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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 (BLMax) ranged from 0.01 to 10.3 × 104 RLU cell-1 s-1-1. BLMax 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.

Vitamins are an important growth factor for the majority of microalgae. Although the effects of light and prey availability on the growth and feeding of mixotrophic dinoflagellates are relatively w...

The key nutrient sources for red-tide species are freshwater and deep cold waters. However, a lack of data on their growth rates at different depths limits our understanding of the effects of deep cold waters on red-tide formation. Offshore water was collected from 0, 20, and 40 m in the South Sea of Korea and the growth rates of major red-tide species were measured after their addition to these waters. The growth rates of Margalefidinium polykrikoides in the waters from 0, 20, and 40 m (0.25, 0.25, and 0.21 d-1) were similar. The growth rates of Prorocentrum donghaiense, Tripos furca, and Alexandrium fraterculus in the water from 20 m (0.30, 0.37, and 0.42 d-1) were similar to those from 40 m but higher than those from 0 m (0.16, 0.04, and 0.21 d-1). The ability of P. donghaiense, T. furca, and A. fraterculus to reach deep waters is therefore a critical factor affecting red-tide formation. Considering their vertical migration depths and growth rates at different depths, P. donghaiense, T. furca, or A. fraterculus can dominate when deep waters are intruded to 10 m, while A. fraterculus or M. polykrikoides can dominate when deep waters retreat to 20 m. Only M. polykrikoides can dominate when deep waters retreat to 30 m. These scenarios are supported by the results recorded in the red-tide events of 2014. Red-tide species can thus be predicted using data on their growth rates at different depths, their vertical migration depths, and the position of deep cold waters.

The dinoflagellate family Suessiaceae comprises cosmopolitan species distributed across polar and tropical waters in both marine and freshwater ecosystems, encompassing free-living forms, symbionts, and parasites. Recently, species diversity within the family has rapidly expanded, now including a few species reported to cause red tides. Despite their ecological and evolutionary importance, classifying them within Suessiaceae is difficult due to the limitations of the existing molecular markers-the highly conserved small subunit ribosomal gene (SSU rDNA) and the presence of two indel regions of sequence fragments of the large subunit ribosomal gene (LSU rDNA)-resulting in poorly resolved phylogenetic relationships. We assessed mitochondrial cytochrome b (cob) and cytochrome c oxidase 1 (cox1) genes to develop robust molecular markers that can reveal the genetic diversity of the family Suessiaceae. The divergences of cob and cox1 sequences among the species in the family were greater than the SSU rDNA but less than the LSU rDNA and the ITS region. Moreover, the distinctive topology inferred from the mitochondrial genes provided high resolution among the suessiacean species. We examined the validity of the genetic markers using phylogenomics based on 2,023 core proteins. The divergence of the cob phylogeny was most consistent with that of the phylogenomic results. Taken together, the cob gene can be a novel marker reflecting topology at the genome-scale within the family Suessiaceae.

Four unarmored heterotrophic dinoflagellates were isolated from the coastal waters of southern Korea. The rDNA sequences of four clonal cultures were determined, and the morphology of one of the four strains was examined using light and scanning and transmission electron microscopy. The large subunit (LSU) and small subunit (SSU) rDNA sequences of each of the strains differed by 0-0.9% from those of the other strains, and the SSU rDNA sequence of the strain differed by 1.8-4.4% from those of other Gyrodinium species, whereas the LSU (D1-D2) rDNA sequence differed by 12.4-22.2%. Furthermore, phylogenetic trees showed that Gyrodinium jinhaense n. sp. formed a distinctive clade among the other Gyrodinium species. Meanwhile, microscopy revealed an elliptical bisected apical structure complex and a cingulum that was displaced by approximately one-quarter of the cell length, which confirmed that the dinoflagellate belonged to the genus Gyrodinium. However, the cell surface was ornamented with 16 longitudinal striations, both on the episome and hyposome, unlike other Gyrodinium species. Furthermore, the cells were observed to have pusule systems and trichocysts but lacked mucocysts. Based on morphology and molecular data, we consider this strain to be a new species in the genus Gyrodinium and thus, propose that it be assigned to the name G. jinhaense n. sp.

