Paralytic Shellfish Research Articles

Effects of Zooplankton Extracts on the Production of Paralytic Shellfish Toxins by Gymnodinium catenatum and Alexandrium pacificum

Effects of Zooplankton Extracts on the Production of Paralytic Shellfish Toxins by Gymnodinium catenatum and Alexandrium pacificum

Unraveling the risks of nAl2O3 on harmful algal blooms: Insights from paralytic shellfish toxins production of Alexandrium tamarense

As one of the commonly used and cost-effective nanomaterials, nanosized aluminum oxide (nAl2O3) posses unique properties and chemical stability. However, its extensive use and resultant dissemination into aquatic ecosystems prompt concerns over the proliferation and repercussions of harmful algal blooms, particularly those caused by dinoflagellates producing toxins. This study investigated the sub-chronic effects of nAl2O3 on growth, physiological activities, and paralytic shellfish toxins (PSTs) production in Alexandrium tamarense. Results showed dose-dependent inhibition in growth (EC50 = 20.6 mg L−1), esterase activity, and photosynthetic efficiency (Fv/Fm) during the sub-chronic exposure (13-day). The internalization of nAl2O3 in microalgal cells and the significant decrease in the total cellular PSTs content were observed under high nAl2O3 concentrations (>40 mg L−1). The study also demonstrated a clear decrease in the content of some derivatives of PSTs (GTX5, C1/2, and GTX2/3) with the increase in nAl2O3 concentrations, accompanied by the induction of an unknown derivative. Excessive ROS production, dissolved Al, and physical inhibition were suggested as potential mechanisms for nAl2O3 toxicity and changes in PSTs toxin profile. Overall, this research enhances our understanding of the potentiated risks and threats on the possible concurrent events of toxic dinoflagellate, such as Alexandrium species and nanoparticles in aquatic environments.

Paralytic Shellfish Toxin Extraction from Bivalve Meat for Analysis Using Potentiometric Chemical Sensors.

A simple and reliable methodology for the detection of paralytic shellfish toxins (PSTs) in bivalve tissues using potentiometric chemical sensors was developed. Five methods of PST extraction from mussel and oyster tissues were evaluated, including the AOAC-recommended method, which served as the reference. The main objective was to minimize the matrix effect of the extracts on the sensors' responses and ensure efficient toxin recovery. Extraction procedures using acetic acid with heating and water yielded the highest responses from the potentiometric chemical sensors to PSTs. The highest recovery of PSTs from bivalve tissues was achieved with extraction using acetic acid and heating. Further extract purification, which is indispensable for liquid chromatography with fluorometric detection (LC-FLD) analysis, was found to be unnecessary for analysis with chemical sensors. While water extraction can also be used as a rapid and simple PST extraction method, the lower recoveries should be considered when interpreting the results. Further research is needed to identify the compounds remaining in the extracts that cause a decrease in sensor responses and to develop procedures for their elimination.

Predator-induced defense decreases growth rate and photoprotective capacity in a nitrogen-limited dinoflagellate, Alexandrium minutum

Some dinoflagellates produce toxic secondary metabolites that correlate with increased resistance to grazers. The allocation costs of toxin production have been repeatedly addressed, but with conflicting results. Few studies have considered the potential costs of this defense to the photosystem, even though defense toxins (e.g., karlotoxins and brevetoxins) are closely linked to the photoprotective process. Here, we used chemical cues from copepods to induce paralytic shellfish toxin (PST) production in resource-limited Alexandrium minutum and quantitatively determined the growth rate and potential trade-offs with the photosystem process. The results show that grazer-induced, more toxic A. minutum had larger cell volume, lower cell division rate, and lower pigment content under nitrogen-limited conditions than control cells. In addition, predator cues led to a lower relative abundance of photoprotective xanthophylls and a reduced de-epoxidation efficiency of the xanthophyll cycle under high light conditions, reducing the ability of the cells to resist photodamage. Decreased photoprotective capacity may reflect an overlooked defense cost of toxin production.

Elevated pCO2 may increase the edible safety risk of clams exposed to toxic Alexandrium spp.

