (TPXM01) and Gymnodinium sp. (GspXM01), by their different binding activities. With the precise quantitative measurements of binding obtained using SFM and FCM, lectins appeared to be useful in distinguishing different strains of the same species. The results also showed that PHA-E could differentiate Alexandrium tamarense (ATDH04) from other strains of this species, and SJA could distinguish A. tamarense (ATMJ02) from other strains of this species (including ATMJ01). Similarly, PNA could identify A. tamarense (ATDH01, 02, 03); UEA I could recognize A. tamarense (ATCI01-JN, ATCI01); and RCA120 could differentiate Alexandrium sp (AspGX01) from strain AspGX02, which was shown to produce different levels of paralytic shellfish poisoning toxin. Lectin probes could also bind these target cells in mixed algal samples. Positive cells identified by FCM were clearer than negative cells thus, in EFM, both GspXM01 and TPXM01 labeled with a WGA lectin probe could be distinguished from target cells of K. mikimotoi, Prorocentrum donghaiense and P. minimum (PMDH01, PMXM01) in mixed algal samples. FCM, EFM and SFM analysis could clearly distinguish lectin-probe-bound cells from negative cells in culture. [ABSTRACT FROM AUTHOR]

• The ciliate communities showed a clear variation among five algal cell concentrations; • Taxonomic breadths maintained at stable levels at concentrations of 102–104 cells ml−1; • The sharp drop in taxonomic breadth was found at the concentration of 105 cells ml−1; • Periphytic ciliates may be used to indicate influence of harmful algae on water quality. Our study focused on ciliates grazing potential against harmful algal blooms, because ciliates are considered as voracious feeders of toxic phytoplankton and major herbivores in marine food webs. Ciliates are major contributors to control the flux of harmful algal blooms by lessen the magnitude of their biomass from top to bottom by high consumption on these blooms. Keeping an eye on harmful algal blooms as common pollutant of marine ecosystem the community-based method was used to test the potential effects of two harmful algal species Alexandrium tamarense and Gymnodinum catenatum on the community patterns of the ciliates. For this purpose, the 14-day (mature) samples of ciliate communities were collected using glass slides as an artificial substratum at a depth of 1 m in coastal waters of the Yellow Sea, northern China. A series of algal cell concentrations of both species was prepared as 100 (control), following 102, 103, 104 and 105 cell ml−1, respectively. The study results indicated that both algal species showed strong effects on the community patterns of the ciliates at high concentration. Species abundance, relative species number and taxonomic distinctness indices of ciliate communities generally increased by increasing the concentration whereas, sharply decreased at the concentration level of (105 cells ml−1) for both algal species. Canonical analysis of principal coordinates demonstrated the variations in community structures of the ciliates driven by the concentrations of both algal species. Ellipse test showed an increased pattern in species departure from an expected breadth of species contour with increasing the algal cell concentrations. Based on our findings, it is suggested that extended studies on community-based bioassay is a valuable tool to strengthen the information about the effects of microalgae on the ciliate community structures. [ABSTRACT FROM AUTHOR]

Widespread harmful cyanobacterial bloom is one of the most pressing concerns in lakes and reservoirs, resulting in a lot of negative ecological consequences and threatening public health. Ocean color instruments with low spatial resolution have been used to monitor cyanobacterial bloom in large lakes; however, they cannot be applied to small water bodies well. Here, the Multi-Spectral Instrument (MSI) onboard Sentinel-2A and -2B and the Operational Landsat Imager (OLI) onboard Landsat-8 were employed to assemble the virtual constellation and to track spatial and seasonal variations in floating algae blooms from 2016 to 2020 in a small eutrophic plateau lake: Lake Xingyun in China. The floating algae index (FAI) was calculated using Rayleigh-corrected reflectance in the red, near-infrared, and short-wave infrared bands. The MSI-derived FAI had a similar pattern to the OLI-derived FAI, with a mean absolute percentage error of 19.98% and unbiased percentage difference of 17.05%. Then, an FAI threshold, 0.0693, was determined using bimodal histograms of FAI images for floating algae extraction. The floating algae had a higher occurrence in the northern region than the southern region in this lake, whilst the occurrence of floating algae in summer and autumn was higher than that in spring and winter. Such a spatial and seasonal pattern was related to the variability in air temperature, wind speed and direction, and nutrients. The climatological annual mean occurrence of floating algae from 2016 to 2020 in Lake Xingyun exhibited a significant decrease, which was related to decreases in nutrients, resulting from efficient ecological restoration by the local government. This research highlighted the application of OLI-MSI virtual constellation on monitoring floating algae in a small lake, providing a practical and theoretical reference to monitor aquatic environments in small water bodies. [ABSTRACT FROM AUTHOR]

A series of batch culture experiments were carried out to compare the specific eco-physiological responses of three typical harmful algae of Chinese coastal waters to environmental phosphorus (P) variations. Results showed that Skeletonema costatum, when compared with Prorocentrum donghaiense or Alexandrium catenella, was a better growth strategist in nutrient-rich condition. Although S. costatum had a greater advantage in phosphate affinity and could save more internal P, it also had a higher P demand for growth and it used up all its resources to sustain a high growth rate. The growth of S. costatum collapsed soon after phosphate depletion. P. donghaiense and A. catenella, with lower growth rates, could survive well under P-limited conditions. With higher affinities for dissolved organic phosphorus (DOP), P. donghaiense and A. catenella might likely make good use of the metabolized DOP in the water after the collapse of S. costatum blooms to sustain their growth. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) are major ecological and environmental problems in China's coastal waters and seriously threaten the stability of the marine ecosystem and human health. Gymnodinium catenatum is a toxic red tide dinoflagellate. It can produce paralytic shellfish toxins (PSP), which cause serious hazards to marine organisms, public health, and safety. In this paper, a test strip based on colloidal gold immunochromatography (GICG) was developed for the rapid detection of Gymnodinium catenatum. The experimental results showed that the test strip has good specificity and sensitivity. It not only detects the different components of Gymnodinium catenatum but also may detect algal toxins. The lowest density of Gymnodinium catenatum that can be detected by this test strip is approximately 120 cells/mL. Cross-reaction indicated that the test strip had a high specificity for Gymnodinium catenatum. This test strip provides a rapid method for in situ detection of Gymnodinium catenatum and a reference method for the monitoring of other harmful algae to serve as an early warning of upcoming red tides. It also provides a new way to prepare more detection methods for toxic algal toxins. [ABSTRACT FROM AUTHOR]

