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To control harmful algae blooms (HABs), methods based on natural mechanisms are now required. We investigated the effects of an algicide derived from macrophyte metabolites, namely mixtures of gallic, tetradecanoic, heptanoic, and octanoic acids (1:1:1:1 mass ratio, a total concentration of 14 mg/L), on the biomass of cyanobacteria and other plankton and the production of microcystins under experimental conditions. Two types of microcosms have been created: simple (microalgae, cyanobacteria, and zooplankton) and complex (microalgae, cyanobacteria, zooplankton, and planktivorous fish). We observed the dynamics of the phytoplankton structure, the concentrations of microcystins and chlorophyll-a, hydrochemistry, and the status of zooplankton and fish in both types of microcosms with and without algicide for one month (from 19 July to 19 August 2021). The introduction of algicide caused changes in phytoplankton structure, a drop in cyanobacterial biomass, and a decrease in the total concentration of microcystins. Surprisingly, the contributions of the most toxic microcystins (LR form) were higher in both types of microcosms exposed to algicide than in microcosms without algicide. The inhibitory effect on the cyanobacterial biomass was most significant in complex ecosystems (containing fish), while it was only observed at the end of the exposure in simple ecosystems. Not only algicide but also phytoplankton consumed by fish and zooplankton, as well as nutrient excretory activity by both consumers, seem to have impact on cyanobacterial biomass. This study found that the using chemical substances similar to macrophyte metabolites can help regulate HABs and cyanotoxins. However, the results differ depending on ecosystem type. [ABSTRACT FROM AUTHOR]

Nutrient-driven cyanobacteria blooms are an increasingly common issue in freshwater environments, particularly in anthropogenically altered landscapes. As stormwater runoff is one of the largest sources of nutrients for freshwater bodies, stormwater retention ponds in urban and suburban areas are likely environments for harmful cyanobacteria blooms and were thus targeted for an in-depth investigation assessing taxonomic composition, bloom morphological composition, toxicity, and impact of nutrients and other environmental drivers. Eighty-seven algal blooms were sampled from 2019 to 2022 in the greater Wilmington, North Carolina, area. Physicochemical parameters were recorded, and blooms were classified by type (defined as surface mat, surface scum, water column distribution, or benthic mat) and dominant taxa. Blooms of potentially toxic cyanobacteria genera in the water column of stormwater retention ponds were most prevalent. Dissolved inorganic phosphorus was significantly related to chlorophyll-α, Microcystis bloom formation, and the production of microcystin. Seventeen potentially toxic cyanobacteria genera were identified in retention ponds, some of whose blooms demonstrated detectable microcystin. Monoclonal cultures isolated from some blooms were found to produce anabaenopeptin and saxitoxin. The results demonstrate a higher incidence of potentially toxic cyanobacteria over other bloom-forming taxa (chlorophytes, euglenoids, chrysophytes, dinoflagellates, and diatoms) in the 39 water bodies sampled. The frequency of blooms occurring in stormwater ponds and the diversity of potentially toxic cyanobacteria identified suggest such harmful blooms are likely widespread in similar freshwater environments across multiple urbanizing areas. The blooms sampled in this study were all within residential, commercial, or recreational areas easily accessible to people, presenting serious hazards to both environmental and public health. [ABSTRACT FROM AUTHOR]

The fermentation processes of algicidal bacteria offer an eco-friendly and promising approach for controlling harmful algae blooms (HABs). The strain Ba3, previously isolated and identified as Bacillus sp., displays robust algicidal activity against HABs dinoflagellate in particular. Microbial fermentation products have also been found to provide metabolites with multiple bioactivities, which has been shown to reduce harmful algae species' vegetative cells and thus reduce red tide outbreaks. In this study, the microbial fermentation of algicidal bacterium Ba3 was analyzed for its potential ability of algicidal compounds. A treatment time increased the algicidal efficiency of the fermentation products against Prorocentrum donghaiense (91%) and Alexandrium tamarense (82%). Among the treatment groups, the changing trend for the 2% treatment group was faster than that for the other treatments, showing that the inhibition rate could reach 99.1% in two days. Active components were separated by organic solvent extraction and macroporous resin, and the molecular weight of the active components was analyzed by LC-MS. The result shows that the microbial fermentation products offer a potential, not practical use for controlling the outbreaks of dinoflagellate blooms. As a result of its potential application for inhibiting HABs, these findings provide an encouraging basis for promoting large-scale fermentation production and the controlling the outbreaks of red tide. [ABSTRACT FROM AUTHOR]

Alexandriumpacificum is a typical toxic bloom-forming dinoflagellate, causing serious damage to aquatic ecosystems and human health. Many bacteria have been isolated, having algicidal effects on harmful algal species, while few algicidal bacteria have been found to be able to lyse A. pacificum. Herein, an algicidal bacterium, Shewanella Y1, with algicidal activity to the toxic dinoflagellate A. pacificum, was isolated from Jiaozhou Bay, China, and the physiological responses to oxidative stress in A. pacificum were further investigated to elucidate the mechanism involved in Shewanella Y1. Y1 exhibited a significant algicidal effect (86.64 ± 5.04% at 24 h) and algicidal activity in an indirect manner. The significant declines of the maximal photosynthetic efficiency (Fv/Fm), initial slope of the light limited region (alpha), and maximum relative photosynthetic electron transfer rate (rETRmax) indicated that the Y1 filtrate inhibited photosynthetic activities of A. pacificum. Impaired photosynthesis induced the overproduction of reactive oxygen species (ROS) and caused strong oxidative damage in A. pacificum, ultimately inducing cell death. These findings provide a better understanding of the biological basis of complex algicidal bacterium-harmful algae interactions, providing a potential source of bacterial agent to control harmful algal blooms. [ABSTRACT FROM AUTHOR]

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

Blooms of the harmful dinoflagellate Karenia brevis on the West Florida Shelf (WFS), Gulf of Mexico, are hypothesized to initiate in association with the colonial cyanobacterium Trichodesmium spp. and benefit from dissolved organic nitrogen (DON) release derived from N2-fixation by the cyanobacteria. Previous studies have detected DON release using direct experimental measurements, but there have been few studies that have followed nutrient release by in situ blooms of Trichodesmium and the associated plankton community. It was determined that long-term Trichodesmium spp. and Karenia brevis abundances on the WFS were related, following a 2-month lag. A separate Eulerian study of a Trichodesmium erythraeum bloom event was conducted over 9 days on the Great Barrier Reef. Concentrations of T. erythraeum increased over the course of the study, with coincident increases in dinoflagellate abundance and decreases in diatom abundance. Inside the bloom, concentrations of NH4+, PO43−, and DON increased significantly. The copepod grazer Macrosetella gracilis also increased in abundance as T. erythraeum numbers increased, contributing to nutrient release. Copepod grazing rates were measured, and N release rates estimated. Together, these studies show that Trichodesmium blooms have consequences for dinoflagellate abundance at both seasonal and ephemeral scales via direct and indirect N release. [ABSTRACT FROM AUTHOR]

