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Margalefidinium polykrikoides blooms resulted in massive fish mortality in many countries around the world. The prevalence of booms is believed to be associated with the eutrophication of the coastal area. Therefore, this study aims to determine the effects of different nitrogen (N) and phosphorus (P) concentrations on the growth of M. polykrikoides. Experiments were conducted on M. polykrikoides isolated from the affected area by exposing the cell to various N and P ratio: seawater without the addition of N and P (SW), equal N:P ratio (NP), trial ratio of N and P (TR), F/2 medium (+NP), deficient N (–N), and deficient P (–P). The experiments were carried out in triplicates for 20 d in similar environmental conditions with the determination of density, specific growth rate, and cell size during the study period. Furthermore, nutrient concentrations nitrite+nitrate (NO2 –+NO3 –), phosphate (PO4 3–), and ammonia (NH4 +) were measured initially in the medium and both nutrients and chlorophyll were determined at the end of the experiment. The results revealed that M. polykrikoides grew in all the experiments, but the growth patterns differed between the treatments. The highest specific growth rate (0.1901 ± 0.017 d–1) with the highest cell density (1709 ± 68.21 cells mL–1) with a long chain of cells was observed in TR during the exponential phase. However, cell size was significantly smaller in SW compared to other nutrient conditions during the exponential phase. This study shows that M. polykrikoides a flexible species in nutrient uptake, thus allowing the species to survive in different nutrient conditions. The understanding of this bloom mechanism is important in monitoring and management of this harmful species, particularly in Sabah coastal waters. [ABSTRACT FROM AUTHOR]

Worldwide used glyphosate-based organophosphorus herbicides may be potential phosphorus sources for phytoplankton in coastal waters. In this study, the changes in growth, fluorescent and cytometric parameters of the potentially toxic dinophytic algae Prorocentrum cordatum under the influence of glyphosate of different concentrations were investigated. The effect of glyphosate on the growth dynamics of P. cordatum under conditions of availability and deficiency of inorganic phosphorus in the medium is estimated. Results showed that P. cordatum could grow due to glyphosate as the only source of phosphorus. The final density of the culture was higher than that of the control (without glyphosate) by 22–136% depending on the applied herbicide concentration. Glyphosate stimulated the growth of microalgae, which was observed in increasing the efficiency of the photosynthetic apparatus of cells and their enzymatic (esterase) activity. P. cordatum used glyphosate as a source of phosphorus only when there was a deficiency in inorganic phosphorus, but it was also susceptible to the herbicide when there was inorganic phosphorus present in the medium. An increase of glyphosate concentration in coastal waters may lead to a change in the species structure of natural biocenoses and increase in the number of potentially harmful species. • Glyphosate stimulates the growth of P. cordatum. • P. cordatum can grow due to glyphosate as the only source of phosphorus. • P. cordatum consumes glyphosate only when there is a deficiency of inorganic phosphorus. • Glyphosate can lead to a change in the species structure of natural biocenoses. [ABSTRACT FROM AUTHOR]

Although microalgae typically serve as prey for jellyfish ephyrae in marine food webs, this study investigated the potential of harmful microalgae to produce detrimental effects on the moon jellyfish Aurelia aurita. Understanding the biological interactions between Aurelia and microalgal species is crucial, particularly considering their common co-occurrence in coastal waters worldwide. We examined the effects of 11 protist strains, comprising seven species of harmful microalgae and two non-toxic microalgae, on A. aurita ephyrae. The rhythmic pulsation behavior of A. aurita was significantly suppressed when exposed to the raphidophytes Heterosigma akashiwo and Chattonella marina var. ovata and the dinoflagellates Amphidinium carterae , Coolia canariensis , and Pfiesteria piscicida. Notably, the media filtrates of all H. akashiwo strains and C. marina var. ovata killed ephyrae, implying a possible extracellular release of chemicals. This study discovered novel interactions between microalgae and jellyfish ephyrae, implying that harmful algal blooms may suppress mass occurrences of Aurelia medusae. • This study explored the effects of harmful microalgae on moon jellyfish (Aurelia aurita) ephyrae. • Harmful microalgae significantly suppressed the rhythmic pulsation of A. aurita ephyrae through diverse mechanisms. • Harmful algal blooms could suppress large populations of A. aurita medusae by negatively affecting their ephyrae. [ABSTRACT FROM AUTHOR]

Invasive species that outcompete endemic ones and toxic harmful algae that cause algal blooms threaten marine resources like fisheries, aquaculture, and even tourism. Environmental DNA (eDNA) metabarcoding can help as a method for early alert. In this study, we have analyzed communities inhabiting six lagoons within the Gulf of Lion (northwest Mediterranean Sea) with spatial protection as RAMSAR and Natura 2000 sites. Employing the COI gene as the only metabarcode, we found 15 genera that have caused recognized algal bloom outbreaks in the studied lagoons since 2000. In addition, seven alien invasive species that can pose risks to the rich marine resources of the zone and lagoons were also found. The results found from eDNA are consistent with events of toxic algae blooms before and after the sampling moment and with reported occurrences of the invasive species in nearby Mediterranean areas. Multivariate multiple analysis showed the importance of anthropic pressure in the abundance of these nuisance species. Mitigation actions and routine eDNA metabarcoding in zones of special interest like these fragile French Mediterranean lagoons are recommended for early alert of nuisance species in order to plan timely management actions. • Mediterranean lagoons are threatened due to anthropogenic activities. • Anthropogenic pressures are significantly and positively associated with nuisance species. • eDNA metabarcoding is a useful tool to early detect nuisance species in Mediterranean lagoons. • Management actions should be taken to detect and control nuisance species before they become established. [ABSTRACT FROM AUTHOR]

• Ostreopsis abundances were quantified at the micro and mesohabitat scale and on artificial macroalgal mimics in two study sites. • Ostreopsis cell assessment can vary in function of the scale (micro and mesohabitat). • The substrate's preferences diminish when cell abundances are very high, while in moderate blooms it is possible to appreciate differences in abundances among substrates. • Higher densities of Ostreopsis cells were associated with Dictyota fasciola in one of the sampling sites. Harmful Algal Blooms (HABs) are increasing in temperate areas, and the growth rates of benthic harmful dinoflagellates may be favoured in the context of global climate change. Benthic dinoflagellates, including species belonging to the Ostreopsis Schmidt genus, are known to develop on the surface of macroalgae and different macroalgal morphotypes and communities could host higher or lower cell abundances. The physical structure of the macroalgal substrate at the small scale (cm, microhabitat scale) and the structural complexity of the macroalgal community at the medium scale (few m, mesohabitat scale) could play a relevant role in bloom facilitation: the hypothesis that Ostreopsis species could be associated with macroalgal turfs and shrubs, structurally less complex communities than canopy-forming macroalgae, is especially under discussion and, if confirmed, could link bloom occurrence to regime shifts in temperate ecosystems. The present study, performed in two locations of the Ligurian Sea (Rochambeau, France and Vernazzola, Italy) aimed at understanding marine vegetation's role at the micro and mesohabitat scales in controlling the distribution and abundance of Ostreopsis. The abundance of the microalgal cells was quantified at different spatial scales, from cm to a few m, on different macroalgal species and communities, including artificial substrates, to tease apart the micro and mesohabitat effects. The results obtained show a high spatio-temporal variability, potentially hiding habitat-related patterns. The substrate's preferences diminish when cell abundances are very high, as in the case of Rochambeau, while in presence of moderate cell abundances as in Vernazzola or the first phases of blooms, it is possible to appreciate differences in abundances among substrates (in our study, Dictyota fasciola (Roth) Lamouroux supporting higher abundances). Our results open new research topics such as the study of blooms at a larger scale (macrohabitat) and testing different sampling methods to standardise the cells' abundances independently on the substrate. [ABSTRACT FROM AUTHOR]

