Conversion of Retinoids along the Marine Food Chain Contributes to Adverse Impacts on the Spine, Liver, and Intestinal Health of the Marine Medaka (Oryzias melastigma).

Marine microalgae serve as an aquaculture bait. To enhance algal cell growth and breeding profits, high-intensity light conditions are standard for cultivating bait microalgae, potentially altering microalgal metabolite production. This research revealed that Thalassiosira pseudonana, when subjected to high-intensity light conditions, accumulated significant quantities of retinal (RAL) that transferred through the food chain and transformed into all-trans retinoic acid (atRA) in marine medaka. The study further explored the toxic effects on individual fish and specific tissues, as well as the mechanisms behind this toxicity. The accumulation of atRA in the liver, intestine, and spinal column resulted in structural damage and tissue inflammation, as well as oxidative stress. It also down-regulated the gene transcription levels of key pathways involved in immune function and growth. Furthermore, it disrupted the homeostasis of the intestinal microbial communities. The implications for wildlife and human health, which are influenced by the regulation of microalgal metabolite accumulation and their transfer via the food chain, require further investigation and could hold broader significance.

Autoactivation of Translation Causes the Bloom of Prorocentrum donghaiense in Harmful Algal Blooms.

Harmful algal blooms (HABs) are symptomatic of ecosystem imbalance, leading to major worldwide marine natural disasters, and seriously threaten the human health. Some HAB algae's exceptional genome size prohibited the genomic investigations on molecular mechanisms, for example, Prorocentrum. This study performed translatome sequencing (RNC-seq) for Prorocentrum donghaiense to assemble the translatome reference sequences on appropriate cost to enable the global molecular study at translatome and proteome levels. By analyzing the translatome and proteome of P. donghaiense in phosphor-rich, phosphor-deficient, and phosphor-restored media, we found massive up-regulation of energy and material production pathways in phosphor-rich conditions that enables autoactivation of translation, which is the key to its exponential growth in HABs. To break down the autoactivation, we demonstrated that mild translation delay using very low concentrations of cycloheximide efficiently controls the blooming without harming other aquatic organisms and humans. Our result provides a novel hint for controlling HABs and demonstrated the RNC-seq as an economic strategy on investigating functions of organisms with large and unknown genomes.

Identifying the Source Organisms Producing Paralytic Shellfish Toxins in a Subtropical Bay in the South China Sea.

Identifying the exact phytoplanktonic sources of paralytic shellfish toxins (PSTs) is crucial for monitoring and preventing the buildup of toxin pollution, especially for causative species occurring at low levels. Phytoplankton and shellfish samples were simultaneously collected from representative mariculture zones in Daya Bay, China. Low concentration/low toxicity PSTs predominated with N-sulfocarbamoyl toxins 1, 2 (C1/2) being detected in phytoplankton (≤6.25 pmol L-1) and shellfish (≤0.21 µg STXeq g-1), which pose a potential risk of seafood poisoning. High-throughput sequencing of the phytoplankton samples based on 18S rDNA V4 regions identified 93 genera in 445 operational taxonomic units (OTUs). Five OTUs were assigned to Alexandrium hiranoi, Ambicodamus leei, Alexandrium pacificum, Alexandrium minutum, and an uncertain Alexandrium sp. A. pacificum and A. minutum are candidate PST producers and observed under the light microscope with densities of 66-972 cells L-1. Three strains of toxigenic species were successfully isolated and identified as A. pacificum and A. minutum based on their 18S rDNA V4 regions. The predominant toxins in A. pacificum were C1/2 (43.9-53.6 fmol cell-1) and resembled the toxins found in field samples predominated with C1/2. A. minutum produced only gonyautoxins 2/3 (8.03 fmol cell-1). Therefore, A. pacificum was identified as the predominant PST contributor in this area. This research makes a valuable contribution to the understanding of the traceability of phycotoxins in marine waters.

