Genetic relatedness of a new Japanese isolates of Alexandrium ostenfeldii bloom population with global isolates

In recent years, blooms of toxic Alexandrium ostenfeldii strains have been reported from around the world. In 2013, the species formed a red tide in a shallow lagoon in western Japan, which was the first report of the species in the area. To investigate the genetic relatedness of Japanese A. ostenfeldii and global isolates, the full-length SSU, ITS and LSU sequences were determined, and phylogenetic analyses were conducted for isolates from western and northern Japan and from the Baltic Sea. Genotyping and microsatellite sequence comparison were performed to estimate the divergence and connectivity between the populations from western Japan and the Baltic Sea. In all phylogenetic analyses, the isolates from western Japan grouped together with global isolates from shallow and low saline areas, such as the Baltic Sea, estuaries on the east coast of U.S.A. and from the Bohai Sea, China. In contrast, the isolates from northern Japan formed a well-supported separate group in the ITS and LSU phylogenies, indicating differentiation between the Japanese populations. This was further supported by the notable differentiation between the sequences of western and northern Japanese isolates, whereas the lowest differentiation was found between the western Japanese and Chinese isolates. Microsatellite genotyping revealed low genetic diversity in the western Japanese population, possibly explained by a recent introduction to the lagoon from where it was detected. The red tide recorded in the shallow lagoon followed notable changes in the salinity of the waterbody and phytoplankton composition, potentially facilitating the bloom of A. ostenfeldii.     

Patterns of Post-Glacial Genetic Differentiation in Marginal Populations of a Marine Microalga

This study investigates the genetic structure of an eukaryotic microorganism, the toxic dinoflagellate Alexandrium ostenfeldii, from the Baltic Sea, a geologically young and ecologically marginal brackish water estuary which is predicted to support evolution of distinct, genetically impoverished lineages of marine macroorganisms. Analyses of the internal transcribed spacer (ITS) sequences and Amplified Fragment Length Polymorphism (AFLP) of 84 A. ostenfeldii isolates from five different Baltic locations and multiple external sites revealed that Baltic A. ostenfeldii is phylogenetically differentiated from other lineages of the species and micro-geographically fragmented within the Baltic Sea. Significant genetic differentiation (F _ST) between northern and southern locations was correlated to geographical distance. However, instead of discrete genetic units or continuous genetic differentiation, the analysis of population structure suggests a complex and partially hierarchic pattern of genetic differentiation. The observed pattern suggests that initial colonization was followed by local differentiation and varying degrees of dispersal, most likely depending on local habitat conditions and prevailing current systems separating the Baltic Sea populations. Local subpopulations generally exhibited low levels of overall gene diversity. Association analysis suggests predominately asexual reproduction most likely accompanied by frequency shifts of clonal lineages during planktonic growth. Our results indicate that the general pattern of genetic differentiation and reduced genetic diversity of Baltic populations found in large organisms also applies to microscopic eukaryotic organisms.     

Bioaccumulation of PSTs produced by Alexandrium ostenfeldii in the northern Baltic Sea

Bioaccumulation of paralytic shellfish toxins (PSTs) produced by the dinoflagellate Alexandrium ostenfeldii was investigated in the northern Baltic Sea. The study was based on the assumption that the toxins released during high magnitude blooms of A. ostenfeldii will accumulate in the biota at the bloom site, especially in bivalves. To test this, experiments with blue mussels (Mytilus trossulus) exposed to toxic A. ostenfeldii in field conditions were carried out together with a field survey aimed to quantify natural distribution of PSTs in the biota. As hypothesized, PSTs accumulated in the tissues of the blue mussels during the incubations. Toxins were also detected in natural bivalve communities at the bloom site, the highest toxin concentrations found in the small Cerastoderma glaucum individuals, exceeding the EC safety limit for shellfish consumption. Relatively high total toxin concentrations were also detected from fish (Perca fluviatilis). These are the first records of PST transfer in the food web of the northern Baltic Sea.     

