Impact of harmful algal bloom severity on bacterial communities in a full-scale biological filtration system for drinking water treatment

The occurrence of harmful algal blooms (HABs) in freshwater environments has been expanded worldwide with growing frequency and severity. HABs can pose a threat to public water supplies, raising concerns about safety of treated water. Many studies have provided valuable information about the impacts of HABs and management strategies on the early-stage treatment processes (e.g., pre-oxidation and coagulation/flocculation) in conventional drinking water treatment plants (DWTPs). However, the potential effect of HAB-impacted water in the granular media filtration has not been well studied. Biologically-active filters (BAFs), which are used in drinking water treatment and rely largely on bacterial community interactions, have not been examined during HABs in full-scale DWTPs. In this study, we assessed the bacterial community structure of BAFs, functional profiles, assembly processes, and bio-interactions in the community during both severe and mild HABs. Our findings indicate that bacterial diversity in BAFs significantly decreases during severe HABs due to the predominance of bloom-associated bacteria (e.g., Spingopyxis, Porphyrobacter, and Sphingomonas). The excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC) confirmed that filter influent affected by the severe HAB contained a higher portion of protein-like substances than filter influent samples during a mild bloom. In addition, BAF community functions showed increases in metabolisms associated with intracellular algal organic matter (AOM), such as lipids and amino acids, during severe HABs. Further ecological process and network analyses revealed that severe HAB, accompanied by the abundance of bloom-associated taxa and increased nutrient availability, led to not only strong stochastic processes in the assembly process, but also a bacterial community with lower complexity in BAFs. Overall, this study provides deeper insights into BAF bacterial community structure, function, and assembly in response to HABs.

An assessment of a biosensor system for the quantification of microcystins in freshwater cyanobacterial blooms

Microcystin-producing cyanobacterial blooms are a global issue threatening drinking water supplies and recreation on lakes and beaches. Direct measurement of microcystins is the only way to ensure waters have concentrations below guideline concentrations; however, analyzing water for microcystins takes several hours to days to obtain data. We tested LightDeck Diagnostics' bead beater cell lysis and two versions of the quantification system designed to give microcystin concentrations within 20 min and compared it to the standard freeze-thaw cycle lysis method and ELISA quantification. The bead beater lyser was only 30 % effective at extracting microcystins compared to freeze-thaw. When considering freeze-thaw samples analyzed in 2021, there was good agreement between ELISA and LightDeck version 2 (n = 152; R2 = 0.868), but the LightDeck slightly underestimated microcystins (slope of 0.862). However, we found poor relationships between LightDeck version 2 and ELISA in 2022 (n = 49, slopes 0.60 to 1.6; R2 < 0.6) and LightDeck version 1 (slope = 1.77 but also a high number of less than quantifiable concentrations). After the quantification issues are resolved, combining the LightDeck system with an already-proven rapid lysis method (such as microwaving) will allow beach managers and water treatment operators to make quicker, well-informed decisions.

Detection of harmful algal blooms from satellite-based inherent optical properties of the ocean in Paracas Bay - Peru

Harmful algal bloom (HAB) events in front of Pisco River, inside Paracas Bay and Lagunillas inlet on the southern coast of Peru was identified from a satellite index (IOPifa) generated with daily high-resolution satellite data of phytoplankton absorption (aphy,GIOP) and non-algal detrital material plus CDOM (adCDOM,GIOP) from the Generalized Inherent Optical Properties (GIOP) model of Modis-Aqua, Viirs-Snpp and Viirs-Jpss1 satellites were used. Phytoplankton density field data sampling from HAB's monitoring programs of IMARPE of 2018 and 2019 were used to validate and identify the extent and spatio-temporal variability of these events. The satellite index (IOPifa) identified for Modis-Aqua 9 active HABs, 8 events in final conditions and 6 events that do not represent HAB conditions, while for Viirs-Snpp found 14 active HABs, 7 events in decaying bloom conditions and 13 events that do not represent HABs; and for Viirs-Jpss1 the index identified 7 active events, 14 in final bloom conditions and 6 that do not represent HABs conditions. The one-factor anova model was applied (p-value = 0.32 > 0.05), indicating that there is no evidence of a difference in the population means of the indices for each sensor. Subsequently, the pairwise multiple comparisons analysis with a 95 % confidence level of Tukey's test confirmed that there are no significant differences in the satellite index value, the differences could be associated with the spectral characteristics of the cell density of the species community and the oceanographic and environmental conditions. The spatial overlap between the in situ harmful algal blooms areas and the calculated satellite index, shows the capacity of the IOP satellite data for the HABs detection. However, it was also evidenced that some HAB events with high phytoplankton cell density had low IOPifa values, while other events with lower cell density were easily identified by the satellite index. This would indicate the ability of the ocean inherent optical properties to differentiate the phytoplankton types that cause algal blooms.

Proteome changes in larval zebrafish (Danio rerio) and fathead minnow (Pimephales promelas) exposed to (±) anatoxin-a

Anatoxin-a and its analogues are potent neurotoxins produced by several genera of cyanobacteria. Due in part to its high toxicity and potential presence in drinking water, these toxins pose threats to public health, companion animals and the environment. It primarily exerts toxicity as a cholinergic agonist, with high affinity at neuromuscular junctions, but molecular mechanisms by which it elicits toxicological responses are not fully understood. To advance understanding of this cyanobacteria, proteomic characterization (DIA shotgun proteomics) of two common fish models (zebrafish and fathead minnow) was performed following  (±) anatoxin-a exposure. Specifically, proteome changes were identified and quantified in larval fish exposed for 96 h (0.01-3 mg/L (±) anatoxin-a and caffeine (a methodological positive control) with environmentally relevant treatment levels examined based on environmental exposure distributions of surface water data. Proteomic concentration - response relationships revealed 48 and 29 proteins with concentration - response relationships curves for zebrafish and fathead minnow, respectively. In contrast, the highest number of differentially expressed proteins (DEPs) varied between zebrafish (n = 145) and fathead minnow (n = 300), with only fatheads displaying DEPs at all treatment levels. For both species, genes associated with reproduction were significantly downregulated, with pathways analysis that broadly clustered genes into groups associated with DNA repair mechanisms. Importantly, significant differences in proteome response between the species was also observed, consistent with prior observations of differences in response using both behavioral assays and gene expression, adding further support to model specific differences in organismal sensitivity and/or response. When DEPs were read across from humans to zebrafish, disease ontology enrichment identified diseases associated with cognition and muscle weakness consistent with the prior literature. Our observations highlight limited knowledge of how (±) anatoxin-a, a commonly used synthetic racemate surrogate, elicits responses at a molecular level and advances its toxicological understanding.

Microcystis genotypes in a tropical freshwater lake: Discovery of novel MIB-producing Microcystis with potentially unique synthesis pathway

Harmful algal blooms (HABs) are a threat to freshwater systems over the world due to the production of hepatotoxins like microcystin (MC), and nuisance taste and odour (T&O) compounds like 2-methylisoborneol (MIB). While MCs are known to cause detrimental effects to both water quality and human health, MIB is only reported to cause aesthetical problems. In this study, we investigated a tropical, urban lake that was experiencing persistent MC and MIB events. Although it was dominated by Microcystis blooms, analysis revealed that the toxigenic Microcystis were not the only species driving the MC concentrations. Additionally, there was also a lack of causative species for the MIB events. Through isolation, we have identified three toxigenic Microcystis found to produce four different variants of MCs, and two novel non-toxigenic Microcystis that were capable of producing MIB. The ability to produce MIB had never been previously reported for this species. Compared to other major producers such as Planktothricoides sp. and Streptomyces sp., the MIB synthase genes of our Microcystis sp. strains were partial, illustrating the possibility of unique synthesis pathways. The Microcystis sp. strains were found to produce about 2.77-5.22 fg MIB cell-1, with a majority of the contents (70-80 %) existing in the extracellular phase. Correlation analysis of field study indicated that phosphorus limitation may have an indirect effect on non-toxigenic Microcystis abundance and proportion by influencing the toxigenic genotype, suggesting that current measures to control HABs may favour the proliferation of the non-toxigenic Microcystis. The potential for Microcystis sp. to produce MIB through unique synthesis pathway, coupled with the potential dominance of non-toxigenic genotypes in Microcystis blooms, signals the possibility that non-toxigenic Microcystis should be monitored as well.

Managing a cyanobacteria harmful algae bloom "hotspot" in the Sacramento - San Joaquin Delta, California

Cyanobacterial harmful algal blooms (CHABs) have become a persistent seasonal problem in the upper San Francisco Estuary, California also known as the Sacramento-San Joaquin Delta (Delta). The Delta is comprised of a complex network of open water bodies, channels, and sloughs. The terminus of the Stockton Channel is an area identified as a CHAB "hotspot." As CHABs increase in severity, there is an urgent need to better understand CHAB drivers to identify and implement mitigation measures that can be used in an estuarine complex like the Delta. We investigated water quality conditions and nutrient dynamics in the Stockton Channel by measuring nutrients in the water column, sediments, and pore waters. In situ nutrient addition bioassay experiments were used to assess the effects of nutrient enrichment on total algal/cyanobacterial growth and pigment concentrations. In both June and September, relative to unamended controls, total chlorophyll and cyanobacterial pigment concentrations were unaffected by nutrient additions; hence, the study area showed signs of classical hypereutrophication, with ambient nitrogen and phosphorus present in excess of algal growth requirements. A cyanobacterial bloom, dominated by Microcystis spp. was present throughout the study area but was most severe and persistent at the shallowest site at the channel terminus. At this site, Microcystis spp. created water quality conditions that allowed for a prolonged bloom from June through September. While targeted nutrient reductions are recommended for long term mitigation, on a shorter timescale, our findings suggest that physical/mechanical controls are the more promising alternative approaches to reduce the severity of CHABs in the terminus of the Stockton Channel.