Photocatalytic inactivation and destruction of harmful microalgae Karenia mikimotoi under visible-light irradiation: Insights into physiological response and toxicity assessment.

Harmful algal blooms (HABs) caused by Karenia mikimotoi have frequently happened in coastal waters worldwide, causing serious damages to marine ecosystems and economic losses. Photocatalysis has potential to in-situ inhibit algal growth using sustainable sunlight. However, the inactivation and detoxification mechanisms of microalgae in marine environment have not been systematically investigated. In this work, for the first time, visible-light-driven photocatalytic inactivation of K. mikimotoi was attempted using g-C3N4/TiO2 immobilized films as a model photocatalyst. The inactivation efficiency could reach 64% within 60 min, evaluated by real-time in vivo chlorophyll-a fluorometric method. The immobilized photocatalyst films also exhibited excellent photo-stability and recyclability. Mechanisms study indicated photo-generated h+ and 1O2 were the dominant reactive species. Algal cell rupture process was monitored by fluorescent microscope combined with SEM observation, which confirmed the damage of cell membrane followed by the leakage of the intracellular components including the entire cell nucleus. The physiological responses regarding up-regulation of antioxidant enzyme activity (i.e. CAT and SOD), intracellular ROSs level and lipid peroxidation were all observed. Moreover, the intracellular release profile and acute toxicity assessment indicated the toxic K. mikimotoi was successfully detoxified, and the released organic matter had no cytotoxicity. This work not only provides a potential new strategy for in-situ treatment of K. mikimotoi using sunlight at sea environments, but also creates avenue for understanding the inactivation and destruction mechanisms of marine microalgae treated by photocatalysis and the toxicity impacts on the marine environments.

Effects of temperature on the growth and carbohydrate production of three benthic dinoflagellate species from Hainan Island, South China Sea.

Dinoflagellates in the genera Ostreopsis and Gambierdiscus are typical members of the marine benthic community particularly in tropical areas. Their geographic distribution has shown an increasing expansion towards temperate waters recently due to the global warming and climate changes; however, the knowledge is little of how the increasing temperatures might influence the physiological characteristics of Ostreopsis spp. and Gambierdiscus spp. Here, we carried out experiments to understand the effect of different temperatures on the growth, chlorophyll a content, and carbohydrate yield of Chinese strains of Ostreopsis cf. ovata, O. lenticularis, and Gambierdiscus caribaeus. Specifically, seven temperatures (15, 17.5, 20, 25, 30, 32.5, and 35 °C) were set for the two Ostreopsis species and five temperatures (15, 20, 25, 30, and 35 °C) were set for G. caribaeus. Our results suggested that both Ostreopsis (both species were 17.5-32.5 °C) and Gambierdiscus (20-35 °C) could survive a wide range of temperatures, consistent with the record worldwide. Cell density and chlorophyll a content were observed to be higher at high temperatures (30 and 32.5 °C) for both Ostreopsis species whereas G. caribaeus reached the maximum cell density and highest growth rate at 20 °C. Higher carbohydrate yield was detected in the suboptimal temperatures for all three dinoflagellates especially during the decaying phase. Our study reveals the optimal temperatures for the growth of three benthic harmful dinoflagellate species and provides insight into how the increasing temperature will affect their abundance as well as distribution.

Alkaline phosphatase activities and regulation in three harmful Prorocentrum species from the coastal waters of the East China Sea.

