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Harmful algal blooms (HABs) are global hazards under global climate change and eutrophication conditions. Modified clay (MC) method is widely used to control HABs in Asian and American coastal waters. However, little research has been conducted on the underlying mechanisms by which MC controls blooms in freshwater environments. Herein, experiments and bioinformatics analyses were conducted for MC-based control of freshwater blooms in a closed water body with an area of approximately 240 m2 in the Fuchun River, China. Results revealed that the dominant bloom species were Microcystis , and an 87.68–97.01% removal efficiency of whole algal biomass was achieved after 3 h of MC treatment. The weaker zeta potentials of Microcystis species and hydrophilic groups such as O-H and P-O-P in the extracellular polymeric substances (EPS) surrounding Microcystis cells made them easier to be flocculated and removed by MC particles, and the relative abundance of Microcystis decreased to 29.12% and that of Cyanobium increased to 40.97%. Therefore, MC changes the cyanobacterial community structure, which is accompanied by the elimination of Microcystis sp. apical dominance and enhanced competition between Cyanobium and Microcystis in the phytoplankton community, increasing cyanobacterial community diversity. Under MC treatment, residual microorganisms, including cyanobacteria, had a high potential for DNA damage repair and were more likely to survive after being subjected to oxidative stress. In the meanwhile, the abundance of genes involved in genetic information processing, signal transduction, and photosynthesis was decreased indicating that the residual microbiome was week in proliferation and light energy harvesting. Therefore, accompanied with the destruction of Microcystis colonies, MC changes the function of cyanobacteria and phycosphere microbiome, further hindering bloom development. These findings illustrate that MC can regulate and optimize the microbial community structure through which MC controls cyanobacterial blooms in ecosystems. [ABSTRACT FROM AUTHOR]

Phaeocystis globosa is an important harmful algal species that is globally distributed. Previous studies have indicated that P. globosa preferentially uptake nitrate, but the underlying mechanism is still unclear. To further verify this preference and reveal the underlying mechanism, the assimilation rates of nitrate and ammonium by P. globosa at different concentrations was quantitatively studied by using a nitrogen stable isotope (15N) tracer technique, and the regulatory mechanism was determined from the physiological and biochemical responses. The findings revealed that the preferential assimilation of nitrate by P. globosa was influenced by the ambient ammonium concentration. When the ambient concentration of ammonium was less than approximately 3.5 μmol·L−1, the assimilation rates of nitrate form P. globosa were as high as 1.05 × 10−5 μmol·L−1·h−1·cell−1. Even though the nitrate assimilation in P. globosa was inhibited at ammonium concentrations greater than this threshold, nitrate assimilation could not be completely suppressed. The activity of NR and the expression of related genes in P. globosa were also affected by ammonium. In addition, 15N signals originally labeled nitrate accumulated in ammonium. This indicated that P. globosa was likely to reduce excess nitrate to ammonium and subsequently release it into the substrate, which might be an important energy dissipation mechanism for P. globosa. These results expand the classical understanding of the utilization of nitrogen nutrients by marine phytoplankton, and offer valuable resources for comprehending the mechanism of harmful algal blooms. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) have occurred more frequently in recent years. In this study, to investigate their potential impact in the Beibu Gulf, short‐read and long‐read metabarcoding analyses were combined for annual marine phytoplankton community and HAB species identification. Short‐read metabarcoding showed a high level of phytoplankton biodiversity in this area, with Dinophyceae dominating, especially Gymnodiniales. Multiple small phytoplankton, including Prymnesiophyceae and Prasinophyceae, were also identified, which complements the previous lack of identifying small phytoplankton and those unstable after fixation. Of the top 20 phytoplankton genera identified, 15 were HAB‐forming genera, which accounted for 47.3%–71.5% of the relative abundance of phytoplankton. Based on long‐read metabarcoding, a total of 147 OTUs (PID > 97%) belonging to phytoplankton were identified at the species level, including 118 species. Among them, 37 species belonged to HAB‐forming species, and 98 species were reported for the first time in the Beibu Gulf. Contrasting the two metabarcoding approaches at the class level, they both showed a predominance of Dinophyceae, and both included high abundances of Bacillariophyceae, Prasinophyceae, and Prymnesiophyceae, but the relative contents of the classes varied. Notably, the results of the two metabarcoding approaches were quite different below the genus level. The high abundance and diversity of HAB species were probably due to their special life history and multiple nutritional modes. Annual HAB species variation revealed in this study provided a basis for evaluating their potential impact on aquaculture and even nuclear power plant safety in the Beibu Gulf. [ABSTRACT FROM AUTHOR]

Modified clay (MC) technology is the most effective method to control harmful algal blooms (HABs) and has been widely testified in many countries in recent decades. Although dissolved algal organic matter (dAOM) has been found to be abundant in HAB-affected waters, little is known about its effect on MC flocculation. Prorocentrum donghaiense was chosen as the model organism in this study. The flocculation of MC with different concentrations of dAOM was observed by particle image velocimeter, and the removal efficiency of MC to microalgae was determined using a fluorometer. The results showed that a small amount of dAOM resulted in faster flocculation, larger flocs, higher floc strength and better floc regeneration capacity, and the removal efficiency of microalgae by MC could reach about 80%. However, large amounts of dAOM produced during the occurrence of HABs could inhibit the flocculation of MC, and the removal efficiency of microalgae was only about 35%. Furthermore, with the increase of dAOM, the zeta potential of MC particles decreases from 1.56 mV to −18.9 mV, and the repulsive force between the particles also increases. The examination of 18-angle laser light scattering gel permeation chromatography and specific ultraviolet absorption (SUVA254) revealed that some hydrophobic organic macromolecules preferred to attach to MC and increase MC flocculation at a tiny amount of dAOM, while a higher concentration of dAOM would inhibits flocculation by reducing surface activity and intergranular repulsion. According to the findings of this study, the dosage of MC must be increased in order to obtain the best algal removal efficiency with MC. [ABSTRACT FROM AUTHOR]

Phycosphere bacteria can regulate the dynamics of different algal blooms that impact marine ecosystems. Phaeocystis globosa can alternate between solitary free-living cells and colonies and the latter morphotype is dominate during blooms. The mechanisms underlying the formation of these blooms have received much attention. High throughput sequencing results showed that the bacterial community composition differed significantly between colony and solitary strains in bacterial composition and function. It was found that the genera SM1A02 and Haliea were detected only among the colony strains and contribute to ammonium accumulation in colonies, and the genus Sulfitobacter was abundant among the colony strains that were excellent at producing DMS. In addition, the bacterial communities of the two colony strains exhibited stronger abilities for carbon and sulfur metabolism, energy metabolism, vitamin B synthesis, and signal transduction, providing inorganic and organic nutrients and facilitating tight communication with the host algae, thereby promoting growth and bloom development. • The bacterial community composition and functions differed significantly between colony and solitary strains. • The genera SM1A02 and Haliea were present only in the colony strains and could cause ammonium enrichment in the colonies. • The genus Sulfitobacter was abundant in the colony strains, and members of this genus are excellent producers of DMS. • The bacterial communities of the two colony strains had stronger capabilities in matter and energy metabolism. • The information communication between the bacteria and the host algae was closer in the colony. [ABSTRACT FROM AUTHOR]