Harmful algal bloom (HAB) formation leads to the eutrophication of water ecosystems and may render recreational lakes unsuitable for human use. We evaluated the applicability and comparison of metabarcoding, metagenomics, qPCR, and ELISA-based methods for cyanobacteria/cyanotoxin detection in bloom and non-bloom sites for the Great Lakes region. DNA sequencing-based methods robustly identified differences between bloom and non-bloom samples (e.g., the relative prominence of Anabaena and Planktothrix). Shotgun sequencing strategies also identified the enrichment of metabolic genes typical of cyanobacteria in bloom samples, though toxin genes were not detected, suggesting deeper sequencing or PCR methods may be needed to detect low-abundance toxin genes. PCR and ELISA indicated microcystin levels and microcystin gene copies were significantly more abundant in bloom sites. However, not all bloom samples were positive for microcystin, possibly due to bloom development by non-toxin-producing species. Additionally, microcystin levels were significantly correlated (positively) with microcystin gene copy number but not with total cyanobacterial 16S gene copies. In summary, next-generation sequencing-based methods can identify specific taxonomic and functional targets, which can be used for absolute quantification methods (qPCR and ELISA) to augment conventional water monitoring strategies. [ABSTRACT FROM AUTHOR]

This comprehensive review explores the escalating challenge of nutrient enrichment in aquatic ecosystems, spotlighting the dire ecological threats posed by harmful algal blooms (HABs) and excessive particulate organic matter (POM). Investigating recent advancements in water treatment technologies and management strategies, the study emphasizes the critical need for a multifaceted approach that incorporates physical, chemical, and biological methods to effectively address these issues. By conducting detailed comparative analyses across diverse aquatic environments, it highlights the complexities of mitigating HABs and underscores the importance of environment-specific strategies. The paper advocates for sustainable, innovative solutions and international cooperation to enhance global water quality and ecosystem health. It calls for ongoing advancement, regular monitoring, and comprehensive research to adapt to emerging challenges, thus ensuring the preservation of aquatic biodiversity and the protection of communities reliant on these vital resources. The necessity of integrating technological innovation, ecological understanding, and global cooperation to safeguard aquatic ecosystems for future generations is paramount. [ABSTRACT FROM AUTHOR]

Curcumin, a natural plant product, was investigated as a mitigation tool against Karenia brevis, the toxic dinoflagellate responsible for Florida red tides. A series of laboratory bench-top studies were conducted with additions of 0.1, 1, 2, 3, 5, 10, 20, 30, and 40 mg/L curcumin to K. brevis at an average of 1.0 × 106 cells/L to determine the efficacy of curcumin against K. brevis cells and brevetoxins and to optimize treatment dosage. Treatment with 5 mg/L of curcumin reduced K. brevis cell abundance by 89% and total brevetoxins by 60% within 24 h. Lower concentrations of curcumin (0.1–3 mg/L) exhibited between a 2 and 45% reduction in K. brevis and a reduction in brevetoxins of between 2 and 44% within 24 h. At the highest curcumin doses, 30 and 40 mg/L, a 100% reduction in cell abundance was observed by 6 h, with reduction in total brevetoxins by at least 64% in 48 h. These results suggest that curcumin, used alone or potentially in combination with other technologies, is a promising K. brevis bloom mitigation option. [ABSTRACT FROM AUTHOR]

The marine dinoflagellate Alexandrium is known to form harmful algal blooms (HABs) and produces saxitoxin (STX) and its derivatives (STXs) that cause paralytic shellfish poisoning (PSP) in humans. Cell growth and cellular metabolism are affected by environmental conditions, including nutrients, temperature, light, and the salinity of aquatic systems. Abiotic factors not only engage in photosynthesis, but also modulate the production of toxic secondary metabolites, such as STXs, in dinoflagellates. STXs production is influenced by a variety of abiotic factors; however, the relationship between the regulation of these abiotic variables and STXs accumulation seems not to be consistent, and sometimes it is controversial. Few studies have suggested that abiotic factors may influence toxicity and STXs-biosynthesis gene (sxt) regulation in toxic Alexandrium, particularly in A. catenella, A. minutum, and A. pacificum. Hence, in this review, we focused on STXs production in toxic Alexandrium with respect to the major abiotic factors, such as temperature, salinity, nutrients, and light intensity. This review informs future research on more sxt genes involved in STXs production in relation to the abiotic factors in toxic dinoflagellates. [ABSTRACT FROM AUTHOR]

Simple Summary: Florida red tides are large algal blooms of the toxic organism Karenia brevis and can have severe ecological impacts along the Gulf Coast regions of Florida, USA. K. brevis blooms produce potent neurotoxins, known as brevetoxins, which are known to cause disease and mortality in various marine species, including sea turtles. This review examines the impact of red tides on sea turtle health by discussing K. brevis blooms in general, as well as the toxin exposure routes and mechanisms of disease. Diagnostic and treatment options are also discussed. Significant research efforts have focused on developing improved therapeutic interventions, and intravenous lipid emulsion therapy has proven highly effective at rapidly alleviating symptoms and accelerating brevetoxin removal from sea turtles. This review synthesizes the current scientific understanding of red tide impacts on threatened and endangered sea turtle health. Continued investigations of outstanding knowledge gaps may help mitigate the threat of harmful algal blooms on sea turtles in the future and may contribute to the conservation of sea turtles. This review summarizes the current understanding of how brevetoxins, produced by Karenia brevis during harmful algal blooms, impact sea turtle health. Sea turtles may be exposed to brevetoxins through ingestion, inhalation, maternal transfer, and potentially absorption through the skin. Brevetoxins bind to voltage-gated sodium channels in the central nervous system, disrupting cellular function and inducing neurological symptoms in affected sea turtles. Moreover, the current evidence suggests a broader and longer-term impact on sea turtle health beyond what is seen during stranding events. Diagnosis relies on the detection of brevetoxins in tissues and plasma from stranded turtles. The current treatment of choice, intravenous lipid emulsion therapy, may rapidly reduce symptoms and brevetoxin concentrations, improving survival rates. Monitoring, prevention, and control strategies for harmful algal blooms are discussed. However, as the frequency and severity of blooms are expected to increase due to climate change and increased environmental pollution, continued research is needed to better understand the sublethal effects of brevetoxins on sea turtles and the impact on hatchlings, as well as the pharmacokinetic mechanisms underlying brevetoxicosis. Moreover, research into the optimization of treatments may help to protect endangered sea turtle populations in the face of this growing threat. [ABSTRACT FROM AUTHOR]