Harmful blooms of Prorocentrum donghaiense occur annually in the phosphorus-scarce coastal waters of the East China Sea (ECS). The enzymatic activities of alkaline phosphatase (AP) and its regulation by external phosphorus were studied during a P. donghaiense bloom in this area. The AP characteristics of P. donghaiense was further compared with Prorocentrum minimum and Prorocentrum micans in monocultures with both bulk and single-cell enzyme-labeled fluorescence AP assays. Concentrations of dissolved inorganic phosphorus (DIP) varied between 0.04 and 0.73 µmol l-1, with more than half recording stations registering concentrations below 0.10 µmol l-1. Concentrations of dissolved organic phosphorus (DOP) were comparable or even higher than those of DIP. P. donghaiense suffered phosphorus stress and expressed abundant AP, especially when DIP was lower than 0.10 µmol l-1. The AP activities showed a negative correlation with DIP but a positive correlation with DOP. The AP activities were also regulated by internal phosphorus pool. The sharp increase in AP activities was observed until cellular phosphorus was exhausted. Most AP of P. donghaiense was located on the cell surface and some were released into the water with time. Compared with P. minimum and P. micans, P. donghaiense showed a higher AP affinity for organic phosphorus substrates, a more efficient and energy-saving AP expression quantity as a response to phosphorus deficiency. The unique AP characteristic of P. donghaiense suggests that it benefits from the efficient utilization of DOP, and outcompete other species in the phosphorus-scarce ECS.

Nontarget Screening and Toxicity Evaluation of Diol Esters of Okadaic Acid and Dinophysistoxins Reveal Intraspecies Difference of Prorocentrum lima.

High-resolution mass spectrometry (HRMS) analysis with the assistance of molecular networking was used to investigate intracellular toxin profiles of five Prorocentrum lima (P. lima) strains sampled from the north Yellow Sea and South China Sea. Mice were used as a model species for testing the acute toxicity of intracellular okadaic acid (OA) and dinophysistoxins (DTXs) in free and esterified states. Results showed that OA and DTX1 esterified derivatives were detected in all P. lima samples, accounting for 55%-96% of total toxins in five strains. A total of 24 esters and 1 stereoisomer of DTX1 (35S DTX1) were identified based on molecular networking and MS data analysis, 15 esters of which have been reported first. All P. lima strains displayed specific toxin profiles, and preliminary analysis suggested that toxin profiles of the five P. lima strains might be region-related. Moreover, acute toxicity in mice suggested higher toxicity of esters compared with free toxins, which highlights the importance and urgency of attention to esterified toxins in P. lima.

Ecological characteristics and teratogenic retinal determination of Cochlodinium geminatum blooms in Pearl River Estuary, South China.

Since 2006, harmful dinoflagellate blooms of Cochlodinium geminatum have infrequently occurred in the Pearl River Estuary, South China. During late October to early November in 2018, C. geminatum blooms occurred again in the region. To investigate the blooming mechanism in certain temporal conditions, we analysed the changes in the environmental parameters and phytoplankton community structure during and after the bloom. The results indicated that the water temperature and salinity had large impacts on the bloom. During the C. geminatum bloom, the phytoplankton community structure changed and the number of dominant species decreased. After the bloom, the species number and abundance of diatoms increased, as the species diversity was recovering. Retinal was detected in the field samples and cultured C. geminatum. It has been demonstrated to exist in some algae species (e.g. Cyanophyta, Chlorophyta, Bacillariophyta, and Euglenophyt), and our results indicates that such teratogens also exist in dinoflagellates. The highest concentration of retinal was detected during the bloom. This result indicates that the retinal content may accumulate during a bloom. Retinal has been demonstrated to be a teratogenic agent and may therefore present a potential risk to aquatic organisms during a bloom episode. This research provided more comprehensive information concerning the ecological influences of C. geminatum blooms.

Effects of palytoxins extracted from Ostreopsis ovata on the oxidative stress and immune responses in Pacific white shrimp Litopenaeus vannamei.