Blooms of the toxic dinoflagellate Karenia mikimotoi could threaten the survival of marine life, and modified clay (MC) is considered a promising method for the control of harmful algal blooms. Here, using marine medaka as the model organism, the toxicity of K. mikimotoi before and after MC disposal was investigated. The results showed that only a certain density of intact K. mikimotoi cells could cause obvious damage to fish gills and lead to rapid death. A systematic analysis of morphology, physiology, and molecular biology parameters revealed that the fish gills exhibited structural damage, oxidative damage, osmotic regulation impairment, immune response activation, and signal transduction enhancement. MC can flocculate K. mikimotoi rapidly in water and reduce its toxicity by reducing the density of intact algae cells and hemolytic toxicity. The results indicate that MC is an effective and safe method for controlling K. mikimotoi blooms. [ABSTRACT FROM AUTHOR]

Dissolved algal organic matter (dAOM) originating from harmful algal blooms (HABs) can deteriorate the quality of municipal water supplies, threaten the health of aquatic environments, and interfere with modified clay (MC)-based HABs control measures. In this study, we explored the composition of dAOM from Prorocentrum donghaiense , a typical HAB organism, and assessed the influence of dAOM on MC flocculation. Our results suggested that dAOM composition was complex and had a wide molecular weight (MW) distribution. MW and electrical properties were important dAOM characteristics affecting flocculation and algal removal efficiency of MC. Negatively charged high-MW components (>50 kDa) critically affected algal removal efficiency, reducing the zeta potential of MC particles and leading to small and weak flocs. However, the effect of dAOM depended on its concentration. When the cell density of P. donghaiense reached HAB levels, the high-MW dAOM strongly decreased the algal removal efficiency of MC. [Display omitted] • Dissolved algal organic matter (dAOM) hinders the effect of modified clay (MC). • Molecular weight (MW) and electrical properties of dAOM determine impact on MC. • Negatively charged high-MW dAOM had a concentration-dependent inhibitory effect. • Flocculation was inhibited by altering surface electrical properties of MC particle. [ABSTRACT FROM AUTHOR]

The abalone industry has suffered immense economic losses due to the occurrence of harmful algal blooms (HABs). Among the methods for mitigating HABs, modified clay is considered the most promising strategy and has been successfully used for field applications in many countries, and its environmental effects have become a subject of global concern. The effects of modified clay on the survival, growth, nutritional quality, and oxidative stress indicators of abalone were studied based on both laboratory and field experiments. The results showed that modified clay at 3–10 times the concentrations used for HAB treatment did not affect the survival of abalone. During the laboratory experiments, the increases in abalone shell length and weight nonsignificantly decreased with increasing concentrations of modified clay at 1–15 d, whereas the weight of abalone in the experimental groups increased rapidly during the recovery period at 16–30 d. The growth and nutrition qualities of abalone in field experiments showed negligible differences between the control and experimental groups. Catalase (CAT) activity in the hepatopancreas and superoxide dismutase (SOD) activity in the gills were significantly affected by certain concentrations of modified clay at individual time points, whereas the malondialdehyde (MDA) content decreased in all experimental groups within 96 h. The removal of bacteria and the mitigation of water quality decline were among the effects of modified clay that contributed to the decrease in MDA content. The present study showed that modified clay had no obvious adverse effects on the survival, growth, quality, or oxidative stress indicators of abalone at the experimental concentrations, thus providing a reference for the field application of modified clay in typical aquaculture areas. Environ Toxicol Chem 2020;39:2065–2075. © 2020 SETAC [ABSTRACT FROM AUTHOR]

Phaeocystis globosa is a harmful algal bloom (HAB) species worldwide. Using modified clay (MC) to control HABs and to mitigate their adverse effects is currently a commonly used method in China. In this paper, the effects of oxidized composite modified clay (OXI-MC) on P. globosa were studied from different perspectives. The results show that the OXI-MC could effectively remove P. globosa and inhibit both the growth of residual algal cells and the formation of new colonies. The P. globosa algal biomass removal efficiencies after 3 h reached 90% at a dose of 0.1 g/L, and the number of colonies with different particle sizes was greatly reduced. Compared with those of the control, the superoxide dismutase (SOD) activity, catalase (CAT) activity, and malondialdehyde (MDA) content of the residual algae significantly increased, indicating that OXI-MC caused oxidative stress in the algal cells. In addition, we evaluated the effects of OXI-MC on the photosynthesis of residual microalgae and found that the maximal photochemical efficiency of photosystem II (PSII) under dark adaptation (Fv/Fm) and actual photochemical efficiency of PSII (ΦPSII) decreased, severely damaging the photosynthesis efficiency, implying that OXI-MC effected the photosynthesis system of P. globosa. The results of this study clarify that OXI-MC could remove the most of algal cells and break up the colonies of P. globosa by collision, flocculation, and releasing active substances, as well as inhibit effectively the growth and colony formation of residual P. globosa by causing oxidative stress, reducing photosynthesis activity, accelerating the degradation of polysaccharides, and inhibiting the formation of colonies. [ABSTRACT FROM AUTHOR]

Microscopic propagules of Ulva species (UMPs) spread on Subei Shoal are believed to play a significant role in the formation of the Yellow Sea green tide. Previous laboratory and ship-based studies indicated that modified clay (MC) can effectively remove UMPs from the water column and restrict their germination. To evaluate the effectiveness of this method under natural conditions, a mesocosm experiment was conducted on the Zhugensha sandbank on Subei Shoal. The results show that the suspended particles on the sandbank would partially disturb the flocculation process between the MC and UMPs. However, the MC at a proper dose could effectively remove UMPs from the water column and decrease the adhesion and germination of UMPs on the nylon ropes that comprised the mariculture rafts by >75%. This method was proven a potential strategy to restrict the initial biomass accumulation of green algae on Subei Shoal. However, field trials in larger time-space scales are still needed to assess the efficiency of this method when used in the open sea. [ABSTRACT FROM AUTHOR]

Algal blooms have emerged as a global phenomenon affecting coastal areas, while the regulatory mechanisms are poorly understood. To explore the effects of environmental factors, especially phosphate concentrations, on the outbreak and maintenance of algal blooms, this study used a metatranscriptomic approach to analyze the molecular responses of phytoplankton during two blooms in 2013 near Qinhuangdao, China. Pico/nanophytoplanktons (< 10 μm) were dominant numerically in the two algal blooms. Significant shifts in KEGG pathway expression were observed with the succession of phytoplankton, suggesting high temporal plasticity in the expressed metabolic capacity. The KEGG pathway expression pattern in the multispecies bloom on August 22 showed higher gene expression of primary metabolic pathways and lower gene expression of secondary metabolic pathways than that in the monospecific bloom on July 20. Pico/nanophytoplankton showed species-specific transcriptional responses to the shifts in N/P ratios and phosphate concentrations. Our results demonstrate how the species specificity and temporal plasticity of resource utilization capacities enable pico/nanophytoplankton to induce monospecific and multispecies blooms under different phosphate conditions. This study provides a basis for further work on the gene responses of multispecies assemblages of algae to different environmental parameters during algal bloom succession. [ABSTRACT FROM AUTHOR]