The successful cultivation of Dinophysis norvegica Claparède & Lachmann, 1859, isolated from Japanese coastal waters, is presented in this study, which also includes an examination of its toxin content and production for the first time. Maintaining the strains at a high abundance (>2000 cells per mL−1) for more than 20 months was achieved by feeding them with the ciliate Mesodinium rubrum Lohmann, 1908, along with the addition of the cryptophyte Teleaulax amphioxeia (W.Conrad) D.R.A.Hill, 1992. Toxin production was examined using seven established strains. At the end of the one-month incubation period, the total amounts of pectenotoxin-2 (PTX2) and dinophysistoxin-1 (DTX1) ranged between 132.0 and 375.0 ng per mL−1 (n = 7), and 0.7 and 3.6 ng per mL−1 (n = 3), respectively. Furthermore, only one strain was found to contain a trace level of okadaic acid (OA). Similarly, the cell quota of pectenotoxin-2 (PTX2) and dinophysistoxin-1 (DTX1) ranged from 60.6 to 152.4 pg per cell−1 (n = 7) and 0.5 to 1.2 pg per cell−1 (n = 3), respectively. The results of this study indicate that toxin production in this species is subject to variation depending on the strain. According to the growth experiment, D. norvegica exhibited a long lag phase, as suggested by the slow growth observed during the first 12 days. In the growth experiment, D. norvegica grew very slowly for the first 12 days, suggesting they had a long lag phase. However, after that, they grew exponentially, with a maximum growth rate of 0.56 divisions per day (during Days 24–27), reaching a maximum concentration of 3000 cells per mL−1 at the end of the incubation (Day 36). In the toxin production study, the concentration of DTX1 and PTX2 increased following their vegetative growth, but the toxin production still increased exponentially on Day 36 (1.3 ng per mL−1 and 154.7 ng per mL−1 of DTX1 and PTX2, respectively). The concentration of OA remained below detectable levels (≤0.010 ng per mL−1) during the 36-day incubation period, with the exception of Day 6. This study presents new information on the toxin production and content of D. norvegica, as well as insights into the maintenance and culturing of this species. [ABSTRACT FROM AUTHOR]

In the marine ecological environment, marine microalgae is an important photosynthetic autotrophic organism, which can carry out photosynthesis and absorb carbon dioxide. With the increasingly serious eutrophication of the water body, under certain environmental factors, the rapid propagation of some algae in the water body gradually forms a harmful bloom, which damages the water environment. Therefore, how to identify the beneficial algae and harmful algae quickly and accurately has gradually become the key to solve the problem. There are more than 30,000 species of marine microalgae in the world, and the sample data are few and the characteristics are not obvious. Many of the algae are similar in shape and difficult to distinguish. The few-shot learning task is very challenging. By training very few labeled samples, the deep learning model has excellent recognition ability. Meanwhile, the few-shot classification method based on metric learning has attracted considerable attention. In this paper, in order to make full use of image features and improve the generalization ability of the model, a multi-scale local feature fusion algorithm was proposed to classify marine microalgae with few shots. First, the input image is gridded and multiscale processed, and then it is sent to the CTM category traversal module for feature extraction to obtain local features. A local feature fusion module based on the SE-NET self-attention mechanism is designed to obtain local enhanced features containing global information to improve the generalization ability of the model. Classification is realized by calculating the distance between the sample feature vector of the query set and the prototype of the support set. Under the settings of 5-way 1-shot and 5-way 5-shot, the classification accuracy of the proposed method is improved by 6.08% and 5.5%, respectively. It provides a new idea for microalgae identification and a new opportunity for the sustainable development of new energy. [ABSTRACT FROM AUTHOR]

The Indian River Lagoon (IRL), a 156-mile-long estuary located on the eastern coast of Florida, experiences phytoplankton bloom events due to increased seasonal temperatures coupled with anthropogenic impacts. This study aimed to gather data on the toxicity to human cells and to identify secondary metabolites found in water samples collected in the IRL. Water samples from 20 sites of the IRL were collected during the wet and dry seasons over a three-year period. A panel of cell lines was used to test cytotoxicity. Hemagglutination, hemolysis, and inhibition of protein phosphatase 2A (PP2A) were also measured. Cytotoxic blooms were seen both in the south ( Microcystis ) and the north ( Pyrodinium ) of the IRL. Each toxin induced a consistent pattern of cytotoxicity in the panel of human cell lines assayed. During blooms, cytotoxicity due to a single type of toxin is obvious from this pattern. In the absence of blooms, the cytotoxicity seen reflected either a mixture of toxins or it was caused by an unidentified toxin. These observations suggest that other toxins with the potential to be harmful to human health may be present in the IRL. Moreover, the presence of toxins in the IRL is not always associated with blooms of known toxin-producing organisms.

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

Riverbed sediments in agricultural landscapes are loaded with phosphorus (P). They may act as a source or sink for riverine P, possibly causing harmful algae blooms and eutrophication in streams and receiving water bodies, including coastal waters. In this study, we aimed at identifying the labile, moderately labile, and stable P fraction (Hedley fractionation) in sediments of a northeastern German river basin (3000 km2). A non-metrical multidimensional scaling (NMDS) was used to identify the most significant environmental predictors of the P fractionation in sediments. The total P contents of the sediments varied over a wide range (698 ± 701 mg P kg−1 sediment−1), spanning from 98 to 2648 mg P kg−1 sediment−1. Adjacent agricultural reference soils had markedly lower total P contents of 354 ± 132 mg P kg−1 soil−1, ranging from 146 to 483 P kg−1 soil−1. There were almost no differences between the P contents of the top (0–2 cm) and the bottom (2–10 cm) layer. The dominant P fractions were the moderately labile (NaOH-P) and the stable (H2SO4-P) fractions, which accounted for more than 50% of the total P at each sampling point. The NMDS revealed that iron and aluminum contents, as well as land use, are significant predictors for the P fractionation of the sediment. The sediment P-composition reflects the P-status of the agriculturally used mineral soils. However, the size of the contributing catchment as well as the length of the water way have no effects on sediment P. In conclusion, sediment P stocks, though variable, may impede the good ecological status of river waters for decades, especially in lowland basins where hydraulic conditions and a very low stream velocity often create low redox and P dissolution conditions in sediments. [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]

Advanced agronomic methods, urbanisation, and industrial expansion contaminate air, water and soil, globally. Agricultural and industrial activities threaten living biota, causing biodiversity loss and serious diseases. Strategies such as bioremediation and physiochemical remediation have not been effectively beneficial at treating pollutants. Metal-based nanoparticles (NPs) such as copper, zinc, silver, gold, etc., in various nanoformulations and nanocomposites are used more and more as they effectively resist the uptake of toxic compounds via plants by facilitating their immobilisation. According to studies, bio-based NP synthesis is a recent and agroecologically friendly approach for remediating environmental waste, which is effective against carcinogens, heavy metal contamination, treating marine water polluted with excessive concentrations of phosphorus, nitrogen and harmful algae, and hazardous dye- and pesticide-contaminated water. Biogenic resources such as bacteria, fungi, algae and plants are extensively used for the biosynthesis of NPs, particularly metallic NPs. Strategies involving green synthesis of NPs are nontoxic and could be employed for commercial scale production. Here, the focus is on the green synthesis of NPs for reduction of hazardous wastes to help with the clean-up process. [ABSTRACT FROM AUTHOR]

Marine algal toxins have garnered significant attention in the research community for their unique biochemical properties and potential medical applications. These bioactive compounds, produced by microalgae, pose significant risks due to their high toxicity, yet offer promising therapeutic benefits. Despite extensive research identifying over 300 marine algal toxins, including azaspiracids, brevetoxins, cyclic imines, and yessotoxins, gaps remain in the understanding of their pharmacological potential. In this paper, we critically review the classification, bioactive components, toxicology, pharmacological activities, and mechanisms of these toxins, with a particular focus on their clinical applications. Our motivation stems from the increasing interest in marine algal toxins as candidates for drug development, driven by their high specificity and affinity for various biological receptors. We aim to bridge the gap between toxicological research and therapeutic application, offering insights into the advantages and limitations of these compounds in comparison to other bioactive substances. This review not only enhances the understanding of marine algal toxins' complexity and diversity, but also highlights their extensive application potential in medicine and bioscience, providing a foundation for future research and development in this field.

