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The presence of nutrients such as nitrate and phosphate can have a positive impact on phytoplankton growth. However, if the nutrient concentration is very high in the waters, it can cause an explosion in the phytoplankton population or Harmful Algae Blooms (HABs) in the waters. Phytoplankton explosions in waters have a negative impact on the surrounding ecosystem, marine biota, and humans. This research aimed to analyze the spatial distribution and structure of phytoplankton communities that can potentially cause HABs in the waters of Laikang Bay, South Sulawesi. This research was conducted in June 2021. The research found 20 species of phytoplankton HABs from 2 classes, namely Bacillariophyceae (8 types) and Dinophyceae (12 species). The Bacillariophyceae class has a higher percentage, 93%, and Dinophyceae at 7%. The abundance status of phytoplankton HABs is classified as not blooming, with the highest abundance found at Station 4 (control), namely 210 ± 80 cells/L. The HABs phytoplankton diversity index (H') is moderate with a value of 1.576 – 2.332, the uniformity index (E) of Station 1 (west) and Station 4 (control) is moderate with a value of 0.568 and 0.582 while Station 2 (north) and Station 3 (south) is classified as high, namely 0.807 and 0.823, the dominance index (D) is classified as low with a value of 0.135 – 0.357. Spatially, phytoplankton HABs based on the station can be divided into five groups. The results of the PCA analysis show that substations 1.A, 1.B, 1.C, 2.A, 2.B, and 2. C are characterized by high temperature and salinity parameters. Substations 3.A, 3.B, and 3.C are characterized by high nitrate and phosphate parameters. Meanwhile, substations 4.A, 4.B, and 4.C are characterized by high parameters of brightness, current speed, and pH and are associated with a high abundance of phytoplankton HABs.

We have developed probabilistic models to estimate the likelihood of harmful algae presence and outbreaks along the Norwegian coast, which can help optimization of the national monitoring program and the planning of mitigation actions. We employ support vector machines to calibrate probabilistic models for estimating the presence and harmful abundance (HA) of eight toxic algae found along the Norwegian coast, including Alexandrium spp., Alexandrium tamarense, Dinophysis acuta, Dinophysis acuminata, Dinophysis norvegica, Pseudo-nitzschia spp., Protoceratium reticulatum, and Azadinium spinosum. The inputs are sea surface temperature, photosynthetically active radiation, mixed layer depth, and sea surface salinity. The probabilistic models are trained with data from 2006 to 2013 and tested with data from 2014 to 2019. The presence models demonstrate good statistical performance across all taxa, with R (observed presence frequency vs. predicted probability) ranging from 0.69 to 0.98 and root mean squared error ranging from 0.84% to 7.84%. Predicting the probability of HA is more challenging, and the HA models only reach skill with four taxa (Alexandrium spp., A. tamarense, D. acuta, and A. spinosum). There are large differences in seasonal and geographical variability and sensitivity to the model input of different taxa, which are presented and discussed. The models estimate geographical regions and periods with relatively higher risk of toxic species presence and HA, and might optimize the harmful algae monitoring. The method can be extended to other regions as it relies only on remote sensing and model data as input and running national programs of toxic algae monitoring.

Environmental mitigation measures are being undertaken as a proactive approach to prevent the adverse consequences associated with Harmful Algal Blooms (HABs). Presently, there is a lack of comprehensive information regarding the occurrence of HABs in the waters surrounding Bintan Island, and routine monitoring to assess the potential for eutrophication is absent. This research should begin by gathering information about potential sources that contribute to the emergence of HABs, the specific types of algae with the capacity to trigger HABs The primary objective of this study is to identify the harmful algae species present in the coastal waters of Bintan Island. The research was conducted in August 2023, with the sampling process taking place at four specific locations within the coastal waters of Bintan Island. These sampling stations were selected deliberately to capture the varying activities predominant in each respective area. The microalgae found consisted of four groups, namely Bacillariophyta, Cyanophyta, Dinophyta, and Chlorophyta. Bacillariophyta is a group of microalgae with the highest abundance proportion at all observation stations. Harmfull Algae found in the coastal waters of Bintan Island generally come from the Dinophyta group of the types Ceratium sp., Peridinium sp., Prorocentrum sp., and Dinophysis sp. Harmful microalgae from the Dinophyta group were found at all research stations, with the highest proportion of abundance at Station 2 (6%) and the lowest at Station 3 (1%). The difference in these findings is thought to be due to the dynamics of the hydrosanographic parameters of the waters, especially nutrient concentrations. Keywords: Bintan Ceratium Dinophyta Harmful Microalgae