Oyster culture is a sustainable solution to food production. However, this activity can be severely impacted by the presence and proliferation of harmful microalgae such as the benthic dinoflagellates Prorocentrum hoffmannianum and Ostreopsis cf. ovata. This study aimed to evaluate the in vitro effects of P. hoffmannianum and O. cf. ovata on immune system cells (hemocytes) of the native cultured oyster Crassostrea gasar. The direct toxicity of both dinoflagellates was first evaluated assessing hemocyte viability exposed to eight concentrations of each HAB species. No reduction in hemocyte viability was found with the exposure to cell culture or the crude extract of P. hoffmannianum , but O. cf. ovata culture induced hemocyte death in a concentration-dependent manner. Ostreopsis cf. ovata concentration that promoted half of maximal reduction in hemocyte viability (EC 50) was 779 cells mL−1. Posteriorly, hemocytes were exposed to both dinoflagellate cells and crude extracts to investigate their effects on hemocyte functional parameters. Despite no direct toxicity of the dinoflagellate cells, P. hoffmannianum extract caused a threefold increase in ROS production and decreased the phagocytosis rate by less than half. Ostreopsis cf. ovata cells and crude extracts also triggered an increase in ROS production (two-fold), but the phagocytosis rate was reduced (by half) only in response to the two lower cell concentrations. These results indicate a harmful potential of both dinoflagellates through a direct toxicity (only for O. cf. ovata) and functional impairment of hemocytes (both species) which could expose C. gasar oyster to opportunistic infections. • Cultures of Prorocentrum hoffmannianum did not cause any direct toxicity in C. gasar hemocytes. • Intracellular compounds from P. hoffmaninanum can affect C. gasar hemocytes. • Direct toxicity of Ostreopsis cf. ovata was demonstrated on C. gasar hemocytes. • O. cf. ovata caused an increase in mortality and ROS production and a decrease in phagocytosis. [ABSTRACT FROM AUTHOR]

The planktonic diatom genus Pseudo-nitzschia contains several genetically closely related species that can produce domoic acid, a potent neurotoxin known to cause amnesic shellfish poisoning (ASP). An early identification and an adequate monitoring of the potential toxic Pseudo-nitzschia spp. are necessary. However, effective monitoring programs are time consuming due, in some cases, to the cell morphology similarities among species, determined with light microscopy, that can result in insufficient data to give a definitive species and toxins attribution. In this paper, Whole-Cell Fluorescent In Situ Hybridization (WC-FISH) has been evaluated as a powerful tool to detect and enumerate harmful cryptic and/or pseudo-cryptic Pseudo-nitzschia spp. collected in the Gulf of Naples. Fluorescently labelled probes directed against the ribosomal RNA (rRNA) of the 28S large subunit (LSU) were used. In particular, five probes detecting four cryptic species of Pseudo-nitzschia delicatissima complex and one specific for Pseudo-nitzschia multistriata gave good results for the molecular identification of potentially toxic target species in natural samples. Finally, we can state that the WC-FISH method, to identify Pseudo-nitzschia species, is faster and more cost-effective if compared with other rDNA-based methods.

In the last decade, there has been a steady stream of information on the methods and techniques available for detecting harmful algae species. The conventional approaches to identify harmful algal bloom (HAB), such as microscopy and molecular biological methods are mainly laboratory-based and require long assay times, skilled manpower, and pre-enrichment of samples involving various pre-experimental preparations. As an alternative, biosensors with a simple and rapid detection strategy could be an improvement over conventional methods for the detection of toxic algae species. Moreover, recent biosensors that involve the use of nanomaterials to detect HAB are showing further enhanced detection limits with a broader linear range. The improvement is attributed to nanomaterials' high surface area to volume ratio, excellent biological compatibility with biomolecules, and being capable of amplifying the electrochemical signal. Hence, this review presents the potential usage of biosensors over conventional methods to detect HABs. The methods reported for the detection of harmful algae species, ranging from conventional detection methods to current biosensor approaches will be discussed, along with their respective advantages and drawbacks to indicate the future prospects of biosensor technology for HAB event management. [ABSTRACT FROM AUTHOR]

Harmful algal bloom (HAB) species Alexandrium catenella and Dinophysis acuminata are associated with paralytic shellfish poisoning (PSP) and diarrhetic shellfish poisoning (DSP) in humans, respectively. While PSP and DSP have been studied extensively, less is known about the effects of these HAB species or their associated toxins on shellfish. This study investigated A. catenella and D. acuminata toxicity in a larval oyster (Crassostrea virginica) bioassay. Larval activity and mortality were examined through 96-h laboratory exposures to live HAB cells (10–1000 cells/mL), cell lysates (1000 cells/mL equivalents), and purified toxins (10,000 cells/mL equivalents). Exposure to 1000 cells/mL live or lysed D. acuminata caused larval mortality (21.9 ± 7.0%, 10.2 ± 4.0%, respectively) while exposure to any tested cell concentration of live A. catenella, but not lysate, caused swimming arrest and/or mortality in >50% of larvae. Exposure to high concentrations of saxitoxin (STX) or okadaic acid (OA), toxins traditionally associated with PSP and DSP, respectively, had no effect on larval activity or mortality. In contrast, pectenotoxin-2 (PTX2) caused rapid larval mortality (49.6 ± 5.8% by 48 h) and completely immobilized larval oysters. The results indicate that the toxic effects of A. catenella and D. acuminata on shellfish are not linked to the primary toxins associated with PSP and DSP in humans, and that PTX2 is acutely toxic to larval oysters. [ABSTRACT FROM AUTHOR]