Electrophysiological techniques, by measuring bioelectrical signals and ion channel activities in tissues and cells, are now widely utilized to study ion channel-related physiological functions and their underlying mechanisms. Electrophysiological techniques have been extensively employed in the investigation of animals, plants, and microorganisms; however, their application in marine algae lags behind that in other organisms. In this paper, we present an overview of current electrophysiological techniques applicable to algae while reviewing the historical usage of such techniques in this field. Furthermore, we explore the potential specific applications of electrophysiological technology in harmful algal bloom (HAB) research. The application prospects in the studies of stress tolerance, competitive advantage, nutrient absorption, toxin synthesis and secretion by HAB microalgae are discussed and anticipated herein with the aim of providing novel perspectives on HAB investigations. [ABSTRACT FROM AUTHOR]

The cosmopolitan alga Phaeocystis globosa forms massive colonies during blooms. In addition to producing haemolytic toxins that affect the ecosystem, centimetre-sized colonies can block nuclear power plant cooling systems. Nitrogen plays a key role in P. globosa blooms; however, the preferred form of inorganic nitrogen taken up by colonies remains unknown. Therefore, we set up four groups with different nitrogen types and levels of enrichment. The culture medium and intracolonial fluid were sampled at different times for the determination of nutrient concentrations to elucidate the nutrient uptake strategy that presumably favours colonies. Although NH 4 + - N and NO 2 - -N were absorbed by the colonies, NO 3 - -N was the favoured nitrogen, and the average uptake rate of NO 3 - -N was significantly higher than that of NH 4 + -N and NO 2 - -N in each group (P < 0.05). In the enriched groups, the replenishment of NO 3 - -N in the intracolonial fluid was faster than that of NH 4 + -N . The symbiotic bacteria and some biochemical processes may explain the differences in the nutrient concentrations inside and outside of the colonies. Considering the high consumption of NO 3 - -N during P. globosa blooms, controlling the concentration of NO 3 - -N is key to preventing P. globosa blooms. [ABSTRACT FROM AUTHOR]

• Apart from flocculation, MC has additional mechanisms of inhibiting residual cell growth and mitigating HAB. • There are two processes underlying the indirect mechanism of HAB control: one is the oxidative stress process, the other is the programmed cell death (PCD) process. • The lysis of damaged residual cells which experience ineffective collision with MC particles induces PCD, that inhibits the growth of residual cells in further and mitigates HAB gradually. On the basis of experiences in mitigating harmful algal blooms (HABs) with modified clay (MC), a bloom does not continue after the dispersal of the MC, even though the density of the residual cells in the water remains as high as 20–30% of the initial cell density. This interesting phenomenon indicates that in addition to flocculation, MC has additional mechanisms of HAB control. Here, Aureococcus anophagefferens was selected as a model organism to study the physiological response dynamics of residual cells treated with MC, and RT-qPCR was used to measure the differential expression of 40 genes involved in anti-oxidation, photosynthesis, phospholipid synthesis, programmed cell death and cell proliferation at five time points. The results showed that every functional gene category exhibited a "V" shaped pattern with a turning point. It was reflected that there were two processes for MC inhibiting the growth of residual cells. One is the oxidative stress process (OSP) caused by ineffective collision with MC, whose effect weakened gradually; another is the programmed cell death process (PCDP) caused by the lysis of damaged residual cells, whose effect enhanced two days after MC treatment. In addition, the scanning electron micrographs verified that some of the residual cells were deformed or even lysed. Combined with the effects of OSP and PCDP in dynamics, the growth of residual cells was inhibited and was followed by gradual bloom disappearance. This study further elucidates the mechanism of MC controlling HABs at the molecular level and enable a more comprehensive understanding of HAB mitigation using MC. [ABSTRACT FROM AUTHOR]

The impacts of harmful algal blooms (HABs) on economies, public health, ecosystems, and aquaculture across the globe have all increased in recent decades, and this has been acutely the case in China. Here, we review the history of HABs and HABs research in China, as well as recent trends in HABs and future prospects of HAB science in China. The most updated analyses demonstrated that the number of HAB events, the number of HAB species, the aerial coverage of HABs, and the impacts of HABs in Chinese waters during the 21st century were all higher than that during the last two decades of the 20th century. The increase in the number of HABs in China has been significantly correlated with the increased discharge of ammonium and total phosphorus into coastal waters (p < 0.01 for both). Notable newly recognized events this century have included chronic HABs caused by Prorocentrum donghaiense and Karenia mikimotoi , a paralytic shellfish poisoning event caused by Gymnodinium catenatum that sickened 80 people, brown tides caused by Aureococcus anophagefferens , green tides caused by Ulva prolifera , golden tides caused by Sargassum horneri , and the disruption of a nuclear power plant caused by a bloom of Phaeocystis globosa. A series of key discoveries regarding HABs has been made this century including documentation of nearly all known HAB toxins in Chinese waters, discovery of novel cyst-formation and/or life stages of multiple HABs-causing species, identification of the chemical and physical oceanographic drivers of multiple HABs including those formed by P. donghaiense, K. mikimotoi , and U. prolifera , and the successful mitigation of HABs via the use of modified clay approaches. Future research prospects highlighted include the use of macroalgae as a means to prevent, mitigate, and control (PCM) HABs and the process by which multi-disciplinary studies involving molecular approaches (omics), remote in situ detection, artificial intelligence, and mega-data analyses might be used to develop refined and realistic HAB forecasting platforms. Collectively, this review demonstrates the significant evolution of HAB science since the 20th century in China and demonstrates that while HABs in China are complex and widespread, recent and on-going discoveries make the development of detailed understanding and effective measures to mitigate the negative effects of HABs a hopeful outcome in the coming years. [ABSTRACT FROM AUTHOR]

Being supplied from both terrestrial inputs and internal regeneration, nitrate is usually in excess in the Changjiang River estuary (CRE) and adjacent waters (CREAW). As significant reactions in the nitrogen cycle, nitrate assimilation and nitrification rates were calculated by field incubation experiments following the isotope dilution method during June and November 2014. Besides this, distribution of other field parameters in the CREAW were also investigated. The results showed that the nitrate assimilation rates were higher in nearshore areas and lower in offshore areas. The nitrate assimilation rates were also higher during June, at 0.3–11.9 μmol L −1 d −1 , whereas the rates were 0–3.2 μmol L −1 d −1 in November. The highest rate was observed in the surface water of the estuary, where the chlorophyll- a (chl- a ) concentration reached 11.02 μg L −1 . In addition, the phytoplankton community structure affected the nitrate assimilation rates, and dinoflagellates presented weaker nitrate assimilation abilities than those of diatoms. By contrast, the nitrification rates were higher in nearshore areas in June but higher in offshore areas in November. The nitrification rates were 0–4.1 μmol L −1 d −1 and 0–3.6 μmol L −1 d −1 in June and November, respectively. At most sites, the nitrification rates were positively correlated with the ammonium concentrations and were higher in November, which might be attributable to the higher temperature. Moreover, a theoretical calculation was used to study the regional nitrate flux throughout the vertical water column. The results showed that a gradual supplement from nitrification might replenish the nitrate consumed by assimilation far from the CRE. The overall result was that terrestrial input remained the primary source of estuarine nitrate; however, the role of internal nitrate regeneration, which would be effective for primary production in the CREAW, should also be highlighted as a source of nitrate, especially in offshore areas. [ABSTRACT FROM AUTHOR]