The presence of the odorant 2-methylisoborneol (2-MIB) in drinking water sources is undesirable. Although 2-MIB production is known to be influenced by temperature, its regulation at the gene level and its relationship with Chlorophyll- a (Chl- a ) at different temperatures remain unclear. This study investigates the impact of temperature on 2-MIB production and related gene expression in Pseudanabaena strains PD34 and PD35 isolated from Lake Paldang, South Korea. The strains were cultured at three temperatures (15, 25, and 30 °C) to examine cell growth, 2-MIB production, and mic gene expression levels. 2-MIB production per cell increased with higher temperatures, whereas mic gene expression levels were higher at lower temperatures, indicating a complex regulatory mechanism involving post-transcriptional and enzyme kinetics factors. Additionally, the relationship between Chl- a and 2-MIB involved in metabolic competition was analyzed, suggesting that high temperatures appear to favor 2-MIB synthesis more than Chl- a synthesis. The distinct difference in the total amount of the two products and the proportion of 2-MIB between the two strains partially explains the variations in 2-MIB production. These findings highlight the significant effect of temperature on 2-MIB biosynthesis in Pseudanabaena and provide a valuable background for gene data-based approaches to manage issues regarding 2-MIB in aquatic environments.

Cyanobacterial blooms are increasingly common during winters, especially when they are mild. The goal of this study was to determine the summer and winter phytoplankton community structure, cyanotoxin presence, and toxigenicity in a eutrophic lake susceptible to cyanobacterial blooms throughout the year, using classical microscopy, an analysis of toxic cyanometabolites, and an analysis of genes involved in biosynthesis of cyanotoxins. We also assessed whether cyanobacterial diversity in the studied lake has changed compared to what was reported in previous reports conducted several years ago. Moreover, the bloom-forming cyanobacterial strains were isolated from the lake and screened for cyanotoxin presence and toxigenicity. Cyanobacteria were the main component of the phytoplankton community in both sampling times, and, in particular, Oscillatoriales were predominant in both summer ( Planktothrix / Limnothrix ) and winter ( Limnothrix ) sampling. Compared to the winter community, the summer community was denser; richer in species; and contained alien and invasive Nostocales, including Sphaerospermopsis aphanizomenoides , Raphidiopsis raciborskii , and Raphidiopsis mediterranea . In both sampling times, the blooms contained toxigenic species with genetic determinants for the production of cylindrospermopsin and microcystins. Toxicological screening revealed the presence of microcystins in the lake in summer but no cyanotoxins in the winter period of sampling. However, several cyanobacterial strains isolated from the lake during winter and summer produced anabaenopeptins and microcystins. This study indicates that summer and winter blooms of cyanobacteria in the temperate zone can differ in biomass, structure, and toxicity, and that the toxic hazards associated with cyanobacterial blooms may potentially exist during winter.

Saxitoxin (STX), an exceptionally potent marine toxin for which no antidote is currently available, is produced by methanogens and cyanobacteria. This poses a significant threat to both shellfish aquaculture and human health. Consequently, the development of a rapid, highly sensitive STX detection method is of great significance. The objective of this research is to create a novel approach for identifying STX. Therefore, amplified luminescent proximity homogeneous assay (AlphaLISA) was established using a direct competition method based on the principles of fluorescence resonance energy transfer and antigen-antibody specific binding. This method is sensitive, rapid, performed without washing, easy to operate, and can detect 8-128 ng/mL of STX in only 10 min. The limit of detection achieved by this method is as low as 4.29 ng/mL with coefficients of variation for the intra-batch and inter-batch analyses ranging from 2.61% to 3.63% and from 7.67% to 8.30%, respectively. In conclusion, our study successfully establishes a simple yet sensitive, rapid, and accurate AlphaLISA method for the detection of STX which holds great potential in advancing research on marine biotoxins.

Dinoflagellates and heterotrophic bacteria are two major micro-organism groups within marine ecosystems. Their coexistence has led to a co-evolutionary relationship characterized by intricate interactions that not only alter their individual behaviors but also exert a significant influence on the broader biogeochemical cycles. Our review commenced with an analysis of bacterial populations, both free-living and adherent to dinoflagellate surfaces. Members of Alphaproteobacteria, Gammaproteobacteria, and the Cytophaga-Flavobacterium-Bacteroides group are repeatedly found to be associated with dinoflagellates, with representation by relatively few genera, such as Methylophaga , Marinobacter , and Alteromonas . These bacterial taxa engage with dinoflagellates in a limited capacity, involving nutrient exchange, the secretion of pathogenic substances, or participation in chemical production. Furthermore, the genomic evolution of dinoflagellates has been profoundly impacted by the horizontal gene transfer from bacteria. The integration of bacterial genes into dinoflagellates has been instrumental in defining their biological characteristics and nutritional strategies. This review aims to elucidate the nuanced interactions between dinoflagellates and their associated bacteria, offering a detailed perspective on their complex relationship.

Cyanobacterial biodiversity and potential toxicity in coastal lagoons have barely been studied despite these transitional water systems being very important in conservation and for the preservation of economic resources. Most of these transitional systems have been affected by eutrophication, and climate change will severely affect them by promoting cyanobacteria growth, especially in Mediterranean areas. This study aims to characterize the diversity of epipelic and epiphytic cyanobacteria species in a Mediterranean coastal lagoon and their potential for toxins production (microcystins and saxitoxins). Strains were isolated and genetically identified. Toxins were extracted and quantified by LC/MS-MS. All the taxa belong to the former Oscillatoriales. The presence of Nodosilinea and Toxifilum is reported for the first time for Spanish waters, but Pseudanabaena, Phormidium , Geitlerinema and Synechococcus also formed part of benthic mats. All the strains contained Microcystin-YR (MC-YR), but saxitoxin (STX) was present only in the extracts of Nodosilinea and Pseudanabena . MC-LY, MC-LW and [D-Asp 3 ] MC-LR were detected in the extracts of Synechococcus and MC-LF in Toxifilum , but at concentrations that did not permit quantification. Toxins production by epipelic and epiphytic strains in coastal lagoons may represent a hazard, but also an opportunity to obtain potentially interesting compounds that should be further studied.

Dinoflagellate species that form some of the most frequent toxic blooms are also bioluminescent, yet the two traits are rarely linked when studying bloom development and persistence. P. bahamense is a toxic, bioluminescent dinoflagellate that previously bloomed in Florida with no known record of saxitoxin (STX) production. Over the past 20 years, STX was identified in P. bahamense populations. The goal of this study was to examine toxin dynamics and associated molecular mechanisms in spatially and temporally distinct P. bahamense populations from the Indian River Lagoon, FL. SxtA4 is a key gene required for toxin biosynthesis. SxtA4 genotype analysis was performed on individual cells from multiple sites. Cell abundance, toxin quota cell -1 , and sxtA4 and RubisCo ( rbcL ) transcript abundance were also measured. There was a significant negative correlation between cell abundance and toxin quota cell -1 . While the sxtA4+ genotype was dominant at all sites, its frequency varied, but it occurred at 90-100% in many samples. The underlying mechanism for toxin decrease with increased cell abundance remains unknown. However, a strong, statistically significant negative correlation was found between stxA4 transcripts and the sxtA4/rbcL ratio, suggesting cells make fewer sxtA4 transcripts as a bloom progresses. However, the influence of sxtA4- cells must also be considered. Future plans include bioluminescence measurements, normalized to a per cell basis, at sites when toxicity is measured along with concomitant quantification of sxtA4 gene and transcript copy numbers as a means to elucidate whether changes in bloom toxicity are driven more at the genetic (emergence of sxtA4- cells) or transcriptional (repression of sxtA4 in sxtA4+ cells) level. Based on the results of this study, a model is proposed that links the combined traits of toxicity and bioluminescence in P. bahamense bloom development.