Amphidinium species are amongst the most abundant benthic dinoflagellates in marine intertidal sandy ecosystems. Some of them are able to produce a variety of bioactive compounds that can have both harmful effects and pharmaceutical potentials. The diversity of Amphidinium in shallow waters along the Chinese coast was investigated by isolating single cells from sand, coral, and macroalgal samples collected from 2012 to 2020. Their morphologies were subjected to examination using light microscopy (LM) and scanning electron microscopy (SEM). A total of 74 Amphidinium strains were morphologically identified, belonging to 11 species: A. carterae, A. gibbosum, A. operculatum, A. massartii, A. cf. massartii, A. fijiensis, A. pseudomassartii, A. steinii, A. thermaeum, A. theodori, A. tomasii, as well as an undefined species. The last seven species have not been previously reported in Chinese waters. Amphidinium carterae subclades I, II, and IV were found in the South China Sea, while subclade III was only found in the Yellow Sea. Threadlike body scales were observed on the surface of subclades III and V, supporting the idea that A. carterae might contain several different species. Large subunit ribosomal RNA (LSU rRNA) sequences-based phylogeny revealed two groups (Groups I and II) within Amphidinium, which is consistent with the relative position of sulcus (in touch with cingulum or not). In addition, large differences in morphology and molecular phylogeny between A. operculatum (the type species of Amphidinium) and other species, suggest that a subdivision of Amphidinium might be needed. The pigment profiles of all available strains were analyzed by high performance liquid chromatography (HPLC). Eleven pigments, including peridinin, diadinoxanthin, diatoxanthin, pheophorbide (and pheophorbide a), antheraxanthin, β-carotene, and four different chlorophylls were detected. The high pheophorbide/pheophorbide a ratio in Amphidinium implies that it may be a good candidate as a natural source of photosensitizers, a well-known anticancer drug. [ABSTRACT FROM AUTHOR]

The southern part of the Okhotsk Sea off Hokkaido has rich fishery resources supported by high primary production. The phytoplankton community has been described by several studies based on size-fractionated chlorophyll a concentration and primary production; however, the details of the species composition of nano- and micro-protist communities have not been well investigated. We evaluated the spatial distribution and relationship with hydrography of nano- and micro-protist communities in the southern region of the Okhotsk Sea off Hokkaido during the summer of 2019. Forty-two species of diatoms from 19 genera, dinoflagellates from 7 genera, tintinnid ciliates, oligotrich ciliates, and 1 genus of silicoflagellates were identified. Their spatial distribution showed distinct differences among the taxa. Cluster analysis based on the protist cell density identified six groups with geographically well-distinguished distributions. Diatom-dominant communities were distributed in the Cold Water Belt and Soya warm current along the coastal area of Hokkaido. Nanoflagellate-dominated communities were distributed in the offshore area. Some harmful species of diatoms (Pseudonitzschia pseudodelicatissima) and dinoflagellates (Alexandrium spp.) were dominant in the Cold Water Belt off Wakkanai. We suggest that the upwelling of cold water could increase the abundance of harmful species, with immanent negative impacts on marine ecosystems or fishery resources. In summary, the species composition and abundance of the summer protist community was strongly related to different water masses in the southern part of the Okhotsk Sea off Hokkaido. [ABSTRACT FROM AUTHOR]

Cyanobacteria often cause harmful algal blooms and release toxic substances that can harm humans and animals. Accurately modeling these phytoplankton is a step towards predicting, preventing, and controlling such blooms. Certain cyanobacteria species are known to migrate vertically in the water column on a daily cycle. Capturing this behavior is one aspect of modeling their dynamics. Previous studies on modeling cyanobacterial vertical migration are reviewed and summarized. Several models of cyanobacteria vertical movement are tested using data from field studies. These models are applied using both continuum and particle-tracking frameworks. Models range in complexity from simple functions of time to more complicated calculations of cyanobacteria buoyancy. Simple models were often able to predict cyanobacteria migration at low values of vertical diffusion in both types of modeling frameworks. More complicated models of buoyancy change performed better in the particle-tracking framework than in the continuum framework. Analysis of the models developed and tested provides information on the applicability of these models in more complex hydrodynamic and water quality models. [ABSTRACT FROM AUTHOR]

Changes in phytoplankton communities due to anthropogenic nutrient load and climate change often lead to eutrophication and harmful algal blooms that can affect biogeochemical cycling. However, little is known about the specific responses of various species to environmental variables. 17-year long data on the midsummer phytoplankton biomass in the Neva Estuary were analyzed to show the changes in the composition of phytoplankton in relation to water depth, transparence, salinity, temperature, concentrations of total phosphorus and chlorophyll a, and plankton primary production. One hundred seventy-four species and forms from eight taxonomic classes were found in phytoplankton. Fifteen species were potentially harmful. The most diverse and abundant groups were cyanobacteria, green algae and diatoms. Canonical Correspondence Analysis showed that the biomass of various species from each phytoplankton group correlated differently with environmental factors. However, within each group, there were some predominant trends in the correlative response to changes in environmental variables. The biomass of cyanobacteria was high in the middle and lower reaches of the estuary and, in general, positively correlated with water salinity. The biomass of most species of green algae and diatoms correlated negatively with it. These algae showed a positive trend in biomass in the upper and middle reaches of the estuary during the last decades that may be explained by changes in weather conditions. Taking into account that climate models predict future increases in precipitation and temperature in the northern Baltic, the future expansion of freshwater phytoplankton species in estuaries of the northern Baltic Sea is very likely.

Lipophilic toxins were investigated in different benthic compartments of Paranaguá Bay, southern Brazil. Relatively low concentrations of okadaic acid (OA) were frequently reported in macrophyte extracts (maximum 0.64 ng g−1), mainly in sheltered estuarine areas, correlated with the cell abundance of toxigenic benthic dinoflagellates, Prorocentrum lima. Non-conjugated OA was also detected in benthic marine animals, mostly during summer-autumn 2016. Higher OA concentrations were found in the viscera of Genidens genidens fish (24.3 ± 3.7 ng g−1) and in soft tissues of Mytella guyanensis bivalves (21.3 ± 2.13 ng g−1), whereas lower levels were less frequently reported in many other benthic feeders, including cephalopods, gastropods, crustaceans and fishes. Although OA concentrations were below the levels associated with acute human intoxication, possible chronic effects to benthic animals and their consumers cannot be disregarded due to the frequent presence of this biotoxin in various fishery resources. Human health risks are substantially enhanced for small-scale fishing communities and other socioeconomically vulnerable populations. [ABSTRACT FROM AUTHOR]

This study investigated the temporal and spatial variations of Takayama blooms in Uranouchi Inlet, Japan. From July to September 2017, Takayama cells appeared (≥1 cell mL-1) at depths of 0-10 m, temperatures of 25.4-31.7°C, and salinities of 23.1-34.2. The maximum cell density was 1.37-103 cells mL-1. By analyzing partial rDNA sequences of Takayama strains collected at the bloom initiation, we found Takayama acrotrocha/Takayama xiamenensis and Takayama tasmanica in the Uranouchi Inlet. This study contributes to understanding of the dynamics of and risk to aquaculture of Takayama blooms in the coastal waters of Japan. [ABSTRACT FROM AUTHOR]