The influence of the toxin-producing dinoflagellate, Alexandrium catenella, on feeding, reproduction and toxin retention in Calanus helgolandicus

Copepods of the genus Calanus dominate the biomass of pelagic ecosystems from the Mediterranean Sea up into the Arctic Ocean and form an important link between phytoplankton and higher trophic levels. Impacts from toxin-producing harmful algae (HA) have been recorded throughout this region over the last 50 years, with potentially negative effects on Calanus spp. populations and the ecosystem functions and services they provide. Here we examine how ingestion, egg-production and egg-viability in Calanus helgolandicus are affected by the relative abundance of the toxin-producing dinoflagellate Alexandrium catenella in their diet. Our four-day experiments demonstrate that the ingestion rate of C. helgolandicus declined significantly as the percentage of toxin-producing A. catenella within their diet increased, whereas egg production and egg viability were unaffected. Toxin profile concentrations for A. catenella are presented alongside body toxin-loads in C. helgolandicus after 4 days of feeding on these cells. The body toxin concentrations of C. helgolandicus were 3.6-356.6 pg STX diHCl eq. copepod-1, approximately 0.02-3.3 % of the toxins ingested. Our work suggests that the effects of exposure to A. catenella may be negligible in the short-term but could manifest if bloom conditions persist for longer than our experimental duration.

Two duckweed species exhibit variable tolerance to microcystin-LR exposure across genotypic lineages

Cyanotoxins produced by harmful cyanobacteria blooms can damage freshwater ecosystems and threaten human health. Floating macrophytes may be used as a means of biocontrol by limiting light and resources available to cyanobacteria. However, genetic variation in macrophyte sensitivity to cyanotoxins could influence their suitability as biocontrol agents. We investigated the influence of such intraspecific variation on the response of two rapidly growing duckweed species, Lemna minor and Spirodela polyrhiza, often used in nutrient and metal bioremediation. We assessed two biomarkers related to productivity (biomass and chlorophyll A production) and two related to fitness measures (population size and growth rate). Fifteen genetic lineages of each species were grown in media containing common cyanotoxin microcystin-LR at ecologically relevant concentrations or control media for a period of twelve days. Genotype identity had a strong impact on all biomarker responses. Microcystin concentration slightly increased the final population sizes of both macrophyte species with a marginal effect on growth rate of L. minor and the chlorophyll A production of S. polyrhiza, but overall these species were very tolerant of microcystin. The strong tolerance supports the potential use of these plants as bioremediators of cyanobacterial blooms. However, differential impact of microcystin exposure discovered in single lineage models among genotypes indicates a potential for cyanotoxins to act as selective forces, necessitating attention to genotype selection for bioremediation.

Division time (td) for in situ growth measurements demonstrates thermal ecotypes of Karlodinium veneficum

The toxic dinoflagellate Karlodinium veneficum forms fish killing blooms in temperate estuaries worldwide. These blooms have variable toxicity which may be related to bloom stage and in situ growth rates of the constituent K. veneficum cells. Measurement of in situ growth rates is challenging and methods such as the mitotic index technique require knowledge of the dynamics of cell division. In order to better understand these dynamics, we determined the duration of cell division (td) in four geographically distinct laboratory strains of K. veneficum at three different environmentally relevant temperatures. The results demonstrated that the td value for each strain, growing at strain-specific optimal temperatures, was 1.6 ± 0.1 h. This value corresponded to a range of growth rates from 0.17 ± 0.08 d-1 to 0.62 ± 0.07 d-1. Equivalent values of td spread across four geographically distinct laboratory strains and a nearly fourfold range of growth rates implies that 1.6 h represents the td value of K. veneficum. Additionally, temperature conditions yielding this value for td and the highest growth rates varied among strains, indicating cold-adapted (Norway), warm-adapted (Florida, USA), and eurythermally-adapted (Maryland, USA) strains. These differences have been apparently retained in culture over many years, indicating a conserved genetic basis that suggests distinct thermal ecotypes of the morphospecies K. veneficum. This knowledge together with the first estimate of td for K. veneficum will be useful in future field studies aimed at correlating bloom toxicity with in situ growth rate using the mitotic index technique.

Gambierdiscus species diversity and community structure in St. Thomas, USVI and the Florida Keys, USA

Ciguatera Poisoning (CP) is a widespread and complex poisoning syndrome caused by the consumption of fish or invertebrates contaminated with a suite of potent neurotoxins collectively known as ciguatoxins (CTXs), which are produced by certain benthic dinoflagellates species in the genera Gambierdiscus and Fukuyoa. Due to the complex nature of this HAB problem, along with a poor understanding of toxin production and entry in the coral reef food web, the development of monitoring, management, and forecasting approaches for CP has lagged behind those available for other HAB syndromes. Over the past two decades, renewed research on the taxonomy, physiology, and toxicology of CP-causing dinoflagellates has advanced our understanding of the species diversity that exists within these genera, including identification of highly toxic species (so called "superbugs") that likely contribute disproportionately to ciguatoxins entering coral reef food webs. The recent development of approaches for molecular analysis of field samples now provide the means to investigate in situ community composition, enabling characterization of spatio-temporal species dynamics, linkages between toxic species abundance and toxin flux, and the risk of ciguatoxin prevalence in fish. In this study we used species-specific fluorescent in situ hybridization (FISH) probes to investigate Gambierdiscus species composition and dynamics in St. Thomas (USVI) and the Florida Keys (USA) over multiple years (2018-2020). Within each location, samples were collected seasonally from several sites comprising varying depths, habitats, and algal substrates to characterize community structure over small spatial scales and across different host macrophytes. This approach enabled the quantitative determination of communities over spatiotemporal gradients, as well as the selective enumeration of species known to exhibit high toxicity, such as Gambierdiscus silvae. The investigation found differing community structure between St. Thomas and Florida Keys sites, driven in part by differences in the distribution of toxin-producing species G. silvae and G. belizeanus, which were present throughout sampling sites in St. Thomas but scarce or absent in the Florida Keys. This finding is significant given the high toxicity of G. silvae, and may help explain differences in fish toxicity and CP incidence between St. Thomas and Florida. Intrasite comparisons along a depth gradient found higher concentrations of Gambierdiscus spp. at deeper locations. Among the macrophytes sampled, Dictyota may be a likely vector for toxin transfer based on their widespread distribution, apparent colonization by G. silvae, and palatability to at least some herbivore grazers. Given its ubiquity throughout both study regions and sites, this taxa may also serve as a refuge, accumulating high concentrations of Gambierdiscus and other benthic dinoflagellates, which in turn can serve as source populations for highly palatable and ephemeral habitats nearby, such as turf algae. These studies further demonstrate the successful application of FISH probes in examining biogeographic structuring of Gambierdiscus communities, targeting individual toxin-producing species, and characterizing species-level dynamics that are needed to describe and model ecological drivers of species abundance and toxicity.

Hydrogen peroxide as a mitigation against Microcystis sp. bloom

Microcystis sp. is a harmful cyanobacterial species commonly seen in earthen ponds. The overgrowth of these algae can lead to fluctuations in water parameters, including DO and pH. Also, the microcystins produced by these algae are toxic to aquatic animals. This study applied hydrogen peroxide (7 mg/L) to treat Microcystis sp. in a laboratory setting and in three earthen pond trials. In the lab we observed a 64.7% decline in Microcystis sp. And in our earthen pond field experiments we measured, on average, 43% reductions in Microcystis sp. cell counts within one hour. The treatment was found to eliminate specifically Microcystis sp. and did not reduce the cell count of the other algae species in the pond. A shift of the algae community towards the beneficial algae was also found post-treatment. Lastly, during the pond trials, the gill status of Tilapia and Giant tiger prawn were not affected by the H2O2 treatment suggesting this may be a good mitigation strategy for reducing cyanobacteria in pond aquaculture.

Mass mortality event of the giant barrel sponge Xestospongia sp.: population dynamics and size distribution in Koh Phangan, Gulf of Thailand

Marine sponges are prominent organisms of the benthic coral reef fauna, providing important ecosystem services. While there have been increasing reports that sponges are becoming one of the dominant benthic organisms in some locations and ecoregions (e.g. Caribbean), they can be impacted by changing environmental conditions. This study presents the first documentation of a mass mortality event of the barrel sponge Xestospongia sp. in the lower Gulf of Thailand and its consequences on population dynamics and size distribution. Two anthropogenic impacted reefs (Haad Khom and Mae Haad) of the island Koh Phangan and two anthropogenic non-impacted reefs of the islands Koh Yippon and Hin Yippon within the Mu Ko Ang Thong Marine National Park were surveyed in the years 2015 and 2016. The results showed a strong shift in population densities at Koh Phangan. Fatal "bleaching" ending up in mass mortality was observed for these reefs in 2015. Xestospongia sp. abundance decreased from 2015 to 2016 by 80.6% at Haad Khom and by 98.4% at Mae Haad. Sponges of all sizes were affected, and mortality occurred regardless of the survey depth (4 and 6 m). However, Xestospongia population densities in the Marine Park were at a constant level during the surveys. The abundances in 2015 were 65% higher at the Marine Park than at Koh Phangan and 92% higher in 2016. The most likely causes of the mass mortality event was a local harmful algal bloom event, pathogens, undetected local higher water temperatures, or a combination of these factors, whereas sea surface temperature analyses showed no marine heatwave during the observed mass mortality event in 2015. Considering the ecological importance of sponges such as Xestospongia sp., long-term monitoring of reefs and their environmental parameters should be implemented to prevent such mass die-offs.