In China, harmful algal blooms (HABs) are one of the most prominent ecological disasters in the coastal areas. Among the harmful algae species that cause HABs, Karen mikimotoi is a kind of algae that appear frequently. It can secrete hemolytic toxins and fish toxins such as glycolipids and unsaturated fatty, posing a significant threat to marine life. In order to establish a fast and effective detection technology for Karen mikimotoi that can be promoted and applied on site, we have developed a test strip which is based on monoclonal antibody technology and the colloidal gold immune-chromatography assay (GICA). The experimental results show that this test strip can detect different growth stages including growth, and stable and recession period of Karen mikimotoi. The detection results can be displayed within 3–15 min. It had high sensitivity and specificity, with a detection limit of 754 cells/mL. A colorimetric card was made to further determine the concentration of algae detected. What is more, we had developed a method that can be used for on-site enrichment of algae cells using a syringe to detect lower concentrations of Karen mikimotoi, with a minimum detection concentration of 100 cells/mL. Also the test strip was used for on-site testing along the coast of China. This test strip not only serves as a warning for the outbreak of red tide, but also provides a new approach for the development of rapid detection technology for red tide algae. [ABSTRACT FROM AUTHOR]

Phaeocystis globose (P. glo) are the most frequent harmful algae responsible for red tides in Qinzhou Bay, Guangxi. They pose a significant threat to the coastal marine ecosystem, making it essential to develop an efficient indicator method tailored to P. glo outbreaks. In remote sensing water quality monitoring, there is a strong correlation between P. glo and cyanobacteria, with phycocyanin (PC) serving as an indicator of cyanobacterial biomass. Consequently, existing research has predominantly focused on remote sensing monitoring of medium to high PC concentrations. However, it is still challenging to monitor low PC concentrations. This paper introduced the BP neural network (BPNN) and particle swarm optimization algorithm (PSO). It selects spectral bands and indices sensitive to PC concentrations and constructs a PC concentration retrieval model, in combination with meteorological factors, offering a comprehensive exploration of the indicative role of low PC concentrations in predicting P. glo red tide outbreaks in Qinzhou Bay. The results demonstrated that the PC concentration retrieval model, based on the backpropagation neural network optimized by the particle swarm optimization algorithm (PSO-BPNN), demonstrated better performance (MAE = 0.469, RMSE = 0.615). In Qinzhou Bay, PC concentrations were mainly concentrated around 2~5 μg/L. During the P. glo red tide event, the area with undetectable PC concentrations (PC < 0.04 μg/L) increased by 4.97 km2, with regions below 0.9 μg/L experiencing exponential growth. Considering the variations in PC concentrations along with meteorological factors, we proposed a straightforward early warning threshold for P. glo red tides: PC < 0.9 μg/L and T < 20 °C. This method, from a remote sensing perspective, analyzes the process of P. glo outbreaks, simplifies PC concentration monitoring, and provides a reasonably accurate prediction of the risk of P. glo red tide disasters. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) cause environmental problems worldwide. Continuous monitoring and forecasting of harmful algal blooms are necessary for marine resources managers to detect the intensity and spatial extent of HABs and provide early warnings to the public. In this study, we introduce an integrated web-based system for the monitoring and forecasting of coastal HABs. The system is named the Harmful Algal Blooms Monitoring and Forecasting System (HMFS). HMFS integrates in situ observations, a remote-sensing-based model, hydrodynamic and water quality model and Web-Based Geographic Information System (GIS) techniques into one environment. The in situ sensors and remote sensing model provide automatic and continuous monitoring of the coastal water conditions. The numerical models provide short-term prediction and early warning of HAB of up to 5 days. The overall forecast accuracy is more than or equal to 50% for the major coastal areas of Shenzhen in 2018. By leveraging a web-based GIS technique and Service-Oriented Architecture (SOA), the web portal of HMFS provides a graphic interface for users and mangers to view real-time in situ measurements and remote sensing maps, explore numerical model forecasts and get early warning information. HMFS was applied to Shenzhen, which is a rising megacity in Southern China. The application study demonstrated the applicability and effectiveness of HMFS for monitoring and predicting HABs. [ABSTRACT FROM AUTHOR]

The intensification of anthropogenic activities has led to the infiltration of enormous quantities of pollutants into rivers and lakes, resulting in significant deterioration in water quality and a more prominent occurrence of eutrophication. Poyang Lake, the largest freshwater lake in China, is facing a severe challenge related to eutrophication, which seriously threatens the delivery of the ecosystem service and the safety of drinking water. To address this challenge, Landsat-8 Operational Land Imager (OLI) data for the Poyang Lake Basin (PLB) from May 2013 to December 2020 were used. Since inland water bodies with complex optical characteristics, we developed a semi-analytical algorithm to assess the trophic state of the water based on two cruise field measurements in 2016 and 2019. Combining the semi-analytical trophic level index (TLI) with an atmospheric correction model is the most suitable model for OLI images of the PLB, this model was then applied to Landsat-8 time series observations. The trends of the trophic state of water bodies in PLB were revealed, and the annual, quarterly and monthly percentages of eutrophic water bodies were calculated. Natural and anthropogenic factors were then used to explain the changes in the trophic state of the PLB waters. The main findings are as follows: (1) From the 8-year observation results, it can be seen that the variation of trophic level of water in PLB showed obviously spatial and temporal variations, characterized by higher in the north than in the south and higher in winter than in summer. (2) Temperature promoted the growth of harmful algae and plays an essential role in affecting changes in the trophic level of the water. (3) Changes in the trophic level of water bodies in PLB were mainly affected by human activities. The results of spatial and temporal variation of the trophic level of water and the driving factors in PLB can extend our knowledge of water quality degradation and provide essential references for relevant policy-making institutions. [ABSTRACT FROM AUTHOR]

Background: Sanniang Bay (SNB) and Dafeng River (DFR), located in the northern Beibu Gulf, is well-known as one of the eight habitats for humpback dolphins in China. This region is representative of typical estuarine and bay ecosystems and produce complex hydrodynamic seawater conditions. Moreover, anthropogenic pressure, such as eutrophication and large-scale infrastructure projects, have caused ongoing habitat deterioration and loss. It is urgent to know the phytoplankton community and their relationships with environmental factors in this region., Results: In this study, we assessed the diversity and assembly mechanisms of phytoplankton communities, as well as their relationship with the physicochemical characteristics of seawater in SNB and DFR region using 18 S rDNA metabarcoding analysis. The results showed that seasonal changes markedly impacted the alpha diversity of the phytoplankton community. From March to July, with the average temperature increasing from 25.2℃ to 28.1℃,the Shannon or Species Richness were negatively correlated with temperature. During hot season (in Sep, average temperature 32.1℃), phytoplankton diversity was negatively correlated with nutrients (NH 4  + , NO 3 - , PO 4 3- , TN). Additionally, during the rainy season, the Bray-Curtis similarity of the phytoplankton community was significantly lower than during the dry season. In March, the distance among the sampling sites was most strongly and positively correlated with the Bray-Curtis dissimilarity. Stochastic processes, specifically dispersal limitation and ecological drift, are the primary drivers of community assembly, while deterministic assembly processes (mainly heterogeneous selection) contribute a relatively minor portion (< 17%)., Conclusions: Rising temperature diminished the diversity of phytoplankton in SNB and DFR, and nutrient inputs and eutrophication in estuarine areas will aggravate the loss of phytoplankton diversity., (© 2024. The Author(s).)

