Harmful algal blooms (HABs) pose a recurrent threat to sub-Antarctic coastal ecosystems such as the Beagle Channel. Here, we used a 15-month high-frequency dataset (January 2021-April 2022) to assess the spatiotemporal dynamics of toxigenic microalgae and associated phycotoxins across multiple compartments, including plankton, bivalves, and passive samplers, together with concurrent oceanographic and meteorological conditions. Alexandrium catenella was the dominant toxic species, producing paralytic shellfish toxins (PST) during two consecutive austral summers with contrasting intensity. The 2021 event was moderate and spatially restricted, with A. catenella abundances reaching 4.2 × 10² cells L⁻¹, whereas the 2022 bloom was severe and widespread, with abundances up to 5.0 × 10⁴ cells L⁻¹. PST levels in plankton and mussels exceeded 2021 values by more than two orders of magnitude, reaching up to ∼3.7 × 10⁵ ng NT⁻¹ and ∼1.9 × 10⁵ µg STXeq kg⁻¹, respectively. Exploratory generalized additive models (GAMs) indicated that A. catenella variability was associated with water temperature, wind speed, ciliate abundance, predominantly positive values of the Southern Annular Mode, and seasonality, suggesting that bloom development reflected by the interaction of these environmental and biological controls rather than by a single controlling factor. During the 2022 event, planktonic PST levels varied markedly among nearby stations, whereas mussels reached similarly high toxicities, consistent with the time-integrated nature of shellfish toxin accumulation, local retention, and hydrodynamic connectivity within the same basin. Additional toxin groups, including DTX1, PTX2, SPX1, 20-Me-G, and domoic acid, were also detected, indicating the presence of multiple potentially toxigenic taxa and suggesting that future HAB risk in the region may extend beyond the historically dominant A. catenella-PST paradigm. These findings highlight the Beagle Channel as a cold sub-Antarctic HAB hotspot and support the need for integrated monitoring frameworks combining species-specific cell counts, targeted toxin analyses, shellfish toxicity records, passive sampling for dissolved lipophilic toxins, and environmental observations.
Six Gloeotrichia echinulata genomes derived from planktonic harmful algal blooms (HABs) with similar colonial morphology have been sequenced from lakes in the west and northeast regions of USA, four of them to completion. The c. 7 Mbp genomes exhibit a high level of conservation, with 98-99% pairwise genome-wide average nucleotide identity and high levels of synteny, representing a single species cluster. We observed strong conservation of gene clusters responsible for the synthesis of the secondary metabolites and bioactive peptides that are characteristic of HAB-forming cyanobacteria. All six G. echinulata genomes lack genes for the synthesis of classic cyanotoxins, including microcystin, but possess genes responsible for the synthesis of the taste and odor compound geosmin. Interestingly, the geoA geosmin synthase gene in three genomes is homologous to other cyanobacterial geoA genes, while the other three geoA genes are related to actinomyces geoA. Phylogenomic analysis places the G. echinulata genomes within a clade of benthic Nostocales, reflecting an ecological niche featuring extensive growth on the sediment surface before colonies disperse into the epilimnion for planktonic growth. We identify genes conserved in all six genomes that could represent physiological adaptations supporting active growth on sediments and pelagic recruitment independent of wind-driven mixing: phycoerythrin light harvesting complexes for optimal photosynthesis at depth; gliding motility to access patchy nutrient distributions; and gas vesicles with relatively small GvpC proteins that predict resistance to higher hydrostatic pressure. The strong genomic similarity across geographically distant populations suggests that G. echinulata in the United States is a tightly related non-toxigenic species group with predictable properties relevant to public health and drinking water management.