Human fatalities related to a Phaeocystis harmful algal bloom in the North Sea

On May 11, 2020, five surfers drowned after asphyxiation in a massive foam bank near the Dutch coast. We present a detailed account of the event and an examination of factors that govern local foam events, that are traditionally caused by Phaeocystis globosa (Prymnesiophyceae). The data support the hypothesis that the foam originated from a Phaeocystis bloom which if correct would make this accident the first report of human fatalities due to a harmful algal bloom in The Netherlands, and the first globally due to a Phaeocystis bloom. The rarity of massive foam banks and the absence of local real-time plankton monitoring makes it difficult to accurately predict dangerous situations as in 2020. As a prevention, surfers and other water sportsmen need to apply good seamanship during stormy and foamy conditions.

Diversity and toxicity of the planktonic diatom genus Pseudo-nitzschia from coastal and offshore waters of the Southeast Pacific, including Pseudo-nitzschia dampieri sp. nov

To expand knowledge of Pseudo-nitzschia species in the Southeast Pacific, we isolated specimens from coastal waters of central Chile (36°S-30°S), the Gulf of Corcovado, and the oceanic Robinson Crusoe Island (700 km offshore) and grew them into monoclonal strains. A total of 123 Pseudo-nitzschia strains were identified to 11 species based on sequencing of the ITS region of the nuclear rDNA and on ultrastructural and morphometric analyses of the frustule in selected representatives of each clade: P. australis, P. bucculenta, P. cf. chiniana, P. cf. decipiens, P. fraudulenta, P. hasleana, P. multistriata, P. plurisecta, P. cf. sabit, the new species P. dampieri sp. nov., and one undescribed species. Partial 18S and 28S rDNA sequences, including the hypervariable V4 and D1-D3 regions used for barcoding, were gathered from representative strains of each species to facilitate future metabarcoding studies. Results showed different levels of genetic, and at times ultrastructural, diversity among the above-mentioned entities, suggesting morphological variants (P. bucculenta), rapidly radiating complexes with ill-defined species boundaries (P. cf. decipiens and P. cf. sabit), and the presence of new species (P. dampieri sp. nov., Pseudo-nitzschia sp. 1, and probably P. cf. chiniana). Domoic acid (DA) was detected in 18 out of 82 strains tested, including those of P. australis, P. plurisecta, and P. multistriata. Toxicity varied among species mostly corresponding to expectations from previous reports, with the prominent exception of P. fraudulenta; DA was not detected in any of its 10 strains tested. In conclusion, a high diversity of Pseudo-nitzschia exists in Chilean waters, particularly offshore.

Does prey availability influence the detection of Dinophysis spp. by the imaging FlowCytobot?

The Imaging FlowCytobot (IFCB) is a field-deployable imaging-in-flow cytometer that is increasingly being used to monitor harmful algae. The IFCB acquires images of suspended particles based on their chlorophyll-a fluorescence and/or the amount of light they scatter (side scattering). The present study hypothesized that fluorescence-based image acquisition would undercount Dinophysis spp., a genus of non-constitutive mixotrophs, when prey is limited. This is because Dinophysis spp. acquire plastids via ingestion of their ciliate prey Mesodinium spp., and lose photosynthetic capacity and autofluorescence in the absence of prey. Even small blooms of Dinophysis spp. can be highly toxic and result in diarrhetic shellfish poisoning (DSP), highlighting the importance of accurately detecting low abundances. To explore this, laboratory experiments were conducted to determine optimal IFCB settings for a fed culture of Dinophysis acuminata, and an existing time series of IFCB observations collected in Puget Sound (Washington, U.S.A) was used to compare Dinophysis spp. abundance estimates from samples triggered via side scattering versus fluorescence in relation to Mesodinium spp. abundance. This study introduces a quantitative approach for optimizing the detection of target harmful algae which can be repeated across multiple IFCBs and demonstrates the effects of IFCB calibration on Dinophysis spp. detection. The laboratory experiments showed that IFCB settings for fluorescence-based image acquisition need to be fairly sensitive to accurately detect D. acuminata cells. A poorly calibrated IFCB can miss a significant proportion of D. acuminata abundance whatever the method used to trigger the image acquisition. Field results demonstrated that the physiological status of Dinophysis spp. can influence their detection by the IFCB when triggering on fluorescence. This was observed during a 7-day period when the IFCB failed to detect Dinophysis spp. cells when triggering on fluorescence while cells were still detected using the side scattering triggering method as well as observed by microscopy. During this period, Mesodinium spp. was not detected, IFCB-derived autofluorescence level of individual cells of Dinophysis spp. was low, and less than 50 % of Dinophysis spp. cells exhibited autofluorescence under the microscope. Together, this indicates that the unique feeding ecology of Dinophysis spp. may affect their detection by the IFCB when cells are starved.

Multi-omics analysis reveals the molecular response to heat stress in a "red tide" dinoflagellate

BACKGROUND

"Red tides" are harmful algal blooms caused by dinoflagellate microalgae that accumulate toxins lethal to other organisms, including humans via consumption of contaminated seafood. These algal blooms are driven by a combination of environmental factors including nutrient enrichment, particularly in warm waters, and are increasingly frequent. The molecular, regulatory, and evolutionary mechanisms that underlie the heat stress response in these harmful bloom-forming algal species remain little understood, due in part to the limited genomic resources from dinoflagellates, complicated by the large sizes of genomes, exhibiting features atypical of eukaryotes.

RESULTS

We present the de novo assembled genome (~ 4.75 Gbp with 85,849 protein-coding genes), transcriptome, proteome, and metabolome from Prorocentrum cordatum, a globally abundant, bloom-forming dinoflagellate. Using axenic algal cultures, we study the molecular mechanisms that underpin the algal response to heat stress, which is relevant to current ocean warming trends. We present the first evidence of a complementary interplay between RNA editing and exon usage that regulates the expression and functional diversity of biomolecules, reflected by reduction in photosynthesis, central metabolism, and protein synthesis. These results reveal genomic signatures and post-transcriptional regulation for the first time in a pelagic dinoflagellate.

CONCLUSIONS

Our multi-omics analyses uncover the molecular response to heat stress in an important bloom-forming algal species, which is driven by complex gene structures in a large, high-G+C genome, combined with multi-level transcriptional regulation. The dynamics and interplay of molecular regulatory mechanisms may explain in part how dinoflagellates diversified to become some of the most ecologically successful organisms on Earth.

Metabolomics and lipidomics reveal the effects of the toxic dinoflagellate Alexandrium catenella on immune cells of the blue mussel, Mytilus edulis

The increasing occurrence of harmful algal blooms, mostly of the dinoflagellate Alexandrium catenella in Canada, profoundly disrupts mussel aquaculture. These filter-feeding shellfish feed on A. catenella and accumulate paralytic shellfish toxins, such as saxitoxin, in tissues, making them unsafe for human consumption. Algal toxins also have detrimental effects upon several physiological functions in mussels, but particularly on the activity of hemocytes - the mussel immune cells. The objective of this work was to determine the effects of experimental exposure to A. catenella upon hemocyte metabolism and activity in the blue mussel, Mytilus edulis. To do so, mussels were exposed to cultures of the toxic dinoflagellate A. catenella for 120 h. The resulting mussel saxitoxin load had measurable effects upon survival of hemocytes and induced a stress response measured as increased ROS production. The neutral lipid fraction of mussel hemocytes decreased two-fold, suggesting a differential use of lipids. Metabolomic 1H nuclear magnetic resonance (NMR) analysis showed that A. catenella modified the energy metabolism of hemocytes as well as hemocyte osmolyte composition. The modified energy metabolism was reenforced by contrasting plasma metabolomes between control and exposed mussels, suggesting that the blue mussel may reduce feed assimilation when exposed to A. catenella.

Mapping harmful microalgal species by eDNA monitoring: A large-scale survey across the southwestern South China Sea

A large-scale sampling was undertaken during a research cruise across the South China Sea in August 2016, covering an area of about 100,000 km2 to investigate the molecular diversity and distributions of micro-eukaryotic protists, with a focus on the potentially harmful microalgal (HAB) species along the east coast of Peninsular Malaysia. Environmental DNAs from 30 stations were extracted and DNA metabarcoding targeting the V4 and V9 markers in the 18S rDNA was performed. Many protistan molecular units, including previously unreported HAB taxa, were discovered for the first time in the water. Our findings also revealed interesting spatial distribution patterns, with a marked signal of compositional turnover between latitudinal regimes of water masses, where dinophytes and diatom compositions were among the most strongly enhanced at the fronts, leading to distinct niches. Our results further confirmed the widespread distribution of HAB species, such as the toxigenic Alexandrium tamiyavaichii and Pseudo-nitzschia species, and the fish-killing Margalefidinium polykrikoides and Karlodinium veneficum. The molecular information obtained from this study provides an updated HAB species inventory and a toolset that could facilitate existing HAB monitoring schemes in the region to better inform management decisions.