Cyanobacterial blooms have become a serious water pollution problem in many parts of the world, and the monitoring and study of the impacts of biotoxins on human health are of vital importance. In this study, the contents of microcystin-LR, 2-methylisoborneol, and geosmin were measured in water and sediment samples from Nanwan Reservoir, China, by means of bimonthly sampling between February and December 2023. The physicochemical and hydrochemical factors and phytoplankton dynamics in the reservoir were also investigated. The results showed that the overall mean concentration of microcystin-LR (0.729 μg/L) in summer approached the guiding standard (1 μg/L) set by the WHO for drinking water. Furthermore, the content of 2-methylisoborneol (143.5 ng/L) was 14 times higher than the national standard (10 ng/L). The results of laboratory cultures showed that lower light levels and medium temperatures were suitable for the growth of Microcystis and Planktothricoides but higher temperatures promoted the synthesis and release of microcystin-LR and 2-methylisoborneol. In addition, the results of co-cultures showed that the growth of Planktothricoides was inhibited by Microcystis . Our results suggest that cyanobacterial bloom and the presence of the metabolites 2-methylisoborneol and microcystin-LR can decrease the drinking water quality of Nanwan Reservoir.

Currently, more and more lakes around the world are experiencing outbreaks of cyanobacterial blooms, and high-precision and rapid monitoring of the spatial distribution of algae in water bodies is an important task. Remote sensing technology is one of the effective means for monitoring algae in water bodies. Studies have shown that the Floating Algae Index (FAI) is superior to methods such as the Standardized Differential Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) in monitoring cyanobacterial blooms. However, compared to the NDVI method, the FAI method has difficulty in determining the threshold, and how to choose the threshold with the highest classification accuracy is challenging. In this study, FAI linear fitting model (FAI-L) is selected to solve the problem that FAI threshold is difficult to determine. Innovatively combine FAI index and NDVI index, and use NDVI index to find the threshold of FAI index. In order to analyze the applicability of FAI-L to extract cyanobacterial blooms, this paper selected multi-temporal Landsat8, HJ-1B, and Sentinel-2 remote sensing images as data sources, and took Chaohu Lake and Taihu Lake in China as research areas to extract cyanobacterial blooms. The results show that (1) the accuracy of extracting cyanobacterial bloom by FAI-L method is generally higher than that by NDVI and FAI. Under different data sources and different research areas, the average accuracy of extracting cyanobacterial blooms by FAI-L method is 95.13%, which is 6.98% and 18.43% higher than that by NDVI and FAI respectively. (2) The average accuracy of FAI-L method for extracting cyanobacterial blooms varies from 84.09 to 99.03%, with a standard deviation of 4.04, which is highly stable and applicable. (3) For simultaneous multi-source image data, the FAI-L method has the highest average accuracy in extracting cyanobacterial blooms, at 95.93%, which is 6.77% and 13.26% higher than NDVI and FAI methods, respectively. In this paper, it is found that FAI-L method shows high accuracy and stability in extracting cyanobacterial blooms, and it can extract the spatial distribution of cyanobacterial blooms well, which can provide a new method for monitoring cyanobacterial blooms., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Microorganisms are crucial components of the aquatic ecosystem due to their immense diversity and abundance. They are vital in sustaining ecological services, especially in maintaining essential biogeochemical cycles. Recent years have seen a substantial increase in surplus nitrogenous pollutants in aquatic ecosystems due to the heightened occurrence of anthropogenic activities. Elevated levels of free ammonia (FA, NH 3 ), stemming from the discharge of excess nitrogenous pollutants, have caused notable fluctuations in aquatic ecosystems, leading to water eutrophication and various ecological challenges. The impact of these oscillations on microbial communities in aquatic ecosystems has not been extensively studied. This study employed 16S rRNA gene amplicon sequencing to systematically investigate the dynamics, co-occurrence networks, and assembly processes of microbial communities and their subcommunities (abundant, moderate, and rare) in the Luanhe River Diversion Project in China. Our findings indicate that NH 3 concentration significantly influences the dynamics of microbial communities, with a notable decrease in community Richness and Phylogenetic Distance alongside increased community dissimilarity under higher NH 3 conditions. The analysis revealed that certain microbial groups, particularly Actinobacteriaota, were notably more prevalent in environments with elevated NH 3 levels, suggesting their potential resilience or adaptive responses to NH 3 stress. Additionally, through co-occurrence network analysis, we observed dynamic changes in network topology and increased connectedness under NH 3 stress. Key nodes, identified as connectors and module hubs, played crucial roles in maintaining network structure, particularly Cyanobacteria and Actinobacteriaota. Furthermore, stochastic processes, particularly drift and dispersal limitation, predominantly shaped the microbial communities. Within the three subcommunities, the impact of drift became more pronounced as the effect of dispersal limitation diminished. Overall, elucidating the dynamics of microbial communities in aquatic ecosystems exposed to NH 3 can enhance our comprehension of the ecological mechanisms of microbial communities and provide new insights into the conservation of microbial community diversity and ecological functions., Importance: The research presented in this paper explores how varying concentrations of free ammonia impact microbial communities in aquatic ecosystems. By employing advanced gene sequencing techniques, the study reveals significant changes in microbial diversity and network structures in response to increased ammonia levels. Key findings indicate that high ammonia concentrations lead to a decrease in microbial richness and diversity while increasing community dissimilarity. Notably, certain microbial groups, like Actinobacteria, show resilience to ammonia stress. This research enhances our understanding of how pollution affects microbial ecosystems and underscores the importance of maintaining balanced ammonia levels to preserve microbial diversity and ecosystem health., Competing Interests: The authors declare no conflict of interest.

Cylindrospermopsis raciborskii- dominated harmful algae blooms have been reported globally in recent years. However, our understanding of the ecology of C. raciborskii in natural conditions is still poor. In this study, we collected the water samples from a C. raciborskii -blooming lake, Yilong Lake, in Yunnan province, China, and used both culture-dependent and culture-independent approaches to investigate their microbial communities and the interactions between C. raciborskii and the other bacteria. The composition and diversity of microbial communities were revealed with 16S rRNA gene high-throughput sequencing data analysis. Microbial co-occurrences analysis suggests C. raciborskii may have complex associations with other bacteria. Based on co-inoculation tests, we obtained 14 strains of bacterial strains from the water samples that exhibited either algicidal or promoting effects on a strain of C. raciborskii. Two bacterial isolates exhibited a consistent performance between co-occurrence analysis and experimental results. Effects of these bacteria-algae interspecies interactions on the bloom event are discussed. All these results may provide new insights into the C. raciborskii -dominated blooms and how its interspecies relationships with other bacteria may influence the bloom events in eutrophic waters throughout the world. [ABSTRACT FROM AUTHOR]

