Alexandrium catenella (Group I) causes paralytic shellfish poisoning. Nitrogen is a critical component for both growth and toxin production in A. catenella, and recent studies have indicated that A. catenella uses both inorganic nitrogen and ammonium as nitrogen sources. However, the molecular mechanism underlying the transportation of ammonium in A. catenella has not been identified. In this study, we attempted to isolate and characterize the ammonium transporter (AMT) in A. catenella. cDNA cloning produced a number of AMT clones. To investigate the ammonium transport capability of A. catenella AMT (AlcAMT), we selected three representative cDNAs and the clones were inserted into expression vectors. These vectors were then transferred into an amt-deficient Schizosaccharomyces pombe transgenic yeast strain and grown on a medium containing NH4Cl as the only nitrogen source. Following transformation, yeast transformants carrying only one of the three AMTs were able to grow on the medium, confirming its ability to transport ammonium. Sequence analysis of the three AMT variants revealed that the successful variant included a K residue at sequence position 450, while the other variants contained a T residue at the same position. Mutation analysis confirmed that K450 is important for the function of AlcAMT.

Diarrhetic shellfish toxins (DSTs) are marine biotoxins produced by the dinoflagellates Dinophysis and Prorocentrum that cause gastrointestinal illness in humans worldwide. While European legislation avoids the risk of acute poisoning, the toxicity associated with repeated dietary exposure to DSTs in low quantities remains incompletely characterized. To address knowledge gaps regarding long-term exposure, we evaluated the toxicity of okadaic acid (OA), dinophysistoxin-1 (DTX1) and dinophysistoxin-2 (DTX2) administered by voluntary ingestion to male and female mice. Toxins were administered for 28 days at an experimentally calibrated dose (90 μg/kg bw) modelling a repeated human dietary exposure scenario derived from regulatory thresholds. Water consumption progressively decreased in treated females; the OA and DTX2 group also exhibited an increased urine protein-to-creatinine ratio, and minor histological renal changes. Repeated administration of DTX1 resulted in the most frequent diarrhea episodes and severe macroscopic damage to the digestive tract. Conversely, DTX2 produced the mildest clinical profile and lowest tissue retention. Furthermore, fecal toxin patterns differed by toxin: OA showed high initial excretion, DTX2 reached the highest fecal levels, and DTX1 was scarcely detected. Our findings indicate that repeated exposure to sublethal doses of DSTs by voluntary ingestion is associated with analogue- and sex-dependent persistent gastrointestinal alterations and subtle organ sensitivity, suggesting potential cumulative effects, which warrants further evaluation within risk assessment frameworks.

The previously developed direct competitive ELISA to detect PSP toxins (PSP-ELISA) was modified by employing an enzyme-conjugated anti-idiotypic antibody as a competing antigen. The detection limit of the modified PSP-ELISA in shellfish tissue was estimated to be 0.07 MU/g. When the modified PSP-ELISA was evaluated using the 192 toxin-contaminated shellfish samples, the modified PSP-ELISA results showed a sensitivity of 100% (88 of 88) and a specificity of 92.3% (96 of 104) compared to the MBA results.

Mussels (Mytilus spp.) are an important seafood product and a sentinel species for environmental contamination. This work aimed to analyze Portuguese monitoring data for mussels to identify seasonal and spatial trends in microbiological, biotoxins, and metal contamination. Data, from 2013 to 2025, were obtained from publicly available records from the official control program. Harvested mussels were generally safe for consumption, with most samples complying with microbiological Class A parameters (75.5%) and metals only exceeding regulatory limits once. Conversely, okadaic acid toxin group (i.e., diarrhetic shellfish poisoning toxins) exceeded limits in 19.5% of samples, identifying marine biotoxins as the greatest concern for mussel harvesting in Portugal. Microbiological contamination with Escherichia coli peaked in winter in estuaries and lagoons, while biotoxins peaked in summer in coastal areas. Both occurred most often in the North and Center regions, likely driven by rainfall-related inputs that may intensify under climate change-related extreme weather events. Therefore, harvesting restrictions did not only reflect food safety issues but also broader ecosystem contamination, requiring strengthened monitoring and mitigation measures to safeguard the ecosystem and public health.