In situ moorings were conducted at salt marsh and bare flat to reveal the environmental disturbance of sedimentary processes in the intertidal flat. Spartina alterniflora (Spartina), an invasive species, grew up to 156 cm in the Ganghwa tidal flat from June to November 2019. This rapid growth has resulted in the dense salt marsh, which complicated hydrodynamics and associated sediment processes. Stems and leaves could effectively trap fine-grained sediments (17.24–20.42 μm) at the bed, increasing the differences in bed elevation between the two sites to up to 5.11 cm. The cohesive sediments accumulated in Spartina communities were resuspended differently by stem-scale turbulence generated from the disturbance of stems and leaves, depending on wind forcing and vegetation conditions. The vegetated sediments, under low wind speeds ( 6 m s−1), stem-scale turbulence was sufficiently strengthened to surpass the sedimentation of suspended sediments; thus, it resuspended additional bed sediments without a loss of the trapped sediment, unlike in the bare flat. The flocculation of suspended sediments in Spartina communities was mainly controlled by stem-scale turbulence. The flocs were confined to a size of 40 μm (settling velocity: 0.17 mm s−1) and developed an approaching spherical shape. After the cut-off of Spartina, a favorable condition for the flocs to grow by 57 μm (settling velocity: 0.23 mm s−1) was established with decrease in stem-scale turbulence. These larger flocs were able to develop into a ramified spherical structure. Despite diminishment of stem-scale turbulence, the disturbed sediments were outflowed, resulting in an abrupt decrease in bed elevation (0.12 cm day−1). The results suggest that the sediment accumulated in Spartina communities remained erodible due to frequent disturbances without sufficient consolidation.

The Yellow and Bohai seas have long been contaminated by persistent toxic substances (PTSs) from numerous (un)known anthropogenic sources. In this study, we used Vibrio fischeri bioassay to evaluate ecotoxicological profiles associated with sedimentary PTSs contamination at a large marine ecosystem (LME) scale. A total of 125 surface sediments collected from the coastal areas of the Yellow and Bohai seas were analyzed both for aqueous and organic extracts. Not surprisingly, the results indicated site-dependent toxicities, but most sites were identified as non-toxic to V. fischeri. For aqueous extracts and organic extracts, 13% and 8% of samples, respectively exhibited marginal toxicity, while 0% and 2% of samples exhibited moderate toxicity. However, it should be noted that organic extracts (mean TU = 56) induced stronger toxicities than aqueous samples (mean TU = 0.4). This result generally back-supported the high toxicity potentials associated with sedimentary sink of organic pollutants. Several PTSs measured in the samples indicated a significant contribution to the observed V. fischeri toxicities. Of note, polycyclic aromatic hydrocarbons (PAHs; r = 0.28, p < 0.05), styrene oligomers (r = 0.41, p < 0.01), and alkylphenols (r = 0.38, p < 0.05) showed significant associations to the observed bacterial inhibition. Among PAHs, benzo[a]anthracene and phenanthrene exhibited a significant contribution to the observed V. fischeri toxicities. Meantime, salinity which reflects the distance from the point sources of land-driven pollutants along the rivers and estuaries in the Yellow and Bohai seas was a key environmental variable representing the sample toxicities. Overall, the present study provides baseline information for evaluating the potential sediment toxicity to implement responsible coastal management at an LME scale, and elsewhere.

A tidal saltmarsh supporting marine ecosystem services becomes more recognized, but an understanding of its trophic dynamics is far limited. We investigated the benthic food-web dynamics in Ganghwa tidal flat, a representative tidal saltmarsh of South Korea. The stable carbon and nitrogen isotope ratio values were analyzed for the sixteen species of macrobenthos and their potential food sources such as microphytobenthos (MPB) and various organic matters. A year-round survey was conducted in the three sites at Ganghwa showing the different types of sediment bottom (sandy mud or mud) and/or vegetation (Phragmites or Suaeda). In general, the isotopic signature fairly well demonstrated that trophic structure is primarily influenced by sediment mud content and/or dominated vegetation. Among the four feeding types of consumers (filter feeder; deposit feeder; omnivore; carnivore), the deposit feeders such as mollusk, arthropod, and annelid showed increased dietary dependency on MPB at bare sites. Whilst they actively utilized 13C-depleted organic matters at vegetated sites. Meantime, significantly enriched stable nitrogen isotopic ratio of macrobenthos was evidenced in fall, which reflected the seasonal variation of food sources and physiological processes in survival strategy. Overall, the stable isotopic approach was useful to address the key factors (in)directly influencing the benthic food web structure and its functioning in a typical tidal saltmarsh of the Yellow Sea.