The coast of the East China Sea (ECS) is one of the regions most frequently affected by harmful algal blooms in China. Remote sensing monitoring could assist in understanding the mechanism of blooms and their associated environmental changes. Based on imagery from the Second-Generation Global Imager (SGLI) conducted by Global Change Observation Mission-Climate (GCOM-C) (Japan), the accuracy of satellite measurements was initially validated using matched pairs of satellite and ground data relating to the ECS. Additionally, using SGLI data from the coast of the ECS, we compared the applicability of three bloom extraction methods: spectral shape, red tide index, and algal bloom ratio. With an RMSE of less than 25%, satellite data at 490 nm, 565 nm, and 670 nm showed good consistency with locally measured remote sensing reflectance data. However, there was unexpected overestimation at 443 nm of SGLI data. By using a linear correction method, the RMSE at 443 nm was decreased from 27% to 17%. Based on the linear corrected SGLI data, the spectral shape at 490 nm was found to provide the most satisfactory results in separating bloom and non-bloom waters among the three bloom detection methods. In addition, the capability in harmful algae distinguished using SGLI data was discussed. Both of the Bloom Index method and the green-red Spectral Slope method were found to be applicable for phytoplankton classification using SGLI data. Overall, the SGLI data provided by GCOM-C are consistent with local data and can be used to identify bloom water bodies in the ECS, thereby providing new satellite data to support monitoring of bloom changes in the ECS. [ABSTRACT FROM AUTHOR]

Graphene photocatalysis is a new method for harmful algae and water pollution control. However, microbial communities undergoing graphene photocatalysis treatment in freshwater lakes have been poorly studied. Here, using 16S rRNA and 18S rRNA gene high-throughput sequencing, the responses of microbial communities to graphene photocatalysis were analyzed in the eutrophic lake, Lake Xinyun, southwestern China. For microeukaryotes, we found that Arthropoda was dominant in summer, while its abundant level declined in spring under natural conditions. The evident reduction of Arthropods was observed after graphene photocatalysis treatment in summer and then reached a relatively stable level. For bacteria, Cyanobacteria decreased in summer due to the graphene photocatalysis-mediated inactivation. However, Cyanobacteria was higher in the treated group in spring with a genera group-shift. Functional analysis revealed that microeukaryotes showed higher potential for fatty acid oxidation and TCA cycle in the treated group in summer, but they were more abundant in control in spring. Pathways of starch and sucrose metabolism and galactose metabolism were more abundant in control in summer, while they were enriched in the treated group in spring for bacteria. This study offers insights into the effects of graphene photocatalysis on microbial communities and their functional potential in eutrophic lake. [ABSTRACT FROM AUTHOR]

The shift of diatom dominance to combination of diatom and dinoflagellate dominance in the Bohai Sea (BS), China might be associated with the change of dissolved nitrogen (DN). This study combines field investigation, ship‐based microcosm experiments, a nitrogen biogeochemical model, and statistical analysis to reveal the impact of DN loading on the dominance of diatoms and dinoflagellates in the BS, considering the quantitative relationship between the algal growth/death and nitrogen migration/transformation processes. The diatom to diatom‐dinoflagellate shift was significantly associated with the DN regime shift of oxidized nitrogen (NO3‐N) to reduced nitrogen (NH4‐N and dissolved organic nitrogen [DON]) since the mid‐1990s. This phenomenon was supported by microcosm and numerical experiments: (a) Gonyaulax verior as a dominant dinoflagellate in the BS efficiently absorbed/assimilated NH4‐N, and it can also utilize DON derived from centric diatoms; Chaetoceros densus as dominant centric diatoms in the BS was able to absorb/assimilate NO3‐N, and it can also utilize DON derived from the Xiaoqing River; (b) The change in dinoflagellates/diatoms ratios was reproduced with the change in DN regime from the 1980s to the 2010s by the proposed nitrogen biogeochemical model based on localized parameters in the BS. Moreover, mixotrophism and stronger survival stability, associated with the faster NH4‐N and DONalgal uptake and slower decomposition of G. verior, also supported the shift from diatoms to diatoms–dinoflagellates during high variations in nutrient supply. This study infers the phytoplankton regime shift mechanism associated with the DN structure in coastal waters, providing a credible scientific basis for the shift from water quality‐based to ecosystem‐based environmental management. Plain Language Summary: Changes in amount and proportion of dissolved nitrogen (DN) might lead to the shift of diatoms to diatoms–dinoflagellates in Bohai Sea (BS), which could result in the degradation of primary productivity, the change of zooplankton and subsequent high‐trophic organisms, and then the change of the entire ecosystem, leading to a series of marine ecosystem health problems such as increasing proportion of toxic/harmful algae blooms, jellyfish blooms and the decline of fishery resources. Our study combines field investigation, ship‐based microcosm experiments, a nitrogen biogeochemical model, and statistical analysis to reveal how changes of DN loading influence the dominant algal species structure in BS. According to microcosm and numerical experiments, we found that the DN forms shift of oxidized nitrogen to reduced nitrogen since the mid‐1990s played an important role in the shift of diatoms to diatoms–dinoflagellates. This is because diatoms can absorb/assimilate oxidized nitrogen faster, while dinoflagellates prefer to absorb/assimilate reduced nitrogen. In addition, dinoflagellates have a slower decomposition rate and stronger survival stability. We infer a mechanism that algal community structure in BS shifted from diatoms to diatoms‐dinoflagellates when the amount/proportion of DN changed, providing a credible scientific basis for the ecosystem‐based environmental management. Key Points: We reproduced the shift of diatoms dominance to diatoms‐dinoflagellates dominance in the Bohai Sea by numerical simulationMicrocosm experiments proved that ammonia and algal dissolved organic nitrogen can promote dinoflagellate (Gonyaulax verior) growthThe numerical model emphasized the driving effect of terrestrial dissolved nitrogen input on the shift of diatoms to dinoflagellates [ABSTRACT FROM AUTHOR]