Toxic harmful algal blooms (HABs) have received increasing attention owing to their threat to the health of aquatic life and seafood consumers. This study evaluated the impacts of elevated atmospheric partial pressure of CO2 (pCO2) on the production of paralytic shellfish toxins (PSTs) in different Alexandrium spp. strains, together with its further effects on the bioaccumulation/elimination dynamics of PSTs in bivalves contaminated with PSTs from toxic dinoflagellates. Our results showed that elevated pCO2 stimulated the growth of the two Alexandrium spp. (A. catenella and A. pacificum) isolated from the northern and southern coastal areas of China, respectively, and affected PST production including content and toxicity of the two strains differently. Further PSTs bioaccumulation/elimination in PSTs-contaminated Manila clam, Ruditapes philippinarum under high pCO2 also occurred. It is worth noting the biotransformation of neosaxitoxin (NEO) with high toxicity through trophic transfer with effect of elevated pCO2. When in microalgae cultured under the control (410 ppm) and elevated pCO2 conditions (495 and 850 ppm), the proportion of NEO in the PST content produced by A. catenella was reduced from 11.1 to 6.4 and 2.6 %, while the proportion of NEO in A. pacificum was increased from 3.1 to 3.6 and 4.7 %, respectively. NEO accounted for >50 % of total PST contents in clams, which were biotransformed via transfer from dinoflagellates and higher pCO2 enhanced this biotransformation leading to increased NEO accumulation. The negatively affected elimination of PSTs, especially NEO, in clams fed with A. catenella or A. pacificum, indicates that the detoxification of PSTs-contaminated clams may be more difficult under elevated pCO2. This study provides reference for developing models to assess the safety of bivalves under the co-stress of environmental change and toxic HABs, suggesting that ocean acidification may lead to the higher safety risk of Manila clams exposed to toxic HAB dinoflagellates.

Optimization of the polyaniline solid contact in potentiometric sensors for detection of paralytic shellfish toxins in mussels

The present study optimized the properties of the electropolymerized polyaniline (PANI) solid inner contact for a potentiometric chemical sensor by varying the thickness of the polymer layer. A potentiometric sensor for detecting one of the paralytic shellfish toxins, decarbamoyl saxitoxin (dcSTX), in mussel extracts was selected as a case study. The plasticized PVC membrane composition, developed in previous work for the detection of this toxin, was used. The structure and electrical properties of PANI layers of different thicknesses were studied using scanning electron microscopy and electrochemical impedance spectroscopy. The effect of PANI solid contact thickness on the characteristics of the potentiometric sensor, including sensitivity, detection limit, and selectivity to dcSTX in buffer solutions and mussel extracts, was evaluated. The formation of a water layer at the inner solid contact and PVC membrane interface was investigated using electrochemical impedance spectroscopy and a water test. PANI layer thickness 1.1 µm was found to be optimal for solid inner contact for potentiometric sensor with PVC membrane providing highest sensitivity and selectivity.

Prevalence and distribution of dissolved paralytic shellfish toxins in seawater in the Yellow Sea and the Bohai Sea, China

Paralytic shellfish toxins (PSTs) could be secreted by PSTs-producing microalgae or released by ruptured cells in seawater. In this study, the distribution of dissolved PSTs in the Yellow Sea and the Bohai Sea, China, was investigated by two cruises in April and July 2023. Seawater samples were collected from the surface, middle and bottom layers, and the profiles of PSTs were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the spatial distribution characteristics of dissolved PSTs and their correlation with environmental factors were explored. Results showed that C1/2, GTX1/4, GTX2/3 and dcGTX2/3, were detected in seawater samples in both spring and summer, with the detection rates 100 % and 97.6 %, respectively. The total PST (ΣPSTs) concentrations ranged in 12 ∼ 590 pmol L−1, 9.3 ∼ 546 pmol L−1, 12 ∼ 2,452 pmol L−1, and not detected (nd) ∼ 188 pmol L−1 in seawater samples collected from the surface, middle and bottom layers in spring, and the surface layer in summer, respectively. Concentrations of PSTs markedly varied in the vertical water column in different sea regions. Generally, concentrations of ΣPSTs in the bottom seawater were higher than those in the surface and middle layers in the Bohai Sea and the North Yellow Sea, but no significant difference in the different water layers in the South Yellow Sea. In addition, concentrations of ΣPSTs in surface waters were much lower in summer than those in spring. In both spring and summer, dissolved PSTs in surface seawater were mainly distributed in the South Yellow Sea. These results indicate that PSTs were prevalent in the Yellow Sea and the Bohai Sea, of which the potential hazard to marine organisms should be highly concerned.

