Alexandrium Species Research Articles

Use of biological trait analysis of periphytic protozoan assemblages for evaluating effects of harmful algal blooms on ecological quality status in marine ecosystem

The effects of two harmful algal bloom (HAB) species Alexandrium tamarense and Gymnodinium catenatum on ecological quality status were studied using 14-day protozoan samples as test organisms. A fuzzy coding system with four traits and 11 categories of the test organisms was used for biological trait analysis. Five treatments were designed following the concentrations of 100, 102, 103, 104 and 105 cell ml‐1 of each algal species. The community-weighted means were used to summarize the functioning process of the test organism assemblages. The community functioning of the protozoa showed a significant change in the treatments with high algal concentrations (104 and 105 cell ml−1). The functional richness of the test organisms showed continuous increasing trend from 102 to 104 cell ml−1, and sharply dropped. These findings suggest that the BTA may be used as a useful tool for assessing the effects of HABs on ecological quality status in marine ecosystems.

Differentiating Two Closely Related Alexandrium Species Using Comparative Quantitative Proteomics.

Alexandrium minutum and Alexandrium tamutum are two closely related harmful algal bloom (HAB)-causing species with different toxicity. Using isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomics and two-dimensional differential gel electrophoresis (2D-DIGE), a comprehensive characterization of the proteomes of A. minutum and A. tamutum was performed to identify the cellular and molecular underpinnings for the dissimilarity between these two species. A total of 1436 proteins and 420 protein spots were identified using iTRAQ-based proteomics and 2D-DIGE, respectively. Both methods revealed little difference (10–12%) between the proteomes of A. minutum and A. tamutum, highlighting that these organisms follow similar cellular and biological processes at the exponential stage. Toxin biosynthetic enzymes were present in both organisms. However, the gonyautoxin-producing A. minutum showed higher levels of osmotic growth proteins, Zn-dependent alcohol dehydrogenase and type-I polyketide synthase compared to the non-toxic A. tamutum. Further, A. tamutum had increased S-adenosylmethionine transferase that may potentially have a negative feedback mechanism to toxin biosynthesis. The complementary proteomics approach provided insights into the biochemistry of these two closely related HAB-causing organisms. The identified proteins are potential biomarkers for organismal toxicity and could be explored for environmental monitoring.

Realised niche and suitability index highlight spatial and temporal distribution of toxic phytoplankton species

Understanding the spatial and temporal preferences of toxic phytoplankton species is of paramount importance in managing and predicting harmful events in aquatic ecosystems. In this study, we addressed the realised niche of the species Alexandrium minutum, Pseudo-nitzschia fraudulenta and P. australis to highlight distribution patterns at different scales and determine possible drivers. To achieve this goal, we developed original procedures coupling niche theory and habitat suitability modelling using abundance data in 4 consecutive steps: (1) estimate the realised niche applying kernel functions, (2) assess differences between the species’ niches as a whole and at the local level, (3) develop habitat and temporal suitability models using niche overlap procedures and (4) explore species temporal and spatial distributions to highlight possible drivers. We used data on species abundance and environmental variables collected over 27 yr (1988-2014), including 139 coastal water sampling sites along the French Atlantic coast. Results showed that the niches occupied by A. minutum and P. australis are very different, although both species exhibit a preference for warmer months. They both respond to decadal summer North Atlantic Oscillation (sNAO) but in an opposite way. P. fraudulenta’s realised niche lies in between that of the 2 other species; it also prefers warmer months but does not respond to decadal sNAO. The Brittany peninsula is now classified as an area of prevalence for the 3 species. The methodology used here will allow us to anticipate species distributions in the event of future environmental challenges resulting from climate change scenarios.