To describe the phytoplankton species composition, spatio-temporal distribution and habitats during different seasons along the central coast of the state of Campeche, Mexico, southeastern Gulf of Mexico, eight shallow-water (ca 1 m) sites from the city of Campeche Southwest to Villamar were monitored monthly from September 2016 to June 2017 by taking water-bottle samples. Average water temperature varied between 22.2 and 30.9°C and average salinity between 26.6 and 35.0. The Kolmogorov–Smirnov test, the Bartlett's test and canonical correspondence analyses were applied. Sixteen potentially harmful microalgal species were found: five species are bloom-forming, nine are potentially toxic to humans, and two affect aquatic organisms. At all sampling sites, massive algal proliferations occurred in June (beginning of rainy season) caused by the dinoflagellates Heterocapsa sp. (2.6 × 105 cells/L) and Blixaea quinquecornis (2.0 × 104 cells/L) and from October to March (windy season) by the cyanobacterium Trichodesmium sp. (2.6 × 105 cells/L). [ABSTRACT FROM AUTHOR]

This study aims at controlling excess nutrients, including nitrogen and phosphorus, and harmful algae that pollute the marine environment using biosynthesized iron oxide nanoparticles. Aqueous extracts of brown seaweeds named Petalonia fascia, Colpomenia sinuosa, and Padina pavonica were selected for iron oxide nanoparticles' biosynthesis. The extracts were used as reductants of ferric chloride, and dark brown colors due to Fe3O4-NPs biosynthesis were observed. Iron signals were recorded in EDX spectra. FTIR analyses showed that the three algae extracts contained proteins and lipids that have the ability to proceed dual functions of bioreduction and stabilization of Fe3O4-NPs, suggesting that proteins in P. fascia, C. sinuosa, and P. pavonica extracts reduced FeCl3, and the aromatic compounds stabilized the biogenic Fe3O4-NPs. The biosynthesized Fe3O4-NPs via P. pavonica had the best nitrogen reduction percentage, followed by C. sinuosa and P. fascia for both concentrations 2 and 4 µg mL−1. The best results of phosphorus removal and Chlorophyll a (Chl a) reduction percentages using the Fe3O4-NPs concentrations were 2 and 4 µg mL−1 with nanoparticles synthesized via P. fascia and P. pavonica, respectively. The highest reduction in optical density for both 2 and 4 µg mL−1 was achieved by the nanoparticles synthesized by P. fascia. Novelty Statement Application of nanoparticles using seaweeds extracts could be alternative safe bioremediation of wastewaters. Currently, iron oxide nanoparticles are used to reduce nitrogen and phosphorus and reduce the blooming of harmful algae; little information about this issue has been reported. Such study also presented the anti-algal impacts of Fe3O4-NPs by tracing optical density and Chl a concentrations in the examined real seawater samples. Modern biotechnology to develop phytoremediation and seaweeds to enhance these remediation methods can be adopted. [ABSTRACT FROM AUTHOR]

Amphidinium species are amongst the most abundant benthic dinoflagellates in marine intertidal sandy ecosystems. Some of them produce a variety of bioactive compounds that have both harmful effects and pharmaceutical potential. In this study, Amphidinium cells were isolated from intertidal sand collected from the East China Sea. The two strains established were subjected to detailed examination by light, and scanning and transmission electron microscopy. The vegetative cells had a minute, irregular, and triangular-shaped epicone deflected to the left, thus fitting the description of Amphidinium sensu stricto. These strains are distinguished from other Amphidinium species by combination characteristics: (1) longitudinal flagellum inserted in the lower third of the cell; (2) icicle-shaped scales, 276 ± 17 nm in length, on the cell body surface; (3) asymmetrical hypocone with the left side longer than the right; and (4) presence of immotile cells. Therefore, they are described here as Amphidinium stirisquamtum sp. nov. The molecular tree inferred from small subunit rRNA, large subunit rRNA, and internal transcribed spacer-5.8S sequences revealed that A. stirisquamtum is grouped together with the type species of Amphidinium, A. operculatum, in a fully supported clade, but is distantly related to other Amphidinium species bearing body scale. Live A. stirisquamtum cells greatly affected the survival of rotifers and brine shrimp, their primary grazers, making them more susceptible to predation by the higher tropic level consumers in the food web. This will increase the risk of introducing toxicity, and consequently, the bioaccumulation of toxins through marine food webs. [ABSTRACT FROM AUTHOR]

The study aimed to examines a case of what constituted the uncommonly reddish-bloom appearance in the fishponds during the dry season (September 2018) at Kingolwira National Fish Farming Center located in Morogoro, Tanzania. The study used a benchtop FlowCAM® to investigate species' morphology. One-time assessment of physico-chemical characteristics during the event was performed from the reddish and non-reddish fishponds. Images were compared with the available literature, but also t-test statistics were performed to examine the difference between the fishponds. The results show that the fishponds were significantly (p

In Brazil, malacoculture is developed mainly in the state of Santa Catarina, followed by São Paulo and Rio de Janeiro. In the course of the development of Brazilian mariculture, legislation has addressed the sanitary requirements necessary for bivalve commercialization. However, monitoring phycotoxins is a challenge, due to often costly reference methods. In this context, this study evaluated the use of alternative ecotoxicological and bioanalytical methods using Artemia franciscana (brine shrimp) lethality assessments. The results confirm that, although correlations between the reference mouse assay and the brine shrimp assays were not high, the alternative brine shrimp assay may be incorporated into phycotoxin monitoring programs, as hepatopancreas methanolic extracts of mussel (Perna perna) containing DSP resulted in high lethality rates. Therefore, further methodological adjustment studies and the inclusion of other enzymatic and toxicological models are required to further assess these differences, and associations between ecotoxicological methods as early-alarm methods are encouraged.

Gonyostomum semen is a bloom-forming freshwater raphidophyte that is currently on the increase, which concerns water managers and ecologists alike. Much indicates that the recent success of G. semen is linked to its diel vertical migration (DVM), which helps to overcome the spatial separation of optimal light conditions for photosynthesis at the surface of a lake and the high concentration of phosphate in the hypolimnion. I here present data from a field study conducted in Lake Lundebyvannet (Norway) in 2017-2019 that are consistent with the idea that the DVM of G. semen also allows for a hypolimnetic uptake of ammonium. As expected, microbial mineralization of organic matter in a low-oxygen environment led to an accumulation of ammonium in the hypolimnion as long as G. semen was absent. In contrast, a decreasing or constantly lower concentration of hypolimnetic ammonium was found in presence of a migrating G. semen population. In summer of 2019, a short break in the DVM of G. semen coincided with a rapid accumulation of hypolimnetic ammonium, which was equally rapidly decimated when G. semen resumed its DVM. Taken together, these data support the idea that G. semen can exploit the hypolimnetic pool of ammonium, which may be one reason for the recent success of the species and its significant impact on the structure of the aquatic food web.