To compare the different effects of petroleum hydrocarbons on intertidal Ulva macroalgae, three dominant Ulva species (U. prolifera, U. linza, and U. lactuca) were exposed to two water-accommodated fractions (WAFs) of 0 # diesel oil and crude oil at three concentration levels. The results indicated that two WAFs had significant concentration effects on the physiological characteristics of Ulva, the toxicity of 0 # diesel oil was greater than crude oil, and crude oil had hormesis effect. Exposure of high WAFs concentrations, the growth, pigment, carbohydrate, and protein contents of Ulva were inhibited, while the antioxidant system was activated. In addition, the integrated biomarker response (IBR) indicated that U. prolifera had higher resistance to WAFs than U. linza and U. lactuca. Considering that U. prolifera is the main species of green tide in the Yellow Sea (YS) of China, the comparative effects of WAFs on different development stages of U. prolifera were also explored. The results showed that spore was the most sensitive to WAFs, while adult thalli was the most tolerant. The increased resistance of U. prolifera thalli and the hormesis effect triggered by crude oil may influence the outbreak scale of green tides. This study provides a new perspective for understanding the formation of green tides in the YS., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Cyanobacterial mats supplanting coral and spreading coral diseases in tropical reefs, intensified by environmental shifts caused by human-induced pressures, nutrient enrichment, and global climate change, pose grave risks to the survival of coral ecosystems. In this study, we characterized Okeanomitos corallinicola gen. and sp. nov., a newly discovered toxic marine heterocyte-forming cyanobacterium isolated from a coral reef ecosystem of the South China Sea. Phylogenetic analysis, based on the 16S rRNA gene and the secondary structure of the 16S-23S rRNA intergenic region, placed this species in a clade distinct from closely related genera, that is, Sphaerospermopsis stricto sensu, Raphidiopsis, and Amphiheterocytum. The O. corallinicola is a marine benthic species lacking gas vesicles, distinguishing it from other members of the Aphanizomenonaceae family. The genome of O. corallinicola is large and exhibits diverse functional capabilities, potentially contributing to the resilience and adaptability of coral reef ecosystems. In vitro assays revealed that O. corallinicola demonstrates notable cytotoxic activity against various cancer cell lines, suggesting its potential as a source of novel anticancer compounds. Furthermore, the identification of residual saxitoxin biosynthesis function in the genome of O. corallinicola, a marine cyanobacteria, supports the theory that saxitoxin genes in cyanobacteria and dinoflagellates may have been horizontally transferred between them or may have originated from a shared ancestor. Overall, the identification and characterization of O. corallinicola provides valuable contributions to cyanobacterial taxonomy, offering novel perspectives on complex interactions within coral reef ecosystems., (© 2024 Phycological Society of America.)

The coastal seas of China are increasingly threatened by algal blooms, yet their comprehensive spatiotemporal mapping and understanding of underlying drivers remain challenging due to high turbidity and heterogeneous water conditions. We developed a singular value decomposition-based algorithm to map these blooms using two decades of MODIS-Aqua satellite data, spanning from 2003 to 2022. Our findings indicate significant algal activity along the Chinese coastline, impacting an average annual area of approximately 1.8 × 10 5 km 2 . The blooms exhibit peak intensity in August, while the maximum affected area occurs in September, featuring multifrequency outbreaks in spring, and pronounced large-scale events in summer and autumn. Notably, our analysis demonstrates a robust 67% increase in bloom occurrences over the study period. This expansion is primarily attributed to increased nutrient inflow from terrestrial sources linked to human activity and precipitation, compounded by rising global sea surface temperatures. These spatiotemporal insights are critical for devising effective management strategies and policies to mitigate the impacts of algal blooms.

The escalating proliferation of cyanobacteria poses significant taste and odor (T/O) challenges, impacting freshwater ecosystems, public health, and water treatment costs. We examined monthly variations in four T/O compounds from September 2011 to August 2012 in Chaohu Lake's eastern drinking water source (DECL). More importantly, we compared the reported T/O occurrence and the related factors in freshwater bodies worldwide. The assessment of T/O issues indicated a severe and widespread problem, with many cases surpassing odor threshold values. Remarkably, China reported the highest frequency and severity of odor-related problems. A temporal analysis revealed variations in odor occurrences within the same water body across different years, emphasizing the need to consider high values in all seasons for water safety. Globally, T/O issues were widespread, demanding attention to variations within the same water body and across different layers. Algae were crucial contributors to odor compounds, necessitating targeted interventions due to diverse odorant sources and properties. A correlation analysis alone lacked definitive answers, emphasizing the essential role of further validation, such as algae isolation. Nutrients are likely to have influenced the T/O, as GSM and MIB correlated positively with nitrate and ammonia nitrogen in DECL, resulting in proposed control recommendations. This study offers recommendations for freshwater ecosystem management and serves as a foundation for future research and management strategies to address T/O challenges.

The cyanosiphophage Mic1 specifically infects the bloom-forming Microcystis aeruginosa FACHB 1339 from Lake Chaohu, China. Previous genomic analysis showed that its 92,627 bp double-stranded DNA genome consists of 98 putative open reading frames, 63% of which are of unknown function. Here, we investigated the transcriptome dynamics of Mic1 and its host using RNA sequencing. In the early, middle, and late phases of the 10 h lytic cycle, the Mic1 genes are sequentially expressed and could be further temporally grouped into two distinct clusters in each phase. Notably, six early genes, including gp49 that encodes a TnpB-like transposase, immediately reach the highest transcriptional level in half an hour, representing a pioneer cluster that rapidly regulates and redirects host metabolism toward the phage. An in-depth analysis of the host transcriptomic profile in response to Mic1 infection revealed significant upregulation of a polyketide synthase pathway and a type III-B CRISPR system, accompanied by moderate downregulation of the photosynthesis and key metabolism pathways. The constant increase of phage transcripts and relatively low replacement rate over the host transcripts indicated that Mic1 utilizes a unique strategy to gradually take over a small portion of host metabolism pathways after infection. In addition, genomic analysis of a less-infective Mic1 and a Mic1-resistant host strain further confirmed their dynamic interplay and coevolution via the frequent horizontal gene transfer. These findings provide insights into the mutual benefit and symbiosis of the highly polymorphic cyanobacteria M. aeruginosa and cyanophages., Importance: The highly polymorphic Microcystis aeruginosa is one of the predominant bloom-forming cyanobacteria in eutrophic freshwater bodies and is infected by diverse and abundant cyanophages. The presence of a large number of defense systems in M. aeruginosa genome suggests a dynamic interplay and coevolution with the cyanophages. In this study, we investigated the temporal gene expression pattern of Mic1 after infection and the corresponding transcriptional responses of its host. Moreover, the identification of a less-infective Mic1 and a Mic1-resistant host strain provided the evolved genes in the phage-host coevolution during the multiple-generation cultivation in the laboratory. Our findings enrich the knowledge on the interplay and coevolution of M. aeruginosa and its cyanophages and lay the foundation for the future application of cyanophage as a potential eco-friendly and bio-safe agent in controlling the succession of harmful cyanobacterial blooms., Competing Interests: The authors declare no conflict of interest.

Although lipophilic shellfish toxins (LSTs) pose a significant threat to the health of seafood consumers, their systematic investigation and risk assessment remain scarce. The goals of this study were as follows: (1) analyze LST levels in commercially available shellfish in Zhejiang province, China, and determine factors influencing LST distribution; (2) assess the acute dietary risk of exposure to LSTs for local consumers during the red tide period; (3) explore potential health risks of LSTs in humans; and (4) study the acute risks of simultaneous dietary exposure to LSTs and paralytic shellfish toxins (PSTs). A total of 546 shellfish samples were collected. LSTs were detected in 89 samples (16.3%) at concentrations below the regulatory limits. Mussels were the main shellfish species contaminated with LSTs. Spatial variations were observed in the yessotoxin group. Acute exposure to LSTs based on multiple scenarios was low. The minimum tolerable exposure durations for LSTs calculated using the mean and the 95th percentile of consumption data were 19.7 and 4.9 years, respectively. Our findings showed that Zhejiang province residents are at a low risk of combined exposure to LSTs and PSTs; however, the risk may be higher for children under 6 years of age in the extreme scenario.