Ground-based remote sensing provides alternative to satellites for monitoring cyanobacteria in small lakes

Cyanobacteria are the most prevalent bloom-forming harmful algae in freshwater systems around the world. Adequate sampling of affected systems is limited spatially, temporally, and fiscally. Remote sensing using space- or ground-based systems in large water bodies at spatial and temporal scales that are cost-prohibitive to standard water quality monitoring has proven to be useful in detecting and quantifying cyanobacterial harmful algal blooms. This study aimed to identify a regional 'universal' multispectral reflectance model that could be used for rapid, remote detection and quantification of cyanoHABs in small- to medium-sized productive reservoirs, such as those typical of Oklahoma, USA. We aimed to include these small waterbodies in our study as they are typically overlooked in larger, continental wide studies, yet are widely distributed and used for recreation and drinking water supply. We used Landsat satellite reflectance and in-situ pigment data spanning 16 years from 38 reservoirs in Oklahoma to construct empirical linear models for predicting concentrations of chlorophyll-a and phycocyanin, two key algal pigments commonly used for assessing total and cyanobacterial algal abundances, respectively. We also used ground-based hyperspectral reflectance and in-situ pigment data from seven reservoirs across five years in Oklahoma to build multispectral models predicting algal pigments from newly defined reflectance bands. Our Oklahoma-derived Landsat- and ground-based models outperformed established reflectance-pigment models on Oklahoma reservoirs. Importantly, our results demonstrate that ground-based multispectral models were far superior to Landsat-based models and the Cyanobacteria Index (CI) for detecting cyanoHABs in highly productive, small- to mid-sized reservoirs in Oklahoma, providing a valuable tool for water management and public health. While satellite-based remote sensing approaches have proven effective for relatively large systems, our novel results indicate that ground-based remote sensing may offer better cyanoHAB monitoring for small or highly dendritic turbid lakes, such as those throughout the southern Great Plains, and thus prove beneficial to efforts aimed at minimizing public health risks associated with cyanoHABs in supply and recreational waters.

The Pacific Northwest Harmful Algal Blooms Bulletin

A bulletin communicating risk of toxic Pseudo-nitzschia blooms to shellfish harvest along the open coast of the Pacific Northwest region of the United States (the northeast Pacific Ocean spanning Washington and Oregon) is discussed. This Pacific Northwest Harmful Algal Blooms (PNW HAB) Bulletin is designed for shellfish managers with a focus on the razor clam fishery, but may also be informative to managers of the Dungeness crab fishery since domoic acid accumulation in crabs tends to lag accumulation in razor clams by a couple of weeks. The Bulletin complements beach phytoplankton monitoring programs by alerting coastal shellfish managers about adverse environmental conditions that could be conducive to a toxic Pseudo-nitzschia bloom. Beach monitoring programs are effective at determining when toxins have arrived at shellfish beaches, but a risk forecast based on near real-time biophysical information can provide managers with additional forewarning about potential future toxin outbreaks. Here, the approaches taken in constructing the risk forecasts, along with the reasoning and research behind them are presented. Updates to a historical PNW HAB Bulletin are described, as are the current workflow and the individual components of the updated Bulletin. Some successes and failures realized throughout the process are also pointed out for the benefit of the broader community. A self-assessment suggests that when the necessary data sources are available, the PNW HAB Bulletin provides an accurate forecast of risk associated with toxic Pseudo-nitzschia blooms. The Bulletin has proven beneficial to coastal shellfish managers by better informing decisions on sample collection, and harvest limits, openings, extensions, and closures.

Thecal plate morphology, molecular phylogeny, and toxin analyses reveal two novel species of Alexandrium (Dinophyceae) and their potential for toxin production

This study describes two novel species of marine dinophytes in the genus Alexandrium. Morphological characteristics and phylogenetic analyses support the placement of the new taxa, herein designated as Alexandrium limii sp. nov. and A. ogatae sp. nov. Alexandrium limii, a species closely related to A. taylorii, is distinguished by having a shorter 2'/4' suture length, narrower plates 1' and 6'', with larger length: width ratios, and by the position of the ventral pore (Vp). Alexandrium ogatae is distinguishable with its metasert plate 1' having almost parallel lateral margins, and by lacking a Vp. Production of paralytic shellfish toxins (PSTs), cycloimines, and goniodomins (GDs) in clonal cultures of A. ogatae, A. limii, and A. taylorii were examined analytically and the results showed that all strains contained GDs, with GDA as major variants (6-14 pg cell-1) for all strains except the Japanese strain of A. limii, which exclusively had a desmethyl variant of GDA (1.4-7.3 pg cell-1). None of the strains contained detectable levels of PSTs and cycloimines.

Efficacy of algaecides for the proactive treatment of overwintering cyanobacteria

Once established within a water resource, harmful algal blooms (HABs) can occur seasonally with an intense and rapid onset, giving water resource managers limited time to respond to lessen risks. An attractive strategy to decrease human, ecological, and economic risks from HABs is to implement proactive algaecide treatments applied to overwintering cyanobacteria (i.e., akinetes and quiescent vegetative cells) in sediments prior to the formation of a HAB; however, this approach is novel and very limited efficacy data exist. Therefore, the specific objectives of this research were to 1) evaluate copper- and peroxide-based algaecides, applied as single and repeat treatments at the bench scale, to identify effective proactive treatments, and 2) compare correlations between cell density and other response measurements (i.e., in vivo chlorophyll a and phycocyanin concentrations and percent benthic coverage), to identify informative metrics to assess overwintering cyanobacteria responses. Twelve treatment scenarios using copper- and peroxide-based algaecides were applied to sediments containing overwintering cyanobacteria prior to a 14 d incubation under favorable growth conditions. Responses of cyanobacteria in the planktonic (i.e., cell density, in vivo chlorophyll a and phycocyanin concentrations) and benthic (percent coverage) phases after a 14 d incubation were evaluated in treatments and controls. The HAB-forming cyanobacteria present after a 14 d incubation were: Aphanizomenon, Dolichospermum, Microcystis, Nostoc, and Planktonthrix. Successive treatments of copper sulfate (CuSulfate) followed by sodium carbonate peroxyhydrate (PeroxiSolid) (second algaecide applied after 24 h) as well as repeat applications of a single algaecide, PeroxiSolid (second treatment applied after 24 h) resulted in statistically significant (p ≤ 0.05; α = 0.05) declines in cell density relative to untreated controls. Planktonic cyanobacteria responses measured in terms of phycocyanin concentrations were strongly correlated with cyanobacteria density measurements (Pearson's correlation coefficient (r) = 0.89). Chlorophyll a concentrations and percent benthic coverage did not correlate with planktonic cyanobacteria density measurements (r = 0.37 and -0.49, respectively) and therefore, were unreliable metrics for cyanobacterial responses in this study. These data provide initial evidence of the efficacy of algaecides for treating overwintering cells in sediments and contribute to our overarching hypothesis that proactive treatments may delay the onset and intensity of HABs in impacted waterbodies.

Effects of developmental exposure to neurotoxic algal metabolites on predator-prey interactions in larval Pimephales promelas

Harmful algal blooms are a growing environmental concern in aquatic systems. Although it is known that some of the secondary metabolites produced by cyanobacteria can alter predator-prey dynamics in aquatic communities by reducing foraging and/or predator evasion success, the mechanisms underpinning such responses are largely unknown. In this study, we examined the effects of a potent algal neurotoxin, β-N-methylamino-L-alanine (BMAA), on the development and behavior of larval Fathead Minnows, Pimephales promelas, during predator-prey interactions. We exposed eggs and larvae to environmentally relevant concentrations of BMAA for 21 days, then tested subjects in prey-capture and predator-evasion assays designed to isolate the effects of exposure at sequential points of the stimulus-response pathway. Exposure was associated with changes in the ability of larvae to detect and respond to environmental stimuli (i.e., a live prey item and a simulated vibrational predator), as well as changes in behavior and locomotor performance during the response. Our findings suggest that chronic exposure to neurodegenerative cyanotoxins could alter the outcomes of predator-prey interactions in natural systems by impairing an animal's ability to perceive, process, and respond to relevant biotic stimuli.

A comparison between the FlowCam 8100, microscopy, and sandwich hybridization assay for quantifying abundances of the saxitoxin-producing dinoflagellate, Alexandrium catenella

Light microscopy, FlowCam, and sandwich hybridization assay (SHA) are three approaches that facilitate the monitoring of harmful algal bloom (HAB) forming phytoplankton. Yet, cross-comparisons among these techniques have not been conducted. This study addressed that gap using the saxitoxin-producing 'red tide' dinoflagellate Alexandrium catenella, a species responsible for blooms and paralytic shellfish poisoning worldwide. To achieve this goal, the dynamic ranges of each technique were compared using A. catenella cultures spanning low (pre-bloom), moderate (bloom), and high (dense bloom) levels. To assess field detection, water samples containing very low (<3 cells mL^-1) A. catenella levels were collected from Long Island Sound, USA (Jun-Aug 2021) and evaluated using each method. Field samples were also spiked with A. catenella to high (160 cells mL^-1) or low (40 cells mL^-1) concentrations. In general, microscopy, FlowCam, and SHA returned comparable A. catenella cell concentrations for all tests. Mean cell concentrations from laboratory intercalibration experiments were not significantly different for any method or concentration (ANOVA, p > 0.05). However, relative to microscopy at times SHA produced non-detect signals <2 cells mL^-1 in field samples and the FlowCam slightly underestimated cell concentrations when A. catenella abundances were high in laboratory and field samples. Mean cell concentrations of spike experiments were not significantly different for any test date, sampling location, or method, despite variability among methods within the high concentration treatment (ANOVA, p > 0.05 for all treatments). Findings are relevant to HAB researchers, managers, and public health officials because they help reconcile disparate cell abundance datasets that inform numerical models and enhance HAB monitoring and prediction. Results are also likely broadly applicable to several HAB species.