Paralytic shellfish poisoning (PSP) has recurred almost every spring for decades in Jinhae Bay, Korea, yet the environmental factors governing its interannual variability remain poorly understood. To investigate the ecological drivers of Alexandrium blooms, we combined long-term field observations with species-specific molecular monitoring. Thirty Alexandrium strains were isolated and identified using LSU rDNA sequences, revealing four co-occurring species (A. catenella, A. pacificum, A. affine, and A. fraterculus). Species-specific TaqMan quantitative PCR (qPCR) assays were developed and applied to a 12-year monitoring dataset (2011-2022). The analyses revealed clear temperature-driven seasonal succession, with A. catenella dominating in spring, A. pacificum in late spring to early summer, and A. affine and A. fraterculus in summer to autumn. Alexandrium abundance was consistently higher under relatively low temperatures, which also coincided with increased PSP intensity. During the spring bloom period, dissolved inorganic phosphate (DIP), but not dissolved inorganic nitrogen (DIN), showed a significant positive association with A. catenella abundance, suggesting that phosphate availability may further promote bloom development. Species composition was closely associated with PSP dynamics, with A. catenella linked to severe toxicity events and A. pacificum contributing to prolonged toxicity periods. Overall, these findings demonstrate that temperature-driven niche differentiation is the primary mechanism governing Alexandrium bloom dynamics in Jinhae Bay, while phosphate availability acts as an additional environmental factor influencing bloom intensity and PSP severity.

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.

Particulate algal toxins are emerging particle-associated pollutants whose seasonal dynamics across planktonic food webs remain poorly understood in marginal seas. Using four seasonal surveys in the Yellow-Bohai Seas, we quantified diarrhetic shellfish poisoning (DSP) and paralytic shellfish poisoning (PSP) toxins in phytoplankton- and zooplankton-sized fractions. Phytoplankton-sized DSP (DSPp) was widespread (40-75% detection), whereas PSP toxins (24-48%) exhibited pronounced seasonal shifts in toxin composition. Zooplankton-sized DSP (DSPz) was predominantly observed in summer, showing the strongest apparent trophic coupling between plankton size fractions during this season. Two-stage generalized additive models (GAMs) suggested distinct environmental and biological associations with toxin occurrence and concentration. Toxin occurrence showed associations with temperature, salinity, nutrients, diatom biomass, and toxin-producing phytoplankton, with relationships varying among toxin groups and seasons. DSPp concentrations showed the strongest association with temperature among the evaluated predictors, whereas DSPz concentrations were more closely associated with particulate DSP availability, with DSPp showing the highest relative contribution among the predictors in the annual DSPz GAM. These findings suggest that the relative distribution of particulate toxins between plankton size fractions is more closely associated with particulate toxin availability than with the occurrence of toxic algae, supporting integrated monitoring strategies for improving ecosystem risk assessment in coastal waters.

Manchineel dermatitis, caused by the sap of the manchineel tree native to the coastlands of the Caribbean, West Africa, and Central America, has received limited attention in the literature despite significant morbidity. The toxic sap causes a burning, blistering rash and conjunctivitis, while ingestion of the fruit may lead to oropharyngeal pain, hemodynamic instability, and gastrointestinal distress. Tourists unfamiliar with the manchineel tree may be exposed through exposure to the tree's sap, contaminated rainwater, or ingestion of the apple-like fruit. We herein present a case of a patient who experienced prolonged symptoms of manchineel toxicity after ingestion of the manchineel fruit for several weeks. Antihistamines, corticosteroids, and a PPI were ineffective. The symptoms eventually resolved after discarding clothing and towels that had come in contact with the tree, raising the possibility that toxins may linger on fabrics. Travellers to regions in the Caribbean or Central America are at particular risk for toxicity from the Manchineel tree if unfamiliar with the associated dangers and should be counselled to avoid contact with the tree or ingesting any unfamiliar fruit on the ground. When exposures do occur, it may be reasonable to dispose of potentially contaminated fabrics to avoid recurrent exposures, particularly if recurrent symptoms are observed, as in our patient. We further contextualize manchineel toxicity within a comparative review of select tropical foodborne intoxications of plant origin (ackee, lychee, cassava, papain) and marine origin (ciguatera, scombroid, neurotoxic and diarrhetic shellfish poisonings, tetrodotoxin), distinguishing manchineel's local irritant mechanism from the systemic toxidromes of these comparators and underscoring the absence of a specific antidote.

A previously overlooked isomer of okadaic acid (OA), which is structurally related to dinophysistoxin-2 (DTX2), was identified in bivalves and water columns from the Northwest Iberian Peninsula. This isomer elutes chromatographically after DTX2 and before DTX1, with mass spectrometric fragmentation patterns distinct from those of OA. It occurs at lower concentrations than OA but at levels comparable to DTX2, showing a consistent presence since monitoring by LC-MS/MS began in 2014. The abundance of this isomer correlated more strongly with OA than with DTX2, suggesting that it originates mainly from phytoplankton species that do not produce DTX2. Seasonal patterns revealed two maxima for the isomer, aligning with OA but differing from the single autumn-winter maximum of DTX2. Spatially, the isomer followed a northeast-southwest gradient along the Galician coast, similar to the OA and DTX2 distributions. The esterification rates of the isomer in mussels are lower than those of OA but similar to those of DTX2, likely resulting in slower depuration and longer persistence. Temporal trends indicate a recent increase in the concentration and seasonality of the isomer, rendering it more conspicuous. These findings highlight the growing significance of this isomer in shellfish toxin profiles throughout the studied period, underscoring the need to determine its structure and potential toxicity to better assess risks to human health.

