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The potential of diatoms as aquatic bait, attribute to their abundance in highly unsaturated fatty acids, has been extensively studied. Temperature plays a crucial role in the synthesis of these fatty acids. This study specifically investigated the impact of temperature on the growth, total lipid content, and fatty acid composition of Skeletonema dohrnii, a planktonic diatom commonly associated with red tides andwater blooms in China. The aim is to evaluate its suitability as an aquatic bait and provide insights for large-scale factory farming. Results indicated that the highest biomass and maximum growth rate occurred at 28°C, with no significant deviation from the control group at 25°C. At 28°C and 15°C, there was a significant increase in the total lipid content and the total fatty acid content, with a more pronounced effect at 15°C. At 28°C, EPA and DHA content measured at 0.97 ± 0.01 mg.DW.L-1 and 0.264 ± 0.01 mg.DW.L-1 respectively, surpass those at 15°C due to lower biomass. Conversely, at 15°C, substantial synthesis of long-chain polyunsaturated fatty acids, with EPA constituting up to 32.24 ± 0.24% of the total fatty acids, is observed. Modulating the temperature could optimize the utilization of S. dohrnii as an aquatic feed source. These findings underscore the potential of S. dohrnii as a high-quality aquafeed and lay the groundwork for its success in ocean warming scenarios. [ABSTRACT FROM AUTHOR]

Algal blooms of the dinoflagellate Karenia mikimotoi are seriously threats to the coastal ecosystems, particularly in developing countries. Many previous studies have focused on the effect of nutrients on algal blooms, but the accurate measurement of nutrients can be time-consuming, particularly in remote areas. Currently, the environmental drivers of K. mikimotoi proliferation are far from clearly understood in many coastal zones in the world. As a result of prevailing climate conditions and increasing eutrophication, the Pingtan Special Bay Area in China is prone to frequent red tide events. Based on field work conducted from 2013 to 2019, this study investigated the meteorological and hydrological variables influencing the proliferation of K. mikimotoi. Results showed that cell density of K. mikimotoi was significantly positively correlated with sea surface temperature (SST), air temperature (AT), and dissolved oxygen (DO) concentration, but negatively correlated with sea surface salinity (SSS) and air pressure (AP). A linear model between cell density and SST, SSS, AP, and DO was developed to assess and predict the risk of K. mikimotoi algal blooms (R2 = 0.810). Results are of practical significance for preventing and controlling the K. mikimotoi algal bloom in Southeast China. Furthermore, this proposed algal bloom prediction method based on the Linear Regression Model may potentially serve as a valuable reference for algal bloom risk forecasting and management. [ABSTRACT FROM AUTHOR]

Blooms of microalgal red tides and macroalgae (e.g., green and golden tides caused by Ulva and Sargassum) have caused widespread problems around China in recent years, but there is uncertainty around what triggers these blooms and how they interact. Here, we use 30 years of monitoring data to help answer these questions, focusing on the four main species of microalgae Prorocentrum donghaiense, Karenia mikimotoi, Noctiluca scintillans, and Skeletonema costatum) associated with red tides in the region. The frequency of red tides increased from 1991 to 2003 and then decreased until 2020, with S. costatum red tides exhibiting the highest rate of decrease. Green tides started to occur around China in 1999 and the frequency of green tides has since been on the increase. Golden tides were first reported to occur around China in 2012. The frequency of macroalgal blooms has a negative linear relationship with the frequency and coverage of red tides around China, and a positive correlation with total nitrogen and phosphorus loads as well as with atmospheric CO2 and sea surface temperature (SST). Increased outbreaks of macroalgal blooms are very likely due to worsening levels of eutrophication, combined with rising CO2 and SST, which contribute to the reduced frequency of red tides. The increasing grazing rate of microzooplankton also results in the decline in areas affected by red tides. This study shows a clear shift of algal blooms from microalgae to macroalgae around China over the past 30 years driven by the combination of eutrophication, climate change, and grazing stress, indicating a fundamental change in coastal systems in the region. [ABSTRACT FROM AUTHOR]

In the coastal areas of China, the eutrophication of seawater leads to the continuous occurrence of red tide, which has caused great damage to Marine fisheries and aquatic resources. Therefore, the detection and prediction of red tide have important research significance. The rapid development of optical remote sensing technology and deep-learning technology provides technical means for realizing large-scale and high-precision red tide detection. However, the difficulty of the accurate detection of red tide edges with complex boundaries limits the further improvement of red tide detection accuracy. In view of the above problems, this paper takes GOCI data in the East China Sea as an example and proposes an improved U-Net red tide detection method. In the improved U-Net method, NDVI was introduced to enhance the characteristic information of the red tide to improve the separability between the red tide and seawater. At the same time, the ECA channel attention mechanism was introduced to give different weights according to the influence of different bands on red tide detection, and the spectral characteristics of different channels were fully mined to further extract red tide characteristics. A shallow feature extraction module based on Atrous Spatial Pyramid Convolution (ASPC) was designed to improve the U-Net model. The red tide feature information in a multi-scale context was fused under multiple sampling rates to enhance the model's ability to extract features at different scales. The problem of limited accuracy improvement in red tide edge detection with complex boundaries is solved via the fusion of deep and shallow features and multi-scale spatial features. Compared with other methods, the method proposed in this paper achieves better results and can detect red tide edges with complex boundaries, and the accuracy, precision, recall, and F1-score are 95.90%, 97.15%, 91.53%, and 0.94, respectively. In addition, the red tide detection experiments in other regions with relatively concentrated distribution also prove that the method has good applicability. [ABSTRACT FROM AUTHOR]

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

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

The viability of both China's offshore fishing operations and the global marine fishing industry is threatened by the occurrence of red tides caused by Gymnodinium catenatum and Karenia mikimotoi. Effective control of these dinoflagellate-mediated red tides has become a pressing issue that requires immediate attention. In this study, High-efficiency marine alginolytic bacteria were isolated and underwent molecular biological identification to confirm their algicidal properties. Based on a combination of morphological, physiological, biochemical, and sequencing results, Strain Ps3 was identified as belonging to the species Pseudomonas sp. We examine the effects of algicidal bacteria on the red tide species G. catenatum and K. mikimotoi within an indoor experimental setting. Then gas chromatography--mass spectrometry (GC-MS) was used to analyze the structure of the algolytic active substances. This investigation demonstrated that with exposure to the algae-lysis experiment, the Ps3 strain has the best algae-lysis effect, with G. catenatum and K. mikimotoi reaching 83.0 and 78.3%. Our results from the sterile fermentation broth experiment showed that the inhibitory effect on the two red tide algae was positively correlated with the concentration of the treatment. At a treatment concentration of 2.0% (v/v), the 48 h lysis rates of G. catenatum and K. mikimotoi due to exposure to the Ps3 bacterial fermentation broth were 95.2 and 86.7%, respectively. The results of this study suggest that the algaecide may be a rapid and effective method to control dinoflagellate blooms, as evidenced by the observed changes in cellular morphology in all cases. In the ethyl acetate phase of Ps3 fermentation broth, the cyclic (leucineleucine) dipeptide was the most abundant. The findings of this study contribute to our understanding of red tide prevention and control and provide a theoretical foundation for further research in this field. [ABSTRACT FROM AUTHOR]