Considering the role of phytoplankton in the functioning and health of marine systems, it is important to characterize its responses to a changing environment. The central Adriatic Sea, as a generally oligotrophic area, is a suitable environment to distinguish between regular fluctuations in phytoplankton and those caused by anthropogenic or climatic influences. This study provides a long-term perspective of phytoplankton assemblage in the central eastern Adriatic Sea, with 14 years of continuous time series data collected at two coastal and two offshore stations. The predominant phytoplankton groups were diatoms and phytoflagellates, but their proportion varied depending on the vicinity of the coast, as evidenced also by the distribution of chlorophyll a . In the coastal environment, the phytoplankton biomass was substantially higher, with a higher proportion of microphytoplankton, while small phytoplankton accounted for the majority of biomass in the offshore area. In addition, a decreasing trend in diatom abundance was observed in the coastal waters, while such trend was not so evident in the offshore area. Using a neural gas algorithm, five clusters were defined based on the contribution of the major groups. The observed increase in diversity, especially in dinoflagellates, which outnumber diatom taxa, could be a possible adaptation of dinoflagellates to the increased natural solar radiation in summer and the increased sea surface temperature.

Dinoflagellate Alexandrium minutum Halim is commonly associated with harmful algal blooms (HABs) in tropical marine waters due to its saxitoxin production. However, limited information is available regarding the cellular and metabolic changes of A. minutum in nutrient-deficient environments. To fill this gap, our study aimed to investigate the transcriptomic responses of A. minutum under nitrogen and phosphorus deficiency. The induction of nitrogen and phosphorus deficiency resulted in the identification of 1049 and 763 differently expressed genes (DEGs), respectively. Further analysis using gene set enrichment analysis (GSEA) revealed 702 and 1251 enriched gene ontology (GO) terms associated with nitrogen and phosphorus deficiency, respectively. Our results indicate that in laboratory cultures, nitrogen deficiency primarily affects meiosis, carbohydrate catabolism, ammonium assimilation, ion homeostasis, and protein kinase activity. On the other hand, phosphorus deficiency primarily affects the carbon metabolic response, cellular ion transfer, actin-dependent cell movement, signalling pathways, and protein recycling. Our study provides valuable insights into biological processes and genes regulating A. minutum 's response to nutrient deficiencies, furthering our understanding of the ecophysiological response of HABs to environmental change.

This study reports the first detection of the marine neurotoxin pinnatoxin-G (PnTX-G) in clams collected in the northwestern Adriatic Sea (Italy). It also represents the first report of the potential toxin-producing dinoflagellate, Vulcanodinium rugosum, in Italian seas. This result, from the coasts of the Emilia-Romagna Region, indicates a successful colonization process, reflecting conditions in France where V. rugosum was initially documented. In this case, the concentration of PnTXs was very low, making further sampling necessary to fully understand the extent of the phenomenon. Discussions on the need to obtain more data to support a proper risk assessment and the need to implement a monitoring program that includes emerging marine biotoxins are also included. [ABSTRACT FROM AUTHOR]

"Red tide" is the popular name for a harmful algal bloom that occurs frequently in Florida waters and has significant impacts on the environment, the economy, and human and animal health. This paper addresses the limited understanding of public attitudes surrounding red tide and the potential for message framing to increase support for mitigation action. A sample of Florida residents (n = 498) was randomly shown a digital article framed around different red tide impacts (economic loss, human health risks, ecosystem damage, or harm to charismatic species) or a control article not framed around a specific red tide impact. Participants were then queried about their emotional responses, support for red tide mitigation policies, and intentions to change their behavior to mitigate impacts. Participants reported higher levels of negative emotions after viewing the harm to charismatic megafauna framing, indicating that messaging may play a significant role in eliciting environmental emotions. Message frames did not significantly impact other policy attitudes. Results demonstrate barriers to shifting support for mitigation where public support for action is already high. [ABSTRACT FROM AUTHOR]

At the end of summer 2020, a moderate (~105 cells L−1) bloom of potential fish-killing Karenia spp. was detected in samples from a 24 h study focused on Dinophysis spp. in the outer reaches of the Pitipalena-Añihue Marine Protected Area. Previous Karenia events with devastating effects on caged salmon and the wild fauna of Chilean Patagonia had been restricted to offshore waters, eventually reaching the southern coasts of Chiloé Island through the channel connecting the Chiloé Inland Sea to the Pacific Ocean. This event occurred at the onset of the COVID-19 lockdown when monitoring activities were slackened. A few salmon mortalities were related to other fish-killing species (e.g., Margalefidinium polykrikoides). As in the major Karenia event in 1999, the austral summer of 2020 was characterised by negative anomalies in rainfall and river outflow and a severe drought in March. Karenia spp. appeared to have been advected in a warm (14–15 °C) surface layer of estuarine saline water (S > 21). A lack of daily vertical migration patterns and cells dispersed through the whole water column suggested a declining population. Satellite images confirmed the decline, but gave evidence of dynamic multifrontal patterns of temperature and chl a distribution. A conceptual circulation model is proposed to explain the hypothetical retention of the Karenia bloom by a coastally generated eddy coupled with the semidiurnal tides at the mouth of Pitipalena Fjord. Thermal fronts generated by (topographically induced) upwelling around the Tic Toc Seamount are proposed as hot spots for the accumulation of swimming dinoflagellates in summer in the southern Chiloé Inland Sea. The results here provide helpful information on the environmental conditions and water column structure favouring Karenia occurrence. Thermohaline properties in the surface layer in summer can be used to develop a risk index (positive if the EFW layer is thin or absent). [ABSTRACT FROM AUTHOR]

Many dinoflagellates of the genus Alexandrium are well known for being responsible for harmful algal blooms (HABs), producing potent toxins that cause damages to other marine organisms, aquaculture, fishery, tourism, as well as induce human intoxications and even death after consumption of contaminated shellfish or fish. In this review, we summarize potential bioprospecting associated to the genus Alexandrium, including which Alexandrium spp. produce metabolites with anticancer, antimicrobial, antiviral, as well as anti-Alzheimer applications. When available, we report their mechanisms of action and targets. We also discuss recent progress on the identification of secondary metabolites with biological properties favorable to human health and aquaculture. Altogether, this information highlights the importance of studying which culturing conditions induce the activation of enzymatic pathways responsible for the synthesis of bioactive metabolites. It also suggests considering and comparing clones collected in different locations for toxin monitoring and marine bioprospecting. This review can be of interest not only for the scientific community, but also for the entire population and industries. [ABSTRACT FROM AUTHOR]

