Search Results (28)

Harmful algal blooms can negatively impact freshwater, estuarine, and coastal marine systems globally and pose serious risks to water quality, human and ecosystem health, and food production. Algae can produce toxic compounds, directly interfere with aquaculture species through (e.g.,) the production of foam or mucilage, as well as causing diseases and disorders in fish, and can result in hypoxic conditions when the bloom senesces. Application of US Environmental Protection Agency (USEPA) registered algaecides can be effective, scalable, and inexpensive, but there is growing interest in plant- or bacterial-derived compounds that do not require the use of chemicals such as hydrogen peroxide or copper. The algaecide C7X1 is a plant-based organic algaecide that proves effective against a wide variety of algae, including harmful algal species such as Microcystis, Heterosigma, and Pseudo-nitzschia. Performance is comparable to other USEPA-registered algaecides, with low to moderate extracellular toxin release and a potential lifetime of weeks in treated waters. The mode of action is inhibition of photosynthesis, suggesting that direct off-target impacts on zooplankton and other organisms would be minimal. Full article

Climate change and anthropogenic alterations in biogeochemical cycles are intensifying the frequency, duration, and potential toxicity of harmful algal blooms (HABs) in marine ecosystems. However, these effects are highly variable and depend on species identity, strain-specific traits, and local environmental conditions. Key drivers include rising sea surface temperatures, changes in salinity resulting from altered precipitation patterns and runoff, and elevated CO₂ levels leading to ocean acidification. Heterosigma akashiwo, a euryhaline raphidophyte responsible for the widespread killing of fish, is particularly responsive to these changes. This study investigated the combined effects of temperature, salinity, and CO₂ concentration on the growth, yield, and cell membrane permeability of H. akashiwo using a Design of Experiment (DOE) approach. DOE facilitates a detailed and systematic analysis of multifactorial interactions, enabling a deeper understanding of complex relationships while maximizing efficiency and minimizing the use of experimental resources. The results revealed that growth and yield were maximized at higher temperatures and salinities, whereas cell permeability increased under cooler, less saline, and lower CO₂ conditions. These findings suggest that projected future ocean conditions may enhance biomass production while potentially reducing cellular permeability and, by extension, toxicity. This study highlights the value of the DOE framework in identifying key interactions among environmental drivers of HABs, offering a practical foundation for future predictive modeling under climate change scenarios. Full article

In this work, the toxicity level of nano- and microparticles obtained by underwater welding was assessed. The toxicity of nano- and microparticles obtained by underwater welding was evaluated on three types of marine microalgae: Heterosigma akashiwo (Ochrophyta), Porphyridium purpureum (Rhodophyta), and Attheya ussuriensis (Bacillariophyta). The aim was to study the environmental risks associated with the ingress of micro- and nanoparticles of metal oxides into the marine environment. Water samples containing suspensions from wet welding and cutting processes were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to determine heavy metal concentrations. Biotesting included evaluation of growth inhibition, cell size change, and membrane potential of microalgae using flow cytometry. The results showed that samples APL-1 and APL-2 (flux-cored wire) were the most toxic, causing concentration-dependent growth inhibition of H. akashiwo and A. ussuriensis (p < 0.0001) as well as membrane depolarization. For P. purpureum, ELc and ELw (coated electrodes) samples stimulated growth, indicating species-specific responses. The stability of the nanoparticles and their bioavailability were found to play a key role in the mechanisms of toxicity. The study highlights the need to control the composition of materials for underwater welding and to develop environmentally friendly technologies. The data obtained are important for predicting the long-term effects of pollution of marine ecosystems by substances formed during underwater welding. Full article

This study investigated the impact of culture medium salinity (5–50 PSU) on the growth and maximum photochemical yield of photosystem II (Fv/Fm) and the composition of carotenoids, fatty acids, and bioactive substances in three marine microalgae (Chrysochromulina rotalis, Amphidinium carterae, and Heterosigma akashiwo). The microalgae were photoautotrophically cultured in discontinuous mode in a single stage (S1) and a two-stage culture with salt shock (S2). A growth model was developed to link biomass productivity with salinity for each species. C. rotalis achieved a maximum biomass productivity (Pmax) of 15.85 ± 0.32 mg·L⁻¹·day⁻¹ in S1 and 16.12 ± 0.13 mg·L⁻¹·day⁻¹ in S2. The salt shock in S2 notably enhanced carotenoid production, particularly in C. rotalis and H. akashiwo, where fucoxanthin was the main carotenoid, while peridinin dominated in A. carterae. H. akashiwo also exhibited increased fatty acid productivity in S2. Salinity changes affected the proportions of saturated, monounsaturated, and polyunsaturated fatty acids in all three species. Additionally, hyposaline conditions boosted the production of haemolytic substances in A. carterae and C. rotalis. Full article