Speculation surrounds the importance of ecologically cryptic Symbiodinium spp. (dinoflagellates) that occur at low abundances in reef-building corals and in the surrounding environment. Evidence acquired from extensive sampling, long-term monitoring, and experimental manipulation can allow us to deduce the ecology and functional significance of these populations and whether they might contribute to the response of coral-dinoflagellate mutualisms to climate change. Quantitative PCR was used here to diagnose the prevalence, seasonal variation, and abundances of Symbiodinium spp. within and between colonies of the coral, Alveopora japonica. Consistent with broader geographic sampling, only one species comprised 99.9 %, or greater, the population of symbionts in every sample. However, other Symbiodinium including the non-mutualistic species, Symbiodinium voratum, were often detected, but at estimated cell densities thousands-fold less than the dominant symbiont. The temporal variation in prevalence and abundances of these "background" Symbiodinium could not be definitively related to any particular environmental factor including seasonality and water chemistry. The prevalence (proportion detected among host samples), but not abundance, of S. voratum may weakly correspond to increases in environmental inorganic silica (SiO2) and possibly nitrogen (NO3). When multiple background Symbiodinium occurred within an individual polyp, the average cell densities were positively correlated, suggesting non-specific processes of cell sorting and retention by the animal. While these findings substantiate the existence of a broader, yet uncharacterized, diversity of Symbiodinium, we conclude that only those species which can occur in high abundance and are temporally stable are ultimately important to coral-dinoflagellate mutualisms. Many transient Symbiodinium spp., which occur only at trace abundances in the coral's microbiome, belong to different functional guilds and likely have little, if any, importance to a coral's physiology. The successful integration between host and symbiont into a stable functional unit should therefore be considered when defining host-symbiont specificity.

Polykrikos hartmannii is a phototrophic dinoflagellate with chloroplasts, and it swims as a single zooid or forms a two-zooid pseudo-colony. To investigate the feeding ability of P. hartmannii, its feeding occurrence, prey species, and feeding mechanism were explored. Furthermore, the growth and ingestion rates of P. hartmannii on the mixotrophic dinoflagellate Cochlodinium polykrikoides, the optimal prey, as a function of prey concentration were measured. This study reported for the first time that P. hartmannii is a mixotrophic dinoflagellate. When diverse algal species were provided as potential prey, P. hartmannii could feed only on chain-forming toxic mixotrophic dinoflagellates C. polykrikoides and Gymnodinium catenatum. P. hartmannii ingested cells of these prey by engulfment after anchoring a prey cell using a nematocyst–taeniocyst complex. With increasing mean prey concentration, the ingestion rate of P. hartmannii on C. polykrikoides increased, but reached saturation at a prey concentration of 945 ng C ml−1 (1350 cells ml−1). The maximum ingestion rate of P. hartmannii on C. polykrikoides was 1.9 ng C predator−1 d−1 (2.7 cells predator−1 d−1). However, the maximum mixotrophic growth rate of P. hartmannii with added C. polykrikoides cells (0.030 d−1), at 20 °C under a 14:10 h light-dark cycle of 100 μE m−2 s−1, was slightly greater than of those without added prey (0.023 d−1). The low maximum ingestion rate of P. hartmannii may be responsible for this small difference between the maximum mixotrophic and autotrophic growth rates. The calculated grazing coefficients for P. hartmannii on co-occurring C. polykrikoides were up to 0.324 d−1 (28% of the population of C. polykrikoides was removed by P. hartmannii populations in 1 d). The results of the present study suggest that P. hartmannii can have a considerable grazing impact on C. polykrikoides populations.

Phytoplankton production in coastal waters influences seafood production and human health and can lead to harmful algal blooms. Water temperature and eutrophication are critical factors affecting phytoplankton production, although the combined effects of warming and nutrient changes on phytoplankton production in coastal waters are not well understood. To address this, phytoplankton production changes in natural waters were investigated using samples collected over eight months, and under 64 different initial conditions, established by combining four different water temperatures (i.e., ambient T, +2, +4, and + 6 °C), and two different nutrient conditions (i.e., non-enriched and enriched). Under the non-enriched conditions, the effect of warming on phytoplankton production was significantly positive in some months, significantly negative in others, or had no effect. However, under enriched conditions, warming affected phytoplankton production positively in all months except one, when the salinity was as low as 6.5. These results suggest that nutrient conditions can alter the effects of warming on phytoplankton production. Of several parameters, the ratio of initial nitrate concentration to chlorophyll a concentration [NCCA, μM (μg L −1 ) −1 ] was one of the most critical factors determining the directionality of the warming effects. In laboratory experiments, when NCCA in the ambient or nutrient-enriched waters was ≥1.2, warming increased or did not change phytoplankton production with one exception; however, when NCCA was

