• ALGAE
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• v.34 no.3
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• pp.237-251
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• 2019

The dinoflagellate genus Alexandrium is known to often form harmful algal blooms causing human illness and large-scale mortality of marine organisms. Therefore, the population dynamics of Alexandrium species are of primary concern to scientists and aquaculture farmers. The growth rate of the Alexandrium species is the most important parameter in prediction models and nutrient conditions are critical parameters affecting the growth of phototrophic species. In Korean coastal waters, Alexandrium affine and Alexandrium fraterculus, of similar sizes, often form red-tide patches together. Thus, to understand bloom dynamics of A. affine and A. fraterculus, growth rates and nitrate uptake of each species as a function of nitrate ($NO_3$) concentration at $100{\mu}mol\;photons\;m^{-2}s^{-1}$ under 14-h light : 10-h dark and continuous light conditions were determined using a nutrient repletion method. With increasing $NO_3$ concentration, growth rates and $NO_3$ uptake of A. affine or A. fraterculus increased, but became saturated. Under light : dark conditions, the maximum growth rates of A. affine and A. fraterculus were 0.45 and $0.42d^{-1}$, respectively. However, under continuous light conditions, the maximum growth rate of A. affine slightly increased to $0.46d^{-1}$, but that of A. fraterculus largely decreased. Furthermore, the maximum nitrate uptake of A. affine and A. fraterculus under light : dark conditions were 12.9 and $30.1pM\;cell^{-1}d^{-1}$, respectively. The maximum nitrate uptake of A. affine under continuous light conditions was $16.4pM\;cell^{-1}d^{-1}$. Thus, A. affine and A. fraterculus have similar maximum growth rates at the given $NO_3$ concentration ranges, but they have different maximum nitrate uptake rates. A. affine may have a higher conversion rate of $NO_3$ to body nitrogen than A. fraterculus. Moreover, a longer exposure time to the light may confer an advantage to A. affine over A. fraterculus.

• Proceedings of the Korean Aquaculture Society Conference
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• 2003.10a
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• pp.136-137
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• 2003

The marine dinoflagellate genus Alexandrium has been recognized as the most representative toxic phytoplankton on account of production of paralytic shellfish poisoning (PSP) throughout the world. PSP producers, generally A, tamarense and A. catenella, within the genus Alexandrium have caused high level intoxicauon of fisheries products and even death of human. In addition, more recent increasing of geographical range of this deleterious species has given rise to alarming tension. The study presented here aimed construction of the molecular phylogenetic relationships through sequences-determination from 16 morphotypic species (containing newly sequenced 3 morphotypic species, A. tamiyavainchii, A. fraterculus and A. pseudogonyaulax) in LSU rDNA D1-D2 and 12 morphotypic species (containing newly sequenced 6 - morphotypic species, A. catenella, A. tamiyavanichii, A. fraterculus, A. affine, A. insuetum and A. pseudogonyaulax) in SSU rDNA region, and the sequences were subjected to comparative-analysis in respect to regional population using functionally expressed rDNA genus and pseudogenes. And we discussed on genetic differentiation between A. tamarense and A. catenella together with putative PSP divegence of the genus Alexandrium. The results of phylogenetic analysis showed the robust monophyletic 14 distinct classes of A. tamarense, A. excavatum, A. catenella, Tasmanian A. tamarense, A. affine (and/or A. concavum), Thai A. tamarense, A. tamiyavanichii, A. fraterculus, A. margalefii, A. andersonii, A. ostenfeldii, A. minutum (and/or A. lusitanicum), A. insuetum, and A, pseudogonyaulx clade. A. fraterculus and A. tamiyavanichii were sister relationship and they were positioned independently between A, affine cluster and those of A. margalefi, A. andersonii, A. ostenfeldii, A. minutum and A. insuetum. A. pseudogonyaulax appeared to be an ancestral taxon among Alexandrium.