The dinoflagellate Noctiluca scintillans is a globally distributed bloom-forming species. Previous studies have shown that the primary reason for the frequent occurrence of N. scintillans blooms may be the proliferation of microalgae due to eutrophication, which provides a sufficient source of food. Meanwhile, N. scintillans may release nutrients into the environment, thus affecting the population dynamics of microalgae. Thus, to investigate the interaction between N. scintillans and co-occurring microalgae, this study examined the population dynamics of N. scintillans and their interaction with three representative microalgae species in response to varying nutrient levels. The findings indicate that the growth of N. scintillans is slow when co-cultured with diatom Skeletonema costatum. Moreover, a high density and rapid growth rate of S. costatum may have an inhibitory effect on the growth of N. scintillans. Conversely, the population abundance of N. scintillans increased with the rise in the population density and nutritional level of Heterocapsa steinii (dinoflagellate) and Heterosigma akashiwo (raphidophyceae). Notably, N. scintillans can discharge specific nutrients into the aquatic environment, which can subsequently be assimilated and exploited by H. steinii. Thus, the interaction between the species and population dynamics of plankton, as well as changes in nutrient levels within the ecosystem, played a significant role in influencing the growth and population dynamics of N. scintillans. The mutualistic association between N. scintillans and microalgae may establish a transient closed loop, thereby fostering the sustained proliferation and subsequent expansion of N. scintillans. Full article

A massive bloom of the raphidophyte Heterosigma akashiwo occurred in summer 2022 in San Francisco Bay, causing widespread ecological impacts including events of low dissolved oxygen and mass fish kills. The rapidly evolving bloom required equally rapid management response, leading to the use of near-real-time image analysis of chlorophyll from the Ocean and Land Colour Instrument (OLCI) aboard Sentinel-3. Standard algorithms failed to adequately capture the bloom, signifying a need to refine a two-band algorithm developed for coastal and inland waters that relates the red-edge part of the remote sensing reflectance spectrum to chlorophyll. While the bloom was the initial motivation for optimizing this algorithm, an extensive dataset of in-water validation measurements from both bloom and non-bloom periods was used to evaluate performance over a range of concentrations and community composition. The modified red-edge algorithm with a simplified atmospheric correction scheme outperformed existing standard products across diverse conditions, and given the modest computational requirements, was found suitable for operational use and near-real-time product generation. The final version of the algorithm successfully minimizes error for non-bloom periods when chlorophyll a is typically <30 mg m⁻³, while also capturing bloom periods of >100 mg m⁻³ chlorophyll a. Full article

Harmful algal blooms (HABs) caused by Heterosigma akashiwo are occurring in coastal waters frequently, posing a great risk to marine environments and subsequent treatment processes like desalination. UV-assisted permanganate oxidation (UV/KMnO₄) is recognized as an innovative advanced oxidation process. This study investigated the inactivation and removal efficiencies of H. akashiwo cells by UV/KMnO₄. Algal cells were effectively disintegrated into fragments by UV/KMnO₄. Also, the degradation of photosynthetic pigments, membrane lipid peroxidation, and severe oxidative stress in algal cells was observed. The removal efficiency of algal cells reached 80.2% by 20 min of UV/KMnO₄ oxidation, with a KMnO₄ dosage of 5 mg L⁻¹. In addition, the residual algal cells could be completely removed by a subsequent self-settling process, without an additional coagulation procedure. The fragmentation of algal cells caused by UV/KMnO₄ may facilitate the formation of algal flocs, thereby improving the cell settleability. Furthermore, UV₂₅₄ was significantly reduced by UV/KMnO₄, which is expected to reduce the formation of disinfection byproducts and membrane fouling. This study elucidates that UV/KMnO₄ can be a promising technique for the efficient treatment of harmful marine algae. Full article

Six new lipids, trichoderols B-G (1–6), along with a known one, triharzianin B (7), were isolated from the culture of Trichoderma sp. Z43 obtained from the surface of the marine brown alga Dictyopteris divaricata. Their structures and relative configurations were identified by interpretation of 1D/2D NMR and MS data. Compounds 1–7 were assayed for inhibiting the growth of three phytopathogenic fungi (Fusarium graminearum, Gaeumannomyces graminis, and Glomerella cingulata), four marine phytoplankton species (Amphidinium carterae, Heterocapsa circularisquama, Heterosigma akashiwo, and Prorocentrum donghaiense), and one marine zooplankton (Artemia salina). Compounds 1, 4, and 7 exhibited weak antifungal activities against three phytopathogenic fungi tested with MIC ≥ 64 μg/mL. All compounds displayed moderate antimicroalgal activity with IC₅₀ ≥ 15 μg/mL and low toxicity to the brine shrimp Artemia salina. Full article