Harmful algal blooms (HABs) can negatively affect coastal water quality, aquatic fauna, and human health from the consumption of toxin-contaminated seafood. Estuaries are especially prone to the incidence of these noxious events and sensitive to the associated damage. This study represents a comprehensive overview of previous investigations reporting the occurrence of harmful algae and/or phycotoxins in the Paranaguá Estuarine Complex (CEP), in Southern Brazil. Secondary data from 2002 to 2021 were combined with new results obtained from widely spaced sampling campaigns performed from 2018 to 2019 to assess the periods and estuarine sectors at greater risk for the incidence of HABs. In total, about 600 water/sediment samples containing harmful microalgae and 675 tissue samples of phycotoxin-contaminated fauna were analyzed. The most frequent and abundant species of potentially toxic microalgae were dinoflagellates belonging to the species complexes Dinophysis acuminata and Prorocentrum lima, producers of diarrhetic shellfish toxins (DSTs), and diatoms of the genus Pseudo-nitzschia, producers of amnesic shellfish toxins (ASTs). Okadaic acid, a DST, was by far the most common toxin in the fauna, reaching higher levels in primary consumers such as bivalve mollusks (mussels, oysters, and clams), zooplankton, and suspension-feeding crustaceans (ghost shrimps), and moderate to low levels in cephalopods, fishes, gastropods, echinoderms, sea turtles, seabirds, and cetaceans. Less rainy periods (winter-early spring) were associated with the highest incidence of DSTs and blooms of their producing algae P. lima and Dinophysis spp., mainly in the middle region of Paranaguá Bay and on the shallow continental platform adjacent to the estuarine mouth. However, certain HAB-forming species may be more successful in inner estuarine areas (Prorocentrum cordatum) and during different periods, such as late summer--early fall (Pseudo-nitzschia spp.). Continuous monitoring of harmful algae and toxins is therefore highly recommended to mitigate the effects of HABs in the entire estuary. [ABSTRACT FROM AUTHOR]

The evaluation of water quality is commonly conducted by measuring physicochemical parameters. However, to enable identification of water quality changes of aquatic ecosystems, such as lakes, requires long time series data sampling. In this study, we performed water quality assessments by utilising the presence of potential harmful algae presence in Lake Ranu Grati, Indonesia. We conducted water sampling to evaluate 13 water quality parameters (in-situ and ex-situ) and identified the phytoplankton community structure of the lake at seven sampling sites from December 2018 to February 2019. To assess the water quality of the lake, we used two approaches. First, calculated the classical water quality index using the STORET method. Second, identified the potential harmful algae from the phytoplankton community structure of Lake Ranu Grati, and then determined the water quality factors related to its occurrence using canonical correspondence analysis. The results showed that water quality condition of Lake Ranu Grati was optimum except for COD, BOD and ammonia. The STORET index also classified the seven sites in Lake Ranu Grati as lightly polluted and moderately polluted. Considering the presence of potentially harmful algae from the Cyanophyta and Euglenophyta divisions, it was suggested that Sites 6 and 7 were the most polluted areas of Lake Ranu Grati, which corresponded to the high concentration of COD and BOD. This finding indicates that agricultural and aquaculture activities around the lake need to be controlled to maintain the sustainability of the water quality condition of Lake Ranu Grati.