Cyst formation plays an important role in the resistance of dinoflagellates to adverse environments, and cyst germination is considered one of the causes of harmful algal blooms (HABs). Among the methods for mitigating HABs, modified clay (MC) is considered a promising strategy because of its high efficiency and low environmental impacts. The typical HAB species Alexandrium pacificum was focused on in this study to clarify the effects of MC on cyst formation and germination. The results showed that more than 90% of the vegetative cells were removed under the 0.6 g/L MC treatment. The vegetative cell density was monitored over 90 d and increased slightly to the peak at 10 d after the cell removal experiment, but persistent growth was not observed. The amount of cysts was maximal at 20 d after removal, however, most of the cysts were temporary cysts that subsequently disappeared. After 80 d, all the remaining cysts were resting ones. The total density of resting cysts was higher under MC concentrations of 0.2 and 0.4 g/L and lower under concentrations of 0.6, 0.8 and 1.0 g/L compared with that in the control. The total formation rate of resting cysts was 29.6% in the control group, and the lowest formation rate in the experimental groups was 15.5% at 0.6 g/L MC. The total germination rate of resting cyst decreased as the MC concentration increased, and approximately 68.0% of the resting cysts in the control group germinated successfully, whereas the addition of MC reduced the germination rate to as low as 12.4%. Our results indicated that the application of appropriate MC concentrations may provide an effective mitigation strategy for A. pacificum blooms because it does not leave more residual cysts, which can act as “seeds” for the initiation of HABs. [ABSTRACT FROM AUTHOR]

Among the strategies for treating harmful algal blooms, flocculation using modified clay (MC) has been widely applied in the field. This paper studied the mitigation of MC on Amphidinium carterae Hulburt, finding that MC could not only effectively remove A. carterae , but also affect the physiological activities of the residual algae and inhibit their normal growth. The superoxide dismutase (SOD) activity, catalase (CAT) activity and malondialdehyde (MDA) content of the residual algae significantly increased compared with the control, indicating that MC stimulated the accumulation of reactive oxygen species (ROS) in algal cells. In addition, the cell density was significantly correlated with the SOD activity, CAT activity and MDA content in the experiment groups, suggesting that intracellular ROS might be the main internal factor inhibiting cell growth. To reveal the mechanism of ROS generation, this paper further evaluated the effect of MC on photosynthesis in the residual microalgae, and found that compared with the control the absorption flux per photosystem II (PSII) reaction center (ABS/RC), the trapping flux per RC (TR 0 /RC) and the electron transport flux per RC (ET 0 /RC) increased, while the TR 0 /ABS and ET 0 /ABS decreased after adding 0.10 g/L and 0.25 g/L MC. These findings indicate that the MC led to an imbalance between photosynthetic light absorption and energy utilization and that the partial RCs became non-primary quinone electron acceptor (Q A )-RCs, further inducing the over-excitation of the active RCs. And MC caused the suppression of the electron transport chain (ETC): the ETC from the Q A to the secondary quinone electron acceptor (Q B ) was blocked and the size of plastoquinone pool decreased, which could induce the over-reduction of PSII. The over-excitation of PSII and the damaged ETC likely induce the generation of ROS during photosynthesis. Thus, MC likely induced the accumulation of intracellular ROS due to photosynthesis inhibition, consequently hindering the growth of the residual algae. [ABSTRACT FROM AUTHOR]

Clay dispersal is one of only a few mitigation methods for harmful algal blooms (HABs) ever applied in the field; however, low flocculation efficiency has always been the most significant drawback associated with natural unmodified clays. This review discusses key factors affecting the flocculation efficiency, based on results obtained in studies of the mechanisms underlying interactions between clay particles and HAB organisms. It further elaborates clay surface modification theory and methods for improving removal efficiency of HAB cells, followed by descriptions of various modified clays successfully prepared with removal efficiencies of HAB cells that are up to hundreds of times greater than natural clays and have lower dosing requirements of 4–10 t/km 2 . Presently, modified clays are the most widely used method for the mitigation of HAB in the field in China. This review also evaluates potential ecological effects of modified clay disposal on water quality, typical aquatic organisms, benthic environments, and ecosystems. Both laboratory and field results have demonstrated that modified clays markedly can actually improve water quality after treatment and pose no negative effects on aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Qingdao waters, including both the semi-enclosed Jiaozhou Bay (JB) and the adjacent water out of JB (OJB), have been the areas that are most frequently affected by harmful algal blooms (HABs) in the western Yellow Sea (west of 124°E). In this research, HAB occurrences in Qingdao waters from 1990 to 2009 were investigated using spatial tools in geographic information system (GIS) and are discussed in terms of their connection to temporal variation. Additionally, the effects of each HAB occurrence were further evaluated using a simple model. The calculated results were then visualized using a GIS software to indicate the effects of HABs in Qingdao waters during the entire period. As a result, the OJB was proven to be responsible for the frequent HAB occurrences in Qingdao waters after 2000, although JB was traditionally believed to be the principle source of HAB occurrences in Qingdao waters. In addition, increasing nitrogen and N/P structure imbalance were essential for increasing HAB occurrences in Qingdao waters throughout the entire period, especially for the recent HAB occurrences in the OJB. The results of this research would improve the current understanding on HAB occurrences in Qingdao waters, which would benefit HAB monitoring and the implementation of a control strategy in China as well. [ABSTRACT FROM AUTHOR]

Prevention of annual 'green tides' caused by blooms of the green macroalga Ulva prolifera, which have occurred in the Yellow Sea since 2007, has received much attention. Increasing evidence indicates that micro-propagules on the rafts used for Porphyra yezoensis aquaculture along the coastline of Jiangsu Province in China, were the primary source of these green tides. In this study, we investigated the effectiveness of a silicone antifouling coating for preventing the adhesion and germination of U. prolifera micro-propagules on bamboo and nylon ropes, which have been used in rafts for P. yezoensis aquaculture. Our results demonstrated that a coating of silicone (Sylgard 184) containing 1.0 wt.% sodium benzoate (NaB) could reduce the adhesion rate to <5% and completely inhibited the growth of U. prolifera propagules on the coated surfaces. Coating bamboo and nylon ropes with NaB-incorporated silicone thus proved a potentially effective method for controlling the initial biomass accumulation of U. prolifera. [ABSTRACT FROM AUTHOR]