Cyanobacteria-derived microcystins (MC) are widespread hepatotoxins threatening water security, with known producers primarily limited to specific genera. To expand the diversity of MC-producing cyanobacteria, we conducted an environmental DNA (eDNA)-based survey of cyanobacterial communities across the Lake Qinghai Basin (Qinghai-Tibet Plateau), a unique high-altitude brackish aquatic system, and isolated six coccoid cyanobacterial strains from Lake Yueya, a shallow sub-lake of Lake Qinghai. These six strains were characterized via a polyphasic approach, and morphological examinations (light and transmission electron microscopy) revealed key diagnostic features of Snowella (Chroococcales, Cyanobacteria), including spherical colonies with radial cell arrangements and central stalks. Further, molecular analyses confirmed their affiliation with Snowella via 16S rRNA gene and 16S-23S ITS phylogeny, and the MC synthesis gene mcyE was successfully detected. UPLC-MS/MS further identified MC variants (MC-LR, MC-RR, MC-YR) in selected strains, and strain CHAB 6606 was detected to have intracellular MC-LR (82.4 fg·cell⁻¹) and MC-YR (247.0 fg·cell⁻¹), higher than the typical Microcystis strains. Notably, our deposited mcyE sequences in Genbank are the sole basis for identifying the three global locations with potential MC-producing Snowella populations. This study provides the first formal confirmation that Snowella produces MC, expanding the diversity of MC-producing cyanobacteria to high-altitude brackish habitats. Our findings establish a molecular framework for global Snowella-associated MC risk surveillance, supporting targeted aquatic toxin monitoring and advance understanding of the taxonomic spectrum of MC-producing cyanobacteria worldwide.
As a dormant stage of the dinoflagellate life cycle, resting cysts play crucial ecological roles, particularly for bloom-forming species, as supported by abundant evidence. They can remain viable in marine sediments for decades to centuries and directly regulate seasonal population dynamics and initiate HABs through germination. Yet the physiological and molecular mechanisms that enable their long-term survival under dark, cold, and anoxic conditions remain largely elusive. Vacuolar H⁺-pyrophosphatase (H⁺-PPase) is a conserved proton pump that hydrolyzes inorganic pyrophosphate (PPi) to drive proton translocation, thereby conferring tolerance to anoxia and cold in plants. Here, we identified and characterized an H⁺-PPase gene (SaH⁺-PPase) from the cosmopolitan bloom-forming dinoflagellate Scrippsiella acuminata. Sequence analysis confirmed that SaH⁺-PPase is a typical type I vacuolar H⁺-PPase with conserved domains and vacuolar membrane localization. Transcriptional profiling revealed significant induction of SaH+-PPase in resting cysts under sediment-mimicking conditions (darkness, 4°C, anoxia), with the expression elevated ∼2.9-fold after one month and sustained for three months. Consistently, parallel reaction monitoring (PRM) and enzyme activity assays verified sustained increases in H⁺-PPase protein abundance and activity during three months of incubation. Since oxygen deprivation sharply reduces cellular ATP levels and triggers cytoplasmic acidification, the markedly upregulation of H⁺-PPase likely not only helped maintain cellular homeostasis by alleviating cytoplasmic acidosis but also enabled resting cysts to utilize PPi as an alternative energy source to compensate for energy deficits under dark, cold, and anoxic conditions, thereby directing limited ATP toward essential processes for long-term dormancy. Collectively, our findings provide novel molecular insights into the survival mechanisms of resting cysts and lay a foundation for understanding the physiological adaptations of dinoflagellates in natural benthic habitats.
Harmful algal blooms (HABs) of toxic phytoplankton species are a prevalent and expensive issue worldwide, with toxin production from blooms impacting aquaculture, human health, and higher trophic levels. Despite widespread impacts, it remains uncertain why specific phytoplankton species produce toxins and how toxin production may be induced (‘triggered’) by ecological conditions. In this study, we develop an idealized theoretical nutrient-phytoplankton-zooplankton model to describe food web dynamics in response to toxin production by phytoplankton. We use our model to analyze three hypothetical cases, motivated by laboratory and field observations: cellular toxicity is constant and unrelated to food web dynamics (Constant Toxins), cellular toxicity is negatively related to toxic phytoplankton abundance (Phyto-triggered), and cellular toxicity is positively related to zooplankton biomass (Zoo-triggered). In all cases, grazing rates are inversely related to cellular toxicity. We examine how the maximum grazing rate of toxic phytoplankton, nutrient supply, and other model parameters impact toxic phytoplankton dominance, zooplankton:phytoplankton ratios, and total toxin load. Our model demonstrates that toxicity triggers can shift the competitive balance between toxic and non-toxic species, with outcomes dependent on total nutrient supply to the system. Total toxin loads were highest under the Constant Toxins and Zoo-triggered cases at high nutrient supply. This idealized model demonstrates how the specific trigger assumed for defense toxicity acts as an ecological feedback that determines food web structure. Our findings highlight the need to better understand the ecological drivers of toxin production in marine food webs before we can predict toxic algal events in natural ecosystems.