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

Harmful algal blooms caused by toxin‐producing species of the diatom genus Pseudo‐nitzschia have been linked to anomalously warm ocean conditions in the Northern California Current System. This study compares summertime concentrations of Pseudo‐nitzschia spp. and the toxin they produce, domoic acid, during a marine heatwave year (2019) and a climatologically neutral year (2021). An Imaging FlowCytobot was installed on a fishery survey vessel alongside environmental sensors to continuously sample phytoplankton and oceanographic parameters. This was paired with targeted manual sample collections for nutrients, chlorophyll, and domoic acid. Accumulations of Pseudo‐nitzschia spp. were associated with upwelling zones and established hotspot regions: the Juan de Fuca Eddy, Heceta Bank, and Trinidad Head. Overall, however, Pseudo‐nitzschia spp. and domoic acid concentrations were low during both summers and appear to have been limited by nitrate. Nutrient availability may therefore modulate the response of Pseudo‐nitzschia spp. to warm anomalies. Comparison of these results with 2015, another marine heatwave year but one that produced record concentrations of Pseudo‐nitzschia spp. and domoic acid, suggests that the timing of marine heatwave conditions in the nearshore relative to seasonal upwelling plays a key role in determining whether a Pseudo‐nitzschia spp. harmful algal bloom will occur. [ABSTRACT FROM AUTHOR]

The toxin‐producing dinoflagellate Alexandrium pseudogonyaulax has become increasingly abundant in northern European waters, replacing other Alexandrium species. A. pseudogonyaulax produces goniodomins and lytic substances, which can be cytotoxic toward other organisms, including fish, but we still know little about the environmental conditions influencing its growth and toxicity. Here, we investigated the impacts of different nitrogen sources and light intensities, common bottom‐up drivers of bloom formation, on the growth and toxin content of three A. pseudogonyaulax strains isolated from the Danish Limfjord. While the growth rates were significantly influenced by nitrogen source and light intensity, the intracellular toxin contents only showed strong differences between the exponential and stationary growth phases. Moreover, the photophysiological response of A. pseudogonyaulax showed little variation across varying light intensities, while light‐harvesting pigments were significantly more abundant under low light conditions. This study additionally highlights considerable physiological variability between strains, emphasizing the importance of conducting laboratory experiments with several algal strains. A high physiological plasticity toward changing abiotic parameters points to a long‐term establishment of A. pseudogonyaulax in northern European waters. [ABSTRACT FROM AUTHOR]

Algae are the naturally produced food for fish in any aquatic ecosystem and an indicator of a productive pond. However, excess abundance of harmful algae can have detrimental effects on fish health. In this study, the algal communities of 30 coastal homestead fish ponds were investigated to identify the diversity, assemblage and controlling environmental variables of harmful algae from a tropical coastal area. The findings showed that 81 of the 89 genera of identified algae were harmful, with the majority of them being in the classes of Cyanophyceae (50.81%), Chlorophyceae (23.75%), Bacillariophyceae (9.5%), and Euglenophyceae (8.47%). Microcystis spp. alone contributed 28.24% to the total abundance of harmful algae. Significant differences (p < 0.05) in algal abundance were found among the ponds with the highest abundance (470 ± 141.74 × 103 cells L−1) at pond (S25) near agricultural fields and the lowest abundance (109.33 ± 46.91 × 103 cells L−1) at pond (S14) which was lacking sufficient sunlight and nutrients. Diversity indices, e.g., dominance (D), evenness (J′), richness (d) and Shannon diversity index (H′) ranged from 0.17 to 0.44, 0.23 to 0.6, 0.35 to 2.23 and 0.7 to 1.79, respectively, indicating a moderate range of diversity and community stability. Community composition analysis showed the assemblage was dominated by Cyanophyceae, Chlorophyceae and Bacillariophyceae, whereas, multivariate cluster analyses (CA) identified 11 major clusters. To identify the factors controlling their distribution or community assemblages, eight environmental variables (temperature, pH, dissolved oxygen (DO), salinity, transparency, nitrates, phosphates and sulphate) were measured. ANOVA analysis showed that the variables significantly differed (p < 0.05) among the ponds, and canonical correspondence analysis (CCA) demonstrated that DO, nitrates, phosphates, sulphates, salinity and transparency have the most impact on the abundance of algal genera. In addition, analyses with Pearson’s correlation coefficient showed that the abundance of total algae, diversity and community were mainly governed by phosphates and sulphates. These results can be used to identify and control these toxic algal groups in the local aquaculture sector.