Centrodinium punctatum (Dinophyceae) produces significant levels of saxitoxin and related analogs

Centrodinium punctatum is a fusiform dinoflagellate with a global marine distribution. Due to a close phylogenetic relationship of one C. punctatum strain to Alexandrium species, toxin production of this C. punctatum strain was assessed using liquid chromatography coupled to tandem mass spectrometry. The paralytic shellfish toxin (PST) profile of C. punctatum was dominated by six analogs, i.e. STX (30%), GTX-1 (20%) and neoSTX (24%), followed by GTX-2 (9%), GTX-4 (9%) and GTX-3 (8%); deoxy-STX was also putatively identified while no gymnodimines, spirolides or goniodomins were detected. This is the first record of C. punctatum producing saxitoxins. The estimated cellular toxicity was rather elevated, between 91 and 212 pg cell−1 (or 259 and 601 fmol cell−1). When considering the toxicity equivalent factors, results suggest that this species can produce high cellular toxicity compared to other STX-producing dinoflagellates. Morphological details of the sulcal area and the hypotheca of Centrodinium punctatum were re-examined by scanning electron microscopy (SEM); this revealed that in the sulcal area, the left posterior sulcal plate (Ssp) is larger and longer than the left posterior sulcal plate and extended into the hypotheca. Based on the morphological observation, a revised interpretation of the sulcus and hypotheca is proposed.

Morphological and phylogenetic data do not support the split of Alexandrium into four genera

A recently published study analyzed the phylogenetic relationship between the genera Centrodinium and Alexandrium, confirming an earlier publication showing the genus Alexandrium as paraphyletic. This most recent manuscript retained the genus Alexandrium, introduced a new genus Episemicolon, resurrected two genera, Gessnerium and Protogonyaulax, and stated that: “The polyphyly [sic] of Alexandrium is solved with the split into four genera”. However, these reintroduced taxa were not based on monophyletic groups. Therefore this work, if accepted, would result in replacing a single paraphyletic taxon with several non-monophyletic ones. The morphological data presented for genus characterization also do not convincingly support taxa delimitations. The combination of weak molecular phylogenetics and the lack of diagnostic traits (i.e., autapomorphies) render the applicability of the concept of limited use. The proposal to split the genus Alexandrium on the basis of our current knowledge is rejected herein. The aim here is not to present an alternative analysis and revision, but to maintain Alexandrium. A better constructed and more phylogenetically accurate revision can and should wait until more complete evidence becomes available and there is a strong reason to revise the genus Alexandrium. The reasons are explained in detail by a review of the available molecular and morphological data for species of the genera Alexandrium and Centrodinium. In addition, cyst morphology and chemotaxonomy are discussed, and the need for integrative taxonomy is highlighted.

A Mediterranean Alexandrium taylorii (Dinophyceae) Strain Produces Goniodomin A and Lytic Compounds but Not Paralytic Shellfish Toxins.

Species of the dinophyte genus Alexandrium are widely distributed and are notorious bloom formers and producers of various potent phycotoxins. The species Alexandrium taylorii is known to form recurrent and dense blooms in the Mediterranean, but its toxin production potential is poorly studied. Here we investigated toxin production potential of a Mediterranean A. taylorii clonal strain by combining state-of-the-art screening for various toxins known to be produced within Alexandrium with a sound morphological and molecular designation of the studied strain. As shown by a detailed thecal plate analysis, morphology of the A. taylorii strain AY7T from the Adriatic Sea conformed with the original species description. Moreover, newly obtained Large Subunit (LSU) and Internal Transcribed Spacers (ITS) rDNA sequences perfectly matched with the majority of other Mediterranean A. taylorii strains from the databases. Based on both ion pair chromatography coupled to post-column derivatization and fluorescence detection (LC-FLD) and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analysis it is shown that A. taylorii AY7T does not produce paralytic shellfish toxins (PST) above a detection limit of ca. 1 fg cell−1, and also lacks any traces of spirolides and gymnodimines. The strain caused cell lysis of protistan species due to poorly characterized lytic compounds, with a density of 185 cells mL−1 causing 50% cell lysis of cryptophyte bioassay target cells (EC50). As shown here for the first time A. taylorii AY7T produced goniodomin A (GDA) at a cellular level of 11.7 pg cell−1. This first report of goniodomin (GD) production of A. taylorii supports the close evolutionary relationship of A. taylorii to other identified GD-producing Alexandrium species. As GD have been causatively linked to fish kills, future studies of Mediterranean A. taylorii blooms should include analysis of GD and should draw attention to potential links to fish kills or other environmental damage.