Temperature Dependence of the Pre-Chromatographic ‘Lawrence’ Method for Bivalves Contaminated with Paralytic Shellfish Poisoning Toxins

AbstractSaxitoxins are potent neurotoxins originating the acute human neurological syndrome of paralytic shellfish poisoning (PSP) via bivalve vectors. The official testing method in the European Union, commonly known as the ‘Lawrence method’, involves pre-column oxidation steps. The Portuguese monitoring adopted the hydrogen peroxide oxidation screening approach for bivalves contaminated with Gymnodinium catenatum toxins, which can quantify chromatographically at once 6 out of 10 analogues commonly found in bivalves. Seasonal fluctuation in the fluorescence yield of calibration curves was observed across years in a consistent manner. It correlated with fluctuations in average monthly air temperature in Lisbon, highlighting the importance of recording the room temperature during the oxidation steps as a matter of routine practice. Incubation experiments also showed an increase in fluorescence yield with temperature, more pronounced for the 11-hydroxysulphate analogues (dcGTX2 + 3, C1 + 2, GTX2 + 3) than for the 11-H toxins (dcSTX, GTX5[B1], STX). Temperature can be exploited to increase fluorescence yield, assisting in spectral confirmation, but must not exceed 40–50 °C to avoid toxin decomposition or production of extra oxidation products.

Resting Cysts of the Toxic Dinoflagellate Gymnodinium catenatum (Dinophyceae) Ubiquitously Distribute along the Entire Coast of China, with Higher Abundance in Bloom-Prone Areas

Blooms of Gymnodinium catenatum have occurred occasionally in different areas of China and caused tremendous economic loss and even threatened human health. Not only is G. catenatum an important harmful-algal-bloom (HAB)-causing species, but also the only gymnodinioid dinoflagellate known to produce paralytic shellfish poisoning toxins (PSTs). Due to the germination of resting cysts, which often initiates blooms, the distribution and abundance of cysts in sediments and particularly the confirmation of cyst beds are important information for understanding and predicting dinoflagellate blooms. In this research, 199 sediment samples were collected from China’s coastal seas, ranging from the Beidaihe in the Bohai Sea (BS) to the southernmost sample from the Nansha Islands of the South China Sea (SCS). TaqMan quantitative PCR (qPCR) assays with species-specific primers and probes were developed to specifically detect the distribution and abundance of cysts in the 199 samples. The detection revealed that G. catenatum cysts were widely present in the sediments (126 of the 199 samples), with 93.55%, 74.65%, 42.37%, and 50% of the samples detected positively from the BS, YS, ECS and SCS, respectively, and covering the vast sea area from Nansha Islands to the Beidaihe area. The single-cyst morpho-molecular identification in the samples from Beidaihe confirmed the existence of G. catenatum cysts in the BS, and the positive detections of G. catenatum cysts using the qPCR methods. While G. catenatum cysts were widely distributed in all four seas of China, the average abundance was relatively low (1.0 cyst per gram of wet sediment). Three samples from the East China Sea (ECS), however, contained G. catenatum cysts at a relatively higher level (23 cysts g−1 wet sediment) than other sea areas, suggesting a pertinence of cyst abundance to the frequent occurrences of G. catenatum blooms in the area during recent years. Collectively, for G. catenatum being such an important toxic and HAB-causing species globally, the ubiquitous distribution of its cysts along the coastal waters of China and higher abundance in the bloom-prone areas warns us of a risk that cyst beds, although currently low in abundance, may seed HABs in any and many sea areas of China at any forthcoming year, and particularly those areas with records of frequent HABs outbreaks in the past.