Few works have been carried out on benthic harmful algal blooms (BHAB) species in the southern Mediterranean and no data are available for the highly dynamic Strait of Gibraltar (western Mediterranean waters). For the first time, Ostreopsis sp. 9, Prorocentrum lima and Coolia monotis were isolated in this key region in terms of exchanges between the Atlantic Ocean and the Mediterranean and subject to intense maritime traffic. Ribotyping confirmed the morphological identification of these three dinoflagellates species. Monoclonal cultures were established and the maximum growth rate and cell yield were measured at a temperature of 24 °C and an irradiance of 90 µmol photons m−2 s−1, for each species: 0.26 ± 0.02 d−1 (8.75 × 103 cell mL−1 after 28 days) for Ostreopsis sp. 9, 0.21 ± 0.01 d−1 (49 × 103 cell mL−1 after 145 days) for P. lima and 0.21 ± 0.01 d−1 (10.02 × 103 cell mL−1 after 28 days) for C. monotis. Only P. lima was toxic with concentrations of okadaic acid and dinophysistoxin-1 measured in optimal growth conditions ranging from 6.4 pg cell−1 to 26.97 pg cell−1 and from 5.19 to 25.27 pg cell−1, respectively. The toxin content of this species varied in function of the growth phase. Temperature influenced the growth and toxin content of P. lima. Results suggest that future warming of Mediterranean coastal waters may lead to higher growth rates and to increases in cellular toxin levels in P. lima. Nitrate and ammonia affected the toxin content of P. lima but no clear trend was noted. In further studies, we have to isolate other BHAB species and strains from Strait of Gibraltar waters to obtain more insight into their diversity and toxicity. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) globally affect marine ecosystems and human health. Significant attention has been paid to understanding the initiation processes of HABs, while much less is known of the mechanisms causing cell demise and bloom decline. Recent evidence reveals that programmed cell death (PCD) can be a possible pathway for HAB termination. However, it is still not clear how PCD expression varies with the growth of marine phytoplankton. In order to characterize how susceptibility to stress-induced cell death changes with the growth of marine harmful algae, we examined the prevalence of PCD markers during 48 h after the addition of H2O2 in dinoflagellate Karenia brevis cultures at the early-log, mid-log and stationary phase. The results show that acute susceptibility to cell death (before time 0.5 h) increased as cultures aged, reflecting a chronological decrease in stress acclimation abilities. However, the youngest cultures showed strong PCD expression and the fastest overall rate of cell loss within the first 24 h, hypothesized to result from the cell-density-dependent H2O2 detoxifying process. This research highlights the existence of PCD in HAB species and that aging marine phytoplankton are more susceptible to exogenous stress, which agrees with previous observations of significant PCD during bloom decline. [ABSTRACT FROM AUTHOR]

Simple Summary: Harmful algal blooms present a particular risk for marine ecosystems and human health alike. In this sense, it is important to accurately predict how toxin-producing microalgae could be affected by future climate change. The present study applied species distribution models (SDMs) to project the potential changes in the habitat suitability and distribution of three key paralytic shellfish toxin (PST)-producing dinoflagellate species (i.e., Alexandrium catenella, A. minutum, and Gymnodinium catenatum), up to 2040/50 and 2090/2100, across four different greenhouse gas emission scenarios, and using four abiotic predictors (i.e., sea surface temperature, salinity, current velocity, and bathymetry). In general, considerable contractions were observed for all three species in the lower latitudes of their distribution, together with projected expansions into higher latitudes, particularly in the Northern Hemisphere. This study aims to entice further research on the future biogeographical impacts of climate change in toxin-producing microalgae species while, at the same time, helping to advise the correct environmental management of coastal habitats and ecosystems. Toxin-producing microalgae present a significant environmental risk for ecosystems and human societies when they reach concentrations that affect other aquatic organisms or human health. Harmful algal blooms (HAB) have been linked to mass wildlife die-offs and human food poisoning episodes, and climate change has the potential to alter the frequency, magnitude, and geographical extent of such events. Thus, a framework of species distribution models (SDMs), employing MaxEnt modeling, was used to project changes in habitat suitability and distribution of three key paralytic shellfish toxin (PST)-producing dinoflagellate species (i.e., Alexandrium catenella, A. minutum, and Gymnodinium catenatum), up to 2050 and 2100, across four representative concentration pathway scenarios (RCP-2.6, 4.5, 6.0, and 8.5; CMIP5). Despite slightly different responses at the regional level, the global habitat suitability has decreased for all the species, leading to an overall contraction in their tropical and sub-tropical ranges, while considerable expansions are projected in higher latitudes, particularly in the Northern Hemisphere, suggesting poleward distributional shifts. Such trends were exacerbated with increasing RCP severity. Yet, further research is required, with a greater assemblage of environmental predictors and improved occurrence datasets, to gain a more holistic understanding of the potential impacts of climate change on PST-producing species. [ABSTRACT FROM AUTHOR]

The uncontrolled growth of harmful algal blooms (HABs) can negatively impact the environment and pose threats to human health and aquatic ecosystems. Titanium dioxide (TiO2) is known to be effective in killing harmful algae through flocculation and sedimentation. However, TiO2 in a dispersed form can harm other non-target marine organisms, which has raised concerns by environmentalists and scientists. This research seeks to explore the utility of immobilized titanium oxide as a photocatalyst for mitigation of HABs, where the Alexandrium minutum bloom was used as a model system herein. Chitosan was modified with 0.2 wt.% TiO2 (Chi/TiO2 (x mL; x = 1, 3 and 5 mL) and the corresponding films were prepared via solvent casting method. Scanning electron microscope (SEM) images of the films reveal a highly uneven surface. X-ray diffraction (XRD) analysis indicates the reduction in chitosan crystallinity, where the presence of TiO2 was negligible, in accordance with its dispersion within the chitosan matrix. The photocatalytic mitigation of A.minutum was carried out via a physical approach in a laboratory-scale setting. The negative surface charge of the films was observed to repel the negatively charged A.minutum causing fluctuation in the removal efficiency (RE). The highest RE (76.1 ± 13.8%) was obtained when Chi/TiO2 (1 mL) was used at 72 h, where the hydroxyl radicals generated were inferred to contribute to the deactivation of the algae cells by causing oxidative stress. An outcome of this study indicates that such hybrid films have the potential to replace the non-immobilized (dispersed) TiO2 for HAB mitigation. However, further investigation is required to deploy these films for field applications at a larger scale. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) in coastal British Columbia (BC), Canada, negatively impact the salmon aquaculture industry. One disease of interest to salmon aquaculture is Net Pen Liver Disease (NPLD), which induces severe liver damage and is believed to be caused by the exposure to microcystins (MCs). To address the lack of information about algal toxins in BC marine environments and the risk they pose, this study investigated the presence of MCs and other toxins at aquaculture sites. Sampling was carried out using discrete water samples and Solid Phase Adsorption Toxin Tracking (SPATT) samplers from 2017-2019. All 283 SPATT samples and all 81 water samples tested positive for MCs. Testing for okadaic acid (OA) and domoic acid (DA) occurred in 66 and 43 samples, respectively, and all samples were positive for the toxin tested. Testing for dinophysistoxin-1 (DTX-1) (20 samples), pectenotoxin-2 (PTX-2) (20 samples), and yessotoxin (YTX) (17 samples) revealed that all samples were positive for the tested toxins. This study revealed the presence of multiple co-occurring toxins in BC's coastal waters and the levels detected in this study were below the regulatory limits for health and recreational use. This study expands our limited knowledge of algal toxins in coastal BC and shows that further studies are needed to understand the risks they pose to marine fisheries and ecosystems.