On the conditions promoting Pseudo-nitzschia spp. blooms in the eastern English Channel and southern North Sea

This study investigated the drivers of the blooms of Pseudo-nitzschia seriata and Pseudo-nitzschia delicatissima complexes in the eastern English Channel and southern North Sea. Phytoplankton data series acquired from 1992 to 2020 were analyzed with a multivariate statistical approach based on Hutchinson's niche concept. P. seriata and P. delicatissima complexes were found to be typically present year round, but they bloomed at different periods because they occupied different realized ecological niches. P. delicatissima complex occupied a more marginal niche and was less tolerant than P. seriata complex. P. delicatissima complex typically bloomed in April-May at the same time as Phaeocystis globosa while P. seriata complex blooms were more frequently observed in June during the decline of low intensity P. globosa blooms. P. delicatissima and P. seriata complexes were both favored by low-silicate environments and relatively low turbulence but they responded differently to water temperature, light, ammonium, phosphate and nitrite + nitrate conditions. Niche shifts and biotic interactions played important roles in the control of the blooms of P. delicatissima and P. seriata complexes. The two complexes occupied different sub-niches during their respective low abundance and bloom periods. The phytoplankton community structure and the number of other taxa presenting a niche overlapping the niches of P. delicatissima and P. seriata complexes also differed between these periods. P. globosa was the taxa contributing the most to the dissimilarity in community structure. P. globosa interacted positively with P. delicatissima complex and negatively with P. seriata complex.

Monitoring bacterial composition and assemblage in the Gulf of Corcovado, southern Chile: Bacteria associated with harmful algae

Harmful Algal Blooms (HABs) have caused damage to the marine environment in Isla San Pedro in the Gulf of Corcovado, Chile. While rising water temperature and artificial eutrophication are the most discussed topics as a cause, marine bacteria is a recent attractive parameter as an algal bloom driver. This study monitored algal and bacterial compositions in the water of Isla San Pedro for one year using microscopy and 16S rRNA metabarcoding analysis, along with physicochemical parameters. The collected data were analyzed with various statistical tools to understand how the particle-associated bacteria (PA) and the free-living (FL) bacteria were possibly involved in algal blooms. Both FL and PA fractions maintained a stable bacterial composition: the FL fraction was dominated by Proteobacteria (α-Proteobacteria and γ-Proteobacteria), and Cyanobacteria dominated the PA fraction. The two fractions contained equivalent bacterial taxonomic richness (c.a. 8,000 Operational Taxonomic Units) and shared more than 50% of OTU; however, roughly 20% was exclusive to each fraction. The four most abundant algal genera in the Isla San Pedro water were Thalassiosira, Skeletonema, Chaetoceros, and Pseudo-nitzchia. Statistical analysis identified that the bacterial species Polycyclovorans algicola was correlated with Pseudo-nitzschia spp., and our monitoring data recorded a sudden increase of particle-associated Polycyclovorans algicola shortly after the increase of Pseudo-nitzschia, suggesting that P. algicola may have regression effect on Pseudo-nitzschia spp. The study also investigated the physicochemical parameter effect on algal-bacterial interactions. Oxygen concentration and chlorophyll-a showed a strong correlation with both FL and PA bacteria despite their assemblage differences, suggesting that the two groups had different mechanisms for interacting with algal species.

Cyanotoxins accumulate in Lake St. Clair fish yet their fillets are safe to eat

Consuming fish exposed to cyanobacterial harmful algal blooms (HABs) may be a major route of microcystin toxin exposure to humans. However, it remains unknown whether fish can accumulate and retain microcystins temporally in waterbodies with recurring seasonal HABs, particularly before and after a HAB event when fishing is active. We conducted a field study on Largemouth Bass, Northern Pike, Smallmouth Bass, Rock Bass, Walleye, White Bass, and Yellow Perch to assess the human health risks to microcystin toxicity via fish consumption. We collected 124 fish in 2016 and 2018 from Lake St. Clair, a large freshwater ecosystem in the North American Great Lakes that is actively fished pre- and post-HAB periods. Muscles were analyzed using the 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) Lemieux Oxidation method for total microcystins, which was used to perform a human health risk assessment for comparison against fish consumption advisory benchmarks available for Lake St. Clair. From this collection 35 fish livers were additionally extracted to confirm the presence of microcystins. Microcystins were detected in all livers at widely varying concentrations (1-1500 ng g^-1 ww), suggesting HABs are an underappreciated and pervasive stressor to fish populations. Conversely, microcystin levels were consistently low in muscles (0-15 ng g^-1 ww) and presented negligible risk, empirically supporting that fillets may be safely consumed before and after HAB events following fish consumption advisories.

Mechanisms of Phaeocystis globosa blooms in the Beibu Gulf revealed by metatranscriptome analysis

The haptophyceae Phaeocystis globosa is a species responsible for harmful algal blooms in the global ocean, forming blooms in the Beibu Gulf annually since 2011. This species can alternate between solitary free-living cells and colonies. Colonies are the dominant morphotype during blooms. To date, the underlying mechanism of P. globosa blooms in the Beibu Gulf is poorly understood. After combining results of ecological surveys, laboratory studies, and metatranscriptome and bioinformatics analyses, it was found that low temperatures, high nitrate, and low organic phosphorus induced P. globosa blooms in the Beibu Gulf. Additionally, the unique genetic and physiological characteristics that allow P. globosa to stand out as a dominant species in such an environment include (1) several genes encoding high-affinity nitrate transport proteins that could be highly expressed under sufficient nitrate conditions; (2) energy metabolism genes involved in photosynthesis and oxidative phosphorylation that were actively expressed at low temperatures to carry out carbon and energy reversion and produce sufficient ATP for various life activities, individually; (3) abundant glycan synthesis genes that were highly expressed at low temperatures, thus synthesizing large quantities of proteoglycans to construct the mucilaginous envelope forming the colony; (4) cells in colonies exhibited active gene expression in DNA replication contributing to a faster growth rate, which could help P. globosa occupy niches quickly; and (5) the energy and material expenditure was redistributed in colonial cells accompanied with chitin filaments and flagella degraded, more expenditure was used for the synthesis of the mucilaginous envelope and the rapid proliferation.

Harmful cyanobacteria-diatom/dinoflagellate blooms and their cyanotoxins in freshwaters: A nonnegligible chronic health and ecological hazard

Human and ecological health depends on the vitality of freshwater systems, but these are increasingly threatened by cyanotoxins released from harmful algal blooms (HABs). Periodic cyanotoxin production, although undesirable, may be tolerable when there is enough time for cyanotoxins to degrade and dissipate in the environment, but the year-round presence of these toxins will be a chronic health for humans and ecosystems. The purpose of this critical review is to document the seasonal shifts of algal species and their ecophysiological acclimatation to dynamic environmental conditions. We discuss how these conditions will create successive occurrences of algal blooms and the release of cyanotoxins into freshwater. We first review the most common cyanotoxins, and evaluate the multiple ecological roles and physiological functions of these toxins for algae. Then, the annual recurring patterns HABs are considered in the context of global change, which demonstrates the capacity for algal blooms to shift from seasonal to year-round growth regimes that are driven by abiotic and biotic factors, leading to chronic loading of freshwaters with cyanotoxins. At last, we illustrate the impacts of HABs on the environment by compiling four health issues and four ecology issues emanating from their presence in the that covers atmosphere, aquatic ecosystems and terrestrial ecosystems. Our study highlights the annual patterns of algal blooms, and proposes that a "perfect storm" of events is lurking that will cause the 'seasonal toxicity' to become a full-blown, 'chronic toxicity' in the context of the deterioration of HABs, highlighting a non-negligible chronic health and ecological hazard.

Mortality and histopathology in sheepshead minnow (Cyprinodon variegatus) larvae exposed to pectenotoxin-2 and Dinophysis acuminata

Toxic species of the dinoflagellate genus Dinophysis can produce diarrheic toxins including okadaic acid (OA) and dinophysistoxins (DTXs), and the non-diarrheic pectenotoxins (PTXs). Okadaic acid and DTXs cause diarrheic shellfish poisoning (DSP) in human consumers, and also cause cytotoxic, immunotoxic and genotoxic effects in a variety of mollusks and fishes at different life stages in vitro. The possible effects of co-produced PTXs or live cells of Dinophysis to aquatic organisms, however, are less understood. Effects on an early life stage of sheepshead minnow (Cyprinodon variegatus), a common finfish in eastern USA estuaries, were evaluated using a 96-h toxicity bioassay. Three-week old larvae were exposed to PTX2 concentrations from 50 to 4000 nM, live Dinophysis acuminata culture (strain DAVA01), live cells resuspended in clean medium or culture filtrate. This D. acuminata strain produced mainly intracellular PTX2 (≈ 21 pg cell^-1), with much lower levels of OA and dinophysistoxin-1. No mortality or gill damages were observed in larvae exposed to D. acuminata (from 5 to 5500 cells mL^-1), resuspended cells and culture filtrate. However, exposure to purified PTX2 at intermediate to high concentrations (from 250 to 4000 nM) resulted in 8 to 100% mortality after 96 h (24-h LC₅₀ of 1231 nM). Histopathology and transmission electron microscopy of fish exposed to intermediate to high PTX2 concentrations revealed important gill damage, including intercellular edema, necrosis and sloughing of gill respiratory epithelia, and damage to the osmoregulatory epithelium, including hypertrophy, proliferation, redistribution and necrosis of chloride cells. Tissue damage in gills is likely caused by the interaction of PTX2 with the actin cytoskeleton of the affected gill epithelia. Overall, the severe gill pathology observed following the PTX2 exposure suggested death was due to loss of respiratory and osmoregulatory functions in C. variegatus larvae.