DISTRIBUTION AND GENETIC DIVERSITY OF THE LUCIFERASE GENE WITHIN MARINE DINOFLAGELLATES1

Dinoflagellates are the most abundant protists that produce bioluminescence. Currently, there is an incomplete knowledge of the identity of bioluminescent species arising from inter‐ and intraspecific variability in bioluminescence properties. In this study, PCR primers were designed to amplify the dinoflagellate luciferase gene (lcf) from genetically distant bioluminescent species. One of the primer pairs was “universal,” whereas others amplified longer gene sequences from subsets of taxa. The primers were used to study the distribution of lcf and assess bioluminescence potential in dinoflagellate strains representing a wide variety of taxa as well as multiple strains of selected species. Strains of normally bioluminescent species always contained lcf even when they were found not to produce light, thus demonstrating the utility of this methodology as a powerful tool for identifying bioluminescent species. Bioluminescence and lcf were confined to the Gonyaulacales, Noctilucales, and Peridiniales. Considerable variation was observed among genera, or even species within some genera, that contained this gene. Partial sequences of lcf were obtained for the genera Ceratocorys, Ceratium, Fragilidium, and Protoperidinium as well as from previously untested species or gene regions of Alexandrium and Gonyaulax. The sequences revealed high variation among gene copies that obscured the boundaries between species or even genera, some of which could be explained by the presence of two genetic variants within the same species of Alexandrium. Highly divergent sequences within Alexandrium and Ceratium show a more diverse composition of lcf than previously known.     

Paralytic shellfish toxins or spirolides? The role of environmental and genetic factors in toxin production of the Alexandrium ostenfeldii complex

Dinoflagellates of the Alexandrium ostenfeldii complex (A. ostenfeldii, A. peruvianum) are capable of producing different types of neurotoxins: paralytic shellfish toxins (PSTs), spirolides and gymnodimines, depending on the strain and its geographic origin. While Atlantic and Mediterranean strains have been reported to produce spirolides, strains originating from the brackish Baltic Sea produce PSTs. Some North Sea, USA and New Zealand strains contain both toxins. Causes for such intraspecific variability in toxin production are unknown. We investigated whether salinity affects toxin production and growth rate of 5 A. ostenfeldii/peruvianum strains with brackish water (Baltic Sea) or oceanic (NE Atlantic) origin. The strains were grown until stationary phase at 7 salinities (6–35), and their growth and toxin production was monitored. Presence of saxitoxin (STX) genes (sxtA1 and sxtA4 motifs) in each strain was also analyzed. Salinity significantly affected both growth rate and toxicity of the individual strains but did not change their major toxin profile. The two Baltic Sea strains exhibited growth at salinities 6–25 and consistently produced gonyautoxin (GTX) 2, GTX3 and STX. The two North Sea strains grew at salinities 20–35 and produced mainly 20-methyl spirolide G (20mG), whereas the strain originating from the northern coast of Ireland was able to grow at salinities 15–35, only producing 13-desmethyl spirolide C (13dmC). The effects of salinity on total cellular toxin concentration and distribution of toxin analogs were strain-specific. Both saxitoxin gene motifs were present in the Baltic Sea strains, whereas the 2 North Sea strains lacked sxtA4, and the Irish strain lacked both motifs. Thus sxtA4 only seems to be specific for PST producing strains. The results show that toxin profiles of A. ostenfeldii/peruvianum strains are predetermined and the production of either spirolides or PSTs cannot be induced by salinity changes. However, changes in salinity may lead to changed growth rates, total cellular toxin concentrations as well as relative distribution of the different PST and spirolide analogs, thus affecting the actual toxicity of A. ostenfeldii/peruvianum populations.     