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

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

Red tides have many harmful effects on offshore ecosystem and even human health, which has become a global marine environmental problem. In recent years, the occurrence of red tides has become more frequent and extensive in the offshore area of China. As one of the important sea areas in northern China, the north of Shandong Peninsula is also facing the impact of red tides. Relevant data and information on red tides outbreaks around the north of Shandong Peninsula (This study refers to the coastal area of Yantai) from 2000 to 2019 were collected in this study, and then, the comprehensive human activity intensity model was constructed. It was found that the occurrence of red tides in this area had a certain aggregation on both temporal and spatial scales, and the reason was related to nearshore human activities. Different types of land cover in coastal zone had a more significant impact on the occurrence of red tides. The types of water and structures had a certain correlation with the occurrence of red tides. [ABSTRACT FROM AUTHOR]

The effective and rapid detection of red tide has significant research implications in China's offshore regions, where severe seawater eutrophication leads to frequent red tide events. With the rapid development and widespread application of remote sensing and deep learning technologies, the technical means for high-performance, large-scale red tide detection are now available. In this paper, aiming at solving the problems of limited number of samples in red tide detection and the limited improvement of red tide detection accuracy based on traditional methods, we propose a red tide detection method based on improved DenseNet, which uses dense convolutional blocks and neighborhood space features to extract information at different levels and scales, makes full use of and integrates underlying boundary details and high-level semantic information, and solves the problem of limited improvement of detection accuracy caused by a small number of samples and an unbalanced sample distribution. At the same time, through the attention mechanism based on the squeeze-and-excitation (SE) module, feature weighting optimization is carried out for the bands conducive to red tide detection, which can further improve the detection accuracy. To verify the effectiveness of this method, we use Geostationary Ocean Color Imager (GOCI) data of the red tide that occurred in the Bohai Sea in 2014 in our experiment. The experimental results show that the proposed method achieves better red tide detection (overall classification accuracy: 98.03%) than state-of-the-art red tide detection methods and is more suitable for red tide detection by remote sensing. [ABSTRACT FROM AUTHOR]

Diatoms are responsible for approximately 40% of the global primary photosynthetic production and account for up to 20% of global carbon fixation. Coscinodiscus granii is a red tide forming species of the phylum Bacillariophyta that has been detected in a wide range of coastal regions, suggesting the possibility of the existence of high genetic diversity with differential adaptation. Common molecular markers including 18S rDNA, 16S rDNA, ITS, cox1, and rbcL do not provide sufficient resolution for distinguishing intra-species genetic diversity, hindering in-depth research on intra-species genetic diversity and their spatial and temporal dynamics. In this project, we aimed to develop molecular markers with high resolution and specificity for C. granii, attempting to identify different taxa of this species, which will set up a stage for subsequent functional assays. Comparative genomics analysis of the mtDNAs of C. granii strains identified a genomic region with high genomic variations, which was used to guide the development of a molecular marker with high resolution and high specificity. This new molecular marker, which was named cgmt1 (C. granii mitochondrial 1), was 376 bp in size and differentiated C. granii samples collected in coastal regions of China into three different clades. Preliminary analysis of field samples collected in various coastal regions in China revealed that C. granii clades were almost exclusively found in the Bohai Sea and the north Yellow Sea. This newly developed molecular marker cgmt1 could be used for tracking intra-species genetic diversity and biogeographic distribution of C. granii in different ecosystems. [ABSTRACT FROM AUTHOR]

• Resting cysts of E. voratum were identified in sediments via multi-approaches. • E. voratum produced asexual resting cysts in laboratory-reared clonal cultures. • Cysts stored for six months germinated and displayed internal development processes. Coral reef ecosystems are the most productive and biodiverse marine ecosystems, with their productivity levels highly dependent on the symbiotic dinoflagellates belonging to the family Symbiodiniaceae. As a unique life history strategy, resting cyst production is of great significance in the ecology of many dinoflagellate species, those HABs-causing species in particular, however, there has been no confirmative evidence for the resting cyst production in any species of the family Symbiodiniaceae. Based on morphological and life history observations of cultures in the laboratory and morpho-molecular detections of cysts from the marine sediments via fluorescence in situ hybridization (FISH), cyst photography, and subsequent singe-cyst PCR sequencing, here we provide evidences for the asexual production of resting cysts by Effrenium voratum , the free-living, red tide-forming, and the type species of the genus Effrenium in Symbiodiniaceae. The evidences from the marine sediments were obtained through a sequential detections: Firstly, E. voratum amplicon sequence variants (ASVs) were detected in the cyst assemblages that were concentrated with the sodium polytungstate (SPT) method from the sediments collected from different regions of China Seas by high-throughput next generation sequencing (NGS); Secondly, the presence of E. voratum in the sediments was detected by PCR using the species-specific primers for the DNA directly extracted from sediment; Thirdly, E. voratum cysts were confirmed by a combined approach of FISH using the species-specific probes, light microscopic (LM) photography of the FISH-positive cysts, and a subsequent single-cyst PCR sequencing for the FISH-positive and photographed cysts. The evidences from the laboratory-reared clonal cultures of E. voratum include that: 1) numerous cysts formed in the two clonal cultures and exhibited a spherical shape, a smooth surface, absence of ornaments, and a large red accumulation body; 2) cysts could maintain morphologically intact for a storage of two weeks to six months at 4 °C in darkness and of which 76–92 % successfully germinated through an internal development processes within a time period of 3–21 days after being transferred back to the normal culturing conditions; 3) two or four germlings were released from each cyst through the cryptopylic archeopyle in all cysts with continuous observations of germination processes; and 4) while neither sexual mating of gametes nor planozygote (cells with two longitudinal flagella) were observed, the haploidy of cysts was proven with flow cytometric measurements and direct LM measurements of fluorescence from cells stained with either propidium iodide (PI) or DAPI, which together suggest that the cysts were formed asexually. All evidences led to a conclusion that E. voratum is capable of producing asexual resting cysts, although its sexuality cannot be completely excluded, which guarantees a more intensive investigation. This work fills a gap in the knowledge about the life cycle, particularly the potential of resting cyst formation, of the species in Symbiodiniaceae, a group of dinoflagellates having unique life forms and vital significance in the ecology of coral reefs, and may provide novel insights into understanding the recovery mechanisms of coral reefs destructed by the global climate change and suggest various forms of resting cysts in the cyst assemblages of dinoflagellates observed in the field sediments, including HABs-causing species. [ABSTRACT FROM AUTHOR]

The characteristics and influencing factors of phytoplankton assemblages were analyzed in July (rainy season) and November (dry season) 2022 in the Qiongzhou Strait, China. A total of 68 species of phytoplankton belonging to 33 genera and 3 phyla were recorded. Diatom was the most dominant group. The broad-temperature widespread species were the most abundant. The dominant species in the rainy season were Skeletonema costatum , S. tropicum , Chaetoceros preseudocurvisetus and Thalassionema nitzschioides while those in the dry season were T. frauenfeldii , T. nitzschioides and Coscinodiscus granii. Phytoplankton cell abundance was significantly positively correlated with nitrite and total nitrogen concentrations, and negatively correlated with temperature and pH. Red tide algae occurred with high frequency. All sites were at eutrophic level except for 3 sites in the rainy season, which were at mesotrophic level. Therefore, there is a potential risk of red tides in the Qiongzhou Strait, which requires long-term monitoring and precautions. • Nutrient Quality Index was higher in the nearshore that that in the offshore. • Red tides species were dominant in both rainy and dry seasons. • Most of the sites of the Qiongzhou Strait were at eutrophication level. • The Qiongzhou Strait has a potential risk of red tides and requires precautions. [ABSTRACT FROM AUTHOR]