Response mechanism of harmful algae Phaeocystis globosa to ocean warming and acidification

Simultaneous ocean warming and acidification will alter marine ecosystem structure and directly affect marine organisms. The alga Phaeocystis globosa commonly causes harmful algal blooms in coastal areas of eastern China. P. globosa often outcompetes other species due to its heterotypic life cycle, primarily including colonies and various types of solitary cells. However, little is known about the adaptive response of P. globosa to ocean warming and acidification. This study aimed to reveal the global molecular regulatory networks implicated in the response of P. globosa to simultaneous warming and acidification. After exposure to warming and acidification, the phosphatidylinositol (PI) and mitogen-activated protein kinase (MAPK) signaling pathways of P. globosa were activated to regulate other molecular pathways in the cell, while the light harvesting complex (LHC) genes were downregulated to decrease photosynthesis. Exposure to warming and acidification also altered the intracellular energy flow, with more energy allocated to the TCA cycle rather than to the biosynthesis of fatty acids and hemolytic substances. The upregulation of genes associated with glycosaminoglycan (GAG) degradation prevented the accumulation of polysaccharides, which led to a reduction in colony formation. Finally, the upregulation of the Mre11 and Rad50 genes in response to warming and acidification implied an increase in meiosis, which may be used by P. globosa to increase the number of solitary cells. The increase in genetic diversity through sexual reproduction may be a strategy of P. globosa that supports rapid response to complex environments. Thus, the life cycle of P. globosa underwent a transition from colonies to solitary cells in response to warming and acidification, suggesting that this species may be able to rapidly adapt to future climate changes through life cycle transitions.

In situ digital holographic microscopy for rapid detection and monitoring of the harmful dinoflagellate, Karenia brevis

Karenia brevis blooms, also known as red tide, are a recurring problem in the coastal Gulf of Mexico. These blooms have the capacity to inflict substantial damage to human and animal health as well as local economies. Thus, monitoring and detection of K. brevis blooms at all life stages and cell concentrations is essential for ensuring public safety. Current K. brevis monitoring methods have several limitations, including size resolution limits and concentration ranges, limited capacity for spatial and temporal profiling, and/or small sample volume processing. Here, a novel monitoring method wherein an autonomous digital holographic imaging microscope (AUTOHOLO), that overcomes these limitations and can characterize K. brevis concentrations in situ, is presented. Using the AUTOHOLO, in situ field measurements were conducted in the coastal Gulf of Mexico during an active K. brevis bloom over the 2020-21 winter season. Surface and sub-surface water samples collected during these field studies were also analyzed in the lab using benchtop holographic imaging and flow cytometry for validation. A convolutional neural network was trained for automated classification of K. brevis at all concentration ranges. The network was validated with manual counts and flow cytometry, yielding a 90% accuracy across diverse datasets with varying K. brevis concentrations. The usefulness of pairing the AUTOHOLO with a towing system was also demonstrated for characterizing particle abundance over large spatial distances, which could potentially facilitate characterization of spatial distributions of K. brevis during bloom events. Future applications of the AUTOHOLO can include integration into existing HAB monitoring networks to enhance detection capabilities for K. brevis in aquatic environments around the world.

Lake Erie fish safe to eat yet afflicted by algal hepatotoxins

Toxic harmful algal blooms (HABs) pose serious threats to human health and instances of wildlife death have been documented across taxa. However, the extent of toxicological impacts on wildlife species is largely unresolved, raising uncertainty about the repercussions of increasingly severe HABs on the biodiversity and functioning of aquatic ecosystems. Here, we conducted a field study to assess human health risks from consuming fish caught across all stages of a HAB and to determine the pervasiveness of potentially harmful levels of the cosmopolitan toxin microcystin on fish populations. We collected 190 fish in 2015 and 2017 from Lake Erie, a large freshwater ecosystem that is highly productive for fisheries and is an epicenter of HABs and microcystin toxicity events. Fish muscles and livers were analyzed for total microcystins, which was used to conduct a human health risk assessment for comparison against fish consumption advisory benchmarks available for Lake Erie. We found microcystins pose low risks to human health from fillet consumption (mean 1.80 ng g^-1 ww) but substantial risks to fish health and recruitment from liver concentrations measured well before and after seasonal bloom events (mean 460.13 ng g^-1 ww). Our findings indicate HABs are a previously underappreciated but pervasive threat to fish populations.

Sub-chronic exposure to waterborne extracellular microcystin-LR impairs calcium homeostasis in rainbow trout

Fish mortality is associated with harmful algal blooms, although whether toxicity is related directly to the presence of cyanotoxins or the prevailing water chemistry remains unclear. Similarly, while planktivorous fish may be exposed to toxin through the diet, the hazard posed by waterborne extracellular toxin to carnivorous fish is less well understood. In this study rainbow trout (Oncorhynchus mykiss) were exposed for up to 28 d to waterborne microcystin-LR at nominal concentrations of 1.5 and 50 µg L^-1 (measured values 2 and 49 µg L^-1, respectively). The former represents the Canadian drinking water guideline, and the latter an elevated environmental level. This study hypothesised that waterborne toxin exposure would specifically impact gill function, and given the importance of this tissue in freshwater fish ion regulation, effects on plasma ions and branchial ion transporter activity would be observed. Microcystin-LR exposure resulted in a significant and persistent hypocalcaemia at the higher exposure concentration, but plasma sodium and branchial activities of the sodium/potassium ATPase, proton ATPase and calcium ATPase enzymes remained unaffected. An in vitro assessment failed to show any effect of microcystin-LR on branchial calcium ATPase activity even at exposure concentrations as high as 1000 µg L^-1. A transient increase in hepatic alkaline phosphatase activity was also observed at 49 µg L^-1, but there were no effects of toxin exposure on branchial or hepatic lactate dehydrogenase activity. These results suggest that microcystin-LR exposure does not have a general effect on ion regulation, but instead produces a novel and specific impact on calcium metabolism in rainbow trout, although the mechanism underlying this effect remains unknown.

Improvement and application of qPCR assay revealed new insight on early warning of Phaeocystis globosa bloom

Phaeocystis globosa bloom develops from its early solitary cells, providing clues for early warning of its bloom and timely responding to possible consequences. However, the early prediction requires quantification of the solitary cells for a thorough understanding of bloom formation. Therefore, we developed an accurate, sensitive, and specific qPCR assay for this need. Results show that the accuracy of qPCR was significantly enhanced by ameliorating DNA barcode design, improving genomic DNA extraction, and introducing a strategy of internal amplification control (IAC). This approach reached a quantification limit of 1 cell/reaction, making low-abundance cells (10¹-10³ cells/L) detection possible, and we also observed a plunge in the abundance of the solitary cells before the bloom outbreak in two winters in 2019 and 2020 for the first time, which is quite unique from laboratory results showing an increase instead. The plunge in solitary-cell abundance might be associated with the attachment of solitary cells to solid matrices to form non-solitary attached aggregate, the precursor of colonies, which gains supports from other studies and needs more investigations in the future. Therefore, as the plunge in solitary-cell abundance is a sign of colony formation, it can be used as an early warning indicator to P. globosa bloom.

Sublethal effect of the toxic dinoflagellate Karlodinium veneficum on early life stages of zebrafish (Danio rerio)

Dinoflagellates of the genus Karlodinium are ichthyotoxic species that produce toxins including karlotoxins and karmitoxins. Karlotoxins show hemolytic and cytotoxic activities and have been associated with fish mortality. This study evaluated the effect of toxins released into the environment of Karlodinium veneficum strain K10 (Ebro Delta, NW Mediterranean) on the early stages of Danio rerio (zebrafish). Extracts of the supernatant of K10 contained the mono-sulfated KmTx-10, KmTx-11, KmTx-12, KmTx-13, and a di-sulfated form of KmTx-10. Total egg mortality was observed for karlotoxin concentration higher than 2.69 μg L^-1. For 1.35 μg L^-1, 87% of development anomalies were evidenced (all concentrations were expressed as KmTx-2 equivalent). Larvae of 8 days postfertilization exposed to 1.35 µg L^-1 presented epithelial damage with 80% of cells in the early apoptotic stage. Our results indicate that supernatants with low concentration of KmTxs produce both lethal and sublethal effects in early fish stages. Moreover, apoptosis was induced at concentrations as low as 0.01 μg L^-1. This is of great relevance since detrimental long-term effects due to exposure to low concentrations of these substances could affect wild and cultured fish.