Cyanobacterial harmful algal blooms (CyanoHABs) are increasing in prevalence and severity in the Great Lakes region, as well as both globally and locally. CyanoHABs have the potential to cause adverse effects on human health due to the production of cyanotoxins from cyanobacteria. Common routes of exposure include recreational exposure (swimming, skiing, and boating), ingestion, and aerosolization of contaminated water sources. Cyanotoxins have been shown to adversely affect several major organ systems contributing to hepatotoxicity, gastrointestinal distress, and pulmonary inflammation. We present three pediatric case reports that coincided with CyanoHABs exposure with a focus on presentation of illness, diagnostic work-up, and treatment of CyanoHAB-related illnesses. Potential cyanotoxin exposure occurred while swimming in the Maumee River and Maumee Bay of Lake Erie in Ohio during the summer months with confirmed CyanoHAB activity. Primary symptoms included generalized macular rash, fever, vomiting, diarrhea, and severe respiratory distress. Significant labs included leukocytosis and elevated C-reactive protein. All patients ultimately recovered with supportive care. Symptoms following potential cyanotoxin exposure coincide with multiple disease states representing an urgent need to develop specific diagnostic tests of exposure. [ABSTRACT FROM AUTHOR]

The presence of yessotoxins (YTXs) was analyzed in 10,757 samples of Galician bivalves from 2014 to 2022. Only YTX and 45-OH YTX were found. YTX was detected in 31% of the samples, while 45-OH YTX was found in 11.6% of them. Among the samples containing YTX, 45-OH YTX was detected in 37.3% of cases. The maximum recorded levels were 1.4 and 0.16 mg of YTX-equivalentsg−1, for YTX and 45-OH YTX, respectively, which are well below the regulatory limit of the European Union. The YTX and 45-OH YTX toxicities in the raw extracts and extracts subjected to alkaline hydrolysis were strongly and linearly related. Due to the lack of homo-YTX in Galician samples, the effect of alkaline hydrolysis on homo-YTX and 45OH-Homo-YTX was only checked in 23 additional samples, observing no negative effect but a high correlation between raw and hydrolyzed extracts. Hydrolyzed samples can be used instead of raw ones to carry out YTXs determinations in monitoring systems, which may increase the efficiency of those systems where okadaic acid episodes are very frequent and therefore a higher number of hydrolyzed samples are routinely analyzed. The presence of YTX in the studied bivalves varied with the species, with mussels and cockles having the highest percentages of YTX-detected samples. The presence of 45-OH YTX was clearly related to YTX and was detected only in mussels and cockles. Wild populations of mussels contained proportionally more 45-OH YTX than those that were raft-cultured. Spatially, toxin toxicities varied across the sampling area, with higher levels in raft-cultured mussels except those of Ría de Arousa. Ría de Ares (ARE) was the most affected geographical area, although in other northern locations, lower toxin levels were detected. Seasonally, YTX and 45-OH YTX toxicities showed similar patterns, with higher levels in late summer and autumn but lower toxicities of the 45-OH toxin in August. The relationship between the two toxins also varied seasonally, in general with a minimum proportion of 45-OH YTX in July–August but with different maximum levels for raft-cultured and wild mussel populations. Interannually, the average toxicities of YTX decreased from 2014 to 2017 and newly increased from 2018 to 2021, but decreased slightly in 2022. The relationship between 45-OH YTX and YTX also varied over the years, but neither a clear trend nor a similar trend for wild and raft mussels was observed. [ABSTRACT FROM AUTHOR]

Algal toxins pose a serious threat to human and coastal ecosystem health, even if their potential impacts are poorly documented in New Caledonia (NC). In this survey, bivalves and seawater (concentrated through passive samplers) from bays surrounding Noumea, NC, collected during the warm and cold seasons were analyzed for algal toxins using a multi-toxin screening approach. Several groups of marine microalgal toxins were detected for the first time in NC. Okadaic acid (OA), azaspiracid-2 (AZA2), pectenotoxin-2 (PTX2), pinnatoxin-G (PnTX-G), and homo-yessotoxin (homo-YTX) were detected in seawater at higher levels during the summer. A more diversified toxin profile was found in shellfish with brevetoxin-3 (BTX3), gymnodimine-A (GYM-A), and 13-desmethyl spirolide-C (SPX1), being confirmed in addition to the five toxin groups also found in seawater. Diarrhetic and neurotoxic toxins did not exceed regulatory limits, but PnTX-G was present at up to the limit of the threshold recommended by the French Food Safety Authority (ANSES, 23 μg kg−1). In the present study, internationally regulated toxins of the AZA-, BTX-, and OA-groups by the Codex Alimentarius were detected in addition to five emerging toxin groups, indicating that algal toxins pose a potential risk for the consumers in NC or shellfish export. [ABSTRACT FROM AUTHOR]

The first ciguatera fish poisoning (CFP) in Portugal dates from 2008 when 11 people reported CFP symptoms after consuming a 30 kg amberjack caught around the Selvagens Islands (Madeira Archipelago). Since then, 49 human poisonings have been reported. The emergence of a new threat challenged scientists and regulators, as methods for toxic microalgae analyses and ciguatoxin (CTX) detection were not implemented. To minimise the risk of ciguatera, the Madeira Archipelago authorities interdicted fisheries in Selvagens Islands and banned the capture of amberjacks weighing more than 10 kg in the entire region of Madeira Archipelago. The accurate identification and quantification of the benthic toxin-producing algae species spreading to new areas require efforts in terms of both microscopy and molecular techniques. Two ciguatera-causing dinoflagellates, Gambierdiscus excentricus and Gambierdiscus australes, were identified in the Madeira Island and Selvagens sub-archipelago, respectively. Regarding the CTX analysis (N2a cell-based assay and LC-MS) in fish, the results indicate that the Selvagens Islands are a ciguatera risk area and that fish vectoring CTX are not limited to top predator species. Nevertheless, advances and improvements in screening methods for the fast detection of toxicity in seafood along with certified reference material and sensitive and selective targeted analytical methods for the determination of CTX content are still pending. This study aims to revise the occurrence of ciguatera cases in the Madeira Archipelago since its first detection in 2008, to discuss the risk management strategy that was implemented, and to provide a summary of the available data on the bioaccumulation of CTX in marine fish throughout the marine food web, taking into consideration their ecological significance, ecosystem dynamics, and fisheries relevance. [ABSTRACT FROM AUTHOR]