Brevetoxins (PbTxs) are marine polyether compounds produced by the alga Karenia brevis, which accumulate in shellfish and fish, and transferred through the marine food web. These toxins impact both marine ecosystems and human health. Consumption of contaminated shellfish is the primary cause of Neurotoxic Shellfish Poisoning (NSP), which presents with neurological, gastrointestinal, and/or cardiovascular symptoms that appear in a few hours and typically resolves within 1-3 days, although some disturbances may persist for weeks or months. The acute toxicity of PbTxs involves activation of voltage-gated sodium channels, leading to sodium influx and membrane depolarization. However, the long-term neurotoxic effects remain poorly understood. To investigate this, we conducted a 14-day neurotoxicity assay in male and female mice that received a single oral dose of PbTx3. Early neurological signs were observed, but muscle strength remained unaffected over the long term. Cold nociceptive sensitivity decreased over time, resulting in sensory hypoalgesia that was particularly pronounced in males. Creatinine levels increased in females at day 14, though no associated kidney histopathology was observed. At the highest dose (750 µg/kg), ultrastructural changes in skeletal muscle, including sarcomere disorganization, calcium overload, and autophagy, were noted. To explore potential mechanisms of action responsible for neurotoxicity, whole-cell patch-clamp recordings were performed in HEK293 cells expressing transient receptor potential vanilloid 1 (TRPV1) channel. PbTx3 modulated TRPV1 currents in a dose-dependent manner, suggesting this receptor may mediate some of the observed sensory effects. Our findings reveal persistent, sex-dependent alterations after PbTx3 exposure and provide insight into mechanisms of sublethal toxicity. The combination of functional testing, histopathology, and electrophysiology offers a sensitive approach for assessing neurotoxicity risk of marine toxins.

In Alaska, paralytic shellfish poisoning (PSP) is associated with the toxic dinoflagellate Alexandrium catenella, which blooms annually along the coastline from the Canadian border to the Beaufort Sea. While it has long been recognized that these blooms cause annual outbreaks of shellfish toxicity each spring and summer, little is known about other pathways for PSP toxins in the marine food web. Here, we present data from a four-year study to characterize the occurrence of PSTs in marine non-bivalve invertebrates, forage fishes and predatory fishes across the breadth of southern Alaska. Samples were obtained at coastal sites throughout the Gulf of Alaska, including the Aleutian Islands, Alaska Peninsula, Cook Inlet region, Prince William Sound and southeast Alaska, as well as sites in the southeastern Bering Sea. Collectively, 235 non-bivalve invertebrate samples, 1511 forage fish samples and 364 commercially important predatory fish were collected and analyzed for PSP toxins (PSTs) via an improved ELISA method. Overall, 41% of specimens exhibited detectable levels of PSTs across 14 invertebrate taxa, 23 forage fish species and 7 species of predatory fishes. In non-bivalve invertebrates, 39.8% of samples were positive for PSTs with the greatest levels in crabs, sea stars and carnivorous snails. In forage fishes, >35% showed detectable PST levels, with the highest in Pacific Sand Lance, Pacific Herring, juvenile Pacific Cod, juvenile Pacific Tomcod, Capelin, Surf Smelt and juvenile salmon. Notably, toxins were commonly present in important prey for seabirds and marine mammals, in addition to juveniles of commercially important fishes. In predatory fishes, PSTs were detected in 60-75% of all tissues tested, with the highest incidence in fish liver and kidney tissue, and lowest in stomach contents. PST levels were low in muscle tissue, signifying low toxicity risks to humans consuming filets. However, the prevalence of these toxins in so many fishes suggests potential impacts to survival and recruitment of juvenile predatory fishes in Alaskan coastal areas.