Modified clay (MC) technology is an effective method for controlling harmful algal blooms (HABs). Based on field experience, a bloom does not continue after treatment with MC, even though the residual HAB biomass accounts for 20–30% of the initial biomass. Laboratory studies using unialgal cultures have found that MC could inhibit the growth of the residual algal cells to prevent HABs. Nevertheless, the phytoplankton in field waters is diverse. Therefore, unclassified complex mechanisms may exist. To illustrate the molecular mechanisms through which MC controls HABs in the field and verify the previous laboratory findings, a series of experiments and bioinformatics analyses were conducted using bloom waters from aquacultural ponds. The results showed that a 72.29% removal efficiency of algal biomass could effectively control blooms. The metatranscriptomic results revealed that the number of downregulated genes (131,546) was greater than that of upregulated genes (24,318) at 3 h after MC addition. Among these genes, several genes related to DNA replication were downregulated; however, genes involved in DNA repair were upregulated. Metabolism-related pathways were the most significantly upregulated (q < 0.05), including photosynthesis and oxidative phosphorylation. The results also showed that MC reduced most of the biomass of the dominant phytoplankton species, likely by removing apical dominance, which increased the diversity and stability of the phytoplankton community. In addition to reducing the pathogenic bacterial density, MC reduced the concentrations of PO 4 3− (96.22%) and SiO 3 2− (66.77%), thus improving the aquaculture water quality, altering the phytoplankton community structure (the proportion of Diatomea decreased, and that of Chlorophyta increased), and inhibiting phytoplankton growth. These effects hindered the rapid development of large phytoplankton biomasses and allowed the community structure to remain stable, reducing HAB threats. This study illustrates the molecular mechanisms through which MC controls HABs in the field and provides a scientific method for removing HABs in aquacultural waters. [Display omitted] • MC causes oxidative stress to residual algal cells, inhibiting growth. • In residual cells, processes of metabolism and genetic information processing are disordered. • MC improves the water quality and decreases nutrients to inhibit growth and regulate the phytoplankton community structure. • MC removes dominant phytoplankton species to increase the diversity and stability of the phytoplankton community. [ABSTRACT FROM AUTHOR]

• By ecological surveys, it was found that low temperatures, high nitrate, and low organic phosphorus induced the P. globosa bloom in the Beibu Gulf. • The unique genetic and physiological characteristics that allow P. globosa to stand out as a dominant species in such an environment. • The high expression of high-affinity nitrate transport protein genes and glycan synthesis genes accelerated the P. globosa bloom. • The energy and material expenditure was redistributed in colonial cells promoting the mucilaginous envelope formation and the rapid proliferation. The haptophyceae Phaeocystis globosa is a species responsible for harmful algal blooms in the global ocean, forming blooms in the Beibu Gulf annually since 2011. This species can alternate between solitary free-living cells and colonies. Colonies are the dominant morphotype during blooms. To date, the underlying mechanism of P. globosa blooms in the Beibu Gulf is poorly understood. After combining results of ecological surveys, laboratory studies, and metatranscriptome and bioinformatics analyses, it was found that low temperatures, high nitrate, and low organic phosphorus induced P. globosa blooms in the Beibu Gulf. Additionally, the unique genetic and physiological characteristics that allow P. globosa to stand out as a dominant species in such an environment include (1) several genes encoding high-affinity nitrate transport proteins that could be highly expressed under sufficient nitrate conditions; (2) energy metabolism genes involved in photosynthesis and oxidative phosphorylation that were actively expressed at low temperatures to carry out carbon and energy reversion and produce sufficient ATP for various life activities, individually; (3) abundant glycan synthesis genes that were highly expressed at low temperatures, thus synthesizing large quantities of proteoglycans to construct the mucilaginous envelope forming the colony; (4) cells in colonies exhibited active gene expression in DNA replication contributing to a faster growth rate, which could help P. globosa occupy niches quickly; and (5) the energy and material expenditure was redistributed in colonial cells accompanied with chitin filaments and flagella degraded, more expenditure was used for the synthesis of the mucilaginous envelope and the rapid proliferation. [ABSTRACT FROM AUTHOR]

The performances of aluminum chloride modified clay (AC-MC), aluminum sulfate modified clay (AS-MC) and polyaluminum chloride modified clay (PAC-MC) in the removal of Aureococcus anophagefferens were compared, and the potential mechanisms were analyzed according to the dispersion medium, suspension pH and clay surface charges. The results showed that AC-MC and AS-MC had better efficiencies in removing A. anophagefferens than PAC-MC. The removal mechanisms of the three modified clays varied. At optimal coagulation conditions, the hydrolysates of AC and AS were mainly monomers, and they transformed into Al(OH) 3(am) upon their addition to algae culture, with the primary mechanism being sweep flocculation. The PAC mainly hydrolyzed to the polyaluminum compounds, which remained stable when added to the algae culture, and the flocculation mainly occurred through polyaluminum compounds. The suspension pH significantly influenced the aluminum hydrolysate and affected the flocculation between the modified clay and algae cells. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) can elicit several negative effects on aquatic environment (such as depleting the oxygen, blocking the sunlight, destroying the habitats of organisms) and life health (including poisoning/killing marine mammals, birds and human). Among the various control strategies for HABs (physical manipulation needs lots of manpower and expensive equipment, chemicals treatment has some toxic byproduct and high residual, microbial agents only has limited in laboratory research), the coagulation-flocculation of HAB species by modified clay (MC) has been proven to be an effective, low-cost and environmentally friendly method that has been widely applied in the field, particularly in eastern Asia. In order to examine the long-term effects of MC treatment, this study investigated the alternations in seawater of Skeletonema costatum, a high biomass dominant HAB species along the Chinese coast, by comparing the degradation of S. costatum detritus (A1) with the application of MC treatment (A2) and MC treatment in sediment condition (A3). The low dosage of 0.25 g/L MC could efficiently remove 4×10 cells/L of S. costatum cells within 3.5 h (approximately 97% removal). In addition, the results showed that both inorganic and organic nutrients were effectively reduced from seawater by MC particles. Compared to the total nitrogen (TN) and total phosphorus (TP) concentrations in A1 seawater, 44% of TN and 93% of TP in A2 seawater, as well as 72% of TN and 93% of TP in A3 seawater were removed during the one-month incubation period. Simultaneously, 64% of DISi in A2 and 44% of DISi in A3 significantly decreased ( P<0.001). This study demonstrated that MC treatment was able to significantly increase the downward flux of nutrients and delay the release velocity of inorganic nutrient from MC-algae matrix into the overlying seawater, particularly within sediment environment. [ABSTRACT FROM AUTHOR]

We present results on the effect of modified clay on cyst formation of Scrippsiella trochoidea in harmful algal bloom (HAB). Modified clay (in concentration of 0, 0.1, 0.5, and 1.0 g/L) were added to cultures, and observations were made on cysts of S. trochoidea under controlled laboratory conditions. Results indicate that the removal rate of algal cells reached 97.7% at the clay concentration of 1.0 g/L. The cyst formation rate increased from 4.6% to 24.6% when the concentration of clay was increased from 0 to 1.0 g/L. Two cyst metamorphs were observed: spinal calcareous cysts and smooth noncalcareous ones. The proportion of the spinal cysts decreased from 76.9% to 24.1% when clay concentration increased from 0 to 1.0 g/L. In addition, modified clay affected cyst germination. The germination rate decreased with the increases in the clay concentrations. Non-calcareous cysts had a lower germination rate with a longer germination time. We conclude that modified clay could depress algal cell multiplication and promote formation of temporal cysts of S. trochoidea, which may help in controlling HAB outbreaks. [ABSTRACT FROM AUTHOR]