Palytoxins (PLTXs) are a group of complex and poisonous marine natural products that are toxic to marine life and even human beings. In the present study, the oxidative stress and immune response in the hepatopancreas and gills of Litopenaeus vannamei were assessed for 72 h after injection with PLTX extracts. Chemical and physiological parameters, e.g., the respiratory burst (O2-), activities of antioxidant enzymes, oxidative damage to lipids, carbonylation of proteins, and immune gene mRNA expression levels, were analysed. The results showed that the PLTX extract was not fatal to the shrimp but could reduce their mobility. The O2- levels in the gills gradually increased after exposure to PLTX extracts and were significantly higher than those in the control from 6 to 72 h. The malondialdehyde content, lipid peroxidation, protein carbonyl levels, and total antioxidant capacity in the gills all peaked at 12 h. At the same time, the gills were loosely connected, there was a clear disintegration of the epithelial tissue, and the stratum corneum disappeared after 12 h. In addition, compared to those in the control group, the PLTX extract treatment increased the O2- content, malondialdehyde content, lipid peroxidation, and protein carbonyl levels from 12 to 72 h, 24-48 h, 12-24 h, and 12-72 h after injection in the hepatopancreas of the shrimp, respectively. Both the Crustin and Toll gene expression levels significantly increased in the hepatopancreas compared to those in the control 6-72 h after injection of the toxin. In parallel, the expression levels of the manganese superoxide dismutase gene gradually decreased from 6 to 48 h and returned to normal levels after 72 h. Interestingly, the total antioxidant capacity also significantly increased compared to that in the control from 6 to 72 h. Our results indicate that although PLTX extracts cause lipid peroxidation and carbonylation of proteins in hepatopancreatic cells, leading to their damage, they did not cause a decrease in the total antioxidant capacity of the hepatopancreas.

Proteomic profile in the mussel Perna viridis after short-term exposure to the brown tide alga Aureococcus anophagefferens.

Blooms of Aureococcus anophagefferens, referred to as brown tides are responsible for massive mortalities and recruitment failure of some bivalves. However, the molecular mechanisms underlying the toxicity remain elusive despite its biological significance, and the information currently available on the molecular effects is still insufficient. In this study, to evaluate the toxicity and associated mechanism of A. anophagefferens on bivalves, we analyzed the protein expression profiles in digestive glands of the A. anophagefferens-exposed Perna viridis by using iTRAQ. A total of 3138 proteins were identified in the digestive glands of A. anophagefferens-exposed P. viridis based on iTRAQ. Amongst, a repertoire of 236 proteins involved in cell, cell part, catalytic activity, metabolic process, biological regulation, immune system process, and response to stimulus were found to be differentially expressed. Functional analysis of the differentially expressed proteins demonstrated that innate immune system of P. viridis was activated, and some proteins associated with stress response and lipid metabolism were induced after exposure to A. anophagefferens. Additionally, MDA content, SOD activity and GSH-Px activity was increased significantly in the digestive gland of A. anophagefferens-exposed P. viridis. Taken together, our results indicated that the A. anophagefferens could induce oxidative stress, activate complement system and alter fat acid metabolism of P. viridis.

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

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

High light stress triggers distinct proteomic responses in the marine diatom Thalassiosira pseudonana.

BACKGROUND: Diatoms are able to acclimate to frequent and large light fluctuations in the surface ocean waters. However, the molecular mechanisms underlying these acclimation responses of diaotms remain elusive. RESULTS: In this study, we investigated the mechanism of high light protection in marine diatom Thalassiosira pseudonana using comparative proteomics in combination with biochemical analyses. Cells treated under high light (800 µmol photons m-2s-1) for 10 h were subjected to proteomic analysis. We observed that 143 proteins were differentially expressed under high light treatment. Light-harvesting complex proteins, ROS scavenging systems, photorespiration, lipid metabolism and some specific proteins might be involved in light protection and acclimation of diatoms. Non-photochemical quenching (NPQ) and relative electron transport rate could respond rapidly to varying light intensities. High-light treatment also resulted in increased diadinoxanthin + diatoxanthin content, decreased Fv/Fm, increased triacylglycerol and altered fatty acid composition. Under HL stress, levels of C14:0 and C16:0 increased while C20:5ω3 decreased. CONCLUSIONS: We demonstrate that T. pseudonana has efficient photoprotective mechanisms to deal with HL stress. De novo synthesis of Ddx/Dtx and lipid accumulation contribute to utilization of the excess energy. Our data will provide new clues for in-depth study of photoprotective mechanisms in diatoms.