Toxic and harmful algal blooms (HABs) are a global problem affecting human health, marine ecosystems, and coastal economies, the latter through their impact on aquaculture, fisheries, and tourism. As our knowledge and the techniques to study HABs advance, so do international monitoring efforts, which have led to a large increase in the total number of reported cases. However, in addition to increased detections, environmental factors associated with global change, mainly high nutrient levels and warming temperatures, are responsible for the increased occurrence, persistence, and geographical expansion of HABs. The Chilean Patagonian fjords provide an “open-air laboratory” for the study of climate change, including its impact on the blooms of several toxic microalgal species, which, in recent years, have undergone increases in their geographical range as well as their virulence and recurrence (the species Alexandrium catenella, Pseudochattonella verruculosa, and Heterosigma akashiwo, and others of the genera Dinophysis and Pseudo-nitzschia). Here, we review the evolution of HABs in the Chilean Patagonian fjords, with a focus on the established connections between key features of HABs (expansion, recurrence, and persistence) and their interaction with current and predicted global climate-change-related factors. We conclude that large-scale climatic anomalies such as the lack of rain and heat waves, events intensified by climate change, promote the massive proliferation of these species by creating ideal conditions for their growth and persistence, as they affect water-column stratification, nutrient inputs, and reproductive rates. Full article

Heterosigma akashiwo is a unicellular microalga which can cause massive mortality in both wild and cultivated fish worldwide, resulting in substantial economic losses. Environmental parameters such as salinity, light, and temperature showed a significant effect on bloom initiation and the toxicity of H. akashiwo. While in previous studies a one-factor-at-a-time (OFAT) approach was utilized, which only changes one variable at a time while keeping others constant, in the current study a more precise and effective design of experiment (DOE) approach, was used to investigate the simultaneous effect of three factors and their interactions. The study employed a central composite design (CCD) to investigate the effect of salinity, light intensity, and temperature on the toxicity, lipid, and protein production of H. akashiwo. A yeast cell assay was developed to assess toxicity, which offers rapid and convenient cytotoxicity measurements using a lower volume of samples compared to conventional methods using the whole organism. The obtained results showed that the optimum condition for toxicity of H. akashiwo was 25 °C, a salinity of 17.5, and a light intensity of 250 μmol photons m⁻² s⁻¹. The highest amount of lipid and protein was found at 25 °C, a salinity of 30, and a light intensity of 250 μmol photons m⁻² s⁻¹. Consequently, the combination of warm water mixing with lower salinity river input has the potential to enhance H. akashiwo toxicity, which aligns with environmental reports that establish a correlation between warm summers and extensive runoff conditions that indicate the greatest concern for aquaculture facilities. Full article

This work is related to the environmental toxicology risk assessment and evaluation of the possible transformation of carbon-based nanomaterials (CNMs) after contact with marine microalgae. The materials used in the study represent common and widely applied multi-walled carbon nanotubes (CNTs), fullerene (C₆₀), graphene (Gr), and graphene oxide (GrO). The toxicity was evaluated as growth rate inhibition, esterase activity, membrane potential, and reactive oxygen species generation changes. The measurement was performed with flow cytometry after 3, 24, 96 h, and 7 days. The biotransformation of nanomaterials was evaluated after 7 days of microalgae cultivation with CNMs by FTIR and Raman spectroscopy. The calculated toxic level (EC₅₀ in mg/L, 96 h) of used CNMs reduced in the following order: CNTs (18.98) > GrO (76.77) > Gr (159.40) > C₆₀ (414.0). Oxidative stress and membrane depolarization were the main toxic action of CNTs and GrO. At the same time, Gr and C₆₀ decreased the toxic action with time and had no negative impact on microalgae after 7 days of exposure even at the concentration of 125 mg/L. Moreover, C₆₀ and Gr after 7 days of contact with microalgae cells obtained structural deformations. Full article