Intracellular abundance, localization, and enzymatic activity of a saxitoxin biosynthesis enzyme, SxtG, in two sister subclones of the dinoflagellate Alexandrium catenella with extremely different levels of paralytic shellfish toxins

Paralytic shellfish poisoning is caused by saxitoxin (STX), and its analogues (paralytic shellfish toxins (PSTs)) produced by marine dinoflagellates. SxtA and SxtG are the most essential enzymes in STX biosynthesis. Previous studies investigated the abundance and subcellular localization (i.e., chloroplasts) of SxtA in dinoflagellates using immunostaining. The present study characterized SxtG, and positive signals were detected in sister subclones of Alexandrium catenella (Group I) with extremely different levels of PSTs. Multiplex fluorescence immunostaining detection of a PST-positive subclone revealed co-localization of SxtA and SxtG, suggesting that SxtG localizes to chloroplasts. In vitro amidino-transfer from arginine to Int-A’, the first intermediate product in the biosynthesis, was presumed to be catalyzed by SxtG, and the reaction was established using crude extracts of PST-positive and negative A. catenella subclones. These analyses suggested that the PST-negative subclone expresses active SxtG but not SxtA. These findings support our hypothesis that decrease of SxtA leads to the loss of toxicity in the PST-negative subclone of A. catenella. Our results identified a key reaction that could enhance understanding of the biochemistry of STX biosynthesis in dinoflagellates.

Two decades of data on the neurotoxic Gymnodinium catenatum dynamics and paralytic shellfish toxins contamination of molluscs in the southwestern Mediterranean: What have we learned?

Harmful algal blooms have been documented in the Moroccan Western Mediterranean region since 1993, primarily associated with the presence of paralytic shellfish toxins (PSTs) produced by the dinoflagellate Gymnodinium catenatum. The proliferation of this neurotoxic species has led to recurring bans on the harvesting of molluscs, resulting in significant socio-economic repercussions and threats to human health. In the present study, we examine the dynamics of G. catenatum and mollusc PST contamination patterns over a 20-year period (2002−2021) in two distinct marine ecosystems: M'diq Bay and the Oued Laou Estuary. For the PST contamination, we considered two commercially important shellfish species: the smooth clam, Callista Chione, and the cockle, Acanthocardia tuberculata. The highest G. catenatum abundances were consistently observed from November to February in both sites. Our data revealed inter-annual variations in G. catenatum abundance, peaking at 91,840 cells.L−1 in November 2011. PST contamination levels in A. tuberculata were significantly higher than those observed in C. chione. Furthermore, we identified a significant correlation (Pearson, P-value <0.05) between PST contamination of smooth clams and the abundance of G. catenatum. The contamination of A. tuberculata by PSTs reached very high levels, with up to 13,500 μg STX di-HCl eq. kg−1 of shellfish meat, exceeding the established safety thresholds by 16-fold. Additionally, there has been an increase in the prevalence and incidence of PSTs over the years. Notably, we observed a substantial increase in G. catenatum blooms and PST events in the Western Mediterranean during the last decade (2010−2021). The examined data suggest that rainfall could play a pivotal role in G. catenatum bloom dynamics by enriching marine waters with nutrients. The statistical model selection approaches indicated that nutrient concentrations (i.e., nitrate and phosphorus) were the most significant parameters for G. catenatum blooms in the studied area.

The Role of Cyano-HAB (Cyanobacteria Harmful Algal Blooms) in the One Health Approach to Global Health

Harmful algal bloom events occur in salt, brackish, and fresh water. In bodies of water such as oceans and estuaries, diatoms or dinoflagellates form “tides” that produce toxins associated with seafood poisoning, including paralytic shellfish poisoning, or respiratory distress from inhalation of aerosolized toxins. Cyanobacteria predominantly bloom in fresh water; they can produce microcystins; cylindrospermopsin; and other toxins that humans or animals might be exposed to through water contact, inhalation, or ingestion. Animals that become ill or die can be sentinels for harmful algal bloom events. In a One Health approach, information about harmful algal bloom exposures and health effects support efforts to detect these events and mitigate and prevent associated illnesses. Human, animal, and environmental health partners can work together to document the occurrence and impacts of harmful algal bloom events and characterize associated illnesses.

First insights into the distribution and diversity of toxic dinoflagellate cysts in the surface sediments of Dakhla Bay (African Atlantic coast): relationships with environmental factors and mollusk intoxication events.