Background: During the bloom season, the colonial cyanobacterium Microcystis forms complex aggregates which include a diverse microbiome within an exopolymer matrix. Early research postulated a simple mutualism existing with bacteria benefitting from the rich source of fixed carbon and Microcystis receiving recycled nutrients. Researchers have since hypothesized that Microcystis aggregates represent a community of synergistic and interacting species, an interactome, each with unique metabolic capabilities that are critical to the growth, maintenance, and demise of Microcystis blooms. Research has also shown that aggregate-associated bacteria are taxonomically different from free-living bacteria in the surrounding water. Moreover, research has identified little overlap in functional potential between Microcystis and members of its microbiome, further supporting the interactome concept. However, we still lack verification of general interaction and know little about the taxa and metabolic pathways supporting nutrient and metabolite cycling within Microcystis aggregates., Results: During a 7-month study of bacterial communities comparing free-living and aggregate-associated bacteria in Lake Taihu, China, we found that aerobic anoxygenic phototrophic (AAP) bacteria were significantly more abundant within Microcystis aggregates than in free-living samples, suggesting a possible functional role for AAP bacteria in overall aggregate community function. We then analyzed gene composition in 102 high-quality metagenome-assembled genomes (MAGs) of bloom-microbiome bacteria from 10 lakes spanning four continents, compared with 12 complete Microcystis genomes which revealed that microbiome bacteria and Microcystis possessed complementary biochemical pathways that could serve in C, N, S, and P cycling. Mapping published transcripts from Microcystis blooms onto a comprehensive AAP and non-AAP bacteria MAG database (226 MAGs) indicated that observed high levels of expression of genes involved in nutrient cycling pathways were in AAP bacteria., Conclusions: Our results provide strong corroboration of the hypothesized Microcystis interactome and the first evidence that AAP bacteria may play an important role in nutrient cycling within Microcystis aggregate microbiomes. Video Abstract., (© 2024. The Author(s).)

Prorocentrum shikokuense (formerly P. donghaiense) is a pivotal dinoflagellate species associating with the HABs in the East China Sea. The complexity of its large nuclear genome hindered us from understanding its genomic characteristics. Full-length transcriptome sequencing offers a practical solution to decipher the physiological mechanisms of a species without the reference genome. In this study, we employed single-molecule real-time (SMRT) sequencing technology to sequence the full-length transcriptome of Prorocentrum shikokuense. We successfully generated 41.73 Gb of clean SMRT sequencing reads and isolated 105,249 non-redundant full-length non-chimeric reads. Our trial has led to the identification of 11,917 long non-coding RNA transcripts, 514 alternative splicing events, 437 putative transcription factor genes from 17 TF gene families, and 34,723 simple sequence repeats. Additionally, a total of 78,265 open reading frames were identified, of them 15,501 were the protein coding sequences. This dataset is valuable for annotating P. shikokuense genome, and will contribute significantly to the in-depth studies on the molecular mechanisms underlining the dinoflagellate bloom formation., (© 2024. The Author(s).)

Paralytic shellfish toxins (PSTs) are widely distributed in shellfish along the coast of China, causing a serious threat to consumer health; however, there is still a lack of large-scale systematic investigations and risk assessments. Herein, 641 shellfish samples were collected from March to November 2020, and the PSTs' toxicity was detected via liquid chromatography-tandem mass spectrometry. Furthermore, the contamination status and potential dietary risks of PSTs were discussed. PSTs were detected in 241 shellfish samples with a detection rate of 37.60%. The average PST toxicities in mussels and ark shells were considerably higher than those in other shellfish. The PSTs mainly included N-sulfonylcarbamoyl toxins (class C) and carbamoyl toxins (class GTX), and the highest PST toxicity was 546.09 μg STX eq. kg -1 . The PST toxicity in spring was significantly higher than those in summer and autumn ( p < 0.05). Hebei Province had the highest average PST toxicity in spring. An acute exposure assessment showed that consumers in Hebei Province had a higher dietary risk, with mussels posing a significantly higher dietary risk to consumers. This research provides reference for the green and sustainable development of the shellfish industry and the establishment of a shellfish toxin prevention and control system.

Lakes worldwide are affected by multiple stressors, including climate change. This includes massive loading of both nutrients and humic substances to lakes during extreme weather events, which also may disrupt thermal stratification. Since multi-stressor effects vary widely in space and time, their combined ecological impacts remain difficult to predict. Therefore, we combined two consecutive large enclosure experiments with a comprehensive time-series and a broad-scale field survey to unravel the combined effects of storm-induced lake browning, nutrient enrichment and deep mixing on phytoplankton communities, focusing particularly on potentially toxic cyanobacterial blooms. The experimental results revealed that browning counteracted the stimulating effect of nutrients on phytoplankton and caused a shift from phototrophic cyanobacteria and chlorophytes to mixotrophic cryptophytes. Light limitation by browning was identified as the likely mechanism underlying this response. Deep-mixing increased microcystin concentrations in clear nutrient-enriched enclosures, caused by upwelling of a metalimnetic Planktothrix rubescens population. Monitoring data from a 25-year time-series of a eutrophic lake and from 588 northern European lakes corroborate the experimental results: Browning suppresses cyanobacteria in terms of both biovolume and proportion of the total phytoplankton biovolume. Both the experimental and observational results indicated a lower total phosphorus threshold for cyanobacterial bloom development in clearwater lakes (10-20 μg P L -1 ) than in humic lakes (20-30 μg P L -1 ). This finding provides management guidance for lakes receiving more nutrients and humic substances due to more frequent extreme weather events., (© 2023 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Abstract: In this paper, we consider the growth of densities of two kinds of typical HAB algae: diatom and dianoflagellate on some coasts of China’s mainland. Since there exist many random factors that cause the change of the algae densities, we shall develop a new nonlinear dynamical model with stochastic excitations on the algae densities. Applying a stochastic averaging method on the model, we obtain a two-dimensional diffusion process of averaged amplitude and phase. Then we investigate the stability and the Hopf bifurcation of the stochastic system with FPK (Fokker Planck–Kolmogorov) theory and obtain the stationary transition probability density of the process. We obtain the critical values of parameters for the occurrences of Hopf bifurcation in terms of probability. We also investigate numerically the effects of various parameters on the stationary transition probability density of the occurrences of Hopf bifurcation. The numerical results are in good correlation with the analysis. We draw the conclusion that if the Hopf bifurcation occurs with a radius large enough, i.e., if the densities of the HAB algae reach a high value, the HAB will take place with comparatively high probability. [Copyright &y& Elsevier]