Due to the continuous intensification of human activities in the ocean, the frequent outbreaks of red tide have caused great harm to the marine environment and ecology. Thus, the rapid detection and monitoring of red tide become particularly important. At present, the main monitoring methods depend on artificial and buoy data, as well as optical satellite remote sensing. However, these methods may not be able to effectively deal with the characteristics of red tide bloom, such as suddenness and unpredictability. The global navigation satellite system-reflectometry (GNSS-R) is an emerging technology that makes use of navigation signals as a remote sensing opportunity to obtain Earth surface information. GNSS-R has already been proved to be capable of retrieving sea surface parameters (e.g., dielectric constant and sea surface roughness) closely related to the outbreak of a red tide. In this article, we proposed a new method to estimate red tide density, which utilizes an all-new model associating GNSS-R observations with sea surface red tide density. This method can remove the weather influence and greatly decrease the revisit period, which is much longer for optical red tide remote sensing methods. The Landsat-8 near-infrared data and TechDemoSat-1 (TDS-1) GNSS-R data of a red tide outbreak in the sea off the Tsingtao coast in China are used to build and test the proposed method. The results demonstrate that the correlation coefficient is 0.73, and the root mean square error of retrieved red tide density is 2.84%, which shows that the GNSS-R technology shows great potential to perform the rapid and preliminary red tide monitoring and judgment. [ABSTRACT FROM AUTHOR]

Globally, climate change impacts on marine ecosystems are evident in physical, chemical, and biological processes, and are generally more extensive in faster warming regions. China makes the largest contribution of any country to global fisheries production and has experienced severe declines in marine health and biodiversity, and so the current and potential impacts of marine climate change are a large concern for both fisheries and biodiversity. China also has marine regions warming in the top 10% globally, necessitating a thorough understanding of how marine systems are changing so that appropriate corresponding countermeasures can be identified and prioritized. Here, we review and collate what is currently understood about documented and projected responses of marine systems to climate change in Chinese coasts and oceans, from physical, biological, and ecological perspectives, through to impacts on key ecosystems. Our results show extensive change attributed to climate change throughout Chinese marine systems, including red tide bloom events that have been recorded an order of magnitude more frequently in recent decades. Ocean acidification has led to the increased mortality of marine calcifying organisms through effects on the biomineralization process and physiological functions. Moreover, many species have been documented undergoing extensive changes in geographic distribution, with potential implications for species interactions and trophic food webs, as well as important habitats like coral reefs, seagrass, and mangroves. Some constructive laws and actions have been introduced in response to these climate-driven changes, such as actions to reduce pollution and increase artificial propagation and replanting of habitat species, however, addressing the impacts of marine climate change remains a considerable and escalating challenge. [ABSTRACT FROM AUTHOR]

Red tide is a marine phenomenon caused by the excessive growth of microscopic algae in the ocean. This study aims to analyze the development trends of red tides in the past 20 years and the dynamic external causes that induce red tides based on existing satellite remote sensing and numerical simulation data. And the changes in dominant species of red tides in different seasons are analyzed. The results show significant temperature fluctuations within the week before the red tide occurs, with an average increase of 1.42 °C. In contrast, the change in salinity is relatively small. Meanwhile, ocean fronts are areas in the ocean where different water masses meet and form boundaries. The average strength of ocean fronts increased by 3.7%, indicating enhanced ocean mixing over a short period of time. Under the combined influence of these factors, the probability of a red tide outbreak in the East China Sea increases rapidly. Therefore, this study has important reference value for further research on the causes of red tides and their response to ocean dynamic changes. • Study analyzes 20-year trend of red tides and their dynamic causes. • Before a red tide, average temperature rises by 1.42 °C; salinity changes little. • Increased ocean front strength by 3.7% boosts East China Sea red tide risk. [ABSTRACT FROM AUTHOR]

Collaborative disaster prevention and reduction in coastal cities is an important measure to enhance disaster prevention capabilities, improve emergency efficiency and reduce disaster losses. Aiming at the problem of coordination assessment of disaster prevention and reduction between coastal cities, combined with the theory of collaborative governance and regional disaster system theory, this paper studies the coordination index system of disaster prevention and mitigation in coastal cities from the aspects of pre-disaster preparation coordination, disaster response coordination and post-disaster recovery coordination. Using principal component analysis to test the feasibility and structural validity of the index system, an evaluation model of synergy degree of disaster prevention and mitigation in coastal cities based on capacity coupling coefficient is constructed. Typhoons, rainstorms, floods, storm surges and red tides which occurred in coastal cities of China from 1990 to 2018 were selected to carry out empirical research. The evaluation results show that the contribution of the disaster response subsystem is higher than that of the pre-disaster preparation subsystem and the post-disaster recovery subsystem. The synergy degree of disaster prevention and mitigation in China's coastal cities is restricted by the economic level of cities covered by disasters. The coastal cities with higher economic levels have higher coordination of disaster prevention and mitigation. However, in general, the synergy degree of disaster prevention and mitigation in coastal cities in China is low. The research results can provide policy basis for the improvement in the synergy degree of disaster prevention and mitigation in China's coastal cities. [ABSTRACT FROM AUTHOR]

Moina mongolica and Daphniopsis tibetana are typical saline Cladocera in China that are characterized by a wide salinity range, rapid reproduction, and high-density culture. In this paper, the characteristics and life history of M. mongolica and D. tibetana are reviewed. The application of these two species of Cladocera to ecotoxicology in recent years is also summarized from the aspects of environmental factors and environmental pollutants, including ultraviolet B radiation, temperature, salinity, alkalinity, pH, heavy metals, harmful red tide, pesticides, and persistent organic pollutants. Additionally, the toxicity sensitivity of saline Cladocera in different reproductive statuses and inter-generational embryos is discussed. Finally, the need to enhance knowledge of the molecular genomics, population dynamics, and strategies for protection of saline Cladocera, along with the need for establishment of estuarine and marine environmental monitoring standards are discussed. Overall, this review highlights the potential for using these Cladocera species as indicator organisms for estuarine and marine ecotoxicology studies. • Moina mongolica and Daphniopsis tibetana had been domesticated in seawater. • They had been applied to the ecotoxicological researches for over 30 years. • This review highlights the potential for them for seawater ecotoxicology. [ABSTRACT FROM AUTHOR]

To explore the causes of red tides in Qinhuangdao coastal water, we conducted surveys on both water quality and red tides during April to September of 2022 and analyzed the relationships between main environmental factors and red tide organisms through the factor analysis and canonical correspondence analysis. The results showed that there were eight red tides along the coast of Qinhuangdao in 2022, with a cumulative blooming area of 716.1 km 2 . The red tides could be divided into three kinds based on the major blooming organisms and occurrence time, Noctiluca scintillans bloom, diatom-euglena ( Skeletonema costatum , Eutreptiella gymnastica , Pseudo-nitzschia spp.) bloom, and dinoflagellate ( Scrippsiella trochoidea and Ceratium furca ) bloom. Seasonal factor played roles mainly during July to September, while inorganic nutrients including nitrogen and phosphorus influenced the blooms mainly in April and July. The canonical correspondence analysis suggested that N. scintillans preferred low temperature, and often bloomed with high concentrations of ammonium nitrogen and dissolved inorganic phosphorus. S. costatum , E. gymnastica , and Pseudo-nitzschia spp. could tolerate broad ranges of various environmental factors, but favored high temperature and nitrogen-rich seawater. C. furca and S. trochoidea had higher survival rate and competitiveness in phosphate-poor waters. Combined the results from both analyses, we concluded that the causes for the three kinds of red tide processes in Qinhuangdao coastal areas in 2022 were different. Adequate diet algae and appropriate water temperature were important factors triggering and maintaining the N. scintillans bloom. Suitable temperature, salinity and eutrophication were the main reasons for the diatom-euglena bloom. The abundant nutrients and seawater disturbance promoted the germination of S. trochoidea cysts, while phosphorus limitation caused the blooming organism switched to C. furca and maintained the bloom hereafter.