Plankton monitoring by microscopy offers a long-term ecological perspective of plankton communities, but detection approaches are uniquely biased. Genetic identification of marine plankton has become standard but is still not used in routine monitoring. This study assesses the value that genetic methods bring to microscopic and flow cytometry monitoring methods in the Western (English) Channel. An 18S high throughput sequencing (HTS) diversity survey of plankton taxa was performed on samples collected from an automated Water and Microplankton Sampler (WaMS) deployed on the Continuous Plankton Recorder platform (CPR) from 2011–2012. This survey detected contrasting but complementary taxa assemblages to that of microscopic surveys, mostly composed of smaller or naked or thin-walled plankton taxa, with most phytoplankton being under 10 µm infrequently recorded by other surveys. Most genetically-detected taxa in the survey were mixotrophic or heterotrophic. In comparison with microscopic phytoplankton counts from the CPR survey and Western Channel Observatory station L4, only 8–12 taxonomic families were common to all three surveys, most of them dinoflagellates, with a bias towards larger diatoms and dinoflagellate taxa in microscopy surveys. Additional quantitative real-time PCR detection of two potentially harmful taxa, the pelagophyte, Aureococcus anophagefferens and four Pseudo-nitzschia from 2011–2013. This revealed that growth of A. anophagefferens was elevated in the summer of 2011, whilst the appearance of Pseudo-nitzschia delicatissima in February of that year contrasted with it’s timing at a coastal station. Smaller phytoplankton measured by flow cytometry had distinct seasonality and abundance in the mid-Atlantic compared to coastal regions reflecting distinct conditions.

Some strains of the dinoflagellate species Prorocentrum hoffmannianum show contrasting ability to produce diarrhetic shellfish poisoning (DSP) toxins. We previously compared the okadaic acid (OA) production level between a highly toxic strain (CCMP2804) and a non-toxic strain (CCMP683) of P. hoffmannianum and revealed that the cellular concentration of OA in CCMP2804 would increase significantly under the depletion of phosphate. To understand the molecular mechanisms, here, we compared and analyzed the proteome changes of both strains growing under normal condition and at phosphate depletion using two-dimensional gel electrophoresis (2-DE). There were 41 and 33 differential protein spots observed under normal condition and phosphate depletion, respectively, of which most were upregulated in CCMP2804 and 22 were common to both conditions. Due to the lack of matched peptide mass fingerprints in the database, de novo peptide sequencing was applied to identify the differentially expressed proteins. Of those upregulated spots in CCMP2804, nearly 60% were identified as peridinin-chlorophyll a-binding protein (PCP), an important light-harvesting protein for photosynthesis in dinoflagellates. We postulated that the high expression of PCP encourages the production of DSP toxins by enhancing the yields of raw materials such as acetate, glycolate and glycine. Other possible mechanisms of toxicity related to PCP might be through triggering the transcription of non-ribosomal peptide synthetase/polyketide synthase genes and the transportation of dinophysistoxin-4 from chloroplast to vacuoles.

Biofilms harbour a wealth of microbial diversity and fulfil key functions in coastal marine ecosystems. Elevated carbon dioxide (CO2) conditions affect the structure and function of biofilm communities, yet the ecological patterns that underpin these effects remain unknown. We used high-throughput sequencing of the 16S and 18S rRNA genes to investigate the effect of elevated CO2 on the early successional stages of prokaryotic and eukaryotic biofilms at a CO2 seep system off Shikine Island, Japan. Elevated CO2 profoundly affected biofilm community composition throughout the early stages of succession, leading to greater compositional homogeneity between replicates and the proliferation of the potentially harmful algae Prymnesium sp. and Biddulphia biddulphiana. Species turnover was the main driver of differences between communities in reference and high CO2 conditions, rather than differences in richness or evenness. Our study indicates that species turnover is the primary ecological pattern that underpins the effect of elevated CO2 on both prokaryotic and eukaryotic components of biofilm communities, indicating that elevated CO2 conditions represent a distinct niche selecting for a distinct cohort of organisms without the loss of species richness.

Eutrophication is recognized as the main water quality problem worldwide, mainly due to the prevalence of harmful cyanobacterial blooms. Submerged macrophytes can control cyanobacterial biomass by removing nutrients from the water column or producing allelopathic compounds. As a result, they are highlighted as a potential strategy for restoring eutrophic waters. However, studies in semi-arid tropical ecosystems have shown inconsistent results regarding the effects of submerged macrophytes on cyanobacterial communities and cyanotoxin production. The aim of this study was to assess the effect of submerged macrophytes on cyanobacterial community structure and microcystin production in a tropical semi-arid reservoir subject to intense periods of water level drawdown. Submerged macrophyte cover, surface water physical and chemical variables, cyanobacterial community biovolume and microcystin concentration were measured monthly between October 2014 and July 2015 at the entrance of the river (Zone I) and dam zones (Zone II) of a reservoir. Although both zones were dominated by the submerged macrophyte Egeria densa, there were significant differences in macrophyte cover: Zone I had greater submerged macrophyte cover and Zone II had lower submerged macrophyte cover. Higher total cyanobacterial biovolume, potential microcystin producer biovolume and microcystin concentrations were observed in the zone with the greater submerged macrophyte cover. Moreover, our results showed that nutrient concentrations (total phosphorous, total nitrogen and ammonium) and physical variables (water temperature and turbidity) were also associated with the zone with greater submerged macrophyte cover. This study highlights that the water level drawdown of the reservoir appears to have favored an increase in nutrient concentration, especially in the zones with dense vegetation, which may have contributed to the coexistence of the high cyanobacteria biomass, high submerged macrophyte coverage and high microcystin concentration. Thus, developing strategies for the management of submerged macrophyte cover during water level drawdown events is essential for improving water quality and reducing the risk of harmful cyanobacterial blooms at the ecosystem level in tropical semi-arid aquatic ecosystems. [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.

The marine dinoflagellate Alexandrium is associated with harmful algal blooms (HABs) worldwide, causing paralytic shellfish poisoning (PSP) in humans. We found that the marine bacterium Pseudoruegeria sp. M32A2M exhibits algicidal activity against Alexandrium catenella (Group I), inhibiting its motility and consequently inducing cell disruption after 24 h of co-culture. To understand the communication between the two organisms, we investigated the time-course cellular responses through genome-wide transcriptome analysis. Functional analysis of differentially expressed genes revealed that the core reactions of the photosystem in A. catenella were inhibited within 2 h, eventually downregulating the entire pathways of oxidative phosphorylation and carbon fixation, as well as associated metabolic pathways. Conversely, Pseudoruegeria upregulated its glycolysis, tricarboxylic acid cycle, and oxidative phosphorylation pathways. Also, the transporters for nutrients such as C3/C4 carbohydrates and peptides were highly upregulated, leading to the speculation that nutrients released by disrupted A. catenella cells affect the central metabolism of Pseudoruegeria. In addition, we analyzed the secondary metabolite-synthesizing clusters of Pseudoruegeria that were upregulated by co-culture, suggesting their potential roles in algicidal activity. Our time-course transcriptome analysis elucidates how A. catenella is affected by algicidal bacteria and how these bacteria obtain functional benefits through metabolic pathways.