Morphology and molecular phylogeny of Chaetoceros dayaensis sp. nov. (Bacillariophyceae), characterized by two 90° rotations of the resting spore during maturation.

Recent studies suggest that a high species diversity of Chaetoceros exists in tropical waters. Based on plankton samples from Chinese tropical waters, Daya Bay of the South China Sea, a new species, Chaetoceros dayaensis sp. nov., is described. Vegetative cells and resting spores were examined by light microscopy as well as transmission and scanning electron microscopy. The nuclear rDNA molecular markers SSU, ITS and D1-D3 of LSU, and the chloroplast rbcL gene were sequenced for information on phylogenetic relationships. The species is characterized by the presence of two 90° rotations of the resting spore during maturation. First a rotation in the apical plane of the mother cell resulting in the valvar plane of the resting spore turning from parallel to perpendicular to that of the mother cell, and a second 90° rotation in the valvar plane of the mother cell resulting in the valve faces of the resting spore turning from facing narrow girdle view to broad girdle view of the mother cell. It is the first report of two 90° rotations of resting spores during maturation in Chaetoceros. Based on this, the maturation rotation of the resting spore of C. rotosporus was reevaluated. C. dayaensis belongs to the subgenus Hyalochaete Gran and we suggest placing it in the section Laciniosa, although a new subdivision of Chaetoceros is needed. The description of C. dayaensis was based on analyses of the phylogenetic relationships combined with morphological comparisons with other similar species.

Refining taxonomic identification of microalgae through molecular and genetic evolution: a case study of Prorocentrum lima and Prorocentrum arenarium.

Species delimitation based on lineage definition has become increasingly popular. However, these methods have been limited, especially for species that lack genomic data and are morphologically similar. The trickiest part for the species identification is that the interspecific and intraspecific boundaries are vague. Taking Prorocentrum (Dinophyta) as an example, analysis of cell morphology, growth, and toxin synthesis in both species of P. lima and P. arenarium does not provide a reliable basis for species delineation. However, through phylogenetic and genetic distance analyses of their ITS and LSU sequences, establishment of evolutionary tree based on orthologous gene sequences, and combining the results of automatic barcode gap discovery and Poisson tree processes models, it was sustained that P. arenarium does not belong to the P. lima complex and should be considered as an independent species. Interspecies genetic evolution analysis revealed that P. lima and P. arenarium may contribute to evolutionary direction that favors combating reverse environmental factors. In P. lima, viral invasion may be one of the reasons for its large genome size. In the study, P. lima complex has been selected as an example to enhance the taxonomic identification of microalgae through molecular and genetic evolution, offering valuable insights into refining taxonomic identification and promoting microbial biodiversity research in other species.IMPORTANCEMicroalgae, especially the species known as Prorocentrum, have received significant attention due to their ability to trigger harmful algal blooms and produce toxins. However, the boundaries between species and within species are ambiguous. Clear and comprehensive species delineation indicates that Prorocentrum arenarium should be considered as an independent species, separate from the Prorocentrum lima complex. Improving the classification and identification of microalgae through molecular and genetic evolution will provide reference points for other cryptic species. Prorocentrum occupy multiple ecological niches in marine environments, and studying their evolutionary direction contributes to understanding their ecological adaptations and community succession.

Prediction of Aureococcus anophageffens using machine learning and deep learning.