• Journal of the korean society of oceanography
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• v.34 no.3
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• pp.167-171
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• 1999

Since toxic Alexandrium catenella and non-toxic A. fraterculus are morphologically similar, they are difficult to discriminate under the light microscope. However, a novel technology, such as fluorescein isothiocyanate (FITC)-conjugated lectin probes enables easy and rapid differentiation. Toxic A. catenella bound seven different lectins, whereas the non-toxic A. fratercuzus did not bind Arachis hypogaea (PNA) lectin. In addition, Pseudo-nitrschia species in this study were also difficult to identify to species level with light microscope techniques, but it was possible to classify them using fluorescent lectins. Pseudo-nitzschia multistriata, P. subfraudulenta and P. pungens bound Canavalia ensiformis (ConA), whereas P. subpaclfica did not, and P. pungens also bound Ricinus communis (RCA). These results imply that lectin could be used as a critical tool in the differentiation of P. multistriata, P. subfraudulenta and P. pungens. However, P. subpacifica was not differentiated by the lectins tested. Therefore, it isconcluded that lectin probes are useful for discriminating toxic A. catenella from non-toxic A. fraterculus, and for the identification of some Pseudo-nitzschia species. In addition, this method has a great potential to speed and detection between non-toxic and toxic harmful algal blooms (HABs) in Korean biotoxin monitoring systems.

• Journal of the korean society of oceanography
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• v.39 no.3
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• pp.172-185
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• 2004

LSU rDNA D1-D2 and SSU rDNA genes of 23 strains in seven Alexandrium (Halim) species, A. tamarense (Lebour) Balech, A. catenella (Whedon et Kofoid), A. fraterculus (Balech) Balech, A. affine (Inoue et Fukuyo) Balech, A. insuetum Balech, A. pseudogonyaulax (Biecheler) Horiguchi ex Yuki et Fukuyo and A. tamiyavanichii Balech, were sequenced and the data were used for molecular phylogenetic analysis. The sequence data revealed 11 and 7 ribotypes in the LSU rDNA D1-D2 region and 4 and 17 ribotypes in the SSU rDNA region of A. catenella and A. tamarense, respectively. Other Alexandrium species had also 1 to 5 ribotypes in the two regions. With the exception of CMC2 and CMC3 of A. catenella, all A. tamarense and A. catenella strains had a common ribotype, a functionally expressed rRNA gene (here termed type A), in both gene regions. In addition to the functionally expressed gene, several pseudogenes were obtained that were found to be good tools to analyze the population designation of regional isolates by grouping them according to shared ribotypes. From the phylogenetic analysis of the sequence data determined in this study and retrieved from GenBank, the genus Alexandrium was divided into 14 groups: 1) A. tamarense, 2) A. excavatum, 3) A. catenella, 4) Tasmanian A. tamarense, 5) A. affine (and/or A. concavum), 6) Thai A. tamarense, 7) A. tamiyavanichii, 8) A. fraterculus, 9) A. margalefii, 10) A. andersonii, 11) A. ostenfeldii, 12) A. minutum (or A. lusitanicum), 13) A. insuetum, and 14) A. pseudogonyaulax. The SSU rDNA gene sequence of A. fundyense was so similar to those of A. tamarense used in this study that the two species were difficult to discriminate each other. A. tamiyavanichii was closest to the A. tamarense strain isolated in Thailand and close to the long chain-forming species of A. affine and A. fraterculus. The phylogenetic tree showed that A. margalefii, A. andersonii, A. ostenfeldii, A. minutum and A. insuetum constituted the basal relative complex, and that A. pseudogonyaulax is an ancestral taxon in the genus Alexandrium.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.21 no.4
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• pp.158-170
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• 2016

We investigated the occurrence of the dinoflagellate genus Alexandrium in the nineteen Korean coastal sites from July to October 2013. Alexandrium-like planktonic cells were microscopically observed only in four out of the 19 sampling sites. From the samples containing Alexandrium-like cells 22 clonal cultures of Alexandrium species were established by single cell or single chain isolation method. Taxonomic identity of the 4 different strains ascertained by the robust analyses of morphological and molecular genetic characteristics were confirmed to be A. catenella, A. affine, A. fraterculus and an unidentified Alexandrium sp. for which strain WEB-Alex-01 was assigned. It was ascertained that in spite of hot summer diverse Alexandrium species attaining up to four were distributed in the study area, in contrast with the long empirical recognition that the emergence of Alexandrium species is restricted to cooler seasons like spring or autumn in Korean coastal waters. Morphology and genetic characteristics of Alexandrium sp. strain WEB-Alex-01 are different from any other previously reported Alexandrium species from Korean seas, which implies that further studies on taxonomic, physiological, ecological and toxicological properties of the newly recorded Alexandrium species are needed.