An integrated methodology for eutrophication assessment, which integrates both water quality indicators (causative factors) and ecological response indicators (effect factors), is described. It is then applied to rank the eutrophication status of the years 2007 and 2008 in the southwest Bohai Sea. The assessment model identified that north Bohai Bay and west Laizhou Bay were the two areas with the most serious eutrophication problems in the southwest Bohai Sea. In addition, compared to that in the west Laizhou Bay, the eutrophication conditions in the north Bohai Bay was more serious in both years. Eutrophication problems such as harmful algal blooms (HABs) and low dissolved oxygen (DO) events in north Bohai Bay were frequent. The integrated method outmatched the currently used Chinese nutrient index method by definitely identifying areas with the most serious eutrophication problems, while the nutrient index method gave ambiguous results between the two years. Inclusion of both causative factors and effect factors, combining concentration, spatial coverage and frequency of indicators, as well as use of multi-season monitoring datasets in the methodology result in a more accurate, representative and useful assessment. [ABSTRACT FROM AUTHOR]

Algal organic materials (AOMs) are one critical factor affecting the efficiency of modified clays used for the mitigation of harmful algal blooms (HABs). This study was conducted to develop a deeper understanding of the mechanisms and factors affecting the adsorption of AOMs onto modified clays. Sodium alginate (polysaccharide) and kaolinite modified with polyaluminium chloride (PACl) were used as AOMs and modified clay model substances, respectively, and the effects of modifier dosage, contact time, solution pH and ionic strength were investigated through batch adsorption experiments. Kinetics revealed that the alginate adsorption rate was described well by a pseudo-second order model. PACl effectively enhanced the adsorption capacity of kaolinite and increased the adsorption rate, and the optimum additive amount of PACl was 5%. The experimental data fitted both the Freundlich and Langmuir adsorption equations well. The adsorption thermodynamics for alginate onto modified clays suggests that alginate adsorption is a spontaneous process. The adsorption of alginate onto modified clays was highly dependent on pH, with a decrease in adsorption observed with increased pH to 9.48, but the opposite was true above pH 9.48. Finally, adsorption increased with increasing ionic strength. [ABSTRACT FROM AUTHOR]

Abstract: Harmful algal blooms (HABs) are harmful to coastal ecosystems, fisheries, the aquaculture industry, and even human health, thus they have received great attention worldwide. In this study, geostatistical tools in Geographic information system (GIS) were used to analyze HAB data collected over the last 11 years in the southwest Bohai Sea with the goal of detecting spatial and temporal characteristics of HAB events in this area. The seasonality, trend of HAB occurrences and the spatial pattern of HAB events were examined by time-series analysis and nearest neighbor analysis, respectively. The frequency of HAB occurrences was mapped using kernel density estimation, and the harm caused by HAB events was assessed and then categorized using a characteristic-based empirical model. The occurrences of HABs not only exhibited significant seasonality and a “single peak” trend in time but also were clustered in space. HABs had both a high frequency of occurrence and a high harm in the north Bohai Bay and the Yellow River estuary. In addition, HABs posed a high harm in the nearshore area near the city of Huanghua in Bohai Bay and the offshore area in the middle Bohai Bay; thus, HAB monitoring and/or management should be concentrated in these locales. Compared to previous descriptions, this research utilized a visualizable approach to more fully identify the scope, distribution, and characteristics of HAB occurrences in the southwest Bohai Sea, thus providing useful information to support the implementation of a monitoring and management program for HABs. [Copyright &y& Elsevier]

For many years, the dispersal of modified clay (MC) has been used to control harmful algal blooms (HABs) in coastal waters of China. MC flocculation efficiency can be influenced by many factors in variable and complex natural environments, including high concentrations of dissolved organic matter (DOM) in the water to be treated. Since many HABs occur in nearshore waters where DOM concentrations are high, this is a significant problem that requires urgent attention. This study involved the use of humic acid as a representative form of DOM to study the influence of organic matter on the MC flocculation process. At high concentrations, humic acid was adsorbed onto MC particles, resulting in a decrease in surface potential and an increase in electrostatic repulsion between the clay particles; this decreased the MC settling rate and increased the water clarification time. Flocs were characterized by their relatively small particle size, high particle concentration, and low collision efficiency, which together resulted in slow clarification of the water after MC spraying. Based on the mechanism of the DOM-MC interaction and combined with the Derjaguin-Landau-Verwey-Overbeek theory and theoretical considerations of clay surface modification, the "ionic atmosphere compression" method was used to improve MC flocculation efficiency in high-organic water. This method increased the ionic strength of the clay stock solution by adding salt, thereby compressing the ionic atmosphere of MC particles and lowering the potential barrier, allowing the MC particles in the treated water to flocculate rapidly and form large flocs, followed by further floc growth and rapid settling via differential sedimentation. The settling rate of MCs improved by a factor of two and the removal efficiency of the HAB cells increased by 7–28%. This study provides important baseline information that will extend the application of MC to HAB control in water bodies with high organic loadings. [Display omitted] • Dissolved organic matter influences the settling rate of MC during HABs control. • "Ionic atmosphere compression" method can improve the MC settling rate by up to 200%. • The high settling rate of MC was caused by large flocs formed in high salinity area. • This study provides a basis for the application of MC in high-organic water. Dissolved organic matter can decrease MC flocculation efficiency and settling rate when the clay is used to control HABs, a limitation that can be addressed by adding salt to the clay slurry before application, thereby implementing the "ionic atmosphere compression" method. [ABSTRACT FROM AUTHOR]

An outbreak of harmful algal blooms (HABs) often leads to the death of fish and other marine organisms and causes serious losses to human economic activities. Modified clay (MC) technology is an effective way to control HABs. Although the material and preparation process are based on the premise of green and safety, the potential eco-environmental impacts of MC on non-target organisms should still have to receive attention before field applications can occur. Therefore, the effects of one commonly used modified clay, polyaluminum chloride-modified clay (PAC-MC), on the survival, growth, and oxidative stress of the marine medaka (Oryzias melastigma) were studied. The toxicity test results showed that the 96-h median lethal concentration (96-h LC50) of PAC-MC for newly hatched medaka larvae was 5.204 g/L, which was much higher than the concentration used on site (4–10 t/km2). Within the concentration range of PAC-MC used in this experiment (≤2 g/L), the morphology, heart rate, growth, and aluminum content of larvae did not change with the increase in the modified clay concentration. Low concentrations of PAC-MC (≤0.5 g/L) did not significantly affect catalase (CAT) activity, superoxide dismutase (SOD) activity, peroxidase (POD) activity, and the content of malondialdehyde (MDA), but higher concentrations of PAC-MC (such as 2 g/L) caused oxidative damage to the larvae and increased the antioxidant enzyme activity of the larvae. The present study revealed that under an effective dosage for treating harmful algal blooms on site, PAC-MC had no adverse effects on the survival, growth, oxidative stress, and aluminum content of the newly hatched marine medaka, which provides a scientific basis for the field application of modified clay. [ABSTRACT FROM AUTHOR]