Bloom forming Alexandrium ostenfeldii (Dinophyceae) in shallow waters of the Åland Archipelago,Northern Baltic Sea

In the past years, late summer blooms of the bioluminescent dinoflagellate Alexandrium ostenfeldii have become a recurrent phenomenon in coastal waters of the central and Northern Baltic Sea. This paper reports exceptionally high cell concentrations (10⁵ to 10⁶ cells L^?1) of the species found during bioluminescent blooms in 2003 and 2004 in a shallow embayment of the Åland archipelago at the SW coast of Finland. Clonal cultures were established for morphological, molecular, toxicological and ecophysiological investigations to characterize the Finnish populations and compare them to other global A. ostenfeldii isolates. The Finnish isolates exhibited typical morphological features of A. ostenfeldii such as large size, a prominent ventral pore and an orthogonally bent first apical plate. However, unambiguous differentiation from closely related Alexandrium peruvianum was difficult due to considerable variation of sulcal anterior plate shapes. The Finnish strains were genetically distinct from other isolates of the species, but phylogenetic analyses revealed a close relationship to isolates from southern England and an A. peruvianum morphotype from the Spanish Mediterranean. Together these isolates formed a distinct clade which was separated from a clade containing other Northern European, North American and New Zealand populations. Toxin analyses confirmed the presence of the PSP toxins GTX2, GTX3 and STX in both Finnish isolates with GTX3 being the dominant toxin. Total relative PSP toxin contents were moderate, ranging from approximately 6 to 15 fmol cell^?1 at local salinities of 5 and 10 psu, respectively. Spirolides were not detected. Salinity tolerance experiments showed that the Finnish isolates were well adapted to grow at the low salinities of the Baltic Sea. With a salinity range of approximately 6 to 20–25 psu, Baltic populations are physiologically distinct from their marine relatives. Vigorous production of different cyst types in the cultures suggest that cysts may play a crucial role in the survival and retainment of A. ostenfeldii populations in the Baltic Sea.     

Toxicity and isolation of the cyanobacterium Nodularia spumigena from the southern Baltic Sea in 1986

Three water bloom samples were collected in August 1986 from the southern Baltic Sea. Acute toxicity of the samples was determined by mouse bioassay and the toxins were further studied by HPLC. The bloom samples contained equal amounts of cyanobacteria Nodularia spumigena and Aphanizomenon flos-aquae and were hepatotoxic. Two hepatotoxic Nodularia spumigena strains were isolated from the samples. The isolates produce a toxic peak indistinguishable from the bloom material in the HPLC analysis. The toxicity of the fractions was verified by mouse bioassay. Thus the toxicity of the bloom samples was in all likelihood caused by Nodularia spumigena.     

Population of <Emphasis Type="Italic">Aphanizomenon</Emphasis> from the Gulf of Gdańsk (Southern Baltic Sea): differences in phenotypic and genotypic characteristics

In this study, one of the major bloom-forming cyanobacteria in the Gulf of Gdańsk (Southern Baltic Sea), Aphanizomenon Morren ex Bornet et Flahaut has been characterized using a polyphasic approach by comparing phenotypic and molecular characteristics. The phenotypic analysis dealt with cell and filament morphology as well as ultrastructure. The molecular phylogenetic analyses were based on sequences of the 16S rRNA gene and the adjacent intergenic transcribed spacer (ITS). We have found the Aphanizomenon population from the Gulf of Gdańsk to be significantly different in ultrastructure, morphology from freshwater A. flos-aquae and according to the traditional approach; it could be assigned to different taxonomic units. However, genetic relationship with regard to sequences of the 16S rRNA gene, showed an high overall sequence identity (97.5–99%) to freshwater isolates. Similarly, ITS sequence identity among populations from the Baltic Sea and different freshwater isolates was as high as 90.3–97.7% suggesting one and the same species. Handling editor: D. Hamilton An erratum to this article can be found at     

Allelopathic activity of the toxic dinoflagellate Alexandrium ostenfeldii: Intra-population variability and response of co-occurring dinoflagellates