Harmful algal blooms in Chinese waters have caused serious domoic acid (DA) contamination in shellfish. Although shellfish are at particular risk of dietary exposure to DA, there have been no systematic DA risk assessments in Chinese coastal waters. A total of 451 shellfish samples were collected from March to November 2020. The presence of DA and four of its isomers were detected using liquid chromatography–tandem mass spectrometry. The spatial-temporal distribution of DA occurrence and its potential health risks were examined. DA was detected in 198 shellfish samples (43.90%), with a maximum level of 942.86 μg/kg. DA was recorded in all 14 shellfish species tested and Pacific oysters (Crassostrea gigas) showed the highest average DA concentration (82.36 μg/kg). The DA concentrations in shellfish showed distinct spatial-temporal variations, with significantly higher levels of occurrence in autumn than in summer and spring (p < 0.01), and particularly high occurrence in Guangdong and Fujian Provinces. The detection rates and maximum concentrations of the four DA isomers were low. While C. gigas from Guangdong Province in September showed the highest levels of DA contamination, the risk to human consumers was low. This study improves our understanding of the potential risk of shellfish exposure to DA-residues. [ABSTRACT FROM AUTHOR]

Nitrogen and phosphorus pollution is of great concern to aquatic life and human well-being. While most of these nutrients are applied to the landscape, little is known about the complex interplay among nutrient applications, transport attenuation processes, and coastal loads. Here, we enhance and apply the Spatially Explicit Nutrient Source Estimate and Flux model (SENSEflux) to simulate the total annual nitrogen and phosphorus loads from the US Great Lakes Basin to the coastline, identify nutrient delivery hotspots, and estimate the relative contributions of different sources and pathways at a high resolution (120 m). In addition to in-stream uptake, the main novelty of this model is that SENSEflux explicitly describes nutrient attenuation through four distinct pathways that are seldom described jointly in other models: runoff from tile-drained agricultural fields, overland runoff, groundwater flow, and septic plumes within groundwater. Our analysis shows that agricultural sources are dominant for both total nitrogen (TN) (58%) and total phosphorus (TP) (46%) deliveries to the Great Lakes. In addition, this study reveals that the surface pathways (sum of overland flow and tile field drainage) dominate nutrient delivery, transporting 66% of the TN and 76% of the TP loads to the US Great Lakes coastline. Importantly, this study provides the first basin-wide estimates of both nonseptic groundwater (TN: 26%; TP: 5%) and septic-plume groundwater (TN: 4%; TP: 2%) deliveries of nutrients to the lakes. This work provides valuable information for environmental managers to target efforts to reduce nutrient loads to the Great Lakes, which could be transferred to other regions worldwide that are facing similar nutrient management challenges.

Photochemistry is one of the key processes that shape the quality of dissolved organic matter (DOM) in aquatic systems, yet the photoreactivity of DOM from different sources remains largely unclear. In this study, DOM from 10 typical autochthonous and allochthonous sources in Lake Taihu basin were exposed to simulated sunlight, and quantitative and compositional changes of the DOM were explored by measuring its UV-Visable absorption and fluorescence spectroscopy. Photochemical release of nutrients was also explored during the incubations. Results showed that, although DOM from most sources experienced photobleaching effects with decreased absorption coefficients at 254 nm (a(254)) and fluorescence component intensities after light exposure, photochemical alterations of DOM linked to their original composition. Macrophyte-derived (Potamogeton malaianus) DOM, with the largest molecular size, showed increased a(254), humic- and protein-like fluorescence component (C1 and C2) abundances, and inorganic nutrient concentrations relative to dark controls, indicating photo-release of labile components. However, DOM with relatively higher aromaticity, e.g., from agricultural water and the lake, showed photobleaching effects and increased humification degree, probably due to the loss of aromatic components. Allochthonous anthropogenic DOM, e.g., from sewage, showed stronger photo-ammonification, likely relating to the fresh labile N-containing compositions. The form of inorganic nutrient releases during the DOM photolysis also varied with the original DOM sources. Macrophyte-derived DOM incubations showed larger photo-releases of NO 3 - and PO 4 3- , while NO 2 - dominated inorganic nutrient releases during groundwater DOM light incubations. Thus, this study concludes that the photoreactivity of DOM closely relates to its original composition and sources., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The intake of paralytic shellfish toxins (PSTs) may adversely affect human health. Therefore, this study aimed to show the prevalence of PSTs from commercially available shellfish in Zhejiang Province, China, during the period of frequent red tides, investigate the factors affecting the distribution of PSTs, and assess the risk of PST intake following the consumption of bivalve shellfish among the Zhejiang population. A total of 546 shellfish samples were collected, 7.0% of which had detectable PSTs at concentrations below the regulatory limit. Temporal, spatial, and interspecific variations in the occurrence of PSTs were observed in some cases. The dietary exposure to PSTs among the general population of consumers only was low. However, young children in the extreme scenario (the 95th percentile of daily shellfish consumption combined with the maximum PST concentration), defined as 89-194% of the recommended acute reference doses, were possibly at risk of exposure. Notably, Arcidae and mussels were the major sources of exposure to toxins. From the public health perspective, PSTs from commercially available shellfish do not pose a serious health risk; however, more attention should be paid to acute health risks, especially for young children, during periods of frequent red tides.

Climate change can induce phytoplankton blooms (PBs) in eutrophic lakes worldwide, and these blooms severely threaten lake ecosystems and human health. However, it is unclear how urbanization and its interaction with climate impact PBs, which has implications for the management of lakes. Here, we used multi-source remote sensing data and integrated the Virtual-Baseline Floating macroAlgae Height (VB-FAH) index and OTSU threshold automatic segmentation algorithm to extract the area of PBs in Lake Dianchi, China, which has been subjected to frequent PBs and rapid urbanization in its vicinity. We further explored long-term (2000-2021) trends in the phenological and severity metrics of PBs and quantified the contributions from urbanization, climate change, and also nutrient levels to these trends. When comparing data from 2011-2021 to 2000-2010, we found significantly advanced initiation of PBs (28.6 days) and noticeably longer duration (51.9 days) but an insignificant trend in time of disappearance. The enhancement of algal nutrient use efficiency, likely induced by increased water temperature and reduced nutrient concentrations, presumably contributed to an earlier initiation and longer duration of PBs, while there was a negative correlation between spring wind speed and the initiation of PBs. Fortunately, we found that both the area of the PBs and the frequency of severe blooms (covering more than 19.8 km 2 ) demonstrated downward trends, which could be attributed to increased wind speed and/or reduced nutrient levels. Moreover, the enhanced land surface temperature caused by urbanization altered the thermodynamic characteristics between the land and the lake, which, in turn, possibly caused an increase in local wind speed and water temperature, suggesting that urbanization can differently regulate the phenology and severity of PBs. Our findings have significant implications for the understanding of the impacts of urbanization on PB dynamics and for improving lake management practices to promote sustainable urban development under global change., (© 2023 John Wiley & Sons Ltd.)