In this study, Karenia brevis 165 (K. brevis 165), a Chinese strain, was used to research brevetoxin (BTX) metabolites. The sample pretreatment method for the enrichment of BTX metabolites in an algal culture medium was improved here. The method for screening and identifying intracellular and extracellular BTX metabolites was established based on liquid chromatography-time-of-flight mass spectrometry (LC-ToF-MS) and liquid chromatography triple quadrupole tandem mass spectrometry (LC-QqQ-MS/MS). The results show that the recovery rates for BTX toxins enriched by a hydrophilic–lipophilic balance (HLB) extraction column were higher than those with a C18 extraction column. This method was used to analyze the profiles of extracellular and intracellular BTX metabolites at different growth stages of K. brevis 165. This is the first time a Chinese strain of K. brevis has been reported that can produce toxic BTX metabolites. Five and eight kinds of BTX toxin metabolites were detected in the cell and culture media of K. brevis 165, respectively. Brevenal, a toxic BTX metabolite antagonist, was found for the first time in the culture media. The toxic BTX metabolites and brevenal in the K. brevis 165 cell and culture media were found to be fully proven in terms of the necessity of establishing a method for screening and identifying toxic BTX metabolites. The results found by qualitatively and quantitatively analyzing BTX metabolites produced by K. brevis 165 at different growth stages show that the total toxic BTX metabolite contents in single cells ranged between 6.78 and 21.53 pg/cell, and the total toxin concentration in culture media ranged between 10.27 and 449.11 μg/L. There were significant differences in the types and contents of toxic BTX metabolites with varying growth stages. Therefore, when harmful algal blooms occur, the accurate determination of BTX metabolite types and concentrations will be helpful to assess the ecological disaster risk in order to avoid hazards and provide appropriate disaster warnings. [ABSTRACT FROM AUTHOR]

• SSSM was used to prepare highly efficient and eco-safe MC for red tide control. • Targeted elemental activation and functional group shaping were achieved. • The algal removal efficiency of the optimum MC was 90.51 % at 0.15 g/L. • Charge neutralization and sweeping are key mechanisms for algal cell removal. Single source with series modifications (SSSM) is a new method to modify clay surfaces by activating clay mineral resources for harmful algal blooms control. In this study, the optimal preparation conditions for this method were obtained using response surface methodology. Based on the material analysis, an important way to obtain modified clay (MC) with the excellent Prorocentrum donghaiense removal performance was explored and the optimum preparation conditions were as follows: calcination temperature 750 °C, alkali neutralization pH 3.7 and clay supplementation ratio 1.3:1. Under these conditions, the calcination treatment can effectively activate the aluminum element in the clay lattice and obtain the largest amount of highly active Al IV and Al V, which are readily released from the lattice as activated aluminum. When the alkali neutralization pH was adjusted to 3.7, the activated aluminum was hydrolyzed and induced into highly positively charged polyhydroxyaluminum compounds. The supplemented kaolin increased the yield of the MC product by surface convergence of the activated aluminum in the system. As a result, the optimized MC can form large particle size flocs with good regeneration and stability during the algal removal process, which greatly improved its ability to coagulate and sediment algal cells. Overall, the MC prepared by the SSSM method achieved high algal removal efficiency through targeted element activation and functional group shaping. [Display omitted] [ABSTRACT FROM AUTHOR]

Among various mitigation strategies for harmful algal blooms (HABs), the flocculation of algal cells by using modified clay (MC) has been widely applied in the field, particularly in Japan, Korea and China. However, to examine the long-term effects and the environmental safety of this method, we investigated alterations in macronutrients and paralytic shellfish poisoning toxins (PSTs) induced by the application of MC treatment to a toxic bloom, Alexandrium tamarense . The control, algal cells grew in nature condition (A1), was compared to the only MC flocculation (A2) and the MC-sediment co-matrix systems of A. tamarense (A3). The low-dosage of 0.25 g L − 1 MC could efficiently remove >90% of the A. tamarense cells within 3.5 h. The mechanisms underlying the effects elicited by MC flocculation on nutrient cycling, PSTs and Chl-a degradation were also discussed. This study demonstrated that MC treatment was able to significantly remove the macronutrients (43–60% TP removal and 17–30% TN removal) and scavenge most of the PSTs from seawater, thereby speeding up the nutrient settling and the transformation and degradation of PSTs (83% decreasing in A2). Simultaneously, the study firstly demonstrated the potential detoxification of PSTs by using MC treatment, from the high toxicity of gonyautoxin 1 and 4 (GTX1 and GTX4) to the lower toxicity decarbamoyl gonyautoxins (dcGTX3) and gonyautoxin 2 (GTX2), particularly within the water-sediment environment during the two month incubation. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs), especially those caused by toxic dinoflagellates, are spreading in marine ecosystems worldwide. Notably, the prevalence of Karenia brevis blooms and potent brevetoxins (BTXs) pose a serious risk to public health and marine ecosystems. Therefore, developing an environmentally friendly method to effectively control HABs and associated BTXs has been the focus of increasing attention. As a promising method, modified clay (MC) application could effectively control HABs. However, the environmental fate of BTXs during MC treatment has not been fully investigated. For the first time, this study revealed the effect and mechanism of BTX removal by MC from the perspective of adsorption and transformation. The results indicated that polyaluminium chloride-modified clay (PAC-MC, a typical kind of MC) performed well in the adsorption of BTX2 due to the elevated surface potential and more binding sites. The adsorption process was a spontaneous endothermic process that conformed to pseudo-second-order adsorption kinetics (k 2 = 6.8 × 10−4, PAC-MC = 0.20 g L−1) and the Freundlich isotherm (K f = 55.30, 20 °C). In addition, detailed product analysis using liquid chromatography−mass spectrometry/mass spectrometry (LC−MS/MS) indicated that PAC-MC treatment effectively removed the BTX2 and BTX3, especially those in the particulate forms. Surprisingly, PAC-MC could promote the transformation of BTX2 to derivatives, including OR-BTX2, OR-BTX3, and OR-BTX-B5, which were proven to have lower cytotoxicity. [Display omitted] • Both Karenia brevis cells and BTXs were effectively removed by MC. • MC was found to outperform kaolin in the adsorption of BTX2. • MC reduced toxicity by promoting the transformation of BTX2 to derivatives. [ABSTRACT FROM AUTHOR]

Polyaluminum chloride modified clay (PAC-MC) is a safe and efficient red tide control agent that has been studied and applied worldwide. Although it is well known that the distribution of hydrolytic aluminum species in PAC affects its flocculation, little is known about the influence of particulars aluminum species on the microalgae removal efficiency of PAC-MC; this lack of knowledge creates a bottleneck in the development of more efficient MCs based on aluminum salts. The ferron method was used in this study to quantitatively analyze the distributions of and variations in different hydrolytic aluminum species during the process of microalgae removal by PAC-MC. The results showed that Al a , which made up 5%–20% of the total aluminum, and Al p , which made up 15%–55% of the total aluminum, significantly affected microalgae removal, with Pearson's correlation coefficients of 0.83 and 0.89, respectively. Most of the aluminum in the PAC-MC sank rapidly into the sediments, but the rate and velocity of settlement were affected by the dose of modified clay. The optimal dose of PAC-MC for precipitating microalgae was determined based on its aluminum profile. These results provide guidance for the precise application of PAC-MC in the control of harmful algal blooms. [Display omitted] [ABSTRACT FROM AUTHOR]