The 5S rRNA genes in Alexandrium: their use as a FISH chromosomal marker in studies of the diversity, cell cycle and sexuality of dinoflagellates

Chromosomal markers of the diversity and evolution of dinoflagellates are scarce because the genomes of these organisms are unique among eukaryotes in terms of their base composition and chromosomal structure. Similarly, a lack of appropriate tools has hindered studies of the chromosomal localization of 5S ribosomal DNA (rDNA) in the nucleosome-less chromosomes of dinoflagellates. In this study, we isolated and cloned 5S rDNA sequences from various toxin-producing species of the genus Alexandrium and developed a fluorescence in situ hybridization (FISH) probe that allows their chromosomal localization. Our results can be summarized as follows: 1) The 5S rDNA unit is composed of a highly conserved 122-bp coding region and an intergenic spacer (IGS), the length and sequence of which are variable even within strains. 2) Three different IGS types, one containing the U6 small nuclear RNA (snRNA) gene, were found among four of the studied species (A. minutum, A. tamarense, A. catenella and A. pacificum). 3) In all strains investigated by FISH (A. minutum, A. tamarense, A. pacificum, A. catenella, A. andersonii and A. ostenfeldii), 5S rDNA gene arrays were separate from the nucleolar organizer region, which contains the genes for the large 45S pre-ribosomal RNA. 4) One to three 5S rDNA sites per haploid genome were detected, depending on the strains/species. Intraspecific variability in the number of 5S rDNA sites was determined among strains of A. minutum and A. pacificum. 5) 5S rDNA is a useful chromosomal marker of mitosis progression and can be employed to differentiate vegetative (haploid) vs. planozygotes (diploid) cells. Thus, the FISH probe (oligo-Dino5Smix5) developed in this study facilitates analyses of the diversity, cell cycle and life stages of the genus Alexandrium.

First Detection of Paralytic Shellfish Toxins from Alexandrium pacificum above the Regulatory Limit in Blue Mussels (Mytilus galloprovincialis) in New South Wales, Australia.

In 2016, 2017 and 2018, elevated levels of the species Alexandrium pacificum were detected within a blue mussel (Mytilus galloprovincialis) aquaculture area at Twofold Bay on the south coast of New South Wales, Australia. In 2016, the bloom persisted for at least eight weeks and maximum cell concentrations of 89,000 cells L−1 of A. pacificum were reported. The identity of A. pacificum was confirmed using molecular genetic tools (qPCR and amplicon sequencing) and complemented by light and scanning electron microscopy of cultured strains. Maximum reported concentrations of paralytic shellfish toxins (PSTs) in mussel tissue was 7.2 mg/kg PST STX equivalent. Elevated cell concentrations of A. pacificum were reported along the adjacent coastal shelf areas, and positive PST results were reported from nearby oyster producing estuaries during 2016. This is the first record of PSTs above the regulatory limit (0.8 mg/kg) in commercial aquaculture in New South Wales since the establishment of routine biotoxin monitoring in 2005. The intensity and duration of the 2016 A. pacificum bloom were unusual given the relatively low abundances of A. pacificum in estuarine and coastal waters of the region found in the prior 10 years.