Complex effects of dissolved organic matter, temperature, and initial bloom density on the efficacy of hydrogen peroxide to control cyanobacteria

Harmful cyanobacterial blooms plague reservoirs and lakes used for a variety of purposes, such as recreation and drinking water. Chemical controls are frequently used to mitigate the occurrence of cyanobacterial blooms given that many are fast-acting and effective at reducing cyanobacterial abundance. Recent research has identified hydrogen peroxide (H₂O₂) as an environmentally friendly alternative to algaecides that have typically been used, such as copper sulfate. To build on past studies, these experiments sought to further understand how well H₂O₂ treatments reduce cyanobacteria in complex eutrophic conditions, as well as to assess treatment effects on a non-target phytoplankter, a green alga. We assessed the effectiveness of H₂O₂ (at treatments of 2-16 mg L^-1) under varying environmental conditions in a controlled laboratory setting, including (1) dissolved organic matter (DOM) concentrations (humic acid; 0-60 mg L^-1), (2) temperature (20, 25, and 32 °C), and (3) initial algal biomass (chlorophyll-a; 82-371 µg L^-1). In contrast to our expectations, neither DOM concentration nor temperature meaningfully impacted the effectiveness of H₂O₂ at reducing cyanobacteria. However, initial algal biomass as well as H₂O₂ treatment dose greatly influenced the effectiveness of the algaecide on cyanobacteria. Treatments of ≥ 8 mg H₂O₂ L^-1 on algal biomass were significantly buffered with higher DOM and lower temperature, and the biological significance of these findings should be explored further. Across all experiments, H₂O₂ concentrations of 0.03-0.12 mg H₂O₂ L^-1 µg chlorophyll L^-1 were effective at significantly reducing cyanobacteria with varying effects on algal biomass. Thus, water resource managers are encouraged to consider how ambient levels of phytoplankton biomass may affect the ability of H₂O₂ to control cyanobacterial blooms prior to treatment.

Detection of numerous phycotoxins in young bull sharks (Carcharhinus leucas) collected from an estuary of national significance

Florida's Indian River Lagoon (IRL) has experienced large-scale, frequent blooms of toxic harmful algae in recent decades. Sentinel, or indicator, species can provide an integrated picture of contaminants in the environment and may be useful to understanding phycotoxin prevalence in the IRL. This study evaluated the presence of phycotoxins in the IRL ecosystem by using the bull shark (Carcharhinus leucas) as a sentinel species. Concentrations of phycotoxins were measured in samples collected from 50 immature bull sharks captured in the IRL between 2018 and 2020. Ultra-performance liquid chromatography/tandem mass spectrometry was used to measure toxins in shark gut contents, plasma, and liver. Analysis of samples (n = 123) demonstrated the presence of multiple phycotoxins (microcystin, nodularin, teleocidin, cylindrospermopsin, domoic acid, okadaic acid, and brevetoxin) in 82 % of sampled bull sharks. However, most detected toxins were in low prevalence (≤25 % of samples, per sample type). This study provides valuable baseline information on presence of multiple phycotoxins in a species occupying a high trophic position in this estuary of national significance.

Effect of dissolved organic nutrients on the bloom of Prorocentrum donghaiense in the East China Sea coastal waters

Prorocentrum donghaiense blooms occur annually in the East China Sea coastal waters, degrading ecosystem functions and impeding economic development. Dissolved organic nitrogen and phosphorus (DON and DOP) are the main components in the marine nutrient pools and are closely related to harmful algal blooms. From April to June 2019, a survey was conducted along the East China Sea coast (Sansha and Lianjiang counties) to investigate the relationship between dissolved organic nutrients and P. donghaiense bloom. Our findings showed that dinoflagellates dominated the phytoplankton community, and dissolved organic nutrients were the major factors influencing community structure during the P. donghaiense bloom. Redundancy analysis indicated that P. donghaiense abundance was primarily affected by DON in the Sansha area while it was primarily affected by DON and DOP in the Lianjiang area. Correlation analysis also confirmed a strong positive correlation between dissolved organic nutrients and P. donghaiense abundance both in the Sansha and Lianjiang coastal areas (p < 0.001). Furthermore, a culture experiment was carried out during the bloom to further investigate the effect of dissolved organic nutrients on the phytoplankton community structure. After 10 days of culture, dinoflagellates' relative abundance decreased from 97.1% to 28.2% in the inorganic treatment, whereas dinoflagellates continued to dominate the phytoplankton community in the organic treatment (76.9%). As a result, we propose that dissolved organic nutrients are responsible for the P. donghaiense bloom outbreak and promote the phytoplankton community shift from diatoms to dinoflagellates.

Usability and acceptance of crowd-based early warning of harmful algal blooms

Crowdsensing has become an alternative solution to physical sensors and apparatuses. Utilizing citizen science communities is undoubtedly a much cheaper solution. However, similar to other participatory-based applications, the willingness of community members to be actively involved is paramount to the success of implementation. This research investigated factors that affect the continual use intention of a crowd-based early warning system (CBEWS) to mitigate harmful algal blooms (HABs). This study applied the partial least square-structural equation modeling (PLS-SEM) using an augmented technology acceptance model (TAM). In addition to the native TAM variables, such as perceived ease of use and usefulness as well as attitude, other factors, including awareness, social influence, and reward, were also studied. Furthermore, the usability factor was examined, specifically using the System Usability Scale (SUS) score as a determinant. Results showed that usability positively affected the perceived ease of use. Moreover, perceived usefulness and awareness influenced users' attitudes toward using CBEWS. Meanwhile, the reward had no significant effects on continual use intention.

Whole genome sequence data of a marine bacterium, Marinobacter adhaerens PBVC038, associated with toxic harmful algal bloom

Marinobacter adhaerens (PBVC038) was isolated from a harmful algal bloom event caused by the toxic dinoflagellate Pyrodinium bahamense var. compressum (P. bahamense) in Sepanggar Bay, Sabah, Malaysia, in December 2012. Blooms of P. bahamense are frequently linked to paralytic shellfish poisoning, resulting in morbidity and mortality. Prior experimental evidence has implicated the role of symbiotic bacteria in bloom dynamics and the synthesis of biotoxins. The draft genome sequence data of a harmful algal bloom-associated bacterium, Marinobacter adhaerens PBVC038 is presented here. The genome is made up of 21 contigs with an estimated 4,246,508 bases in genome size and a GC content of 57.19%. The raw data files can be retrieved from the National Center for Biotechnology Information (NCBI) under the Bioproject number PRJNA320140. The assessment of bacterial communities associated with harmful algal bloom should be studied more extensively as more data is needed to ascertain the functions of these associated bacteria during a bloom event.

Strategies to control the growth of cyanobacteria and recovery using adsorption and desorption

In this study, adsorption strategy using diethylenetriamine-modified cotton fiber (DETA-cotton) was investigated to control the target cells in aqueous phase. Adsorptive removal of M. aeruginosa using the DETA-cotton showed decrease in cell concentration from (100 ± 4.0) × 10⁴ cells/mL to (32.1 ± 0.7) × 10⁴ cells/mL in 24 h, and the concentration of microcystin did not increase during the removal process. Also, an increase in the amine groups on the surface was confirmed through the surface characterization by FT-IR and XPS. Desorption process was performed to analyze total lipid and fatty acid contents for potential use as bio-energy resources. About 90 % of the adsorbed cells were recovered through desorption, and the lipid content and composition were more suitable for use as biodiesel raw materials. Our adsorption-based approach might provide feasible solution not only to counteract environmental issue HABs but also to recover energy-resources from the harmful cyanobacterial species.

Impact of melatonin on the hydrogen peroxide treatment efficacy in Microcystis aeruginosa: Cell growth, oxidative stress response, and gene transcription

A study was conducted to determine how melatonin (MLT), a growth regulator, affects Microcystis aeruginosa cell behaviour and how MLT exposed cells respond to hydrogen peroxide (H₂O₂) treatment. MLT promotes the growth, chl-a content, Fv/Fm values, and microcystins (MCs) production of M. aeruginosa at low concentrations of 1-2.5 μmol/L but suppresses the growth at high concentrations (5-10 μmol/L). The cellular and genetic responses of MLT pre-treated cells to H₂O₂ treatment were examined further. Further research found that the cells pre-treated with MLT were susceptible to a range of growth-promoting, inhibiting and lethal effects when exposed to higher levels of H₂O₂. A dose-dependent pattern was observed under conditions of 0.05-0.2 mmol/L H₂O₂ with 0.5-2.5 μmol/L MLT concentrations to different degrees. High doses of H₂O₂ (0.2 and 0.3 mmol/L) typically lead to cell lysis and release of MCs in 5.0 and 10 μmol/L MLT pre-treated cells. A decrease in SOD/CAT activities and an increase in MDA levels validated the growth reduction. Furthermore, higher cell lysis and release of intracellular MCs were observed when H₂O₂ was increased for 5-10 μmol/L MLT pre-treated cells. This led to a higher accumulation of extracellular MCs. The results provide insight into how MLT influences H₂O₂ damage and assist in identifying situations where H₂O₂ treatment of cyanobacterial blooms is most appropriate.

Storm-induced coastward expansion of Margalefidinium polykrikoides bloom in Chesapeake Bay

An unusual coastward expansion of the toxic dinoflagellate species Margalefidinium polykrikoides was observed in 2020 summer after a tropical storm passing Chesapeake Bay. Such coastward expansion was only recorded in 2007. A newly developed coupled Lagrangian particle tracking and harmful algal bloom model driven by environmental variables was used to investigate the underlying mechanisms and successfully reproduced the expansion patterns. Persistent pre-storm southerly winds favored the delivery of bloom source water originated inside the bay to the coast. Storm-induced strong upwelling of denser subsurface water interacted with the after-storm outflow plume (steered southward as the storm's impacts waned), forming a transport barrier to accumulate algae and delineate the coastwide bloom extent. Algal diel vertical migrations and transport barrier enable algae to stay in the nearshore regions. The storm-induced coastward expansion of M. polykrikoides might increase future bloom possibility in the coastal area.