The nutrient regime has changed significantly in the Bohai Sea (BS) during the past six decades because of anthropogenic perturbations. Specifically, the concentration of DIN increased by about 7-fold from the end of the 1950s to the mid-2010s, while DIP and DSi concentrations decreased from the end of the 1950s to the beginning of the 1990s, and have since increased again. Unsynchronized changes in nutrient levels have led to changes in the nutrients structure, which has caused a series of ecological effects. Phytoplankton biomass increased by 6-fold from the 1960s to the mid-2010s. Additionally, phytoplankton composition shifted from a diatom-dominated to a dinoflagellate-dominated system, and the dominant species of macrozoobenthos changed. Red tides rarely occurred before the 1980s, but have occurred periodically and frequently since the 1990s. Finally, the BS ecosystem has shifted from an N-limited oligotrophic state before the 1990s to a potentially P-limited eutrophic state. • Dissolved inorganic nitrogen increased by 7-fold over the past 60 years in Bohai Sea • Dissolved inorganic phosphorus, dissolved silica decreased first and then increased • Phytoplankton biomass increased by 6-fold and the dominant species changed • Bohai Sea shifted from N-limited oligotrophic state to P-limited eutrophic state [ABSTRACT FROM AUTHOR]

Chen, B.; Dong, D.; Qin, X.; Xu, M.; Chen, X., and Shi, M., 2019. Relationship between the occurrence of red tides and the dynamic response mechanisms in the northern Beibu Gulf. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 185–193. Coconut Creek (Florida), ISSN 0749-0208. Unlike the common outbreak mechanism of red tides, the northern Beibu Gulf in the Guangxi Zhuang Autonomous Region of China experiences frequent red tides with distinct characteristics, such as large distances from the mainland and the presence of industrial pollution. By tracing the sources and transport of the high concentrations of nitrogen and phosphorus, the relationship between pollutant transport and the dynamic response mechanisms was explored. The results showed that the concentrations of nitrogen and phosphorus nutrients in the areas of red tide outbreaks near Weizhou Island and in the Qinzhou Gulf in the northern Beibu Gulf were higher than those in the surrounding areas. However, the high concentrations of nitrogen and phosphorus nutrients in the northern Beibu Gulf did not originate from terrestrial pollution from Guangxi Province; rather, these pollutants originated on the east coast of China and were transported through the Qiongzhou Strait. The primary sources were the Pearl River Estuary and the coastal waters of eastern Guangdong. In addition, the differences in the concentration distributions of nitrogen and phosphorus nutrients between the east and west coasts of the Qinzhou Gulf in the northern Beibu Gulf were clearly related to dynamic response mechanisms. [ABSTRACT FROM AUTHOR]

The Ulva prolifera green tides in the Yellow Sea, China, which have been occurring since 2007, are a serious environmental problem attracting worldwide attention. Despite extensive research, the outbreak mechanisms have not been fully understood. Comprehensive analysis of anthropogenic and natural biotic and abiotic factors reveals that human activities, regional physicochemical conditions and algal physiological characteristics as well as ocean warming and biological interactions (with microorganism or other macroalgae) are closely related to the occurrence of green tides. Dynamics of these factors and their interactions could explain why green tides suddenly occurred in 2007 and decreased abruptly in 2017. Moreover, the consequence of green tides is serious. The decay of macroalgal biomass could result in hypoxia and acidification, possibly induce red tide and even have a long-lasting impact on coastal carbon cycles and the ecosystem. Accordingly, corresponding countermeasures have been proposed in our study for future reference in ecosystem management strategies and sustainable development policy. [ABSTRACT FROM AUTHOR]

China now accounts for over 2/3 of the world's production of marine-based seafood. Chinese mariculture has contributed to the stability of the global food supply, but millions of tons of excess feed and drugs are threatening the sustainability of the waters in which it is conducted. Over 26% of the excess nitrogen in China's waters is likely a result of shrimp production alone, worsening eutrophication and the resulting 'red tide' in China. While some Chinese operations require the destruction of carbon-rich wetlands, the sector as a whole can be considered a net CO 2 sink at the immediate time of harvest; each year, Chinese mariculture extracts the same quantity of CO 2 from the atmosphere as 5000 km2 of forest. Novel technical practices, improved management of the harvested products in the food versus industrial supply chain, optimized sea-use and land-use plans, and the encouragement of participatory decision-making by provincial entities offer some promise to ensure the sustainability of this global public resource – but the national Chinese government will have to step up to address the challenges. [ABSTRACT FROM AUTHOR]

High incident rates of red tide have occurred off the coast of the Changjiang (Yangtze) River Estuary in summer, resulting from a magnified population growth discharging substantial nutrient loads into this vicinity. The presence of elevated Chlorophyll-a concentrations (≥36.3 μg/l), low suspended sediment concentrations in surface and mid-layers (<10 mg/l), a strong saline front and surface water temperature gradient, veering surface winds, and a bimodal shape to the Changjiang Diluted Water (CDW) revealed two red tide patches appearing between August 6–13, 2010. Two distinguishable hydrodynamic driving mechanisms, connected to these incidents, are diagnosed. Field observations and numerical simulations determined a red tide patch in the northeastern offshore area is caused by a northeast transport of the CDW truncated by a northwest intrusion of the Taiwan Warm Current (TWC) as winds deviated. Red tide occurrence in the southern nearshore area originated from a plume front where CDW interfaces with the TWC. • Hydrodynamic environment variability determines the pattern of red tide incidents. • Southeast winds >8 m/s correlates with detachment event's timing and red tide events. • Plume front created by current mixing and presence of coastal upwelling region. • Light intensity and nutrient loads yield chlorophyll- a concentrations to >20 μg/l. [ABSTRACT FROM AUTHOR]

Unlike the common outbreak mechanism of red tides, the northern Beibu Gulf in the Guangxi Zhuang Autonomous Region of China experiences frequent red tides with distinct characteristics, such as large distances from the mainland and the presence of industrial pollution. By tracing the sources and transport of the high concentrations of nitrogen and phosphorus, the relationship between pollutant transport and the dynamic response mechanisms was explored. The results showed that the concentrations of nitrogen and phosphorus nutrients in the areas of red tide outbreaks near Weizhou Island and in the Qinzhou Gulf in the northern Beibu Gulf were higher than those in the surrounding areas. However, the high concentrations of nitrogen and phosphorus nutrients in the northern Beibu Gulf did not originate from terrestrial pollution from Guangxi Province; rather, these pollutants originated on the east coast of China and were transported through the Qiongzhou Strait. The primary sources were the Pearl River Estuary and the coastal waters of eastern Guangdong. In addition, the differences in the concentration distributions of nitrogen and phosphorus nutrients between the east and west coasts of the Qinzhou Gulf in the northern Beibu Gulf were clearly related to dynamic response mechanisms. [ABSTRACT FROM AUTHOR]