Insights into identifying the effect of harmful algae on ecological quality status using periphytic ciliates in marine ecosystems

Abstract Our study focused on ciliates grazing potential against harmful algal blooms, because ciliates are considered as voracious feeders of toxic phytoplankton and major herbivores in marine food webs. Ciliates are major contributors to control the flux of harmful algal blooms by lessen the magnitude of their biomass from top to bottom by high consumption on these blooms. Keeping an eye on harmful algal blooms as common pollutant of marine ecosystem the community-based method was used to test the potential effects of two harmful algal species Alexandrium tamarense and Gymnodinum catenatum on the community patterns of the ciliates. For this purpose, the 14-day (mature) samples of ciliate communities were collected using glass slides as an artificial substratum at a depth of 1 m in coastal waters of the Yellow Sea, northern China. A series of algal cell concentrations of both species was prepared as 100 (control), following 102, 103, 104 and 105 cell ml−1, respectively. The study results indicated that both algal species showed strong effects on the community patterns of the ciliates at high concentration. Species abundance, relative species number and taxonomic distinctness indices of ciliate communities generally increased by increasing the concentration whereas, sharply decreased at the concentration level of (105 cells ml−1) for both algal species. Canonical analysis of principal coordinates demonstrated the variations in community structures of the ciliates driven by the concentrations of both algal species. Ellipse test showed an increased pattern in species departure from an expected breadth of species contour with increasing the algal cell concentrations. Based on our findings, it is suggested that extended studies on community-based bioassay is a valuable tool to strengthen the information about the effects of microalgae on the ciliate community structures.

Revival of Ancient Marine Dinoflagellates Using Molecular Biostimulation.

The biological processes involved in the preservation, viability, and revival of long-term dormant dinoflagellate cysts buried in sediments remain unknown. Based on studies of plant seed physiology, we tested whether the revival of ancient cysts preserved in century-old sediments from the Bay of Brest (France) could be stimulated by melatonin and gibberellic acid, two molecules commonly used in seed priming. Dinoflagellates were revived from sediments dated to approximately 150years ago (156±27, 32cm depth), extending the known record age of cyst viability previously established as around one century. A culture suspension of sediments mixed with melatonin and gibberellic acid solutions as biostimulants exhibited germination of 11 dinoflagellate taxa that could not be revived under controlled culture conditions. The biostimulants revived some dinoflagellates from century-old sediments, including the potentially toxic species Alexandrium minutum. The biostimulants showed positive effects on germination on even more ancient cysts, showing dose-dependent effects on the germination of Scrippsiella acuminata. Concentrations of 1, 10, and 100µM melatonin and gibberellic acid promoted germination. In contrast, 1,000µM solutions, particularly for melatonin, drastically decreased germination, suggesting a potential noxious effect of high doses of these molecules on dinoflagellate revival. Our findings suggest that melatonin and gibberellic acid are involved in the stimulation of germination of dinoflagellate cysts. These biostimulants can be used to germinate long-term stored dinoflagellate cysts, which may promote studies of ancient strains in the resurrection ecology research field.

Morphology and molecular phylogeny of a new PST-producing dinoflagellate species: Alexandrium fragae sp. nov. (Gonyaulacales, dinophyceae)

The genus Alexandrium comprises some of the most potentially toxic marine algae. A new toxic species of Alexandrium, A. fragae sp. nov., was found in Guanabara Bay, Rio de Janeiro, southern Brazil. The new species produces GTX2&3 and STX. The cell morphology of A. fragae resembles A. minutum in many characters, including the small size; the rounded-elliptical shape; and the shapes of the apical pore complex (APC), first apical plate (1′), sixth precingular plate (6″), and anterior and posterior sulcal plates (s.a. and s.p.). The main diagnostic characters of A. fragae are the ornamentation pattern, smooth epitheca and reticulated hypotheca, all of which were present in both natural populations and cultures. Phylogenies inferred from the ITS, LSU, and SSU rDNA of A. fragae showed that A. fragae clustered in a well-supported clade, distinct from other Alexandrium species. Morphology and molecular analyses based on ITS and LSU rDNA indicated that A. fragae strains and Alexandrium sp. from Japan (D163C5, D164C6) are a single species. Our findings suggest that the Alexandrium morphotype with a smooth epitheca and reticulated hypotheca, previously identified as A. minutum in different geographic regions, may corresponds to A. fragae.

Over 30 years of HABs in the Philippines and Malaysia: What have we learned?