Karenia mikimotoi is a common species of red tide dinoflagellate that causes the mass mortality of marine fauna in coastal waters of Republic of Korea. Despite continuous studies on the ecophysiology and toxicity of K. mikimotoi, the underlying molecular mechanisms remain poorly understood. Red sea bream, Pagrus major, is a high-value aquaculture fish species, and the coastal aquaculture industry of red sea bream has been increasingly affected by red tides. To investigate the potential oxidative effects of K. mikimotoi on P. major and the molecular mechanisms involved, we exposed the fish to varying concentrations of K. mikimotoi and evaluated its toxicity. Our results showed that exposure to K. mikimotoi led to an accumulation of reactive oxygen species (ROS) and oxidative DNA damage in the gill tissue of P. major. Furthermore, we found that K. mikimotoi induced the activation of antioxidant enzymes, such as superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase, in the gill tissue of P. major, with a significant increase in activity at concentrations above 5000 cells/mL. However, the activity of glutathione S-transferase did not significantly increase at the equivalent concentration. Our study confirms that oxidative stress and DNA damage is induced by acute exposure to K. mikimotoi, as it produces ROS and hypoxic conditions in P. major. In addition, it was confirmed that gill and blood samples can be used as biomarkers to detect the degree of oxidative stress in fish. These findings have important implications for the aquaculture of red sea bream, particularly in the face of red tide disasters. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) have wide-ranging environmental impacts, including on aquatic species of social and commercial importance. In New Zealand (NZ), strategic growth of the aquaculture industry could be adversely affected by the occurrence of HABs. This review examines HAB species which are known to bloom both globally and in NZ and their effects on commercially important shellfish and fish species. Blooms of Karenia spp. have frequently been associated with mortalities of both fish and shellfish in NZ and the sub-lethal effects of other genera, notably Alexandrium spp., on shellfish (which includes paralysis, a lack of byssus production, and reduced growth) are also of concern. Climate change and anthropogenic impacts may alter HAB population structure and dynamics, as well as the physiological responses of fish and shellfish, potentially further compromising aquatic species. Those HAB species which have been detected in NZ and have the potential to bloom and harm marine life in the future are also discussed. The use of environmental DNA (eDNA) and relevant bioassays are practical tools which enable early detection of novel, problem HAB species and rapid toxin/HAB screening, and new data from HAB monitoring of aquaculture production sites using eDNA are presented. As aquaculture grows to supply a sizable proportion of the world's protein, the effects of HABs in reducing productivity is of increasing significance. Research into the multiple stressor effects of climate change and HABs on cultured species and using local, recent, HAB strains is needed to accurately assess effects and inform stock management strategies. [ABSTRACT FROM AUTHOR]

Evidence for shellfish toxin illness in British Columbia (BC) on the west coast of Canada can be traced back to 1793. For over two hundred years, domestically acquired bivalve shellfish toxin illnesses in BC were solely ascribed to paralytic shellfish poisonings caused by algal blooms of Alexandrium. This changed in 2011, when BC experienced its first outbreak of diarrhetic shellfish poisoning (DSP). As a result of this outbreak, Canada's first DSP symposium was held in November, 2012, in North Vancouver, BC. Three of the objectives of the symposium were to provide a forum to educate key stakeholders on this emerging issue, to identify research and surveillance priorities and to create a DSP network. The purpose of this paper is to review what is known about shellfish poisoning in BC and to describe a novel volunteer network that arose following the symposium. The newly formed network was designed for industry shellfish growers to identify harmful algae bloom events, so that they may take actions to mitigate the effects of harmful blooms on shellfish morbidity. The network will also inform public health and regulatory stakeholders of potentially emerging issues in shellfish growing areas. [ABSTRACT FROM AUTHOR]

Despite the fact that the first red tide reported on the coasts of the Iberian Peninsula was due to Lingulodinium polyedra , knowledge about their frequency and, particularly, about the environmental conditions contributing to bloom initiation is still scarce. For this reason, L. polyedra bloom episodes were observed and studied in three Galician rias during the summer season based on the 1993-2008 record database period; additionally, samples were collected in summer 2008. Proliferations of L. polyedra occurred in the rias of Ares and Barqueiro in June and August, respectively, while in the Ria of Coruña, they persisted from the end of June to early September. Red tides developed when the surface temperature reached 17 °C, with "seasonal thermal window" conditions, and when salinities were ≥30, i.e., an "optimal salinity window"; when these parameters were lower than these thresholds, cyst germination decreased. A cyst transport mechanism from sediments to the surface must also exist; this mechanism was found to be natural (tidal currents) in the ria of Barqueiro or anthropogenic (dredging) in the rias of Ares and Coruña. Surface temperatures during summer were usually favorable for cyst germination (85 to 100%) during the 1993-2008 period; however, water temperatures below 10 m depth only rarely reached the 17 °C threshold (2 to 18%). During this 16-year period, dredging activities could explain 71% (Coruña) and 44% (Ares) of the recorded bloom events. When a bloom episode developed in early summer, favorable conditions did not lead to a new red tide, probably due to the lag period required by cysts for germination. Moreover, blooms did not develop when high densities of diatoms (>1,000,000 cells·L -1 ) remained in the water column as a result of summer upwelling pulses occurring in specific years. The temperature-sediment disturbance pattern found in this study provides a useful tool for the prevention of eventual risks resulting from red tides of this dinoflagellate., Competing Interests: The authors declare no conflicts of interest.

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

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

Cyanobacterial harmful algal blooms (cyanoHABs) occur in fresh water globally. These can degrade water quality and produce toxins, resulting in ecological and economic damages. Thus, short-term management methods (i.e., algaecides) are necessary to rapidly mitigate the negative impacts of cyanoHABs. In this study, we assess the efficacy of a hydrogen peroxide-based algaecide (PAK ® 27) on a Microcystis dominated bloom which occurred within the Pahokee Marina on Lake Okeechobee, Florida, USA. We observed a significant reduction in chlorophyll a (96.81%), phycocyanin (93.17%), and Microcystis cell counts (99.92%), and a substantial reduction in microcystins (86.7%) 48 h after treatment (HAT). Additionally, there was a significant shift in bacterial community structure 48 HAT, which coincided with an increase in the relative abundance of photosynthetic protists. These results indicate that hydrogen peroxide-based algaecides are an effective treatment method for cyanoHAB control and highlight their effects on non-target microorganisms (i.e., bacteria and protists).

In Western Europe, the incidence of DST is likely the highest globally, posing a significant threat with prolonged bans on shellfish harvesting, mainly caused by species of the dinoflagellate genus Dinophysis . Using a time series from 2014 to 2020, our study aimed (i) to determine the concentration of D. acuminata in water at which shellfish toxin levels could surpass the regulatory limit (160 µg OA equiv kg -1 ) and (ii) to assess the predictability of toxic events for timely mitigation actions, especially concerning potential harvesting bans. The analysis considered factors such as (i) overdispersion in the data, (ii) distinct periods of presence and absence, (iii) the persistence of cells, and (iv) the temporal lag between cells in the water and toxins in shellfish. Four generalized additive models were tested, with the Tweedie (TW-GAM) model showing superior performance (>85%) and lower complexity. The results suggest existing thresholds currently employed (200 and 500 cells L -1 ) are well-suited for the Portuguese coast, supported by empirical evidence (54-79% accuracy). The developed algorithm allows for thresholds to be tailored on a case-by-case basis, offering flexibility for regional variations.