• Modified clay is an efficient and environmentally friendly technology for mitigating HABs. • MC can alter nutrient cycling, reduce algal toxins in water and decrease the cyst's germination rate. • The dosage of MC removing HAB effectively has no effect on most cultured organisms. • MC had no significant impacts on the benthic environment in the field application. The application of modified clay (MC) to mitigate harmful algal blooms (HABs) is becoming a widespread practice in China because of its low cost, high efficiency and environmental friendliness. Due to its success in China, this technology has also gained international recognition in recent years. Nevertheless, the eco-environmental impacts of this technology still remain to be a concern to many customers and government agencies, which has motivated scientists in both China and many other countries to evaluate its potential effects on nontarget aquatic organisms, water quality and the benthic environment. This paper reviews the results from these studies both in the laboratory and in the field, which showed that MC does not harm nontarget aquatic organisms and has no negative impact on water quality or the benthic environment. Additionally, findings show that MC can alter nutrient cycling and reduce algal toxins in water bodies. Furthermore, researchers also found that MC affects cyst formation and germination in sedimentary environments. This review is expected to provide scientific guidance for mitigating HABs in China and worldwide using clay or MC. [ABSTRACT FROM AUTHOR]

The circulation systems and ecological environment of the East China Sea (ECS) are greatly influenced by the Kuroshio. The nutrient-rich Kuroshio Subsurface Water (KSSW) has been subject to considerable research attention, but the intrusion pathway, extent and variation of the KSSW over the entire southern ECS shelf are still debated. In June 2015, the dissolved inorganic iodine species (DIIS) were determined, and hydrographic data were collected and analyzed in the southern ECS. Analysis of the collected data suggests that the KSSW mainly intrudes onto the ECS shelf from northeast of Taiwan and bifurcates into a nearshore branch and an offshore branch. The nearshore branch ultimately appears in the subsurface layer within the 50-m isobath off the Zhejiang coast, north of 30 °N, and the offshore branch flows along the 100-m isobath and covers the area outside the 80-m isobath. Another KSSW intrusion along the shelf edge is located at ∼28 °N. This additional KSSW intrusion is weaker, and the offshore area in the southern ECS is mainly influenced by the KSSW intrusion northeast of Taiwan. Compared with the KSSW intrusion on the ECS continental shelf (depth < 100 m) in May 2014, the KSSW intrusion northeast of Taiwan in June 2015 was shifted seaward, had a greater geographical reach and intruded farther north off the Zhejiang coast. The KSSW intrusion in the nearshore area off the Zhejiang coast may promote a decrease in dissolved oxygen (DO) in the bottom water as well as the growth of phytoplankton in the upper water. The expansion of the range of the KSSW intrusion northward in 2015 led to the movement of the low-DO, high-chlorophyll area farther north in 2015 relative to its position in 2014 and may have contributed to the variations in hypoxia and algal blooms. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new method was proposed for preparing modified clays to control harmful algae blooms: single source with series modifications. • Kaolin that was modified by the new method could remove over 85% of Prorocentrum donghaiense cells. • Calcination, acid–alkali treatment, and the supplementation of raw kaolin during aging were indispensable processing steps in the new method. • A schematic mechanism of kaolin modification by the new method to obtain modified clay with high algal cell removal efficiency was illustrated. Modified clay (MC) is an effective and eco-friendly material that is widely used for controlling harmful algae blooms (HABs). In this study, a new method—single source with series modifications (SSSM)—was optimized for preparing a high-quality MC, and aluminum-rich clay (kaolin) was activated with a multistep treatment that included calcination (Cal), acid etching with alkali neutralization (Al–An), and raw clay supplementation and aging (RSA). The results showed that the removal efficiency of Prorocentrum donghaiense by the SSSM–MC exceeded 85%; Cal, Al–An, and RSA were indispensable processing steps for preparing the best MC with the SSSM method. The changes occurring in the mineral structure and chemical composition of kaolin treated by the different steps were characterized by FT-IR, XRD, 27Al-NMR and Al-Ferron. Surface dehydroxylation and disruption of the kaolin lattice after calcination significantly changed the aluminum structure from AlVI to AlV and AlIV. The relatively reactive AlV was readily released from the kaolin lattice with acid etching, and it subsequently reacted with external OH– to generate different polyhydroxyaluminum species because alkali was added during the Al–An step. The acidity of the above complex was further decreased by RSA, greatly increasing the yield of SSSM–MC while assuring the quality. [ABSTRACT FROM AUTHOR]

• COX1 is an effective molecular marker in differentiating P. globosa strains for its low intra-genome variations and high resolution. • High P. globosa genetic diversity was uncovered using COX1. • The chloroplast genome-based molecular marker pgcp1 and mitochondrion genome-based COX1 should be used in parallel for analyzing P. globosa genetic diversity. Accumulating evidence indicates that the haptophyte species Phaeocystis globosa , which plays an important role in climate control and may cause harmful algal blooms (HABs), displays a rich genetic diversity that may be responsible for differences in colonial sizes, different toxicity during blooms, and differential optimum growth temperature. In this project, we demonstrated that COX1 can be used as an effective molecular marker for its low intra-genome variations and high resolution in differentiating different P. globosa strains. Analyzing 57 P. globosa strains and seven field samples revealed high P. globosa genetic diversity with at least seven distinct clades. This study not only demonstrated for the first time that the common molecular marker COX1 can be used for differentiating P. globosa strains with high-resolution, and for tracking dynamics of different P. globosa strains during bloom development, but also revealed that P. globosa had high genetic diversity in the field. [ABSTRACT FROM AUTHOR]

• Through comparative analysis of chloroplast genomes of 13 P. globosa strains, we have developed a molecular marker pgcp1 that can distinguish P. globosa strains with high resolution and high specificity. • The newly developed molecular marker pgcp1 enabled us to uncover high genetic diversity of P. globosa with at least four major clades. The phytoplankton Phaeocystis globosa thrives in a wide range of marine regions and plays an important role in climate control. It can also form harmful algal blooms (HABs) that threaten environments and impact important coastal infrastructures. Mechanisms underlying the formation of P. globosa blooms still remain poorly understood. Accumulating evidence suggests that P. globosa has high genetic diversity and different P. globosa strains may have differential contributions to the development of P. globosa blooms. However, due to the lack of molecular markers with adequate resolution for distinguishing P. globosa genetic diversity, such differential contributions by different P. globosa strains could not be accurately ascertained. As such, high-resolution molecular markers need to be developed and applied to distinguish P. globosa genetic diversity. In this study, we undertook to define high-resolution molecular marker by assembling and comparing the whole chloroplast genomes of P. globosa strains isolated from different regions of the world. Through comparative analysis of P. globosa cpDNAs and detection of single nucleotide variations (SNVs), a molecular marker pgcp1 with improved resolution was developed. The pgcp1 demonstrated the highest resolution compared with other regions including 18S rDNA V4 region, 28S rDNA D1–D2 region and rbcL region, through genetic distance and phylogenetic analysis of 13 P. globosa strains. Molecular analysis of environmental samples and strains collected in multiple expeditions from a wide range of ocean regions including multiple regions in China, Vietnam, Thailand and Western Pacific using pgcp1 as the molecular marker displayed high genetic diversity of P. globosa with at least four major P. globosa clades. In conclusion, we have developed pgcp1 as a high-resolution molecular marker for the harmful algal bloom species P. globosa , which can be used to track intra-species genetic diversity and dynamics of P. globosa during bloom development. [ABSTRACT FROM AUTHOR]