The paralytic shellfish toxin (PST) producing dinoflagellate Alexandrium ostenfeldii forms dense, recurrent blooms during summer in shallow coastal areas of the Baltic Sea. We studied the intra-population variability of its allelochemical potency and the responses of co-occurring and potentially competing dinoflagellates to the allelochemicals. The lytic activity of 10 northern Baltic A. ostenfeldii strains was evaluated by their EC₅₀ values (i.e. the cell concentration yielding a 50% decline in cryptophyte density), which were found to vary between 236 and 1726 cells ml⁻¹. When co-occurring dinoflagellates (Kryptoperidinium foliaceum, Levanderina fissa and Heterocapsa triquetra) were exposed to filtrate of A. ostenfeldii, short-term (<1 h) responses of the target species after an initial immobilization were species-specific. Almost all of the K. foliaceum cells formed cysts, L. fissa cells lost their cell shape and lysed, whereas H. triquetra cells shed their thecae. After 24 h, K. foliaceum had returned into vegetative cells and the number of immotile L. fissa and H. triquetra cells had significantly decreased. The results indicate that A. ostenfeldii can disturb the growth of competing dinoflagellates by excreting allelochemicals at bloom concentrations and that co-occurring species may develop efficient means to escape and recover from the allelochemicals, allowing them to coexist with A. ostenfeldii.     

The extensive bloom of alternate-stage Prymnesium polylepis (Haptophyta) in the Baltic Sea during autumn–spring 2007–2008

During autumn 2007, an unusual increase in an algal species belonging to the order Prymnesiales was observed throughout the Baltic Sea Proper during routine national monitoring. Electron microscopical examination of the blooming species showed two types of flat scales – small and large – that resembled those of the alternate stage of Prymnesium polylepis. No spine-bearing scales were found. The 18S rDNA sequence data (n?=?20, c. 1500?bp) verified the species identification as P. polylepis. There was up to 0.5% (7?bp) variability in the P. polylepis partial 18?S rDNA sequences from the Baltic Sea. These environmental sequences differed by 0–0.35% (0–4?bp) from cultured P. polylepis (isolate UIO036), and by 1.0–3.7% from other available Prymnesium sequences. The number of cells assumed to be P. polylepis began to increase in October 2007 coincidently with significantly calm and dry weather, and at their maximum the cells accounted for over 80% of the total phytoplankton biovolume in December–January. During February–April 2008, 95% of the Prymnesiales cells were in the size class of P. polylepis (>6?µm). The species attained bloom concentrations (>1?×?10⁶?cells?l^–1) from March to May 2008. The species was observed throughout the Baltic Sea, except the Bothnian Bay, Gulf of Riga and the Kattegat. No toxic effects of the bloom were observed.     

Ecological niche partitioning of the invasive dinoflagellate Prorocentrum minimum and its native congeners in the Baltic Sea

This study analyses three decades of the peculiar bloom-formation history of the potentially toxic invasive planktonic dinoflagellates Prorocentrum minimum (Pavillard) Schiller in the SW Baltic Sea. We tested a research hypothesis that the unexpectedly long delay (nearly two decades) in population development of P. minimum prior to its first bloom was caused by competition with one or several closely related native dinoflagellate species due to ecological niche partitioning which hampered the spread and bloom-forming potential of the invader. We applied the ecological niche concept to a large, long-term phytoplankton database and analysed the invasion history and population dynamics of P. minimum in the SW Baltic Sea coastal waters using the data on phytoplankton composition, abundance and biomass. The ecological niche dimensions of P. minimum and its congener P. balticum were identified as the optimum environmental conditions for the species during the bloom events based on water temperature, salinity, pH, concentration of nutrients (PO₄³⁻; total phosphorus, TP; total nitrogen, TN; SiO₄⁴⁻), TN/TP-ratio and habitat type. The data on spatial distribution and ecological niche dimensions of P. minimum have contributed to the development of the “protistan species maximum concept”. High microplankton diversity at critical salinities in the Baltic Sea may be considered as a possible reason for the significant niche overlap and strong competitive interactions among congeners leading to prolonged delay in population growth of P. minimum preceding its first bloom in the highly variable brackishwater environment.     