• ALGAE
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• v.36 no.4
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• pp.299-314
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• 2021

Some species in the dinoflagellate genus Alexandrium are bioluminescent. Of the 33 formally described Alexandrium species, the bioluminescence capability of only nine species have been tested, and eight have been reported to be bioluminescent. The present study investigated the bioluminescence capability of seven Alexandrium species that had not been tested. Alexandrium mediterraneum, A. pohangense, and A. tamutum were bioluminescent, but A. andersonii, A. hiranoi, A. insuetum, and A. pseudogonyaulax were not. We also measured the bioluminescent intensity of A. affine, A. fraterculus, A. mediterraneum, A. ostenfeldii, A. pacificum, A. pohangense, A. tamarense, and A. tamutum. The mean 200-second-integrated bioluminescence intensity per cell ranged from 0.02 to 32.2 × 10⁴ relative luminescence unit per cell (RLU cell^-1), and the mean maximum bioluminescence intensity per cell per second (BL_Max) ranged from 0.01 to 10.3 × 10⁴ RLU cell^-1 s^-1. BL_Max was significantly correlated with the maximum growth rates of Alexandrium species, except for A. tamarense. A phylogenetic tree based on large subunit ribosomal DNA (LSU rDNA) showed that the bioluminescent species A. affine, A. catenella, A. fraterculus, A. mediterraneum, A. pacificum, and A. tamarense formed a large clade. However, the toxicity or mixotrophic capability of these species was split. Thus, their bioluminescence capability in this clade was more consistent than their toxicity or mixotrophic capability. Phylogenetic trees based on LSU rDNA and the luciferase gene of Alexandrium were consistent except for A. pohangense. The results of the present study can provide a basis for understanding the interspecific diversity in bioluminescence of Alexandrium.

• Proceedings of the Korean Aquaculture Society Conference
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• 2003.10a
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• pp.35-35
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• 2003

We, for the first time, reported molecular sequences of large subunit ribosomal DNA Dl-D3 region of A. hiranoi, A. leei and A. satoanum hitherto unreported. In addition, this study presented the full-length sequences of A. affine, A. fraterculus, A. catenella and A. tamarense occurring in Korean coastal waters. In total, 17 Alexandrium morphospecies were subjected to the phylogenetic analysis using the Maximum-likelihood (ML) method. The alignment result of sequences of A. hiranoi and A. pseudogonyaulax showed that there were only two substitutions without length heterogeneity implying their genetic affiliation. In ML tree, A. leei formed a deeply diverging branch probably because of the accelerated evolutionary rate, and its phylogenetic position was so ambiguous to resolve the phylogenetic relationship to the residual taxa. An A. satoanum culture showing morphological variation in the sulcal plate formed an independent divergent branch with consistent sister relationship to A. hiranoi/A. pseudogonyaulax clade supported by the high posterior probability (PP) value. Blast search in GenBank showed the sequence data of A. affine, A. fraterculus, A. catenella and A. tamarense corresponded to their morphological species designation. In ML tree, Alexandrium species were commonly split into four main clades. The inter-clade relationships were not clear and usually supported by the week PP values. In general, the sulcal plate of Alexandrium species seemed to reflect the true phylogeny at the main clade level, and the connection between the 1 and the apical pore complex seemed to reflect the phylogeny at the subclade level.

• ALGAE
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• v.32 no.2
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• pp.101-130
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• 2017

The ichthyotoxic Cochlodinium polykrikoides red tides have caused great economic losses in the aquaculture industry in the waters of Korea and other countries. Predicting outbreak of C. polykrikoides red tides 1-2 weeks in advance is a critical step in minimizing losses. In the South Sea of Korea, large C. polykrikoides red tide patches have often been recorded offshore and transported to nearshore waters. To explore the processes of offshore C. polykrikoides red tides, temporal variations in 3-dimensional (3-D) distributions of red tide organisms and environmental parameters were investigated by analyzing 4,432 water samples collected from 2-5 depths of 60 stations in the South Sea, Korea 16 times from May to Nov, 2014. In the study area, the vegetative cells of C. polykrikoides were found as early as May 7, but C. polykrikoides red tide patches were observed from Aug 21 until Oct 9. Cochlodinium red tides occurred in both inner and outer stations. Prior to the occurrence of large C. polykrikoides red tides, the phototrophic dinoflagellates Prorocentrum donghaiense (Jun 12 to Jul 11), Ceratium furca (Jul 11 to Aug 21), and Alexandrium fraterculus (Aug 21) formed red tides in sequence, and diatom red tides formed 2-3 times without a certain distinct pattern. The temperature for the optimal growth of these four red tide dinoflagellates is known to be similar. Thus, the sequence of the maximum growth rates of P. donghaiense > C. furca > A. fraterculus > C. polykrikoides may be partially responsible for this sequence of red tides in the inner stations following high nutrients input in the surface waters because of heavy rains. Furthermore, Cochlodinium red tides formed and persisted at the outer stations when $NO_3$ concentrations of the surface waters were < $2{\mu}M$ and thermocline depths were >20 m with the retreat of deep cold waters, and the abundance of the competing red-tide species was relatively low. The sequence of the maximum swimming speeds and thus potential reachable depths of C. polykrikoides > A. fraterculus > C. furca > P. donghaiense may be responsible for the large C. polykrikoides red tides after the small blooms of the other dinoflagellates. Thus, C. polykrikoides is likely to outgrow over the competitors at the outer stations by descending to depths >20 m and taking nutrients up from deep cold waters. Thus, to predict the process of Cochlodinium red tides in the study area, temporal variations in 3-D distributions of red tide organisms and environmental parameters showing major nutrient sources, formation and depth of thermoclines, intrusion and retreat of deep cold waters, and the abundance of competing red tide species should be well understood.