Blooms of Karenia brevis occur almost annually in the eastern Gulf of Mexico (Gulf of America). Submarine ground water discharges (SGD) have been previously suggested as a potential nutrient source in sustaining blooms. The West Florida Shelf is dotted with blue holes, or underwater sinkholes, which may be a route by which SGD seeps into offshore waters. Previously reported measurements within the holes demonstrated potentially high rates of denitrification, and dissimilatory nitrate reduction to ammonia (DNRA). Here, multiple water column stations were monitored monthly for four years near to-and away from-these sinkholes to assess the nitrogen (N) isotopic signatures of the particulate material. One offshore site, but not others, had mean δ15N values of 13.28 in surface samples and 12.58 in bottom samples, with the highest value reaching 38.86, reflecting highly processed N. Other sites had much lower δ15N values. Higher δ15N values were associated with lower river flows, as N would have a longer time to undergo processing. The microbiome of the free-living (>0.22 μm) planktonic communities of this site, examined via 16S rRNA amplicon sequencing, confirmed the presence of putative denitrifying bacteria. Following Hurricane Ian, a K. brevis bloom formed with low δ15N (<5), but as the bloom was sustained, the δ15N of the particulate material increased significantly, reflecting greater reliance on recycled N. Historical reports of Karenia within 10 km of known blue holes show that K. brevis can concentrate in these locations, which may be hot spots for a diversity of Karenia species.
The Pacific Arctic region is warming faster than almost any other region on Earth, and reductions in sea ice extent and the increased northward transport of warmer Pacific-origin water are expected to favour the poleward expansion of harmful algal blooms (HABs). The dinoflagellate Alexandrium catenella produces paralytic shellfish toxins (PSTs) that accumulate through marine food webs, and recent recurring blooms in the Chukchi Sea have been linked to wildlife mortality and risk to subsistence harvesters. Offshore monitoring in this remote region is sparse. Using the Continuous Plankton Recorder (CPR) Survey, we describe four Alexandrium bloom events sampled along a transect in the Bering Sea between 2021 and 2024, including the largest Alexandrium bloom recorded in the >60-year history of the CPR Survey (750,000 cells per 10 nautical-mile sample, July 2023). DNA was extracted from formalin-preserved CPR silks using three protocols, and partial large subunit (LSU) rDNA sequencing identified the cells as A. catenella. Bloom peaks occurred in shelf waters near the Pribilof Islands and St. Matthew Island, within Bering Summer Water (∼32 salinity, ∼9°C). The findings extend the known offshore distribution of potentially toxic A. catenella in the eastern Bering Sea, demonstrate the value of the CPR Survey as a cost-effective platform for HAB monitoring in difficult-to-access waters, and add to growing evidence that warming is increasing HAB risk to ecosystem function and food security in the Pacific Arctic.
Harmful algal blooms (HABs) of the dinoflagellate Gymnodinium catenatum, a producer of paralytic shellfish toxins (PSTs), are a recurrent environmental and socioeconomic problem in the northern Gulf of California (NGC). We describe an extensive HAB that occurred in early 2015 that caused the dead of 1017 seabirds and 249 marine mammals. Also, we analyze bloom recurrence between 2015 and 2024 to identify potential environmental drivers for the development of these phenomena. From January to March 2015, widespread mortality of seabirds and marine mammals was related to an extensive HAB of G. catenatum with maximum cell abundance of 266 × 103 cells l-1 and a maximum toxin concentration of 36 μg PSTs l-1 in particulate matter. Affected organisms exhibited signs of acute PSTs intoxication and these toxins were detected in different organs, gut contents, urine, and feces. Histopathological analyses revealed lesions consistent with systemic hypoxia and neurological effects of PST intoxication, suggesting respiratory paralysis as the primary cause of death. HABs of G. catenatum in the NGC have a clear temporal pattern of occurrence. From 2015 to 2024, G. catenatum proliferated from November/December to March/April every year with high abundances in January. PSTs in geoduck clams were detected in January of all years, except in 2016. Long-term observations indicate that blooms are driven by regional oceanographic processes. Recurrent HABs have generated important socioeconomic impacts through prolonged fishery closures causing job affectations, product losses and direct economic losses to local communities, highlighting the need for integrated monitoring and ecosystem-based management in the NGC.