Noctiluca scintillans is one of the most common harmful algal species and widely known due to its bioluminescence. In this study, the spatial distribution, seasonal variations, and long-term trends of N. scintillans blooms in China and the related drivers were analyzed and discussed. From 1933 to 2020, a total of 265 events of N. scintillans blooms were recorded in Chinese coastal waters, with a total duration of 1052 days. The first N. scintillans bloom occurred in Zhejiang in 1933, and only three events were recorded before 1980. From 1981 to 2020, N. scintillans caused harmful algal blooms (HABs) almost every year, both the average duration and the proportion of multiphase HABs showed an increasing trend. 1986-1992, 2002-2004, and 2009-2016 were the three peak periods with a frequency of no less than five events of N. scintillans blooms per year. In terms of spatial distribution, N. scintillans blooms spread from the Southeast China Sea to the Bohai Sea after 2000, Guangdong, Fujian, and Hebei were the three provinces with the highest numbers of recorded events of N. scintillans blooms. Moreover, 86.8% of the events of N. scintillans blooms occurred in spring (March, April, and May) and summer (June, July, and August). Among environmental factors, the dissolved inorganic phosphate, dissolved silicate and chemical oxygen demand were significantly correlated with the cell density of N. scintillans during N. scintillans blooms, and most of N. scintillans blooms were recorded in the temperature range of 18.0-25.0°C. Precipitation, hydrodynamics, water temperature, and food availability might be the main factors affecting the spatial-temporal distribution of N. scintillans blooms along the Chinese coast., (© 2023 John Wiley & Sons Ltd.)

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In the past three decades, harmful algal blooms (HAB) have become more frequent and widespread in southeast Chinese sea areas. Resting stages are regarded as the "seed bank" of algal blooms, and play an important role in initiating HABs. The distribution of resting stages in sediments especially those of HAB species can make good predictions about the potential risk of future blooms, however with limited reports. In this study, surface sediment samples were collected in the four sea areas along the southeast Chinese coasts, including Dafeng Port (DF) in the southern Yellow Sea, Xiangshan Bay (XS), Funing Bay (FN), and Dongshan Bay (DS) in the East China Sea. Diversity and community structure of eukaryotic microalgae in surface sediments were assessed by metabarcoding V4 region of the 18S rDNA, focusing on the distribution of HAB species. Biogenic elements including total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), biogenic silicon (BSi), and moisture content (MC) were analyzed. A total of 454 eukaryotic algal OTUs were detected, which belonged to 31 classes of 9 phyla. Altogether 149 algal species were detected in this study, and 59 taxa have been reported to form resting stages. Eukaryotic algal community was similar in XS, FN and DS of the East China Sea, which were predominated by dinoflagellates. However, algal community was different in DF of the Yellow Sea, and characterized by the dominance of chrysophytes and low OTU richness. The distribution of most abundant HAB species showed positive correlations with TN, BSi, and TOC, suggesting that eutrophication and consequent increase in diatom productivity may have a significant influence on the distribution of HAB species and facilitate the occurrence of HABs. Furthermore, HAB species occurredmore abundantly and widely in FN. Our results suggest high potential risks of HABs in the southeast Chinese coast especially in Funing Bay. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) are a worldwide problem with substantial adverse effects on the aquatic environment as well as human health, which have prompted researchers to study measures to stem and control them. Meanwhile, it is key to research and develop monitoring methods to establish early warning HABs. However, both the current monitoring methods and control methods have some shortcomings, making the field application limited. Thus, we need to improve current approaches for monitoring and controlling HABs efficiently. Based on the freshwater system features in China, we review various monitoring and control methods of HABs, summarize and discuss the problems with these methods, and propose the future development direction of monitoring and control HABs. Finally, we envision that it can combine physical, chemical, and biological methods to inhibit HAB expansion in the future, complementing each other with advantages. Further, we promise to establish a long-term strategy of controlling HABs with various algicidal bacteria co-cultivate for field applications in China. Efforts in studying algicidal bacteria must be increased to better control HABs and mitigate the risks of aquatic ecosystems and human health in China. [ABSTRACT FROM AUTHOR]

The species Karenia mikimotoi is a common nearshore red tide alga that can secrete hemolytic exotoxin and ichthyotoxin, which can induce the death of fish and shellfish, causing severe economic losses. In this study, loop-mediated isothermal amplification (LAMP) was employed in combination with the lateral flow dipstick (LFD) visual detection method to establish the LAMP-LFD rapid detection method for K. mikimotoi. The internal transcribed spacer ITS1-5.8S-ITS2 of K. mikimotoi was used as the target sequence and was amplified with specific primers designed in this study. The results indicated that the amplification optimal reaction conditions for LAMP in this paper were for 20 min at 65 °C. Moreover, LAMP had excellent specificity, showing negative results for other common red tide causing algal species. In field samples, we successfully reduced the total time, with only 23 min needed from LAMP amplification to LFD result display, which was shorter than that of conventional PCR. Consequently, LAMP-LFD should be useful for rapid field detection of low-density K. mikimotoi and for the early prevention of red tide induced by such algae. • The first report of LAMP-LFD assay established for the harmful alga K. mikimotoi. • The LAMP-LFD can serve as a rapid detection means for low-density K. mikimotoi. • The LAMP-LFD assay is more ideal for on-site detection. [ABSTRACT FROM AUTHOR]

The foreign dinoflagellate cysts in ships' ballast water tank sediments (BWTS) can be viable for a long time under hostile storage conditions. It is crucial to understand the detailed mechanisms of harmful biological invasions in estuary ecosystems. To study the relationship between the abundance of dinoflagellate cysts and environmental factors, cyst assemblages were analyzed in 7 sediment samples, collected from one international commercial ship that arrived in Shanghai in August 2020. Twenty-three dinoflagellate cyst taxa were identified in 5 groups, including autotrophic (9) and heterotrophic (14) species. Distribution of dinoflagellate cysts in the different ballast water tanks is heterogeneous. Dinoflagellate cysts in BWTS of the repaired ship were dominated by Scrippsiella acuminata, Protoperidinium leonis, Protoperidinium oblongum, Lingulodinium polyedra, Alexandrium tamarense/A. catenella, Protoperidinium pentagonum, and Protoperidinium subinerme. The abundance of the dinoflagellate cysts in each tank ranged from 80.69 to 330.85 cysts g -1 DS (dry sediment). Multivariate statistical analyses revealed that the variation in cysts from different tanks had positive correlations with total nitrogen (TN), total phosphorus (TP), and pH and negative correlations with total organic carbon (TOC) except for sample TK5. For germination of dinoflagellate cysts in BWTS, 12 species were germinated in 40 days and cysts of potentially toxic dinoflagellate species were more abundant than those of non-toxic species. Results show that potentially viable and harmful/toxic dinoflagellate cysts are present in BWTS of ships arriving in Shanghai, China. Consequently, knowledge obtained in this study can be valuable for further managing of potential biological invasion of the Yangtze River Estuary., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)