Harmful red tides in China have caused paralytic shellfish toxins (PSTs) pollution and led to severe socioeconomic effects in shellfish aquaculture. Although shellfish can survive harmful algal blooms, the effects on their Condition Index (CI) have been underestimated. This study sought to evaluate the effects of the profiles and levels of paralytic shellfish toxins on variations in the CI in bivalves under natural blooming conditions. We observed clear soft tissue lesions to varying degrees except in Mytilus galloprovincialis after toxin exposure. Among the five species of shellfish exposed in situ, only M. galloprovincialis accumulated PSTs content above the maximum permitted level (800 μg STX di-HCl eq./kg). The highest toxin content in all sample tissues was observed in Patinopecten yessoensis. Significant interspecies differences in PSTs accumulation among the five bivalve species were observed in the hepatopancreas. A total of nine PSTs components and four new C-11 hydroxyl metabolites (so-called M-toxins) toxins were detected, and detoxification diversity was observed among bivalves. We observed a higher proportion of M-toxin in early stages, and the proportions changed only slightly over time in M. galloprovincialis and Magallana gigas , thus accounting for the significantly higher metabolism rate. Notably, the CI in M. gigas and Argopecten irradians was positively correlated with lowest toxin accumulation of PSTs content, but significantly inhibited. In conclusion, our results revealed a significant inhibitory effect on the CI in shellfish, in a species specific manner, with distinct levels of inhibition correlated with different toxin metabolites. Our study revealed the toxin content of different bivalves exposed to a natural red tide environment and the consequent effects on growth, thus building a foundation for research on the mechanisms underlying the effects of PSTs on growth. These data establish the ecological and economic significance of the effects of harmful algal blooms on bivalves. [Display omitted] • The diversity in the PST accumulation capacity of bivalves was observed in situ. • PSTs negatively affected the CI values in distinct levels. • P. yessoensis had the most rapid PST accumulation and clearance rates. • The CI values of mussels showed an S-shaped correlation with toxin distribution. • Metabolite M-toxins were estimated, to expand on prior work. [ABSTRACT FROM AUTHOR]

This paper presents a case study of red tide hazards around the Pearl River Estuary (PRE). Red tide hazards, meteorological data, and seawater monitoring data were collected from 1996 to 2020 at different locations around the PRE to investigate the internal and external factors influencing the occurrence of red tides. The enhancement of the assessment of estuarine trophic status (ASSETS) method enables us to evaluate the effects of meteorological factors and seawater eutrophication status on the red tide risk level. Using ASSETS, we established a framework for red tide risk assessment of the Pearl River Estuary. We analysed the external and internal factors causing the red tide based on meteorological data and seawater monitoring data in the PRE. The results show that the temperature was higher than the annual monthly average temperature of 1.265 °C, and east and north winds at velocities of 3-4 m/s could result in the formation of red tides. However, precipitation inhibits the formation of the red tide in PRE., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Chen, B.; Dong, D.; Qin, X.; Xu, M.; Chen, X., and Shi, M., 2019. Relationship between the occurrence of red tides and the dynamic response mechanisms in the northern Beibu Gulf. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 185–193. Coconut Creek (Florida), ISSN 0749-0208. Unlike the common outbreak mechanism of red tides, the northern Beibu Gulf in the Guangxi Zhuang Autonomous Region of China experiences frequent red tides with distinct characteristics, such as large distances from the mainland and the presence of industrial pollution. By tracing the sources and transport of the high concentrations of nitrogen and phosphorus, the relationship between pollutant transport and the dynamic response mechanisms was explored. The results showed that the concentrations of nitrogen and phosphorus nutrients in the areas of red tide outbreaks near Weizhou Island and in the Qinzhou Gulf in the northern Beibu Gulf were higher than those in the surrounding areas. However, the high concentrations of nitrogen and phosphorus nutrients in the northern Beibu Gulf did not originate from terrestrial pollution from Guangxi Province; rather, these pollutants originated on the east coast of China and were transported through the Qiongzhou Strait. The primary sources were the Pearl River Estuary and the coastal waters of eastern Guangdong. In addition, the differences in the concentration distributions of nitrogen and phosphorus nutrients between the east and west coasts of the Qinzhou Gulf in the northern Beibu Gulf were clearly related to dynamic response mechanisms. [ABSTRACT FROM AUTHOR]

We conducted field sampling over 19 months to investigate eelgrass population reproduction status and ecological interactions in a large seagrass meadow in a eutrophic bay in northern China. The results showed asexual growth played an important role in the maintenance of existing meadows, and sexual reproduction played a critical role in the colonization of new areas. We conclude that adult eelgrass shoots do rule the fate of seedlings in the large seagrass meadow. Additionally, nutrient resources (N and P) at this location were found to meet eelgrass growth demand. The N/P ratios of seawater and seagrass indicated N limitation relative to P in the eutrophic bay based on the seagrass Redfield ratio (25–30). Nutrient uptake by seagrass might be an important factor in reducing the probability of a red tide in the study area. The results of this study provide fundamental information for eelgrass restoration and conservation. • N/P ratios of seawater and seagrass indicated N limitation in the eutrophic bay. • The top-down regulation might play an important factor removing nutrients. • Asexual reproduction plays a critical role in the eelgrass reproduction. • Sexual reproduction plays a critical role in the colonization of seagrass gaps. • Adult shoots rule its seedling fate. [ABSTRACT FROM AUTHOR]

Harmful Algal Blooms (HABs), those proliferations of algae that cause environmental, economic, or human health problems, are increasing in frequency, duration, and geographic extent due to nutrient pollution. The scale of the HAB problem in Asia has escalated in recent decades in parallel with the increase in use of agricultural fertilizer, the development of aquaculture, and a growing population. Three examples, all from China but illustrative of the diversity of events and their ecological, economic, and human health effects throughout Asia, are highlighted here. These examples include inland (Lake Tai or Taihu) as well as offshore (East China Sea and Yellow Sea) waters. The future outlook for controlling these blooms is bleak. The effects of advancing industrialized agriculture and a continually growing population will continue to result in more nutrient pollution and more HABs—-and more effects - in the foreseeable future. [ABSTRACT FROM AUTHOR]