The genus Prorocentrum comprises several benthic dinoflagellate species known to produce diarrhetic shellfish poisoning (DSP) toxins. However, information on their distribution and toxic potential remains limited across large areas of the Polynesian region. In this study, a clonal strain D008-7, isolated from intertidal tide pools in Rapa Nui (Easter Island), was analyzed using an integrative approach combining morphological observations, molecular phylogenetic analyses, and toxicological characterization by LC-MS/MS. Morphological and molecular results conclusively identified the strain as P. caipirignum. Toxin analysis revealed the production of okadaic acid (OA), predominantly in esterified form, while dinophysistoxins DTX1 and DTX2 were not detected. These findings extend the known geographic range of P. caipirignum to the easternmost boundary of the Polynesian Triangle and offer novel insights into its toxin profile in a highly isolated oceanic island environment.
Dinophysis species are the main producers of diarrhetic shellfish toxins (DSTs) in the Southwestern Atlantic, where recurrent blooms frequently lead to shellfish harvesting bans. In 2024, an extreme rainfall event over Rio Grande do Sul State, southern Brazil, caused one of the most severe floods ever recorded in the country, and generated an anomalous freshwater discharge through the Patos Lagoon estuary. The resulting low-salinity plume spread northward along the southern Brazilian coast, reaching aquaculture areas hundreds of kilometers away from the estuary. Here, we integrate hydrological data, satellite imagery, phytoplankton monitoring, shellfish toxin records, long-term regional datasets, and laboratory grazing experiments to characterize a large-scale toxic bloom of Dinophysis acuminata complex that developed after the flood event. Surface salinity decreased by 6-7 psu below historical values, while D. acuminata complex reached up to 6.8 × 10⁴ cells L⁻¹ further north in Santa Catarina State by mid-July 2024. The bloom caused harvesting bans in 17 of the 19 main bivalve farming areas in the state, with 61% of mussel and 43% of oyster samples exceeding the regulatory limit for DSTs, reaching concentrations as high as 4140 and 820 µg DST kg⁻¹, respectively. Comparison with long-term monitoring data from Uruguay and Brazil (Santa Catarina and Paraná states) showed that massive D. acuminata complex blooms in the region are episodic, seasonally structured, and often associated with anomalous meteoceanographic conditions. Field observations, satellite imagery and laboratory experiments further indicated that heterotrophic protists, particularly Noctiluca scintillans, may be likely contributors to bloom decline by grazing and act as transient vectors of okadaic acid within the planktonic food web. These findings highlight the vulnerability of coastal aquaculture areas to increasingly frequent and extreme hydrological disturbances, and reinforce the need for integrated analytical approaches combining microscopy, toxin analyses, remote sensing, and long-term ecological monitoring.