The recurrent brown tide phenomenon, attributed to Aureococcus anophagefferens (A. anophagefferens), constitutes a significant threat to the Qinhuangdao sea area in China, leading to pronounced ecological degradation and substantial economic losses. This study utilized machine learning and deep learning techniques to predict A. anophagefferens population density, aiming to elucidate the occurrence mechanism and influencing factors of brown tide. Specifically, Random Forest (RF) algorithm was utilized to impute missing water quality data, facilitating its direct application in subsequent algal population prediction models. The results revealed that all four models-RF, Support Vector Regression (SVR), Multilayer Perceptron (MLP), and Convolutional Neural Network (CNN)-exhibited high accuracy in predicting A. anophagefferens population densities, with R2 values exceeding 0.75. RF, in particular, showed exceptional accuracy and reliability, with an R2 value surpassing 0.8. Additionally, the study ascertained five critical factors influencing A. anophagefferens population density: ammonia nitrogen, pH, total nitrogen, temperature, and silicate.

Adaptive responses of geographically distinct strains of the benthic dinoflagellate, Prorocentrum lima (Dinophyceae), to varying light intensity and photoperiod.

The toxic Prorocentrum lima complex can potentially cause serious harm to the benthos and entire food chain. Studies have revealed physiological differences in strains from different regions related to local environment, while differences in the adaptive responses of P. lima complex should be urgently assessed. Hence, this study explored the adaptive responses to varying light intensities and photoperiods of two P. lima complex strains SHG101 and 3XS34, isolated from the Bohai Sea and the South China Sea, respectively. We found the highest cell density of 7.49 × 104 cells mL-1 recorded in the 3XS strain in the stationary phase with high light intensity exposure. No significant difference was observed in growth rate among SHG groups, however, significant differences were found among 3XS groups ranging from 0.176 to 0.311 d-1. Three key pigments Chl a, Peri, and Fuco accounted for up to 60% of the total pigments. Production and concentrations of pigments and Fv/Fm values exhibit a significant negative correlation with high light intensity and growth. Conversely, total diarrhetic shellfish toxin content and the proportion of diol esters increased to varying degrees after high intensity light exposure, with 3XS strain under high light intensity and a photoperiod of light and darkness (12L:12D) consistently exhibiting the highest levels, finally reaching a maximum (21.6 pg cell-1) at day 28. A shortened photoperiod of high light intensity (8L:16D) resulted in impaired recovery compared with 12L:12D. Furthermore, 3XS showed more delayed and intense adaptive responses, indicating a stronger tolerance compared to SHG. Collectively, these results directly characterized variation in the adaptive responses of geographically distinct strains of P. lima complex, highlighting the previously ignored potential risk diversity of this species.

RA-induced prominence-specific response resulted in distinctive regulation of Wnt and osteogenesis.

Proper retinoic acid (RA) signaling is essential for normal craniofacial development. Both excessive RA and RA deficiency in early embryonic stage may lead to a variety of craniofacial malformations, for example, cleft palate, which have been investigated extensively. Dysregulated Wnt and Shh signaling were shown to underlie the pathogenesis of RA-induced craniofacial defects. In our present study, we showed a spatiotemporal-specific effect of RA signaling in regulating early development of facial prominences. Although inhibited Wnt activities was observed in E12.5/E13.5 mouse palatal shelves, early exposure of excessive RA induced Wnt signaling and Wnt-related gene expression in E11.5/E12.5 mouse embryonic frontonasal/maxillary processes. A conserved regulatory network of miR-484-Fzd5 was identified to play critical roles in RA-regulated craniofacial development using RNA-seq. In addition, subsequent osteogenic/chondrogenic differentiation were differentially regulated in discrete mouse embryonic facial prominences in response to early RA induction, demonstrated using both in vitro and in vivo analyses.

Sublethal effects on the hard clam Mercenaria mercenaria after exposure to Aureococcus anophagefferens Chinese strain isolates.