Dakhla Bay, situated on the African Atlantic coast, has witnessed sporadic harmful algal blooms (HABs) caused by toxic dinoflagellate species over the past two decades. In this study, we investigated the distribution, abundance, and diversity of dinoflagellate cysts, with a focus on potentially toxic species that develop in this ecosystem where such data are lacking. Sediment samples were collected in April 2018 through coring at 49 stations distributed across the bay. The highest abundance of dinoflagellate cysts was recorded at 304 cysts/g dry sediment, observed at the inner part of the bay, indicating that this area is the preferential zone for cyst accumulation. Pearson's tests revealed significant positive correlations (P < 0.05) between cyst abundance and the water content, organic matter, and fine fraction (< 63μm) of the sediment. Cyst morphotypes of potentially toxic dinoflagellate species known to produce saxitoxins, such as Alexandrium minutum, Alexandrium tamarense species complex, Gymnodinium catenatum, and yessotoxins, such as Lingulodinium polyedrum and Gonyaulax cf. spinifera, were identified in the sediment of Dakhla Bay. These findings were further supported by our long-term monitoring period (2005-2018), underscoring the presence of these HAB species in Dakhla Bay. During our survey, sporadic mollusk intoxication events were recorded at station PK25 for the grooved razor shell Solen marginatus and at station Boutelha for the oyster Crassostrea gigas. Paralytic shellfish toxin concentrations exceeded the sanitary threshold (80μg STX di-HCl eq/100g of shellfish meat) only twice, in December 2006 and January 2007 at station PK25. Contamination by amnesic shellfish toxins occurred sporadically but never reached the sanitary threshold of 20µg/g of shellfish meat. Lipophilic shellfish intoxication occurred multiple times in the two investigated areas. These observations suggest that the cysts of the identified HAB species germinated and inoculated the water column, resulting in the observed intoxication events. Relatively low levels of intoxication could be attributed to the moderate abundances of cysts, which may reduce the seeding capacity. This could be explained by the significant interaction of Dakhla Bay with the Atlantic Ocean, characterized by hydrological dynamics that impede the deposition and accumulation of cysts in the bay's sediments. This study reaffirms the importance of investigating dinoflagellate cysts in assessing the diversity of HAB species and evaluating associated sanitary risks.

Biogeochemical conditions controlling the intensity of paralytic shellfish poisoning (PSP) outbreak caused by Alexandrium blooms: Results from 6-year field observations in Jinhae-Masan Bay, Korea

Previous field observations from 2018 to 2019 revealed that paralytic shellfish poisoning (PSP) caused by the blooms of toxic dinoflagellate Alexandrium species occurred under low concentrations of dissolved inorganic nitrogen (DIN) and high concentrations of dissolved organic nitrogen (DON) and humic-like fluorescent dissolved organic matter (FDOMH) in Jinhae-Masan Bay, Korea. In this study, we obtained more data for DIN, DON, FDOMH, and Alexandrium cell density from 2020 to 2023 to further validate environmental conditions for the PSP outbreak. We also measured total hydrolyzed amino acids (THAA) to determine the bioavailability of DON fueling the PSP outbreak. Over the 6-year observations, there was a consistent pattern of low DIN concentrations and high DON and FDOMH concentrations during the PSP outbreak periods. The Alexandrium cell densities, together with the PSP toxin concentrations, increased rapidly under this environmental condition. The PSP outbreak occurs when a large amount of DIN originating from the stream waters near the upstream sites is transformed into DON by biological production before entering the PSP outbreak area. The produced DON is characterized by high bioavailability based on the various AA-derived indices (enantiomeric ratio, degradation index, non-protein AA mole%, and nitrogen-normalized AA yield). In addition, the intensities of PSP outbreaks are mainly dependent on the conversion stage of DIN to DON and enhanced FDOMH. We found that the strong PSP outbreak occurred consistently under a low level of DIN (<1.0 μM) and high levels of DON (>9.0 μM) and FDOMH (>1.5 R.U.). Thus, our results suggest that the monitoring data of environmental conditions can be used to predict the PSP outbreak in the coastal oceans.