Red tides – discolorations of the sea surface due to dense plankton blooms – occur regularly in coastal and offshore waters along much of the world's coastline. Red tides often cause large-scale mortalities of fish and shellfish and significant losses to the aquaculture and tourist industries of many countries. Therefore, understanding and predicting the mechanisms controlling the outbreak, persistence, spread, and decline of red tides are important concerns to scientists, officials, industry, and the public. With increasing knowledge of red-tide species and red-tide events, new mechanisms have been discovered. Based on the nutrition and behaviors of red-tide organisms and biological interactions among them, red-tide outbreaks can be categorized into a hierarchy of four generation mechanisms (GM1–GM4). In the simplest, GM1, all phototrophic red-tide species were treated as exclusively autotrophic organisms without the ability to swim. However, this GM cannot explain red-tide outbreaks in oligotrophic surface waters offshore. Vertical migration (considered in GM2) and mixotrophy (GM3) enable red-tide flagellates to acquire growth factors from nutrient-rich deep waters or co-occurring prey, respectively. In natural environments, all red tides occur by those species outgrowing co-occurring organisms; red-tide species dominate communities by eliminating other species or reducing their abundances. Thus, GM4 contains the direct biological interactions (i.e., inhibition by physical contact or chemical effects) and indirect biological interactions (i.e., acquiring resources faster than others) that can affect the dominance of red-tide species under given conditions. Correctly choosing one of these four GMs for red tides dominated by one causative species is important because the accuracy of predictions may be outweighed by the costs and time required to acquire the relevant information. In this study, mechanisms describing the outbreak, persistence, and decline of red tides were reviewed, the advantages and limitations of each mechanism were evaluated, and insights about the evolution of the mechanisms were developed.

Biecheleriopsis is a genus of small marine planktonic dinoflagellates. Here, we present detailed morphological, molecular and ecophysiological characterizations of Biecheleriopsis adriatica based on a number of strains from Korea. The small subunit (SSU) ribosomal DNA (rDNA) sequences of two of the three Korean strains were closely related to those of previously described B. adriatica, and one was identical. However, the large subunit (LSU) and internal transcribed spacer region (ITS1, ITS2 and 5.8S) sequences from the Korean strains differed by 0.1–0.6% and 1.0–1.6%, respectively, from the non-Korean strains. In phylogenetic trees built on the basis of the SSU and LSU (D1-D3) rDNA and ITS region sequences, the Korean strains clustered within a clade including all the other B. adriatica strains. Morphologically, the Korean strains resemble those described from the Adriatic Sea. However, some cells of the Korean strains had nine latitudinal rows of amphiesmal vesicles (AVs): three episomal, three c...

The harmful dinoflagellate Cochlodinium polykrikoides is known to cause fish death by gill-clogging when its abundance exceeds approximately 1000 cells ml−1. Thus, red tides of this dinoflagellate have caused considerable loss in the aquaculture industry worldwide. Typhoons carrying strong winds and heavy rains may alter the process of red tide events. To investigate the effects of typhoons on C. polykrikoides red tides, daily variations in the abundance of C. polykrikoides, and wind speeds in three study areas in the South Sea of Korea were analyzed during the periods of C. polykrikoides red tides and the passage of 14 typhoons during 2012–2014. The typhoons differentially affected Cochlodinium red tides during the study period, and the daily maximum wind speed generated by the typhoon was critical. Four typhoons with daily maximum wind speeds of >14 m s−1 eliminated Cochlodinium red tides, while three typhoons with daily maximum wind speed of 5–14 m s−1 only lowered the abundance. However, other typhoons with daily maximum wind speeds of

A heterotrophic dinoflagellate isolated from the waters of Masan Bay, Korea was, at first glance, morphologically similar to Katodinium glandulum, yet had unreported plate patterns and DNA sequences. This dinoflagellate had thin plates arranged in a Kofoidian series Po, X, 4′, 2a, 6″, 6c, PC, 3 + s, 5‴, 0p, and 2⁗, similar to species in the family Pfiesteriaceae. However, it did not have a closing plate (cp) and only small sulcal plates (3 + s). Furthermore, this dinoflagellate had a conspicuous apical hook (finger-like projection) on the epitheca, like K. glandulum and Katodinium asymmetricum, but unlike the other Katodinium species and the other species in the family Pfiesteriaceae. The epitheca had a conical shape and was markedly larger than the hemispherical hypotheca. Cell lengths and widths of live biflagellate cells satiated with the phototrophic dinoflagellate Heterocapsa triquetra were 21.2–29.2 μm and 18.1–24.9 μm, respectively, while those of biflagellate cells starved for 4 d were 10.2–17.3 μm and 7.7–14.6 μm, respectively. The ratio of the width of the epitheca relative to the hypotheca (0.9) is similar to that of K. glandulum, but larger than that of K. asymmetricum (0.5–0.7). The dinoflagellate had a peduncle but lacked an eyespot. The DNA sequences differed from those of K. glaucum, the only Katodinium species with reported rDNA sequences. Compared to the other known genera in the family Pfiesteriaceae, the rDNA sequences of the small subunit (SSU), ITS regions (ITS1, 5.8S, ITS2), and D1–D3 large subunit (LSU) differed by 1.9–6.8%, ≥4.4%, and ≥5.6%, respectively. In a phylogenetic tree based on the SSU and LSU rDNA, a clade containing this species belonged to a larger clade of the family Pfiesteriaceae, but was divergent from a clade containing K. glaucum. Due to its morphological similarity to K. glandulum and genetic differences from K. glaucum and the other species in the family Pfiesteriaceae, it is proposed that this species Aduncodinium glandula be assigned to be a new genus and a new combination, A. glandula.