Brown tides caused by Aureococcus anophagefferens occur frequently worldwide and have contributed to the collapse of Mercenaria mercenaria farming in the United States. This economically valuable hard clam has been used in China for more than 20 years. To date, it has remained unknown whether A. anophagefferens Chinese strain has an impact on hard clam cultivation in the coastal areas of China or other sea areas worldwide if it enters through ship ballast water and other ways. In this study, a Chinese strain of A. anophagefferens isolated from the brown tide waters of Bohai Bay, China, was selected to explore its influence on the feedback of hard clams. After being fed with A. anophagefferens, hard clams showed characteristics similar to starvation. The reduced feeding efficiency of hard clams leads to reduced energy intake. However, the immune response and oxidative stress, result in increased energy consumption. An imbalance in the energy budget may be an important reason for hard clam starvation. This study has described the response characteristics of the A. anophagefferens Chinese strain to M. mercenaria, explored the reasons for the negative impact of A. anophagefferens on hard clams, and provides ideas for reducing shellfish aquaculture caused by brown tides.

An overview of Prorocentrum donghaiense blooms in China: Species identification, occurrences, ecological consequences, and factors regulating prevalence.

Prorocentrum donghaiense Lu (also identified as Prorocentrum shikokuense Hada and Prorocentrum obtusidens Schiller) is a bloom-forming dinoflagellate species distributed worldwide. Blooms of P. donghaiense occur annually in adjacent waters of the East China Sea (ECS), especially in the waters near the Changjiang River Estuary. Blooms of this species have also been reported in nearby Japanese and Korean waters. There has been an apparent bloom-forming species succession pattern in the ECS since 2000, with diatom blooms in the early spring, shifting to long-lasting and large-scale dinoflagellate blooms dominated by P. donghaiense during the spring, and finally ended by diatom and/or Noctiluca scintillans blooms in summer. These bloom succession patterns were closely correlated with changes in environmental factors, such as temperature increase and anthropogenic eutrophication. Decreasing silicate by the construction of the Three Gorges Dam and increasing dissolved inorganic nitrogen flux were mainly influenced by high intensity human activities in the Changjiang River watershed, resulting in low Si/N ratio and high N/P ratios, possibly accelerating outbreak of P. donghaiense blooms. Phosphorous deficiency might be the most critical factor controlling the succession of microalgal blooms from diatoms to dinoflagellates. Prorocentrum donghaiense is a nontoxic species, but it can disrupt marine ecosystem by decreasing phytoplankton biodiversity and changing the structure of the food chain. Prorocentrum donghaiense blooms in the ECS have been intensively studied during the last two decades. Several possible mechanisms that contribute or trigger the annual blooms of this species have been proposed, but further research is required particularly on the aspect of nutrient budget, ecosystem impacts, as well as social-economic impact assessment.

Emerging harmful algal bloom species over the last four decades in China.

The first recorded micro-algae bloom in Chinese coastal waters dates back to 1933 and was caused by a mixture of Noctiluca scintillans and Skeletonema costatum sensu lato along the Zhejiang coast (the East China Sea). While well-documented harmful algal blooms (HABs) appeared to be extremely scarce from the 1950s to 1990, both the frequency and intensity have been reportedly increasing since 1990. Among them, the fish-killing HABs, mainly caused by Karenia mikimotoi, Karlodinium digitatum, Karlodinium veneficum, Margalefidinium polykrikoides, and Heterocapsa spp., have intensified. Karenia mikimotoi was responsible for at least two extremely serious events in the Pearl River Estuary in 1998 and the Taiwan Strait (in the East China Sea) in 2012, which appeared to be associated with abnormal climate conditions and excessive nutrients loading. Other major toxic algal blooms have been caused by the species responsible for paralytic shellfish poisoning (including Alexandrium catenella, Alexandrium pacificum, Gymnodinium catenatum) and diarrhetic shellfish poisoning (including Dinophysis spp., and a couple of benthic dinoflagellates). Consequent closures of shellfish farms have resulted in enormous economic losses, while consumption of contaminated shellfish has led to occasional human mortality in the Bohai Sea and the East China Sea. Expansions of these HABs species along the coastline of China have occurred over the last four decades and, due to the projected global changes in the climate and marine environments and other anthropological activities, there is potential for the emergence of new types of HABs in China in the future. This literature review aimed to present an updated overview of HABs species over the last four decades in China.