In the Southeast Asian region, the Philippines and Malaysia are two of the most affected by Harmful Algal Blooms (HABs). Using long-term observations of HAB events, we determined if these are increasing in frequency and duration, and expanding across space in each country. Blooms of Paralytic Shellfish Toxin (PST)-producing species in the Philippines did increase in frequency and duration during the early to mid-1990s, but have stabilized since then. However, the number of sites affected by these blooms continue to expand though at a slower rate than in the 1990s. Furthermore, the type of HABs and causative species have diversified for both toxic blooms and fish kill events. In contrast, Malaysia showed no increasing trend in the frequency of toxic blooms over the past three decades since Pyrodinium bahamense was reported in 1976. However, similar to the Philippines, other PST producers such as Alexandrium minutum and Alexandrium tamiyavanichii have become a concern. No amnesic shellfish poisoning (ASP) has been confirmed in either Philippines or Malaysia thus far, while ciguatera fish poisoning cases are known from the Philippines and Malaysia but the causative organisms remain poorly studied. Since the 1990s and early 2000s, recognition of the distribution of other PST-producing species such as species of Alexandrium and Gymnodinium catenatum in Southeast Asia has grown, though there has been no significant expansion in the known distributions within the last decade. A major more recent problem in the two countries and for Southeast Asia in general are the frequent fish-killing algal blooms of various species such as Prorocentrum cordatum, Margalefidinium polykrikoides, Chattonella spp., and unarmored dinoflagellates (e.g., Karlodinium australe and Takayama sp.). These new sites affected and the increase in types of HABs and causative species could be attributed to various factors such as introduction through mariculture and eutrophication, and partly because of increased scientific awareness. These connections still need to be more concretely investigated. The link to the El Niño Southern Oscillation (ENSO) should also be better understood if we want to discern how climate change plays a role in these patterns of HAB occurrences.

The relationship between toxic phytoplankton species occurrence and environmental and meteorological factors along the Eastern Adriatic coast

In this study, the time series of toxic phytoplankton species collected between 2004 and 2018 from the Northern Adriatic, Šibenik Bay, and Mali Ston Bay was analyzed in relation to environmental (temperature, salinity, water column stability, and river flow) and meteorological parameters (precipitation and wind). Because of the mostly non-linear relation between biotic and abiotic parameters, self-organizing maps (SOM) were used to identify these relationships.SOM analysis distinguished species of the genus Dinophysis from Gonyaulax spinifera and Lingulodinium polyedrum species, which better tolerate wind-induced disturbance. Among the Dinophysis species, Dinophysis fortii, Dinophysis tripos, and Dinophysis acuta preferred higher precipitation rate and river flow in addition to optimal temperatures. The abundances of Alexandrium species, which occurred more frequently in estuarine areas, were associated with river flow and maximum stable water column. Regardless of the ecological preferences of individual harmful algae, freshwater inflow-caused stratification is present in all clusters of environmental conditions associated with increased abundances of harmful algae in the SOM analysis. It is highly likely that stratification represents an important factor for the development and maintenance of HABs. The non-linear relationship between the NAO index and rainfall was noted, of which the most important for the development of harmful algae is the proportional correlation between the positive phase of the NAO index and higher rainfall, especially in winter and spring. Such conditions are conducive to the development of harmful algae because, with the increase in temperature accompanying the positive phase of the NAO index, increased rainfall further stimulates their growth. This can be achieved either through nutrient yields or through higher freshwater inflow that further stabilizes the water column.

Redefinition of the Dinoflagellate GenusAlexandriumBased onCentrodinium: Reinstatement ofGessneriumandProtogonyaulax, andEpisemicolongen. nov. (Gonyaulacales, Dinophyceae)