Intense blooms of the toxic dinoflagellate Ostreopsis producing palytoxin (PlTX) analogs, mainly ovatoxins (OVTXs), have been a recurrent phenomenon along several Mediterranean coasts. Although there is evidence of seafood contamination by these toxins, the dynamics of their bioaccumulation during Ostreopsis blooms is not yet clear. Toxin concentrations in wild mussels at two sites in the Conero Riviera, along the northern Adriatic Sea (Portonovo and Passetto), were analyzed from August to October 2021, throughout an Ostreopsis cf. ovata bloom, to investigate their relationships with the bloom pattern and abundances. Contaminated mussels showed the typical toxin profile dominated by OVTX-a and -b, with levels lower than the threshold considered unsafe for human consumption (30 µg PlTX-equivalent kg−1 soft tissue). The toxin content reached 36.4 µg PlTX kg−1 soft tissue only in a single sampling date. A clear correlation between the bioaccumulation of OVTXs in mussels and the abundance of Ostreopsis was observed. Our results highlighted, however, that bioaccumulation in the mussels is not affected merely by the abundance of toxic microalgae, since higher toxin levels were recorded at Portonovo, where the cell abundances were lower than at Passetto. The results from this study indicate that the Italian guidelines for the management of Ostreopsis blooms in bathing waters are also useful in managing the risks of human intoxication through ingestion, as mussel contamination was detected only during the alert phase (10,000–30,000 cells L−1).

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.

Paralytic shellfish toxin (PST) content in the dinoflagellate Gymnodinium catenatum changes with culture age, with a higher toxin concentration in the logarithmic phase that decreases when the culture ages. The gene copy number (GCN) of domains sxtA1 and sxtA4 was higher in the lag and stationary phase, and lag phase, respectively. No relationship was found between the GCN of the domains sxtA4 and sxtA1 with the PST content in G. catenatum. [Display omitted] • The paralytic shellfish toxins (PST) content does not have significant change with the growth phases. • The copy number of the domains sxtA1 and sxtA4 changes with the growth phase. • There is not correlation between PST content and sxtA gene copies. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms are expected to intensify and become more widespread with climate change and sustained nutrient pollution, subsequently increasing threats to lentic ecosystems, water quality, and human health. However, little is known about their rates of change because long‐term monitoring data are rare, except for some well‐studied individual lakes, which typically are large and broadly dispersed geographically. Using monitoring data spanning 1987–2018 for 20 temperate reservoirs located in the USA, we found that cyanobacteria cell densities mostly posed low‐to‐moderate human health risks until 2003–2005, after which cell densities rapidly increased. Increases were greatest in reservoirs with extensive agriculture in their watersheds, but even those with mostly forested watersheds experienced increases. Since 2009, cell densities posing high human health risks have become frequent with 75% of yearly observations exceeding 100,000 cells ml−1, including 53% of observations from reservoirs with mostly forested watersheds. These increases coincided with progressively earlier and longer summer warming of surface waters, evidence of earlier onset of stratification, lengthening durations of deep‐water hypoxia, and warming deep waters in non‐stratifying reservoirs. Among years, higher cell densities in stratifying reservoirs were associated with greater summer precipitation, warmer June surface water temperatures, and higher total Kjeldahl nitrogen concentrations. These trends are evidence that expected increases in cyanobacterial blooms already are occurring as changing climate conditions in some regions increasingly favor their proliferation. Consequently, their negative effects on ecosystems, human health, and socioeconomic wellbeing could increase and expand if warming trends and nutrient pollution continue. [ABSTRACT FROM AUTHOR]

A novel Ag 3 PO 4 /ZnWO 4 -modified graphite felt electrode (AZW@GF) was prepared by drop coating method and applied to photoelectrocatalytic removal of harmful algae. Results showed that approximately 99.21% of chlorophyll a and 91.57% of Microcystin-LR (MCLR) were degraded by the AZW@GF-Pt photoelectrocatalytic system under the optimal operating conditions with a rate constant of 0.02617 min−1 and 0.01416 min−1, respectively. The calculated synergistic coefficient of photoelectrocatalytic algal removal and MC-LR degradation by the AZW@GF-Pt system was both larger than 1.9. In addition, the experiments of quenching experiments and electron spin resonance (ESR) revealed that the photoelectrocatalytic reaction mainly generated •OH and •O 2 - for algal removal and MC-LR degradation. Furthermore, the potential pathway for photoelectrocatalytic degradation of MC-LR was proposed. Finally, the photoelectrocatalytic cycle algae removal experiments were carried out on AZW@GF electrode, which was found to maintain the algae removal efficiency at about 91% after three cycles of use, indicating that the photoelectrocatalysis of AZW@GF electrode is an effective emergency algae removal technology. [Display omitted] • AZW@GF electrode was prepared by drop-coating method. • AZW@GF electrode exhibited significant photoelectrocatalytic synergistic effects. • Photoelectrocatalytic algal removal mechanism could be ascribed to·OH and·O 2 -. • Photoelectrocatalysis is an effective emergency algae removal technology. [ABSTRACT FROM AUTHOR]