The process and management of red tide in oligotrophic waters are poorly understood as most studies on red tide were focused on eutrophic areas. In this study, 404 red tide events together with the historical water quality dynamics during 1991-2020 were investigated in an anthropogenically influenced bay in China - Mirs Bay, whose most region is oligotrophic except small inshore areas. Red tides of oligotrophic offshore accounted for 20 % of all. With the effective governmental management on inshore areas, concentration of PO 4 and DIN has been decreased to a low level (PO 4 <0.01 mg/L while DIN <0.1 mg/L) in the bay since about 2000. However, the reduction of nutrients was still accompanied by the frequent outbreaks of red tides, as well as a shift of dominant algae from diatoms to dinoflagellates, which might be due to the unbalanced nutrient reduction, such as N:P ratio fluctuation and organic nutrient increase. This shift might trigger more red tide events and even some super ones (long-duration or large-scale) in oligotrophic areas. Detailed analysis on red tide events combined with model simulation proved that the outbreak of red tide in Mirs Bay was caused by the joint contribution of nutrients and hydrodynamics. Nutrients of inshore area supported the red tides there, and with the help of physical conditions, red tides inshore could be transferred to offshore areas and then were likely to bloom again or be preyed to support blooms of other organisms. This study acknowledged that the reduction of both N and P either inorganic or organic nutrients was essential to control red tides, even in oligotrophic waters, but a balanced strategy considering the dual reduction of both nitrogen and phosphorus was of pivotal role to restore the health of coastal water systems disturbed by human., Competing Interests: Declaration of competing interest The authors have no conflicts of interest to declare., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Abstract: Karenia mikimotoi is a dinoflagellate that is widely distributed in China that has recently become increasingly involved in harmful algal blooms (HABs). Therefore, it is urgent and necessary to study this dinoflagellate in order to monitor and forecast HABs. In this study, we designed a set of primers and a probe specific to K. mikimotoi (within its internal transcribed spacer (ITS) regions) and developed a real-time quantitative PCR (qPCR) method for the purpose of identification and quantification. We successfully prepared a 10-fold series of recombinant plasmid solutions containing ITS regions of K. mikimotoi as standard samples; these were used to generate a standard curve. Additionally, we quantified the genomic DNA of K. mikimotoi cells and utilized this DNA to prepare another 10-fold standard sample series and standard curve. The mathematic relationship between the cell numbers and their corresponding plasmid copy numbers was also established. We used laboratory and field samples to test the effectiveness of the qPCR method. For the laboratory samples, greater than 102 cells of K. mikimotoi could be quantified precisely utilizing both centrifugation and filtration techniques. The qPCR method was efficient even at low cell density and could detect 5 cells of K. mikimotoi. Field samples were collected from the East China Sea during a spring cruise in 2011; K. mikimotoi was detected (147±20cellsL−1) in these samples while light microscopy failed to detect K. mikimotoi. The qPCR and conventional PCR amplification products (utilizing dinoflagellate-specific primers LH2 and Dlam) were sequenced, and two sequences of 111bp and 684bp were determined to be highly similar to K. mikimotoi. Therefore, we conclude that the microalgae detected by the qPCR method was K. mikimotoi. [Copyright &y& Elsevier]

Abstract: The effects of temperature, salinity and irradiance on the growth of the causative organism of large-scale red tide along the east Chinese coast Prorocentrum donghaiense were examined in the laboratory. The optimum irradiance for growth was >30μmolm−2 s−1. A moderate specific growth rate of 0.33d−1 was observed at 2μmolm−2 s−1, the minimum irradiance in the experiments, and photoinhibition did not occur even at 230μmolm−2 s−1, the maximum irradiance in the experiments. From 42 different combinations of temperature (10–31°C) and salinity (10–40psu) under saturated irradiance, P. donghaiense exhibited its maximum specific growth rate of 0.77d−1 at a combination of 27°C and salinity of 30psu. Optimum growth rates of >0.60d−1 were observed at temperatures ranging from 20 to 27°C and at salinities from 25 to 35psu. The organism was able to grow at temperatures ranging from 10 to 27°C and at salinities from 20 to 40psu, but it could not grow at temperature ≥31°C or at salinities ≤10psu. Temperature had the greatest influence on the growth rate, followed by salinity and the interaction between temperature and salinity. It is noteworthy that P. donghaiense adapts to low irradiance, low temperature ranging from 10 to 20°C and a broad range of salinities, demonstrating its ability to dominate in estuaries, and bloom in early spring. [Copyright &y& Elsevier]

It is important to map dissolved inorganic nitrogen (DIN) concentrations in order to accurately predict the outbreak of red tides. This study aims to determine the feasibility of retrieving DIN in Haizhou Bay, East China from multi-temporal MODIS satellite data and to assess the impact of DIN concentration level on its inversion accuracy. DIN was modeled from the reflectance of MODIS bands and their combinations both linearly and nonlinearly. It was found that individual MODIS bands are loosely correlated with DIN concentrations. Of the various combinations of multiple bands, bands 3 and 4 bear a highly positive correlation with DIN concentrations. In particular, (R3 + R4)/(R3 - R4) is a more accurate predictor of DIN than R3 × R4/(R3 - R4). All the regression models involving this exploratory variable have an R2 value over 0.7 and a relative accuracy of around 70%. However, regression residuals are dependent of each other for DIN <70 μg/L. The removal of these observations from the regression analysis led to the establishment of the best model in the form of DIN<70 = 7.403 (R3 + R4)/(R3 - R4) + 37.14 (R2 = 0.87, n = 19). It improved the model accuracy to RMSE = 17.48 μg/L (15.8%) against the validation dataset. MODIS data allow accurate retrieval of DIN concentrations >70 μg/L in murky coastal waters. During the study period of 2004-2006, Haizhou Bay experienced a deteriorating trend in DIN in that low concentration areas decreased while areas of a high DIN concentration level expanded. [ABSTRACT FROM AUTHOR]

Abstract: Red tides (high biomass phytoplankton blooms) have frequently occurred in Hong Kong waters, but most red tides occurred in waters which are not very eutrophic. For example, Port Shelter, a semi-enclosed bay in the northeast of Hong Kong, is one of hot spots for red tides. Concentrations of ambient inorganic nutrients (e.g. N, P), are not high enough to form the high biomass of chlorophyll a (chl a) in a red tide when chl a is converted to its particulate organic nutrient (N) (which should equal the inorganic nutrient, N). When a red tide of the dinoflagellate Scrippsiella trochoidea occurred in the bay, we found that the red tide patch along the shore had a high cell density of 15,000cellsml−1, and high chl a (56μgl−1), and pH reached 8.6 at the surface (8.2 at the bottom), indicating active photosynthesis in situ. Ambient inorganic nutrients (NO3, PO4, SiO4, and NH4) were all low in the waters and deep waters surrounding the red tide patch, suggesting that the nutrients were not high enough to support the high chl a >50μgl−1 in the red tide. Nutrient addition experiments showed that the addition of all of the inorganic nutrients to a non-red-tide water sample containing low concentrations of Scrippsiella trochoidea did not produce cell density of Scrippsiella trochoidea as high as in the red tide patch, suggesting that nutrients were not an initializing factor for this red tide. During the incubation of the red tide water sample without any nutrient addition, the phytoplankton biomass decreased gradually over 9 days. However, with a N addition, the phytoplankton biomass increased steadily until day 7, which suggested that nitrogen addition was able to sustain the high biomass of the red tide for a week with and without nutrients. In contrast, the red tide in the bay disappeared on the sampling day when the wind direction changed. These results indicated that initiation, maintenance and disappearance of the dinoflagellate Scrippsiella trochoidea red tide in the bay were not directly driven by changes in nutrients. Therefore, how nutrients are linked to the formation of red tides in coastal waters need to be further examined, particularly in relation to dissolved organic nutrients. [Copyright &y& Elsevier]

Abstract: Nutrient input from the Changjiang River (Yangtze River) has been increasing dramatically since the 1960s. At the mouth of the Changjiang River, the nitrate concentration has increased about three-fold in 40 years, from 20.5μmol/L in the 1960s to 59.1μmol/L in the 1980s and to 80.6μmol/L in 1990–2004. Phosphate concentration increased by a factor of 30%, from 0.59μmol/L in the 1980s to 0.77μmol/L in 1990–2004. The increasing nitrate input has arisen mostly from the mid and lower reaches of the Changjiang River, where the river meets one of the most strongly developed agriculture areas in China. Responses of the coastal phytoplankton community to the increasing nutrient inputs are also seen in the available monitoring data. First, a trend of increasing phytoplankton standing stock from 1984 to 2002 appeared in the Changjiang River estuary and adjacent coastal waters, especially in late spring. Secondly, the proportion of diatoms in the whole phytoplankton community showed a decreasing trend from about 85% in 1984 to about 60% in 2000. Finally, red tides/harmful algal blooms increased dramatically in this area in terms of both number and scale. About 30–80 red tide events were recorded each year from 2000 to 2005 in the East China Sea. The scale of some blooms has been in excess of 10,000km2. [Copyright &y& Elsevier]