Molecular identification of bacteria associated with filaments of Nodularia spumigena and their effect on the cyanobacterial growth

Colonial and filamentous cyanobacteria frequently have bacteria associated with their extracellular mucus zone or more tightly attached to their cells surface. The toxin-producing cyanobacterium Nodularia spumigena is an important component of the Baltic Sea plankton community, and its filaments are likely to provide a microenvironment suitable for the development of a particular bacteria flora. In the present work, 13 bacterial strains associated with filaments of N. spumigena from the Baltic Sea were isolated and identified by sequencing the 16S rRNA gene. Different bacterial lineages were found associated with the cyanobacterial filaments, including the alpha, beta, and gamma subdivisions of the class Proteobacter and the division Firmicutes (Gram-positive bacteria). Several 16S rRNA gene sequences were not closely related to previously reported sequences of cultured bacteria from the Baltic Sea or to any other reported sequence. Conversely, sequences related to the gamma Proteobacter genus Shewanella, a group previously described in the Baltic Sea, were found among the isolates. The bacterial isolates were grown and added to cultures of exponentially growing N. spumigena. Five isolates, related to the alpha and gamma Proteobacter and Firmicutes, affected negatively the cyanobacterial growth, leading to a lower biomass yield up to 38% relative to controls with no bacteria addition. Five gamma Proteobacter-related strains had no effect on the cyanobacterial growth, while three strains related to Shewanella baltica had a positive effect. Although none of the bacterial isolates showed strong algicidal effect, the observed stimulatory and retarding effects on N. spumigena growth under culture conditions denotes the importance of the associated bacterial community for the dynamics of these cyanobacterial populations in nature. Moreover, several new taxa recovered in this study probably belong to species not yet described.     

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.     

Occurrence of the hepatotoxic cyanobacterium Nodularia spumigena in the Baltic Sea and structure of the toxin

Water blooms formed by potentially toxic species of cyanobacteria are a common phenomenon in the Baltic Sea in late summer. Twenty-five cyanobacterial bloom samples were collected from open and coastal waters of the Baltic Sea during 1985 to 1987, and their toxicity was determined by mouse bioassay. All of 5 bloom samples from the southern Baltic Sea, 6 of 6 from the open northern Baltic Sea (Gulf of Finland), and 7 of 14 Finnish coastal samples were found to contain hepatotoxic cyanobacteria. Nodularia spumigena and Aphanizomenon flos-aquae occurred together in high amounts in blooms from the open-sea areas. In addition, coastal samples contained the species Anabaena lemmermannii, Microcystis aeruginosa, and Oscillatoria agardhii. Eighteen hepatotoxic N. spumigena cultures were isolated from water bloom and open-sea water samples. High-pressure liquid chromatographic analysis of both hepatotoxic bloom samples and Nodularia strains showed a single toxic fraction. The toxin concentrations of the blooms were less than or equal to 2.4 mg/g of freeze-dried material, and those of laboratory-grown cultures were 2.5 to 8.0 mg/g of freeze-dried cells. A single toxin was isolated from three N. spumigena-containing bloom samples and three N. spumigena laboratory isolates. Amino acid analysis and low- and high-resolution fast-atom bombardment mass spectroscopy indicated that the toxin from all of the sources was a cyclic pentapeptide (molecular weight, 824) containing glutamic acid, beta-methylaspartic acid, arginine, N-methyldehydrobutyrine, and 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4,6-decadienoic acid.(ABSTRACT TRUNCATED AT 250 WORDS)     

Occurrence of the hepatotoxic cyanobacterium Nodularia spumigena in the Baltic Sea and structure of the toxin.