• MC II removed K. brevis cells but was less effective at toxin removal than expected. • MC II removed dissolved and particulate phosphorus from the water column. • MC II significantly reduced pH and alkalinity over the 72-hour observation period. • Lethal and sublethal measures in animals were unaffected by MC II treatment. • Effectiveness of MC II may be impacted by factors affecting particle collision. Modified clay compounds are used globally as a method of controlling harmful algal blooms, and their use is currently under consideration to control Karenia brevis blooms in Florida, USA. In 1400 L mesocosm tanks, chemical dynamics and lethal and sublethal impacts of MC II, a polyaluminum chloride (PAC)-modified kaolinite clay, were evaluated over 72 h on a benthic community representative of Sarasota Bay, which included blue crab (Callinectes sapidus), sea urchin (Lytechinus variegatus), and hard clam (Mercenaria campechiensis). In this experiment, MC II was dosed at 0.2 g L -1 to treat bloom-level densities of K. brevis at 1 × 106 cells L -1. Cell removal in MC II-treated tanks was 57% after 8 h and 95% after 48 h. In the water column, brevetoxin analogs BTx-1 and BTx-2 were found to be significantly higher in untreated tanks at 24 and 48 h, while in MC II-treated tanks, BTx-3 was found to be higher at 48 h and BTx-B5 was found to be higher at 24 and 48 h. In MC II floc, we found no significant differences in BTx-1 or BTx-2 between treatments for any time point, while BTx-3 was found to be significantly higher in the MC II-treated tanks at 48 and 72 h, and BTx-B5 was higher in MC II-treated tanks at 24 and 72 h. Among various chemical dynamics observed, it was notable that dissolved phosphorus was consistently significantly lower in MC II tanks after 2 h, and that turbidity in MC II tanks returned to control levels 48 h after treatment. Dissolved inorganic carbon and total seawater alkalinity were significantly reduced in MC II tanks, and partial pressure of CO 2 (p CO 2) was significantly higher in the MC II-only treatment after 2 h. In MC II floc, particulate phosphorus was found to be significantly higher in MC II tanks after 24 h. In animals, lethal and sublethal responses to MC II-treated K. brevis did not differ from untreated K. brevis for either of our three species at any time point, suggesting MC II treatment at this dosage has negligible impacts to these species within 72 h of exposure. These results appear promising in terms of the environmental safety of MC II as a potential bloom control option, and we recommend scaling up MC II experiments to field trials in order to gain deeper understanding of MC II performance and dynamics in natural waters. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) pose a significant threat to human and marine organism health, and negatively impact coastal economies around the world. An improved understanding of HAB formation and transport is required to improve forecasting skill. A realistic numerical simulation of the US Pacific Northwest region is used to investigate transport pathways from known HAB formation hot spots, specifically for Pseudo-nitzschia (Pn), to the coast. We show that transport pathways are seasonal, with transport to the Washington (WA) coast from a northern source (the Juan de Fuca Eddy) during the summer/fall upwelling season and from a southern source (Heceta Bank) during the winter/early spring due to the predominant wind-driven currents. Interannual variability in transport from the northern source is related to the degree of wind intermittency with more transport during years with more frequent relaxation/downwelling events. The Columbia River plume acts to mitigate transport to the coast as the plume front blocks onshore transport. The plume's influence on alongshore transport is variable although critical in aiding transport from the southern source to the WA coast via plume entrainment. Overall transport from our simulations captures most observed Pn HAB beach events from 2004 to 2007 (characterized by Pseudo-nitzschia cell abundance); however, numerous false positives occur. We show that incorporating phytoplankton biomass results from a coupled biogeochemical model reduces the number of false positives significantly and thus improves our Pn HAB predictions. Key Points Potential PNW HAB transport is seasonal, consistent with regional currents Transport is blocked by the Columbia River plume unless entrainment occurs A coupled hydrodynamic-biological model can predict PNW Pn HAB transport paths © 2014. American Geophysical Union. All Rights Reserved.

In this paper, we survey recent developments of mathematical modeling and analysis of the dynamics of harmful algae in riverine reservoirs. To make the models more realistic, a hydraulic storage zone is incorporated into a flow reactor model and new mathematical challenges arise from the loss of compactness of the solution maps. The key point in the study of the evolution dynamics is to prove the existence of global attractors for the model systems and the principal eigenvalues for the associated linearized systems without compactness.

Cyanobacteria are well recognised as producers of a wide range of natural compounds that are in turn recognised as toxins that have potential and useful applications in the future as pharmaceutical agents. The order Nostocales, which is largely overlooked in this regard, has become increasingly recognised as a source of toxin producers including Anabaena, Nostoc, Hapalosiphon, Fischerella, Anabaenopsis, Aphanizomenon, Gloeotrichia, Cylindrospermopsis, Scytonema, Raphidiopsis, Cuspidothrix, Nodularia, Stigonema, Calothrix, Cylindrospermum and Desmonostoc species. The toxin compounds (i.e., microcystins, nodularin, anatoxins, ambiguines, fischerindoles and welwitindolinones) and metabolites are about to have a destructive effect on both inland and aquatic environment aspects. The present review gives an overview of the various toxins that are extracted by the order Nostocales. The current research suggests that these compounds that are produced by cyanobacterial species have promising future considerations as potentially harmful algae and as promising leads for drug discovery. The cyanobacteria are well recognized as producers of a wide range of toxin compounds that have useful application in the future as pharmaceutical agents. The present review gives an overview of the various toxins (i.e., microcystins, nodularin, anatoxins, ambiguines, fischerindoles, and welwitindolinones) extracted by the Nostocales. Table 1 shows toxins and toxin‐producing strains, application, molecular formula, mechanism of action, and structure of toxins [ABSTRACT FROM AUTHOR]

In the last decade, there has been a steady stream of information on the methods and techniques available for detecting harmful algae species. The conventional approaches to identify harmful algal bloom (HAB), such as microscopy and molecular biological methods are mainly laboratory-based and require long assay times, skilled manpower, and pre-enrichment of samples involving various pre-experimental preparations. As an alternative, biosensors with a simple and rapid detection strategy could be an improvement over conventional methods for the detection of toxic algae species. Moreover, recent biosensors that involve the use of nanomaterials to detect HAB are showing further enhanced detection limits with a broader linear range. The improvement is attributed to nanomaterials’ high surface area to volume ratio, excellent biological compatibility with biomolecules, and being capable of amplifying the electrochemical signal. Hence, this review presents the potential usage of biosensors over conventional methods to detect HABs. The methods reported for the detection of harmful algae species, ranging from conventional detection methods to current biosensor approaches will be discussed, along with their respective advantages and drawbacks to indicate the future prospects of biosensor technology for HAB event management.

Cyanobacteria often cause harmful algal blooms and release toxic substances that can harm humans and animals. Accurately modeling these phytoplankton is a step towards predicting, preventing, and controlling such blooms. Certain cyanobacteria species are known to migrate vertically in the water column on a daily cycle. Capturing this behavior is one aspect of modeling their dynamics. Previous studies on modeling cyanobacterial vertical migration are reviewed and summarized. Several models of cyanobacteria vertical movement are tested using data from field studies. These models are applied using both continuum and particle-tracking frameworks. Models range in complexity from simple functions of time to more complicated calculations of cyanobacteria buoyancy. Simple models were often able to predict cyanobacteria migration at low values of vertical diffusion in both types of modeling frameworks. More complicated models of buoyancy change performed better in the particle-tracking framework than in the continuum framework. Analysis of the models developed and tested provides information on the applicability of these models in more complex hydrodynamic and water quality models.