The genusCentrodiniumcontains oceanic and predominantly tropical species that have received little attention. Three species ofCentrodiniumwere examined using thecal plate dissociation, scanning electron microscopy, and molecular sequences. The apical horn ofCentrodinium intermediumandC. eminensis formed by the elongation of the fourth apical plate, and a second apical split into two plates. InC. punctatumtwo apical plates (2′ and 4′) almost completely encircle the apical pore plate (Po), while the contact with the plate 1′ in the ventral side is much reduced, and the plate 3′ does not reach the Po. Moreover, its left posterior lateral sulcal plate is longer than its right pair, while reversed in the typicalCentrodiniumspp. The sulcal posterior plate ofC. punctatumis located in the left-ventral side below the plates 1′′′ and 2′′′, while the sulcal posterior plate located in the right face below the plates 4′′′ and 5′′′ in the typicalCentrodiniumspp. Phylogenetic analyses based on the small and large subunit of the rRNA gene showed thatCentrodiniumspp. andAlexandrium affine/A. gaarderaeclustered as a sister clade of theAlexandrium tamarense/catenella/fraterculusgroups. The clade of the subgenusGessnerium, and the clade of the type species ofAlexandrium,A. minutum, with four divergent species, clustered in more basal positions. The polyphyly ofAlexandriumis solved with the split into four genera: (1)Alexandriumsensu stricto for the species of the clade ofA. minutumand four divergent species; (2) the reinstatement of the genusGessneriumfor the species of the clade ofA. monilatum; (3) the reinstatement of genusProtogonyaulaxfor the species of thetamarense/catenella/fraterculusgroups, and (4) the new genusEpisemicolongen. nov. forA. affineandA. gaarderae.New combinations in the generaGessnerium,Protogonyaulax,andEpisemicolonare proposed.

Recent findings of paralytic shellfish toxins linked to the genus Alexandrium Halim in Mediterranean mollusc production areas

Paralytic shellfish poisoning is a human intoxication syndrome associated with the consumption of seafood that has been contaminated with paralytic shellfish toxins (PSTs), a group of natural neurotoxic alkaloids produced by marine dinoflagellates, including some Alexandrium species. This study presents findings of PSTs in mussels (Mytilus galloprovincialis) during 2018–2019 in several mollusc production areas of Sardinia (Italy, western Mediterranean). Investigations of the presence and abundance of PST-producing microalgal species in marine water and of the toxins associated with shellfish were carried out concomitantly. Overall, the results suggested a spatio-temporal expansion of Alexandriumpacificum and Alexandriumminutum in recent years, with an increasing number of PSTs present in molluscs and increased occurrences of toxicity cases. Liquid chromatography with fluorescence detection determined the toxin profile to be composed primarily of the carbamate gonyautoxin-5 and N-sulphocarbamoyltoxins 1 and 2. The study highlights the potential high risk to consumers of poisoning by bivalve molluscs bred in Sardinia, where shellfish production is a very important industrial sector. For this reason, routine monitoring is strongly recommended in order to mitigate any harm to human health as well as negative socio-economic consequences.

Quantification of the paralytic shellfish poisoning dinoflagellate Alexandrium species using a digital PCR

A ubiquitous dinoflagellate, Alexandrium, produces paralytic shellfish toxin (PST), and its outbreaks have negative impacts on aquaculture, fisheries, human health, and the marine ecosystem. To minimize such damages, a routine monitoring program of toxic species must be implemented with a suitable analytical technique for their identification and quantification. However, the taxonomic identification and cell quantification of Alexandrium species based on their external morphology under a light microscope, or by using conventional molecular approaches have limited sensitivity and reproducibility. To address these challenges, we have developed an advanced protocol using droplet-digital PCR (ddPCR) for the discrimination and enumeration of three co-occurring Alexandrium species (A. affine, A. catenella, and A. pacificum) in environmental samples. Copies of species-specific internal transcribed spacer (ITS) per cell, which were calculated from environmental samples spiked with various numbers of culture cells, were used to estimate the abundance of species in the field samples. There were no significant differences in ITS copies estimated by the digital PCR assay between environmental samples from different localities, spiked artificially with a consistent number of cells from Alexandrium cultures. This sensitive assay was applied to determine the abundance and vertical distribution of those populations in the southern coastal waters of Korea. In spring, A. catenella was the dominant species, followed by the non-toxic A. affine in summers. A novel digital PCR assay can also be used to monitor other harmful marine protists that require high sample throughput and low detection limit with high accuracy and precision.