Water blooms formed by potentially toxic species of cyanobacteria are a common phenomenon in the Baltic Sea in late summer. Twenty-five cyanobacterial bloom samples were collected from open and coastal waters of the Baltic Sea during 1985 to 1987, and their toxicity was determined by mouse bioassay. All of 5 bloom samples from the southern Baltic Sea, 6 of 6 from the open northern Baltic Sea (Gulf of Finland), and 7 of 14 Finnish coastal samples were found to contain hepatotoxic cyanobacteria. Nodularia spumigena and Aphanizomenon flos-aquae occurred together in high amounts in blooms from the open-sea areas. In addition, coastal samples contained the species Anabaena lemmermannii, Microcystis aeruginosa, and Oscillatoria agardhii. Eighteen hepatotoxic N. spumigena cultures were isolated from water bloom and open-sea water samples. High-pressure liquid chromatographic analysis of both hepatotoxic bloom samples and Nodularia strains showed a single toxic fraction. The toxin concentrations of the blooms were less than or equal to 2.4 mg/g of freeze-dried material, and those of laboratory-grown cultures were 2.5 to 8.0 mg/g of freeze-dried cells. A single toxin was isolated from three N. spumigena-containing bloom samples and three N. spumigena laboratory isolates. Amino acid analysis and low- and high-resolution fast-atom bombardment mass spectroscopy indicated that the toxin from all of the sources was a cyclic pentapeptide (molecular weight, 824) containing glutamic acid, beta-methylaspartic acid, arginine, N-methyldehydrobutyrine, and 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4,6-decadienoic acid.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phytoplankton vertical distributions and composition in Baltic Sea cyanobacterial blooms

We studied the vertical structure of the phytoplankton community in two toxic cyanobacterial blooms in the offshore Baltic Sea. In 1994, vertically separated potentially toxic, diazotrophic and mixotrophic species (belonging to Cyanophyceae, Dinophyceae and Prymnesiophyceae) dominated. In 1997, picocyanobacteria, mainly in colonies, made up 40–50% of the total phytoplankton carbon biomass in the top 20 m both day and night. Colony-forming species of picocyanobacteria seem to be occasionally important and hitherto underestimated in the Baltic Sea.We found species-specific depth distribution patterns. Nodularia spumigena and Anabaena spp. were observed mainly above 10 m depth, while Aphanizomenon sp. was mostly found deeper, especially at night. Dinophysis norvegica was only abundant near the seasonal pycnocline and showed very limited diurnal migration. Other flagellates, including small Cryptophyceae and 10 identified Chrysochromulina species, occurred down to 40 m depth. Their vertical migration may help to retrieve nutrients from below the summer pycnocline.We conclude that considerable differences in dominating functional groups may occur between years/bloom stages, and that the vertical distribution pattern of many species is recurring at similar environmental conditions, suggesting species-specific niche-separation.     

A Kinetic and Factorial Approach to Study the Effects of Temperature and Salinity on Growth and Toxin Production by the Dinoflagellate Alexandrium ostenfeldii from the Baltic Sea

Alexandrium ostenfeldii is present in a wide variety of environments in coastal areas worldwide and is the only dinoflagellate known species that produces paralytic shellfish poisoning (PSP) toxins and two types of cyclic imines, spirolides (SPXs) and gymnodimines (GYMs). The increasing frequency of A. ostenfeldii blooms in the Baltic Sea has been attributed to the warming water in this region. To learn more about the optimal environmental conditions favoring the proliferation of A. ostenfeldii and its complex toxicity, the effects of temperature and salinity on the kinetics of both the growth and the net toxin production of this species were examined using a factorial design and a response-surface analysis (RSA). The results showed that the growth of Baltic A. ostenfeldii occurs over a wide range of temperatures and salinities (12.5–25.5°C and 5–21, respectively), with optimal growth conditions achieved at a temperature of 25.5°C and a salinity of 11.2. Together with the finding that a salinity > 21 was the only growth-limiting factor detected for this strain, this study provides important insights into the autecology and population distribution of this species in the Baltic Sea. The presence of PSP toxins, including gonyautoxin (GTX)-3, GTX-2, and saxitoxin (STX), and GYMs (GYM-A and GYM-B/-C analogues) was detected under all temperature and salinity conditions tested and in the majority of the cases was concomitant with both the exponential growth and stationary phases of the dinoflagellate’s growth cycle. Toxin concentrations were maximal at temperatures and salinities of 20.9°C and 17 for the GYM-A analogue and > 19°C and 15 for PSP toxins, respectively. The ecological implications of the optimal conditions for growth and toxin production of A. ostenfeldii in the Baltic Sea are discussed.