Bacteria associated with phytoplankton can profoundly influence host physiology and bloom dynamics. Yet it remains poorly understood whether the microbiota of dinoflagellates is restructured across host growth phases, and how such dynamics differ from those of other phytoplankton. Here, we tracked the microbiota of three harmful algal bloom (HAB)-forming dinoflagellates (Alexandrium catenella, A. pacificum, Gymnodinium catenatum) and three diatoms (Cylindrotheca closterium, Pseudo-nitzschia pungens, Coscinodiscus granii), each represented by two strains of distinct spatiotemporal origin and sampled at three growth phases (P1, P2, and P3). Microbiota composition was clearly differentiated by host species (PERMANOVA, R² = 0.799, n = 72, P < 0.001). However, the temporal dynamics of microbiota differed markedly between taxonomic groups. In dinoflagellates, microbiota was consistently restructured with each growth phase transition; in G. catenatum, growth phase accounted for the majority of microbiota variation (PERMANOVA, R² = 0.849, n = 12, P < 0.001) while intraspecific strain identity had negligible effect (PERMANOVA, R² = 0.014, n = 12, P > 0.05). In diatoms, by contrast, microbiota composition was strongly tied to intraspecific strain identity, with limited phase-dependent shifts. Dinoflagellates also harbored larger core microbiota than diatoms (15-37 vs. 2-9 core microbial lineages per host), exhibited higher centrality of core taxa within co-occurrence networks, and showed markedly lower normalized stochasticity ratios (NST; mean 15.7% vs. 35.5%). Microbiota dissimilarity was most strongly correlated with host phylogenetic distance (Mantel r = 0.617, P < 0.001), and the Bray-Curtis-based microbiota dendrogram was in complete topological congruence with the host phylogeny (nRF = 0.00, P < 0.01). Together, these findings demonstrate that dinoflagellates maintain a more deterministic and growth phase-linked microbiota than diatoms, indicative of strong host filtering.
The SoundToxins phytoplankton monitoring and research partnership supports the Washington State Department of Health (WDOH) biotoxin monitoring program by providing an early warning system of harmful algae bloom species, and monitoring phytoplankton at strategic locations near shellfish harvesting sites throughout Puget Sound. SoundToxins partners are Tribal biologists, Federal, State and County researchers, University staff and students, environmental educators, shellfish and finfish producers and community members. When harmful algae are detected by SoundToxins, an alert notifies WDOH managers who can take action including prioritizing shellfish sample analysis at the Public Health Laboratory and request shellfish samples. This study is the first to estimate company-level valuation of the benefits provided by SoundToxins program to the shellfish industry using an economic survey distributed using both in-person and online convenience sampling approaches. This study demonstrated that the average shellfish grower is willing to pay $533.31 per year to support SoundToxins. These findings are consistent with other studies which concluded that protecting public health and resilient coastal industries via continuous environmental monitoring and management of early warning systems is worthwhile.
As cyanobacterial blooms intensify globally, persistent microcystins (MCs) in surface waters present a growing water-quality challenge. Engineered solutions exist but are often costly and impractical for large-scale or natural settings. In contrast, wetlands, with their diverse microbial assemblages and habitats, offer a promising but underexplored pathway for MC removal. We tested this potential through in situ mesocosm experiments in two prairie wetlands; a hypereutrophic system receiving livestock and urban wastewater, and a less-impacted meso‑eutrophic site. Microcystin degradation was measured using 15N-labelled MC-LR added to mesocosms containing water, sediments, and macrophytes under natural conditions. Toxin concentrations declined in all treatments, with decay rates of 0.05-0.23 d-1, consistent with the lower end of laboratory-reported values. Isotope tracing and congener analysis revealed limited incorporation of MCs into sediments or plant tissues, pointing to planktonic degradation by microbes and possibly photolysis as the dominant pathways. Despite high ambient toxin levels, upscaling experiment results to an entire ecosystem suggested that wetlands degrade or retain 99% of MCs, effectively eliminating export to downstream ecosystems.
The marine toxigenic dinoflagellate family Amphidomataceae, comprising Amphidoma and Azadinium, has been primarily characterized by thecal morphology examined by SEM. To further clarify the detailed morphology, the intracellular ultrastructure of five Azadinium species, encompassing two toxigenic species (Azadinium poporum and Az. spinosum) and three non-toxigenic species (Az. inconspicuum, Az. dalianense, and Az. zhuanum), was examined using TEM. The ultrastructure of two Amphidoma species was also examined for comparison. All species exhibited typical dinoflagellate organelles, i.e., nucleus, fibrous vesicles, and trichocysts. Vesicles containing crystalline structures were found in all strains. The type of pyrenoid varied among Azadinium species; a stalked pyrenoid from the chloroplast in Az. spinosum, bulged in Az. dalianense and Az. inconspicuum, stalked or bulged in Az. poporum, and embedded in Az. zhuanum. Among the bulged pyrenoids, that of Az. inconspicuum was surrounded by thylakoids, whereas that of Az. dalianense lacked underlying thylakoids. Such intrageneric variations of pyrenoids may provide a useful diagnostic character for species discrimination. Cytoplasmic invaginations that reported in Amphidoma species were not observed in pyrenoids of five Azadinium species. Lipofuscin-like granules exhibiting broad-wavelength autofluorescence observed under LM, likely lipidic bodies associated with multilayered membranes observed under TEM, were found in all species. A microtubular strand and electron-opaque vesicles associated with the peduncle, as well as mucocysts surrounding a canal, were observed for the first time in the Amphidomataceae. The absence of a striated root connective in the flagellar root, as reported in Amphidoma, is consistent with a phylogenetic affinity between the Amphidomataceae and Peridiniales.