• ALGAE
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• v.32 no.3
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• pp.199-222
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• 2017

Occurrence of Cochlodinium polykrikoides red tides have resulted in considerable economic losses in the aquaculture industry in many countries, and thus predicting the process of C. polykrikoides red tides is a critical step toward minimizing those losses. Models predicting red tide dynamics define mortality due to predation as one of the most important parameters. To investigate the roles of heterotrophic protists in red tide dynamics in the South Sea of Korea, the abundances of heterotrophic dinoflagellates (HTDs), tintinnid ciliates (TCs), and naked ciliates (NCs) were measured over one- or two-week intervals from May to Nov 2014. In addition, the grazing impacts of dominant heterotrophic protists on each red tide species were estimated by combining field data on red tide species abundances and dominant heterotrophic protist grazers with data obtained from the literature concerning ingestion rates of the grazers on red tide species. The abundances of HTDs, TCs, and NCs over the course of this study were high during or after red tides, with maximum abundances of 82, 49, and $35cells\;mL^{-1}$, respectively. In general, the dominant heterotrophic protists differed when different species caused red tides. The HTDs Polykrikos spp. and NCs were abundant during or after C. polykrikoides red tides. The mean and maximum calculated grazing coefficients of Polykrikos spp. and NCs on populations of co-occurring C. polykrikoides were $1.63d^{-1}$ and $12.92d^{-1}$, respectively. Moreover, during or after red tides dominated by the phototrophic dinoflagellates Prorocentrum donghaiense, Ceratium furca, and Alexandrium fraterculus, which formed serial red tides prior to the occurrence of C. polykrikoides red tides, the HTDs Gyrodinium spp., Polykrikos spp., and Gyrodinium spp., respectively were abundant. The maximum calculated grazing coefficients attributable to dominant heterotrophic protists on co-occurring P. donghaiense, C. furca, and A. fraterculus were 13.12, 4.13, and $2.00d^{-1}$, respectively. Thus, heterotrophic protists may sometimes have considerable potential grazing impacts on populations of these four red tide species in the study area.

• Fisheries and Aquatic Sciences
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• v.7 no.4
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• pp.175-183
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• 2004

The dinoflagellate Alexandrium tamiyavanichii Balech, a producer of toxins causing paralytic shellfish poisoning (PSP), has recently been considered as one of main organisms responsible for toxication of shellfish in Japan. In this study, A. tamiyavanichii was subjected to a molecular phylogenetic analysis inferred from 28S rDNA D1-D2 sequences and a species-specific LSU rRNA-targeted oligonucleotide DNA probe was designed to identify A. tamiyavanichii using the whole cell-FISH (fluorescence in situ hybridization). The sequences of the 28S rDNA D1-D2 region of A. tamiyavanichii showed no difference from A. cohorticular AF1746l4 (present name A. tamiyavanichii) and formed a distinct clade from the 'tamarensis species complex'. The probe, TAMID2, reacted specifically with A. tamiyavanichii cultured cells, without any cross-reaction with other species belonging to the same genus, including A. tamarense, A. catenella, A. affine, A. fraterculus, A. insuetum and A. pseudogonyaulax. In a test of cross-reactivity with a field sample, TAMID2 reacted consistently with only A. tamiyavanichii, indicating that the present protocol involving the TAMID2 probe might be useful for detecting toxic A. tamiyavanichii in a simple and rapid manner.