The Arctic Ocean is currently undergoing significant transformations due to climate change, leading to profound changes in its microbial planktonic communities. These communities consist of a wide range of organisms, including photoautotrophic prokaryotes and eukaryotes, as well as heterotrophic, phagotrophic, and mixotrophic protistan species. Here, for simplicity, we refer to these single-celled species as phytoplankton. Within this diversity, potentially toxic and/or harmful algal species (hereafter abbreviated as "HA") are of particular concern. These organisms have the potential to spread into Arctic waters, posing threats to both human and ecosystem health. Despite their importance, the spatial and temporal distribution of phytoplankton communities, including HA species, in the North American Arctic, remains poorly understood. To address this gap, we compiled and synthesized the largest possible body of data from different databases, individual published and unpublished datasets, and partitioned it into nine regions based on the Large Marine Ecosystem classification. Our dataset contains 385 800 individual georeferenced data points and 18 268 unique sampling events, revealing greater diversity than previously thought, with 1445 unique taxa. Heterokontophyta (which notably included diatoms) and Dinoflagellata were the most dominant phyla. Our results indicate distinct spatial patterns of diversity, with the highest diversity observed in Atlantic-influenced regions of the North American Arctic. For most of the HA species recorded in our database, no evidence was found for an increase in the northernmost latitude where HA species are observed over the years, meaning that there is no substantial spread of HA species into the North American part of the Arctic. Our study challenges the traditional view of the Arctic as being unsuitable for toxin-producing and harmful algae and highlights the importance of extensive and long-term sampling efforts to understand the region's biodiversity. Overall, our findings provide new insights into the spatial patterns and biodiversity of phytoplankton and other protists in the North American Arctic and have implications for understanding the ecological functioning and response of this region to ongoing climate change. [ABSTRACT FROM AUTHOR]

In British Columbia (BC), harmful algal blooms (HABs) regularly cause severe economic losses through finfish mortalities and shellfish harvest closures due to toxin accumulation, gill damage, or hypoxia. As there is no routine governmental monitoring of HAB phenomena in BC, HAB variability, and its potential links to environmental drivers are not well understood. Here we present results from a well-managed citizen science program which collected an unprecedented 4 year, high-resolution (∼bi-monthly, ∼80 stations) dataset of harmful algae (HA) concentrations and corresponding physical and chemical properties of seawater throughout the Strait of Georgia (SoG), BC. Analysis of this dataset revealed statistically significant interannual and seasonal relationships between environmental drivers and the most common HA taxa: Rhizosolenia setigera, Dictyocha spp., Alexandrium spp., Heterosigma akashiwo, Chaetoceros convolutus, and C. concavicornis. HABs exhibited significant interannual variations; specifically, no HABs were found during the summer of 2015, blooms of Dictyocha occurred in 2016 and 2017, and dense blooms of Heterosigma and Noctiluca occurred in 2018. In addition, HA prevalence corresponded with negative effects observed in local aquaculture facilities where higher toxins concentrations (causing Paralytic and Diarrhetic Shellfish Poisonings) in shellfish flesh were detected during years with greater abundance of Alexandrium and Dinophysis. Furthermore, salmon mass mortality at fish farms corresponded to years with high concentrations of Heterosigma and Dictyocha. As such, these results highlight the need for long-term data to evaluate the potential role of HA as a stressor on the SoG ecosystem.