Allelochemicals determine competition and grazing control in Alexandrium catenella

The production of allelochemicals by the toxigenic dinoflagellate Alexandrium catenella is one of the suggested mechanisms to facilitate its bloom formation and persistence by outcompeting other phototrophic protists and reducing grazing pressure. In Southern California, toxic events caused by A. catenella and paralytic shellfish toxins (PSTs) regularly impact coastal ecosystems; however, the trophic interactions and mechanisms promoting this species in a food web context are still not fully understood. In the present study, we combined a dynamical mathematical model with laboratory experiments to investigate potential toxic and allelochemical effects of an A. catenella strain isolated off the coast of Los Angeles, Southern California, on competitors and a common zooplankton consumer. Experiments were conducted using three toxigenic strains of A. catenella, comparing the new Californian isolate (Alex Cal) to two strains previously described from the North Sea, a lytic (Alex2) and non-lytic (Alex5) strain, testing for donor density-dependent effects on two phytoplankton species (Rhodomonas salina, Tetraselmis sp.) and on the rotifer Brachionus plicatilis. Bioassays revealed a steep decline in competitor and consumer populations with increasing Alex Cal concentrations, indicating an intermediate lytic activity compared to the North Sea strains (lytic Alex2 and non-lytic Alex5). The rotifer fed and grew well on the PST- toxic, but non-lytic Alex5 strain, while its survival significantly decreased with increasing concentrations of the two lytic strains Alex Cal and Alex 2, indicating that negative effects on the rotifer were mediated by allelochemicals rather than PST-toxins. Mixed culture experiments including both competitors and consumers demonstrated that the intensity of allelochemical effects not only depended on the A. catenella density but also on the target density. Negative effects on grazers were alleviated by co-occurring competitors with a lower sensitivity to allelochemicals, thus reducing harmful compounds and allowing grazing control on the dinoflagellate to come into effect again. Results from mixed culture experiments were supported by the mathematical approach used in this study which was calibrated with data from simple monoculture growth, pairwise competition and predator-prey experiments, demonstrating the applicability of this model approach to predict the outcome of more complex food web dynamics at the community level.

Variability in Paralytic Shellfish Toxin Profiles and Dinoflagellate Diversity in Mussels and Seawater Collected during Spring in Korean Coastal Seawater.

Paralytic shellfish toxins (PSTs) are potent neurotoxins produced by certain microalgae, particularly dinoflagellates, and they can accumulate in shellfish in coastal seawater and thus pose significant health risks to humans. To explore the relationship between toxicity and PST profiles in seawater and mussels, the spatiotemporal variations in PST concentrations and profiles were investigated along the southern coast of Korea under peak PST levels during spring. Seawater and mussel samples were collected biweekly from multiple stations, and the toxin concentrations in the samples were measured. Moreover, the dinoflagellate community composition was analyzed using next-generation sequencing to identify potential PST-producing species. The PST concentrations and toxin profiles showed substantial spatiotemporal variability, with GTX1 and GTX4 representing the dominant toxins in both samples, and C1/2 tending to be higher in seawater. Alexandrium species were identified as the primary sources of PSTs. Environmental factors such as water temperature and salinity influenced PST production. This study demonstrates that variability in the amount and composition of PSTs is due to intricate ecological interactions. To mitigate shellfish poisoning, continuous monitoring must be conducted to gain a deeper understanding of these interactions.

Why cysts of Alexandrium catenella and/or A. pacificum (Gonyaulacales, Dinophyceae) do not remain in sediments as fossils?

The dinoflagellate genus Alexandrium contains a number of species that produce paralytic shellfish toxins and have been the focus of attention as toxic plankton for harmless algal studies. Among Alexandrium species, A. catenella and A. pacificum form ellipsoidal-shaped resting cysts, which are preserved in marine sediments, and have attracted attention as potential seeds for future proliferation after favorable environmental conditions environmental improvement. However, although these cysts are preserved in surface of marine sediments, there is no record of their occurrence from solidified sediments as fossils. In order to clarify the reason for this, we investigated the differences in the chemical composition of cyst walls between colorless cyst of Alexandrium catenella/pacificum and Lingulodinium machaerophorum, Polysphaeridium zoharyi, Spiniferites spp. by measuring the thickness of cyst walls and using Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy. The results showed that the cyst wall of A. catenella/pacificum and L. machaerophorum were all composed of cellulosic organic matter. However, A. catenella/pacificum have the higher percentage of α−/β-glucosidic linkages and that the thickness of their cyst walls is about one-third of that of L. machaerophorum. Therefore, these are reasons for the cysts of A. catenella/pacificum being more easily degraded in the sediment.