The red tide-forming microalga Heterosigma akashiwo has been associated with massive events of fish deaths, both wild and cultured. Culture conditions are responsible for the synthesis or accumulation of some metabolites with different interesting bioactivities. H. akashiwo LC269919 strain was grown in a 10 L bubble column photobioreactor artificially illuminated with multi-coloured LED lights. Growth and production of exopolysaccharides, polyunsaturated fatty acids (PUFAs), and carotenoids were evaluated under different culture modes (batch, fed-batch, semicontinuous, and continuous) at two irradiance levels (300 and 700 µE·s⁻¹·m⁻²). Continuous mode at the dilution rate of 0.2·day⁻¹ and 700 µE·s⁻¹·m⁻² provided the highest production of biomass, PUFAs (132.6 and 2.3 mg·L⁻¹·day⁻¹), and maximum fucoxanthin productivity (0.16 mg·L⁻¹·day⁻¹). The fed-batch mode accumulated exopolysaccharides in a concentration (1.02 g·L⁻¹) 10-fold over the batch mode. An extraction process based on a sequential gradient partition with water and four water-immiscible organic solvents allowed the isolation of bioactive fucoxanthin from methanolic extracts of H. akashiwo. Metabolites present in H. akashiwo, fucoxanthin and polar lipids (i.e., eicosapentaenoic acid (EPA)), or probably such as phytosterol (β-Sitosterol) from other microalgae, were responsible for the antitumor activity obtained. Full article

Antibiotics have been identified as emerging pollutants, and they increasingly threaten the safety of mariculture; thus, effective treatment methods are urgently needed. In this study, Fe(II)-peroxymonosulfate-modified clay (Fe-PMS-MC), an effective mineral complex for harmful algal bloom control, was tested for sulfamethoxazole (SMX) removal from seawater. The results showed that SMX removal efficiency increased gradually from 42.3% to 100% in seawater in 6 h as the Fe-PMS-MC dose increased from 0.1 g/L to 1.0 g/L; this removal was more efficient than that in freshwater. Both an increase in temperature and the addition of inorganic anions such as Cl⁻, HCO₃⁻, and SO₄²⁻ improved the SMX removal efficiency; in contrast, there was no noticeable influence of a pH change from 3.0 to 9.0 or of Heterosigma akashiwo biomass addition from 10³ cells/mL to 10⁵ cells/mL. Oxidation was the main mechanism for the removal of SMX by Fe-PMS-MC treatment, and the mechanisms included radical oxidation and non-radical oxidation. PMS was the key component in Fe-PMS-MC for the production of radicals, which increased with temperature. Similarly, both radical oxidation and non-radical oxidation increased when PMS was attacked by Cl⁻, HCO₃⁻, and SO₄²⁻ in seawater. Full article

The more frequent occurrence of marine harmful algal blooms (HABs) and recent problems with newly-described toxins in Puget Sound have increased the risk for illness and have negatively impacted sustainable access to shellfish in Washington State. Marine toxins that affect safe shellfish harvest because of their impact on human health are the saxitoxins that cause paralytic shellfish poisoning (PSP), domoic acid that causes amnesic shellfish poisoning (ASP), diarrhetic shellfish toxins that cause diarrhetic shellfish poisoning (DSP) and the recent measurement of azaspiracids, known to cause azaspiracid poisoning (AZP), at low concentrations in Puget Sound shellfish. The flagellate, Heterosigma akashiwo, impacts the health and harvestability of aquacultured and wild salmon in Puget Sound. The more recently described flagellates that cause the illness or death of cultivated and wild shellfish, include Protoceratium reticulatum, known to produce yessotoxins, Akashiwo sanguinea and Phaeocystis globosa. This increased incidence of HABs, especially dinoflagellate HABs that are expected in increase with enhanced stratification linked to climate change, has necessitated the partnership of state regulatory programs with SoundToxins, the research, monitoring and early warning program for HABs in Puget Sound, that allows shellfish growers, Native tribes, environmental learning centers and citizens, to be the “eyes on the coast”. This partnership enables safe harvest of wholesome seafood for consumption in the region and helps to describe unusual events that impact the health of oceans, wildlife and humans. Full article

The raphidophyte Heterosigma akashiwo is a harmful algal species. The bloom of this organism has been associated with the massive mortality of fish in many coastal waters. To investigate the molecular mechanism of H. akashiwo blooms, having a reliable reference transcriptome of this species is essential. Therefore, in this study, a full-length transcriptome of H. akashiwo was obtained by single-molecule real-time sequencing. In total, 45.44 Gb subread bases were generated, and 16,668 unigenes were obtained after the sequencing data processing. A total of 8666 (52.00%) unigenes were successfully annotated using seven public databases. Among them, mostly phosphorus and nitrogen metabolism genes were detected. Moreover, there were 300 putative transcription factors, 4392 putative long non-coding RNAs, and 7851 simple sequence repeats predicted. This study provides a valuable reference transcriptome for understanding how H. akashiwo blooms at a molecular level. Full article