Reduced representation sequencing accurately quantifies relative abundance and reveals population-level variation in Pseudo-nitzschia spp

Certain species within the genus Pseudo-nitzschia are able to produce the neurotoxin domoic acid (DA), which can cause illness in humans, mass-mortality of marine animals, and closure of commercial and recreational shellfisheries during toxic events. Understanding and forecasting blooms of these harmful species is a primary management goal. However, accurately predicting the onset and severity of bloom events remains difficult, in part because the underlying drivers of bloom formation have not been fully resolved. Furthermore, Pseudo-nitzschia species often co-occur, and recent work suggests that the genetic composition of a Pseudo-nitzschia bloom may be a better predictor of toxicity than prevailing environmental conditions. We developed a novel next-generation sequencing assay using restriction site-associated DNA (2b-RAD) genotyping and applied it to mock Pseudo-nitzschia communities generated by mixing cultures of different species in known abundances. On average, 94% of the variance in observed species abundance was explained by the expected abundance. In addition, the false positive rate was low (0.45% on average) and unrelated to read depth, and false negatives were never observed. Application of this method to environmental DNA samples collected during natural Pseudo-nitzschia spp. bloom events in Southern California revealed that increases in DA were associated with increases in the relative abundance of P. australis. Although the absolute correlation across time-points was weak, an independent species fingerprinting assay (Automated Ribosomal Intergenic Spacer Analysis) supported this and identified other potentially toxic species. Finally, we assessed population-level genomic variation by mining SNPs from the environmental 2bRAD dataset. Consistent shifts in allele frequencies in P. pungens and P. subpacifica were detected between high and low DA years, suggesting that different intraspecific variants may be associated with prevailing environmental conditions or the presence of DA. Taken together, this method presents a potentially cost-effective and high-throughput approach for studies aiming to evaluate both population and species dynamics in mixed samples.

Modeling Dinophysis in Western Andalucía using an autoregressive hidden Markov model

Dinophysis spp. can produce diarrhetic shellfish toxins (DST) including okadaic acid and dinophysistoxins, and some strains can also produce non-diarrheic pectenotoxins. Although DSTs are of human health concern and have motivated environmental monitoring programs in many locations, these monitoring programs often have temporal data gaps (e.g., days without measurements). This paper presents a model for the historical time-series, on a daily basis, of DST-producing toxigenic Dinophysis in 8 monitored locations in western Andalucía over 2015-2020, incorporating measurements of algae counts and DST levels. We fitted a bivariate hidden Markov Model (HMM) incorporating an autoregressive correlation among the observed DST measurements to account for environmental persistence of DST. We then reconstruct the maximum-likelihood profile of algae presence in the water column at daily intervals using the Viterbi algorithm. Using historical monitoring data from Andalucía, the model estimated that potentially toxigenic Dinophysis algae is present at greater than or equal to 250 cells/L between < 1% and >10% of the year depending on the site and year. The historical time-series reconstruction enabled by this method may facilitate future investigations into temporal dynamics of toxigenic Dinophysis blooms.

Evolution of harmful algal blooms in the East China Sea under eutrophication and warming scenarios

Harmful algal blooms (HABs) worldwide are experiencing obvious changes under the combined impacts of global warming, eutrophication, and other driving forces. In the East China Sea (ECS), large-scale blooms caused by dinoflagellates occurred since 2000 and there has been an apparent shift of bloom-causative microalgae from diatoms to dinoflagellates. To predict the future evolution of HABs in this region, a model was developed based on the competition between diatoms and dinoflagellates, which would serve to reproduce the seasonal succession of microalgal blooms driven by multiple environmental factors. The evolution features of HABs were then projected under different scenarios of eutrophication and global warming. Under the 'business as usual' scenario, dinoflagellate blooms are expected to become more frequent with higher peak biomass concentrations over the next 30 years. Changes in nutrient composition of the Changjiang riverine discharge may largely give rise to this phenomenon, and accelerated warming associated with climate change may result in earlier occurrence of dinoflagellate blooms. To prevent further intensification of dinoflagellate blooms, efforts could be made to reduce nitrogen inputs and maintain or even increase silicate inputs from the Changjiang river.

Functional role of a novel algicidal compound produced by Pseudoruegeria sp. M32A2M on the harmful algae Alexandrium catenella

A marine phytoplankton dinoflagellate, Alexandrium sp. is known to cause worldwide harmful algal blooms, resulting in paralytic shellfish poisoning. In this study, we isolated a novel compound secreted by the marine bacterium Pseudoruegeria sp. M32A2M, and showed that it displays algicidal activity against A. catenella (group I). The molecular structure of the compound was analyzed by using ¹H nuclear magnetic resonance (NMR), ¹³C NMR, and gas chromatography-mass spectrometry, which revealed that the compound was a diketopiperazine, cyclo[Ala-Gly]. Cyclo[Ala-Gly] induced a rapid decrease in the active chlorophyll a content and maximal quantum yield of photosystem II, leading to membrane disintegration after 24 h of its treatment. It showed the highest algicidal effect against diketopiperazines and also showed specific algicidal activities against several dinoflagellate species, but not for diatom species. In particular, cyclo[Ala-Gly] caused the transcriptional downregulation of the photosynthesis-related membrane complex in A. catenella, but not in the diatom Chaetoceros simplex. Based on structural modeling, we elucidated that cyclo[Ala-Gly] has a structure similar to that of plastoquinone, which transfers electrons by binding to the photosystem II core proteins PsbA and PsbD. This suggests a novel role for cyclo[Ala-Gly] as a potential inhibitor of photosynthesis.

Hierarchical deep learning model to simulate phytoplankton at phylum/class and genus levels and zooplankton at the genus level

Harmful algal blooms (HABs) have become a global issue, affecting public health and water industries in numerous countries. Because funds for monitoring HABs are limited, model development may be an alternative approach for understanding and managing HABs. Continuous monitoring based on grab sampling is time-consuming, costly, and labor-intensive. However, improving simulation performance remains a major challenge in modeling, and current methods are limited to simulating phytoplankton (e.g., Microcystis sp., Anabaena sp., Aulacoseira sp., Cyclotella sp., Pediastrum sp., and Eudorina sp.) and zooplankton (e.g., Cyclotella sp., Pediastrum sp., and Eudorina sp.) at the genus level. The traditional modeling approach is limited for evaluating the interactions between phytoplankton and zooplankton. Recently, deep learning (DL) models have been proposed for solving modeling problems because of their large data handling capabilities and model structure flexibilities. In this study, we evaluated the applicability of DL for simulating phytoplankton at the phylum/class and genus levels and zooplankton at the genus level. Our work was an explicit representation of the taxonomic and ecological hierarchy of the DL model structure. The prerequisite for this model design was the data collection at two taxonomic and hierarchical levels. Our model consisted of hierarchical DL with classification transformer (TF) and regression TF models. These DL models were hierarchically connected; the output of the phylum/class level model was transferred to the genus level simulation model, and the output of the genus level model was fed into the zooplankton simulation model. The classification TF model determined the phytoplankton occurrence initiation date, whereas the regression TF model quantified the cell concentration of plankton. The hierarchical DL showed potential to simulate phytoplankton at the phylum/class and genus levels by producing average R^2, and root mean standard error values of 0.42 and 0.83 [log(cells mL^-1)], respectively. All simulated plankton results closely matched the measured concentrations. Particularly, the simulated cyanobacteria showed good agreement with the measured cell concentration, with an R² value of 0.72. In addition, our simulated result showed good agreement in peak concentration compared to observations. However, a limitation remained in following the temporal variation of Tintinnopsis sp. and Bosmia sp. Using an importance map from the TF model, water temperature, total phosphorus, and total nitrogen were identified as significant variables influencing phytoplankton and zooplankton blooms. Overall, our study demonstrated that DL can be used for modeling HABs at the phylum/class and genus levels.

Can correlational analyses help determine the drivers of microcystin occurrence in freshwater ecosystems? A meta-analysis of microcystin and associated water quality parameters

Microcystin (MC) is a toxic secondary metabolite produced by select cyanobacteria that threatens aquatic and terrestrial organisms over a diverse range of freshwater systems. To assess the relationship between environmental parameters and MC, researchers frequently utilize correlational analyses. This statistical methodology has proved useful when summarizing complex water quality monitoring datasets, but the correlations between select parameters and MC have been documented to vary widely across studies and systems. Such variation within the peer-reviewed literature leaves uncertainty for resource managers when developing a MC monitoring program. The objective of this research is to determine if correlational analyses between environmental parameters and MC are helpful to resource managers desiring to understand the drivers of MC. Environmental (i.e., physical, chemical, and biological) and MC correlation data were retrieved from an estimated 2,643 waterbodies (largely from the north temperate region) and synthesized using a Fisher's z meta-analysis. Common water quality parameters, such as chlorophyll, temperature, and pH, were positively correlated with MC, while transparency was negatively correlated. Interestingly, 12 of the 15 studied nitrogen parameters, including total nitrogen, were not significantly correlated with MC. In contrast, three of the four studied phosphorus parameters, including total phosphorus, were positively related to MC. Results from this synthesis quantitatively reinforces the usefulness of commonly measured environmental parameters to monitor for conditions related to MC occurrence; however, correlational analyses by themselves are often ineffective and considering what role a parameter plays in the ecology of cyanobacterial blooms in addition to MC production is vital.