Microalgal toxins have been studied for decades, yet their occurrence and ecological role in offshore environments remain poorly understood due to the scarcity of observations. The external margin of the Patagonian continental shelf (Southwest Atlantic, Argentina) is a highly productive region supporting intensive fisheries. Phytoplankton phenology and biomass have been assessed largely through remote sensing, while direct assessment of toxin-producing microalgae remains limited, despite recent reports of exceptionally intense blooms. Here, we investigated the co-occurrence of multiple phycotoxins across the transition between the outer Patagonian shelf and adjacent oceanic waters, integrating toxin profiles with protistan community structure and hydrographic conditions. Hydrographic analyses were consistent with differences between stratified shelf waters and mixed, nitrate- and phosphate-richer off-shelf waters. Dinoflagellates dominated on the shelf, including two high-biomass blooms of Karenia sp. and the Amphidomataceae family, whereas diatoms increased toward the off-shelf area, as observed for Pseudo-nitzschia. All detected phycotoxins, including saxitoxins, spirolides, azaspiracid-2, domoic acid, pectenotoxins, and dinophysistoxin-1, were concentrated on the stratified shelf, despite occasionally high abundances of potential toxin-producing taxa in off-shelf waters. Additionally, most phycotoxins were detected within the 20-250 µm plankton size-fraction, whereas little or no toxins were detected in organisms > 250 µm. The predominance of toxins within the 20-250 µm plankton fraction is consistent with observations obtained during an early stage of trophic transfer under active bloom conditions, before substantial toxin accumulation in the > 250 µm plankton fraction. Overall, our findings highlight the combined influence of hydrographic retention, bloom dynamics and trophic processes on phycotoxin distribution.
With the intensification of global climate change and human activities, the frequent occurrence of harmful algal blooms (HABs) poses threats to aquaculture, coastal tourism, and other industries. The demand for HAB mitigation has shifted from algal removal to multifunctional approaches including algal removal, toxin reduction, and eco-environmental regulation. As an efficient and environmentally friendly method for HAB mitigation, the modified clay (MC) technology has made significant progress in theory, technological innovation, and standardized application in recent years. This paper systematically reviews the new developments in MC technology. In terms of surface modification, advanced methods such as functional group grafting modification and microbial composite modification have been developed to address organic matter-rich waters and multiple mitigation demands. The former significantly enhances flocculation efficiency against high-density, pico-sized HAB species and resistance to organic matter interference through organic quaternization and organic-inorganic composite strategies; the latter achieves multiple effects of "algicidal-toxin reduction" and "algal removal-water purification" by combining specific functional microorganisms. Regarding application standardization, a numerical model of the dosage-effectiveness relationship for MC has been established, providing a quantitative basis for the standardized field application of MC technology and forming standards that support large-scale applications. In addition, this paper introduces the eco-environmental regulation effects of this technology in intensive pond aquaculture (IPA), and its effects on the quality and yield of cultured organisms. Successful field practices in countries such as Turkey and Malaysia are also presented, offering references for integrated HAB prevention and control globally.