Hong Kong's wastewater collection and treatment systems did not keep the pace with population growth and economic development in the past. The discharge of wastewater from domestic and industrial sources led to the deterioration of aquatic and marine ecological systems, the closure of beaches, the occurrence of red tides, and the bioaccumulation and contamination of seafood. Similar to other major cities in the world, Hong Kong has been working diligently to improve her water quality. The enactment of the Water Pollution Control Ordinance was a sign of the beginning of the fight on water pollution. In 1986, a flexible environmental management master plan was designed, and implemented over the following two decades. Currently, of the 2.6 million cubic meters of wastewater generated each day in Hong Kong, 98% receives suitable treatment. The deterioration in the quality of aquatic environments in the territory has been effectively controlled. [ABSTRACT FROM AUTHOR]

Experiments were carried out to investigate interspecific interactions between the rotifer Brachionus plicatilis and two harmful algal bloom (HAB) species using single and mixed culture methods. B. plicatilis populations and the growth of two algae were compared at different algal cell densities. The results demonstrate that B. plicatilis obtained sufficient nutrition from Alexandrium tamarense to support net population increase. When exposed to a density of 8 × 104 cells ml−1 A. tamarense, the number of B. plicatilis increased faster than it did when exposed to other four algal densities (16 × 104, 24 × 104, 32 × 104, and 40 × 104 cells ml−1). Cell densities of A. tamarense decreased due to the grazing of B. plicatilis. In contrast, Heterosigma akashiwo had an adverse effect on the B. plicatilis population and its growth was largely unaffected by rotifer grazing. In this case, the B. plicatilis population decreased and H. akashiwo grew at a rate similar to that of a control without addition of rotifers. Mixed culture experiments showed that A. tamarense could partly counteract the effect of H. akashiwo in limiting the rate of population increase of rotifer. In addition, the effect of different initial cell densities on interspecific competition between A. tamarense and H. akashiwo in mixed culture(s) was also investigated. The results show that A. tamarense competed very successfully when the inoculation proportions of A. tamarense and H. akashiwo were 40:5 and 40:30. [ABSTRACT FROM AUTHOR]

Abstract: Harmful algal blooms, which are considered a serious environmental problem nowadays, occur in coastal waters in many parts of the world. They cause acute ecological damage and ensuing economic losses, due to fish kills and shellfish poisoning as well as public health threats posed by toxic blooms. Recently, data-driven models including machine-learning (ML) techniques have been employed to mimic dynamics of algal blooms. One of the most important steps in the application of a ML technique is the selection of significant model input variables. In the present paper, we use two extensively used ML techniques, artificial neural networks (ANN) and genetic programming (GP) for selecting the significant input variables. The efficacy of these techniques is first demonstrated on a test problem with known dependence and then they are applied to a real-world case study of water quality data from Tolo Harbour, Hong Kong. These ML techniques overcome some of the limitations of the currently used techniques for input variable selection, a review of which is also presented. The interpretation of the weights of the trained ANN and the GP evolved equations demonstrate their ability to identify the ecologically significant variables precisely. The significant variables suggested by the ML techniques also indicate chlorophyll-a (Chl-a) itself to be the most significant input in predicting the algal blooms, suggesting an auto-regressive nature or persistence in the algal bloom dynamics, which may be related to the long flushing time in the semi-enclosed coastal waters. The study also confirms the previous understanding that the algal blooms in coastal waters of Hong Kong often occur with a life cycle of the order of 1–2 weeks. [Copyright &y& Elsevier]

Sediment geochemical technique was employed to assess how the sediment records reflect the environmental changes of Jiaozhou Bay, a semi-enclosed bay adjacent to Qingdao, China. In the past hundred years, Jiaozhou Bay has been greatly impacted by human interventions. A dated core sediment by 210Pb chronology was analyzed for trace metals including Li, Cd, Cr, Pb, Cu, Ni, Co, Zn together with C, N, P and BSi. Based on the research, the development of Jiaozhou Bay environment in the past hundred years can be divided into three stages: (1) before the 1980s characterized by relatively low sedimentation rate, weak heavy metal pollution and scarce eutrophication; (2) from the 1980s to 2000, accelerating in the 1990s, during which high sedimentation rates, polluted by heavy metals and the frequent occurrence of red tide; (3) after 2000, the period of the improvement of environment, the whole system has been meliorated including the heavy metal pollution and hypernutrification. [Copyright &y& Elsevier]

No abstract available. [ABSTRACT FROM AUTHOR]

Red tides and eutrophication have been frequently observed over the past two decades in coastal waters around Hong Kong, which are caused by many factors and one of them is the nutrient from nonpoint source pollution (NSP). This paper concentrates on the nutrients carried by river flow from watersheds. Since there are no systematical data sets of nonpoint source pollution in Hong Kong, monthly river water quality measurements, rainfall and river flow data, land uses, and other related information are used to analyze the characteristics of NSP and estimate the nutrient loads for Hong Kong region. Main achievements are as follows: firstly, besides mean concentration for single land use, the concept of integrated mean concentration for mixed land uses was proposed and applied. Secondly, mean concentrations were carried out for different land uses (agriculture, town, grassland, shrubland and woodland), each Water Control Zone, and Hong Kong region. Thirdly, the annual nutrient loads were estimated, for the first time in this paper, with various methods for the whole area of Hong Kong, and about 8,000 tons of TN and 1,500 tons TP are transported into coastal waters from Hong Kong's land in 1998. [ABSTRACT FROM AUTHOR]

In this paper, the semi-enclosed bay named Tolo Harbour and Channel in Hong Kong, which was frequently attacked by red tides, was used as a case study. Data sets related to marine water quality, river nutrients, and meteorological conditions recorded between 1988 and 1999 were chosen for statistical analysis. A multivariate analysis showed that algal growth, represented by the chlorophyll a concentration, had obvious spatial and temporal variations in the study area. The chlorophyll a concentration had a consistently decreasing trend from the inner part of the Harbour and surface waters to the outer part and bottom waters. The temporal variations had a markedly seasonal variation with high bioproductivity in spring and winter. There were long-term fluctuations in the chlorophyll a concentration with a high-low-high pattern in the study period. Nutrients and hydrological and meteorological conditions were important factors of algal bloom. Besides nitrogen, which was the most critical factor of algal bloom for the whole water body, total phosphorus in the surface waters and phosphate (PO4) and silica (SiO2) in the bottom waters also showed strongly positive or negative correlations with the chlorophyll a level. For the meteorological conditions, global solar radiation was the key factor of massive algal bloom in the study period, while rainfall and wind direction were the most important factors of seasonal variation. [ABSTRACT FROM AUTHOR]