Ignited competition: Impact of bioactive extracellular compounds on organelle functions and photosynthetic systems in harmful algal blooms.

Prevalent interactions among marine phytoplankton triggered by long-range climatic stressors are well-known environmental disturbers of community structure. Dynamic response of phytoplankton physiology is likely to come from interspecies interactions rather than direct climatic effect on single species. However, studies on enigmatic interactions among interspecies, which are induced by bioactive extracellular compounds (BECs), especially between related harmful algae sharing similar shellfish toxins, are scarce. Here, we investigated how BECs provoke the interactions between two notorious algae, Alexandrium minutum and Gymnodinium catenatum, which have similar paralytic shellfish toxin (PST) profiles. Using techniques including electron microscopy and transcriptome analysis, marked disruptions in G. catenatum intracellular microenvironment were observed under BECs pressure, encompassing thylakoid membrane deformations, pyrenoid matrix shrinkage and starch sheaths disappearance. In addition, the upregulation of gene clusters responsible for photosystem-I Lhca1/4 and Rubisco were determined, leading to weaken photon captures and CO2 assimilation. The redistribution of lipids and proteins occurred at the subcellular level based on in situ focal plane array FTIR imaging approved the damages. Our findings illuminated an intense but underestimated interspecies interaction triggered by BECs, which is responsible for dysregulating photosynthesis and organelle function in inferior algae and may potentially account for fitness alteration in phytoplankton community.

Alexandrium catenella (Group I) Causes Higher and Faster Toxicity Than A. pacificum (Group IV) in Mytilus eduis

Consuming poisoned shellfish can lead to severe health problems and even death. Alexandrium catenella (Group I) and A. pacificum (Group IV) cause paralytic shellfish poisoning (PSP) in Korea, and PSP is detected more in a wider area. However, the association between toxic dinoflagellates and shellfish poisoning is unclear. Therefore, it is necessary to understand the toxicity, detoxification, and compositional differences in PSP in Mytilus edulis exposed to PSP caused by A. catenella and A. pacificum. High-performance liquid chromatography with post-column oxidation was used to analyze PSP toxicity in poisoned M. edulis. PSP in M. edulis increased as the A. catenella and A. pacificum cell density increased. However, the cell density of A. catenella peaked faster than that of A. pacificum, and a high level of toxicity was detected. In the detoxification experiment, PSP in M. edulis decreased rapidly within 24 h in filtered seawater. However, PSP was continuously detected without decreasing below the detection limit until the last day of the experiment. In addition, the carbamate composition (GTX1+4) was detected as the main toxic composition in poisoned M. edulis, unlike in vegetative cells. GTX1+4 can poison shellfish quickly when toxic dinoflagellates appear in the marine environment. However, poisoned shellfish take a long time to be completely detoxified. Moreover, if shellfish continuously feed on poisonous dinoflagellates, their toxicity can increase rapidly due to biotransformation. Our results can help identify the mechanisms of shellfish toxicity and detoxification after PSP caused by toxic dinoflagellates.

Tracking a large‐scale and highly toxic Arctic algal bloom: Rapid detection and risk communication

AbstractIn recent years, blooms of the neurotoxic dinoflagellate Alexandrium catenella have been documented in Pacific Arctic waters, and the paralytic shellfish toxins (PSTs) that this species produces have been detected throughout the food web. These observations have raised significant concerns about the role that harmful algal blooms (HABs) will play in a rapidly changing Arctic. During a research cruise in summer 2022, a massive bloom of A. catenella was detected in real time as it was advected through the Bering Strait region. The bloom was exceptional in both spatial scale and density, extending &gt; 600 km latitudinally, reaching concentrations &gt; 174,000 cells L−1, and producing high‐potency PST congeners. Throughout the event, coastal stakeholders in the region were engaged and a multi‐faceted community response was mobilized. This unprecedented bloom highlighted the urgent need for response capabilities to ensure safe utilization of critical marine resources in a region that has little experience with HABs.