Five <italic>Alexandrium</italic> species lacking mixotrophic ability

Five <italic>Alexandrium</italic> species lacking mixotrophic ability

Dinoflagellate Cysts of the Genus Alexandrium Halim, 1960 (Dinophyceae: Gonyaulacales) in Recent Sediments from the Northwestern Pacific Ocean

This paper summarizes information on the resting cysts of the dinoflagellate genus Alexandrium Halim, 1960 from the northwestern Pacific Ocean and the Chukchi Sea. Species of the genus Alexandrium, which are known as producers of paralytic toxins, cause large-scale algal blooms that pose a serious threat to marine coastal ecosystems and human health. Data are presented on the diversity, abundance, and distribution of Alexandrium spp. cysts in the Far Eastern seas of Russia and adjacent waters. The possible role of resting cysts in initiating toxic blooms of Alexandrium spp. is discussed.

Vertical and horizontal distributions of ellipsoidal <i>Alexandrium</i> (Dinophyceae) cysts in coastal sediment with special reference to paralytic shellfish poisoning caused by tsunamis - a case study of Osaka Bay (Japan) and the southern coast of the Korean Peninsula

Severe damages will result in human society, when several different critical natural phenomena coincide. One example relates to the resting cysts of Alexandrium species (dinoflagellates that cause paralytic shellfish poisoning), which are preserved in surface sediments throughout Osaka Bay, Japan. These cysts have been found to accumulate particularly densely in shallow areas in the inner parts of Osaka Bay, where a tsunami caused by an earthquake could occur any time. Damage by a tsunami could cause a change of the coastal ecosystems at Osaka Bay including the resuspension of surface sediments containing resting Alexandrium tamarense cysts and the subsequent redistribution of the cysts in newly deposited sediment. Under certain environmental conditions, these cysts could germinate and form dense blooms, leading to paralytic shellfish poisoning. Such a scenario could also affect other coastal areas, including the southern coast of the Korean Peninsula.

Distributions of three Alexandrium species and their toxins across a salinity gradient suggest an increasing impact of GDA producing A. pseudogonyaulax in shallow brackish waters of Northern Europe

Blooms of Alexandrium spp. are a well-known phenomenon in Northern European waters. While A. tamarense/catenella, and A. pseudogonyaulax have been reported from marine waters, high densities of A. ostenfeldii are mainly observed at lower salinities in North Sea estuaries and the Baltic Sea, suggesting salinity as a driver of Alexandrium species composition and toxin distribution. To investigate this relationship, an oceanographic expedition through a natural salinity gradient was conducted in June 2016 along the coasts of Denmark. Besides hydrographic data, phytoplankton and sediment samples were collected for analyses of Alexandrium spp. cell and cyst abundances, for toxin measurement and cell isolation. Plankton data revealed the predominance of A. pseudogonyaulax at all transect stations while A. ostenfeldii and A. catenella generally contributed a minor fraction to the Alexandrium community. High abundances of A. pseudogonyaulax in the shallow enclosed Limfjord were accompanied by high amounts of goniodomin A (GDA). This toxin was also detected at low abundances along with A. pseudogonyaulax in the North Sea and the Kattegat. Genetic and morphological characterization of established strains showed high similarity of the Northern European population to distant geographic populations. Despite low cell abundances of A. ostenfeldii, different profiles of cycloimines were measured in the North Sea and in the Limfjord. This field survey revealed that salinity alone does not determine Alexandrium species and toxin distribution, but emphasizes the importance of habitat conditions such as proximity to seed banks, shelter, and high nutrient concentrations. The results show that A. pseudogonyaulax has become a prominent member of the Alexandrium spp. community over the past decade in the study area. Analyses of long term monitoring data from the Limfjord confirmed a recent shift to A. pseudogonyaulax dominance. Cyst and toxin records of the species in Kiel Bight suggest a spreading potential into the brackish Baltic Sea, which might lead to an expansion of blooms under future climate conditions.