Eastern boundary upwelling systems sustain among the highest marine primary productivity globally, yet diatom assemblage responses to persistent upwelling and episodic hydroclimatic disturbances remain critically undercharacterised along the North African Atlantic margin. This study examines diatom spatiotemporal dynamics along the Aglou-Sidi Ifni coastline (~29°N, Moroccan Atlantic), a transitional sector of the Canary Current Upwelling System, over two annual cycles (2014-2016) at three coastal stations. A total of 126 diatom taxa were identified among 233 phytoplankton species (54% of total richness). Taxonomic revision against WoRMS and AlgaeBase yielded 20 nomenclatural updates. Total phytoplankton cell density exhibited a pronounced seasonal pattern, peaking in spring 2015 (65,890 cells L[-1]), exceeding spring 2014 by 24-31%. This amplification coincided with elevated nitrate (up to 390.6 μg L[-1]) and phosphate (up to 147.8 μg L[-1]), consistent with a flood-driven nutrient priming hypothesis, although single-event design precludes causal attribution. Molar N:P ratios ranged 2.58-6.32 (station means: 4.17-4.28), remaining below Redfield (16:1), evidencing chronic nitrogen limitation. Absent dissolved silicate data preclude complete bloom stoichiometry characterisation. Multivariate analysis explained 58.6% variance, with temperature and nitrate as primary community drivers. A southward gradient in diatom dominance (46-52%) and richness was consistent with spatial upwelling intensity differences. Six Pseudo-nitzschia morpho-groups were recorded, including P. multiseries near Massa Marine Protected Area. Confirmatory transmission electron microscopy (TEM), quantitative PCR (qPCR), and shellfish domoic acid assays are required before regulatory conclusions; this study provides a preliminary precautionary baseline signal.

Paralytic shellfish toxins (PSTs) produced during harmful algal blooms (HABs) threaten seafood safety and public health. This study examined the spatiotemporal variability of PST contamination and species-specific accumulation and depuration in two Mediterranean bivalves, Acanthocardia tuberculata and Callista chione, along the Moroccan coast during a continuous two-year monitoring period (2022-2023). Phytoplankton communities were dominated by Gymnodinium catenatum, while Alexandrium spp. occurred sporadically. Although algal abundance was higher in M'diq Bay, maximum PST concentrations were recorded in Oued Laou, indicating a weak relationship between bloom intensity and shellfish toxicity. Marked interspecific differences were observed. A. tuberculata exceeded the regulatory limit (800 μg STX·di-HCl eq·kg[-1]), reaching 10,041 μg STX·di-HCl eq·kg[-1], mainly due to persistent decarbamoylsaxitoxin (dcSTX), and showed high acute risk (HQ(ARfD) up to 114.76). In contrast, C. chione displayed lower toxin accumulation (HQ(ARfD) 0.15-0.24) and faster depuration, although transient peaks indicated short-term risk during blooms. These findings demonstrate species-specific PST dynamics and support the use of C. chione as a rapid-response sentinel, while highlighting the need for toxin-based monitoring in high-risk areas such as Oued Laou.

Saxitoxin (STX) is among the most potent toxins known, is classified as a chemical weapon, and is the archetype of the paralytic shellfish toxin (PST) family produced by marine and freshwater harmful algal blooms (HAB). STX causes paralysis and death through inhibition of voltage-gated sodium channels (NaVs), has no antidote, and poses a public health and commercial fishing threat due to its accumulation in seafood and increasing HAB occurrences. Although STX is lethal to varied vertebrates, including humans, certain frogs resist STX poisoning. This phenotype is thought to depend on soluble toxin sponge high-affinity STX binding proteins (saxiphilins, Sxphs) that provide resistance through a competition mechanism different from classic target site ion channel mutation mechanisms. Here, we test this idea and show that a single dose of American bullfrog (Rana catesbeiana) Sxph (RcSxph) is sufficient to counteract STX neurotoxicity and lethality in female mice using paradigms where STX and Sxph are administered together or sequentially in either order. Importantly, this function requires the RcSxph high-affinity STX binding site. Our findings provide in vivo validation that Sxphs are toxin sponges that protect against STX poisoning and highlight the potential to harness this protein class as antidotes for PSTs and other toxins.

To investigate the dynamics of paralytic shellfish toxins (PSTs) and tetrodotoxins (TTX) in scallops, PSTs and TTX were analyzed in the hemolymph supernatant (hemolymph-S) and digestive gland in Yesso and Akazara scallops cultured in eastern Japan. In Yesso scallops sampled between 22 April 2025 and 21 October 2025, the PST concentrations in the hemolymph-S were 1.6-17% of those in the digestive gland, showing a positive correlation (r = 0.753). However, the PST composition in the hemolymph-S and digestive gland differed; the hemolymph-S composition initially resembled that of laboratory-cultured dinoflagellates, coinciding with typical onset of toxic dinoflagellate blooms in late April. Following this period, the PST composition in the hemolymph-S gradually converged with that of the digestive gland, via chemical transformation in the digestive gland followed by release into the hemolymph. The ratios of 11β-OSO3H toxins (C2, GTX4, GTX3) to 11α-OSO3H toxins (C1, GTX1, GTX2), which exist in chemical equilibrium, exhibited a similar trend. TTX was detected in both tissues of Yesso and Akazara scallops collected from 28 August 2025 to 27 January 2026, with the hemolymph-S concentration being 0.5-5.4% of that in the digestive gland. These results suggest that these toxins are sequestered into the digestive gland from the PST-producing dinoflagellates and certain TTX-bearing organisms, and then they partially flow into the hemolymph for circulation throughout the body.