Over the past four decades, at least twenty species of the benthic dinoflagellate genus Gambierdiscus have been described worldwide, with the highest diversity reported from the South Pacific. Species delimitation within this genus is often challenging due to subtle morphological differences, and reliable identification frequently requires molecular confirmation. In the present study, epiphytic dinoflagellates collected along the coast of Viet Nam were examined using an integrative approach combining morphology and molecular phylogenetics. A new, potentially toxic species, Gambierdiscus larsenii sp. nov. was identified, increasing the number of Gambierdiscus species reported from Vietnamese waters to eight. Cells of G. larsenii sp. nov. measured 75.5 ± 5.4 μm in dorsoventral diameter (DV), 80.3 ± 6.1 μm in width (W), and 57.7 ± 3.9 μm in apical-antapical length (L), with a DV:W ratio of 0.94 ± 0.04. The thecal plates were smooth and densely perforated with pores, a broad pentagonal 2⁗, and rectangular 2' plates represented key morphological features. Morphological characteristics and plate tabulation were consistent with those of the genus Gambierdiscus. Phylogenetic analyses based on LSU rDNA (D1-D3), SSU rDNA, and ITS1-5.8S-ITS2 regions demonstrated that G. larsenii sp. nov. was closely related to, but genetically distinct from, other species possessing a broad 2⁗ plate. Toxin analysis confirmed the production of putative 51-OH-CTX3C at a cellular content in the lower pg cell⁻¹ range, indicating that G. larsenii sp. nov. may represent a potential risk for ciguatera poisoning in Viet Nam.
Ciguatera poisoning (CP) is the most prevalent marine toxin illness globally and disproportionately affects people from circumtropical regions due to the occurrence of the causative microalgae, Gambierdiscus. Increased reports of CP cases globally are linked to changing ocean temperatures, localized outbreaks in new regions and importation of ciguatoxin-contaminated fish into non-endemic regions. Gambierdiscus spp. produce several classes of bioactive polyether metabolites in addition to ciguatoxins, including gambierones, maitotoxins, gambieroxide, gambierol and gambieric acids. The role of these additional metabolites in CP remains unclear. In this study, non-targeted analysis using LC-HRMS was used to examine gambieroxide profiles in Gambierdiscus and Fukuyoa species. Initially purified gambieroxide was compared with a tentatively assigned gambieroxide analogue detected in G. pacificus and G. lewisii. The method was then used to characterize gambieroxide-like analogue profiles in the extracts of thirteen Gambierdiscus and two Fukuyoa species, with over thirty different analogues detected based on characteristic mass spectral fragmentation patterns in both positive and negative ionization modes. With few prior reports of these compounds, their detection across various species and strains provides valuable insight into the diversity of polyether compounds produced by Gambierdiscus and Fukuyoa. Future work will focus on understanding the significance of these gambieroxide-like analogues in CP.
The green tide alga Ulva prolifera shifts from an attached to a floating state during bloom formation, yet the physiological basis of this transition remains unclear. Here, using attached and floating thalli derived from a single parental clonal line and cultured under identical controlled conditions, we combined physiological measurements, protein-fraction analysis, and transcriptomics to compare growth and resource-allocation patterns between the two states. Despite similar bulk carbon and nitrogen contents, floating thalli reached significantly greater thallus length than attached thalli. Attached thalli showed higher maximum photosynthetic rate (Pmax), dark respiration (Rd), effective PSII quantum yield (Y(II)), and photosynthetic nitrogen-use efficiency (PNUE), whereas floating thalli showed higher maximum PSII efficiency (Fv/Fm) but lower Pmax, Rd, and PNUE. Together, these physiological patterns suggest that floating thalli maintain PSII efficiency while operating with lower photosynthetic capacity and respiratory demand. Floating thalli also exhibited higher levels of water-soluble (Pr) and SDS-soluble (Pp) proteins, together with lower levels of the SDS-insoluble fraction (Pw), consistent with reduced investment in detergent-insoluble structural pools. Transcriptomic analysis further showed enrichment of chloroplast- and photosynthesis-related functions in attached thalli, but cytoskeletal, cell-cycle, and DNA-repair functions in floating thalli. Together, these results support a lower-cost, resilience-oriented state in floating U. prolifera, in which rapid proliferation is associated with reduced structural investment rather than maximized instantaneous photosynthetic capacity. This resilience-associated strategy may help explain how floating thalli sustain rapid proliferation and contribute to the persistence of large-scale green tides under the fluctuating light and physical stress encountered at the sea surface.