Between the years 1933-2001, 460 red tide events were found in China's coastal water. The scope of red tide occurrence has extended over all the coastal provinces of China, and the three major areas with high red tide frequency are the Bohai sea, the sea area near the Shengsi Archipelago and Huaniaoshan Island on the outer side of the Changjiang River estuary and the Hangzhou Bay, and the coastal waters on the east side of the Zhujiang River estuary from Hong Kong to East Guangdong. In the past 20 years, the frequency of red tides has been tending upwards. The years of 1988-1990 and 1998-2001 saw the most serious red tides along China's coastal waters, with the latter period as the peak. The average area of a single red tide, i.e., the scale of red tides, is expanding every year, and in 2001 rose to about 500 km2. Every year, China's red tides occur from south to north, with those in the South China Sea occurring from March to May, those in the East China Sea from April to August and those in the Bohai and Huanghai Seas from May to September. [ABSTRACT FROM AUTHOR]

In subtropical coastal waters around Hong Kong, algal blooms and red tides have been frequently observed over the past two decades. In particular, in March-April 1998, a massive red tide invaded the northeastern and southern coastal waters of Hong Kong. The devastating red tide resulted in the worst fish kill in Hong Kong's history, the most significant impacts being at the Lo Tik Wan and Sok Kwu Wan fish culture zones on Lamma Island. This work reports the first scientific investigation of the cause of this massive red tide. A calibrated three-dimensional (3D) hydrodynamic model for the Pearl River Estuary, Delft3D, is applied to study the advective transport of red tides. Based on the tidal boundary conditions and the measured wind data for a typical spring season, the 3D flow field is computed and extensive surface drogue tracking performed for releases in different parts of the coastal waters and for different tidal and wind conditions. The results show that a bloom initiated in Mirs Bay (Nan Au or Tap Mun) in the northeastern water would likely be transported to the southern coastal waters under the combined action of tidal current and wind. The computed bloom tracking patterns are generally supported by observations and are consistent with the temporal and spatial patterns of individual fish kill events in the 1998 red tide. We conclude that the major cause of the bloom being transported into the southern waters and East Lamma Channel (and causing the massive fish kill) is the generally strong wind in March-April 1998 and the change in wind direction in early April under almost diurnal tidal conditions. Further, it is most probable that the red tide originated in Mirs Bay rather than from outside Hong Kong. The findings provide a firm basis for environmental and fisheries management. [ABSTRACT FROM AUTHOR]

Eutrophication is becoming a serious problem in coastal waters in many parts of the world. It induces the phytoplankton blooms including `Red Tides', followed by heavy economic losses to extensive aquaculture area. Some cultivated seaweeds have very high productivity and could absorb large quantities of N, P, CO2, produce large amount of O2 and have excellent effect on decreasing eutrophication. The author believes that seaweed cultivation in large scale should be a good solution to the eutrophication problem in coastal waters. To put this idea into practice, four conditions should be fulfilled: (a) Large-scale cultivation could be conducted within the region experiencing eutrophication. (b) Fundamental scientific and technological problems for cultivation should have been solved. (c) Cultivation should not impose any harmful ecological effects. (d) Cultivation must be economically feasible and profitable. In northern China, large-scale cultivation of Laminaria japonica Aresch. has been encouraged for years to balance the negative effects from scallop cultivation. Preliminary research in recent years has shown that Gracilaria lemaneiformis (Bory) Daws. and Porphyra haitanensis Chang et Zheng are the two best candidates for this purpose along the Chinese southeast to southern coast from Fujian to Guangdong, Guangxi and Hong Kong. Gracilaria tenuistipitata var. liui Chang et Xia is promising for use in pond culture condition with shrimps and fish. [ABSTRACT FROM AUTHOR]

The long-term temporal and spatial dynamics of marine coastal water quality in Tolo Harbor. Hong Kong were explored. The Harbor is divided into three zones represented as Harbor, Buffer, and Channel Subzones. The time range for the study covers the period from the 1970s to the 1990s. The selected indicators for the comprehensive assessment of water quality consist of physical, chemical and biological aspects, including suspended solids (SS). Secchi disk depth (SD). 5-day biochemical oxygen demand (BOD5), total nitrogen (TN), total phosphorus (TP), faecal coliform, chlorophyll-a (Chl-a), and the number of red tide occurrences. The results indicated the presence of obvious temporal and spatial trends with regard to changes in water quality. Spatially, water quality in the Channel Subzone is the best, while that in the Harbor Subzone Is the worst. On a temporal basis, the average trend from bad to good was 1980s > 1990s > 1970s as indicated by most of the selected water quality indicators. Water quality during the late 1980s reached its worst level with the lowest SD, the highest BOD3 TN, TP, Chl-a concentrations, and the number of red tide occurrences. These long-term temporal-spatial water quality trends were also found in other studies of the Tolo Harbor. The large quantity of pollutants produced as a result of increasing population, industrial and commercial actives, and urbanization and industrialization trends in both Shatin and Tai Po seem to be primarily responsible for the changes in marine coastal water quality. [ABSTRACT FROM AUTHOR]

The Yellow Sea (YS) has been subjected to harmful algal blooms (HABs) for several decades. In this study, we compiled and analyzed a dataset of 165 red tides from 1972 to 2017 and a dataset of green tides from 2008 to 2017 in the YS. The most notable feature of red tides in the YS is the increasing dominance of dinoflagellate red tides in terms of frequency, scale, seasonal distribution, spatial coverage, and red tide causative species. The increasing dominance of dinoflagellate red tides is closely related to eutrophication and the development of the mariculture industry in the YS. However, the dinoflagellate red tides in the northern Yellow Sea (NYS) and the southern Yellow Sea (SYS) have different features. The apparent changes in red tides in the SYS in terms of frequency and seasonal patterns might have been caused by recurrent large-scale green tides in the last decade. • Datasets of red tides and green tides recorded in Yellow Sea (YS) were analyzed. • Dominance of dinoflagellate red tides increased in YS after 2000. • Dinoflagellate red tides in northern and southern YS exhibited different features. • Dinoflagellate red tides in YS were related to mariculture and eutrophication. • Red tides in southern YS might be affected by recurrent green tides. [ABSTRACT FROM AUTHOR]

Data on red tide (harmful algae blooms, HABs) from 1986 to 2017 in Xiamen Bay of Fujian province in China was collected. In these 30 years, a total of 53 red tide events were recorded, which mostly happened in West sea (47.3%) and Tong'an Bay (40.5%). And, red tide areas in Xiamen Bay have expanded, with the most prone area changing from West sea to Tong'an Bay. Furthermore, red tide focused on late spring and summer, including the months of May, June and July, with the percentage of occurrence of 13.8%, 26.2% and 27.7%, respectively. By contrast, red tide seldom occurred in autumn. Skeletonema costatum , Chaetoceros curvisetus and Akashiwo sanguinea were dominant red tide species in the bay responsible for red tide events on 24, 8 and 6 occasions so far, respectively. Red tide events caused by Dinoflagellates have been increasing in these 30 years. While red tide events caused by Diatom decreased in 2010s obviously compared to those in 2000s. It was suggested that changes of eutrophication degree and nutrient ratios, climate change, and sediment property maybe important factors to the long-term changes in red tide outbreaks in Xiamen Bay. 1. Trends of red tide in a subtropical bay of China were studied. 2. Dominant red tide species have changed from diatom to dinoflagellate. 3. Akashiwo sanguinea blooms always break out at the same site in the Bay. 4. Eutrophication and climate change were important reasons for the changes. [ABSTRACT FROM AUTHOR]