Photocatalysis has attracted much attention as an emerging algae removal technology, but the inactivation performance is inevitably affected by the extracellular polymeric substance (EPS) produced by algae. In this study, a photocatalyst (Ag2O/g‐C3N4) with efficient algae inactivation is adopted to investigate the interactions with EPS, and the impact of EPS on photocatalytic algae removal is studied. The results show that EPS can adhere to the surface of Ag2O/g‐C3N4 by electrostatic force. The interaction with EPS decreases the surface zeta potential of the Ag2O/g‐C3N4 from 7.71 to −22.3 mV with the increase in EPS concentration, and the maximum ratio of particle size increases from 825 to 1281 nm. In addition, the interaction with EPS inhibits the release of Ag+ in Ag2O/g‐C3N4 by half, thus, the toxicity of metal ions will be alleviated. Meanwhile, EPS can also be degraded by Ag2O/g‐C3N4, indicating that EPS can work as a radical scavenger to protect the algae cells. Without the protection of EPS, 97.8% of algae cells are inactivated after 5 h photocatalysis. Therefore, more attention should be given to the interaction between EPS and photocatalyst to promote the design and application of the photocatalytic. [ABSTRACT FROM AUTHOR]

Phytoplankton community species composition, diversity, biomass, and distribution experience constant changes because of seasonal and temporal variations. This study was done with the aim of describing the response to environmental and seasonal changes of the phytoplankton communities of a tropical estuary in the south of the Colombian Caribbean Sea (Gulf of Urabá) with an emphasis on potential producers of toxin genera. To do these, 15 sites along the Gulf were studied during two cruises in the rainy season and one during the dry season. In each site, water samples from above and below the halocline were collected. Environmental factors such salinity, pH, dissolved oxygen, and nutrient concentration were correlated with diatoms, dinoflagellate, cyanobacteria, and biotoxin producer abundance. The results showed that the number of diatoms was at a maximum of 11,166 cell/L in the fluvial zone. Dinoflagellates were at a maximum of 4250 cell/L in the same zone during the dry season and cyanobacteria blooms during the rainy season. Four genera of potential biotoxin producers were found: Dolichospermum, Prorocentrum, Dinophysis, and Pseudo-nitzschia; this last genus represents 44% of the total diatom abundance during the rainy season with a detectable domoic acid production in a range between 25.54 and 1580.7 pg/mL; this substance can affect different trophic levels in the Gulf, especially mammals due to its non-reversible amnesic effect. Overall, this study shows that the phytoplankton community structure in this tropical stratified estuary presents environment conditions during the rainy season that increase the abundance of phytoplankton that may thrive into blooms. [ABSTRACT FROM AUTHOR]

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Harmful algal blooms (HABs) are a growing problem worldwide, damaging human and ecosystem health. In this study, a novel buoyant-bead flotation (BBF) method using chitosan-coated fly ash cenospheres (CFACs) was developed to remove HABs in freshwater. To achieve a high removal efficiency of harmful algae (Chlorella vulgaris, Scenedesmus quadricauda, and Microcystis aeruginosa), this study investigated the effects of chitosan/fly ash ratios in CFAC composite, CFAC concentration, flotation time, and pH values on the microalgae removal. The optimized ratio of CFACs is 0.1:12, and the optimized CFAC concentration is 0.3–0.7 g L−1. However, the lower or higher ratios (0.1:4, 0.1:8, 0.1:16) result in microalgae reaching a zero-point charge too late or early, which failed to effectively remove HABs with an appropriate coal fly ash dosage. An optimized removal efficiency of 98.50% for Microcystis aeruginosa was reached at pH of 6.0. The optimized efficiency of Scenedesmus quadricauda and Chlorella vulgaris was 99.37% and 91.63%, respectively, at pH of 8.0. At neutral pH conditions, the surface charge of microalgae cells and CFACs are different, promoting aggregate formation. When CFACs were used to remove microalgae, aggregate size significantly influenced removal efficiency. Meanwhile, at the optimized pH and concentration, the removal efficiency of all three algal species exceeded 90.00% in 5 min. The study highlights an efficient and inexpensive method for removing HABs and obtains the optimized operational conditions. [ABSTRACT FROM AUTHOR]

Filamentous cyanobacteria have been observed to become the dominant species in reservoirs, especially in small reservoirs for drinking water supply in southern China. The occurrences of filamentous cyanobacteria blooms in such reservoirs add additional costs for water plants by decreasing the filtration efficiency and the potential of toxin production. To serve the purpose of drinking water supply, the effective risk assessment requires the dynamic pattern of filamentous cyanobacteria. This study seasonally collected samples from 25 reservoirs in Dongguan, one of the most important 'world factories' in China in July, December and March, and investigated the temporal dynamics of phytoplankton, particularly cyanobacteria community. Our investigation showed that filamentous cyanobacteria, Planktothrix sp, Limnothrix sp. and Cylindrospermopsis raciborskii dominated in these reservoirs and climate-related water temperature was the primary factor for the seasonal shift of filamentous cyanobacteria. High abundance of filamentous cyanobacteria occurred in the high water level period with increasing temperature but less relevant with nutrient conditions. Our study observed the seasonal dynamics of filamentous cyanobacteria in tropical urban reservoirs and highlighted the association between temperature and filamentous cyanobacteria. our data and analysis provided an evidence that increased temperature could increase the likelihood of frequency and intensity of filamentous cyanobacteria blooms. In the scenario of global warming, more frequent monitoring of filamentous cyanobacteria and the potential to produce toxin should be considered for water quality and reservoir management. [ABSTRACT FROM AUTHOR]

In this study, biocontrol of harmful effect of cyanobacterial blooms and their toxins by "flocculation-biosorption" was achieved. Five fungal species were isolated from decayed cyanobacterial bloom which are: Aspergillus fumigatus, A. niger, Penicillium, Trichoderma ressei and Mucor rouxii. We chose the last species' pellets because they are the most stable and cocultured with Anabeana sp. (1:5 fungal: cyanobacteria ratio) of dry weight, Harvest Efficacy HE% by fungal pellets started after 12h of co-culturing about (4%) and almost complete harvesting after 48h with (98%), then we add 0.1g of Magnetite nano Fe3o4 to facilitate removing cyanobacterial blooms. Microcystin-LR extracted from Anabaena sp. were purified and collected by preparative high-performance liquid chromatography (HPLC) was 75.1 (µg ml-1), M. rouxii pellet absorbed about 85% of Microcystin-LR after 72 h of incubation at 25 °C. [ABSTRACT FROM AUTHOR]

The dinoflagellate Prorocentrum minimum is a common harmful algal bloom-forming microalgal species worldwide. Because of its harmfulness, accurate detection of P. minimum by convenient method has become a hotspot for field monitoring of this alga. The recently developed nucleic acid isothermal amplification technology is a promising tool for diagnosis and on-site detection of harmful microalgae. In this study, a novel assay based on isothermal amplification referred to recombinase polymerase amplification (RPA) combined with lateral-flow dipstick (LFD) was established for the detection of P. minimum. The specificity of the proposed RPA-LFD was validated by test with control algae. Various RPA conditions including amplification time, amplification temperature, and magnesium ion concentration in the amplification reaction were optimized. The RPA-LFD displayed a stable performance for the detection of P. minimum that is not disturbed by non-specific species. The optimal RPA-LFD could recognize the target algal species from water samples with a cell density of 10 cells mL−1 within 30 min, displaying a detection limit that was 10-fold lower than that of conventional PCR. The practicability of the proposed RPA-LFD was also confirmed by test with natural samples. In conclusion, the developed RPA-LFD is promising for rapid on-site detection of P. minimum in the future. [ABSTRACT FROM AUTHOR]