Copyright © 2014 The Korean Society of Phycology 137 http://e-algae.kr pISSN: 1226-2617 eISSN: 2093-0860 Mixotrophy in the newly described dinoflagellate Ansanella granifera: feeding mechanism, prey species, and effect of prey concentration Sook Kyung Lee, Hae Jin Jeong*, Se Hyeon Jang, Kyung Ha Lee, Nam Seon Kang, Moo Joon Lee and Eric Potvin KHNP-Central Research Institute, Korea Hydro & Nuclear Power Corporation, Daejeon 305-343, Korea School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea Advanced Institutes of Convergence Technology, Suwon 443-270, Korea

Dinoflagellates in the genus Symbiodinium are ubiquitous in shallow marine habitats where they commonly exist in symbiosis with cnidarians. Attempts to culture them often retrieve isolates that may not be symbiotic, but instead exist as free-living species. In particular, cultures of Symbiodinium clade E obtained from temperate environments were recently shown to feed phagotrophically on bacteria and microalgae. Genetic, behavioral, and morphological evidence indicate that strains of clade E obtained from the northwestern, southwestern, and northeastern temperate Pacific Ocean as well as the Mediterranean Sea constitute a single species: Symbiodinium voratum n. sp. Chloroplast ribosomal 23S and mitochondrial cytochrome b nucleotide sequences were the same for all isolates. The D1/D2 domains of nuclear ribosomal DNA were identical among Western Pacific strains, but single nucleotide substitutions differentiated isolates from California (USA) and Spain. Phylogenetic analyses demonstrated that S. voratum is well-separated evolutionarily from other Symbiodinium spp. The motile, or mastigote, cells from different cultures were morphologically similar when observed using light, scanning, and transmission electron microscopy; and the first complete Kofoidian plate formula for a Symbiodinium sp. was characterized. As the largest of known Symbiodinium spp., the average coccoid cell diameters measured among cultured isolates ranged between 12.2 (± 0.2 SE) and 13.3 (± 0.2 SE) μm. Unique among species in the genus, a high proportion (approximately 10-20%) of cells remain motile in culture during the dark cycle. Although S. voratum occurs on surfaces of various substrates and is potentially common in the plankton of coastal areas, it may be incapable of forming stable mutualistic symbioses.

Amphidinium massartii Biecheler is an epiphytic and toxic dinoflagellate. Prior to the present study, A. massartii has been reported in the waters off the Mediterranean, Australian, USA, and Canadian coasts. We isolated Amphidinium cells from the coastal waters of Jeju Island, Korea and their morphology and rDNA sequences indicated that they were A. massartii. Herein, we report for the first time the occurrence of A. massartii in the waters of the temperate region in the northwestern Pacific Ocean. The large subunit (LSU) rDNA sequences of the Korean strains were 0.7% different from those of an Australian strain of A. massartii CS-259, the closest species, but were 4.1-5.8% different from those of the other Australian strains and the USA strains of A. massartii and from those of Amphidinium sp. HG115 that was isolated from subtropical Okinawan waters. In phylogenetic trees based on LSU, internal transcribed spacer, small subunit rDNA, and cytochrome b sequences, the Korean strains belonged to the A. massartii clade, which was clearly divergent from the A. carterae clade. The morphology of the Korean A. massartii strains was similar to that of the originally described French strain and recently described Australian strain. However, we report for the first time here that scales were observed on the surface of the flagella. In conclusion, the Korean A. massartii strains have unique rDNA sequences, even though they have a very similar morphology to that of previously reported strains. This report extends the known range of this dinoflagellate to the temperate waters of the northwestern Pacific Ocean.

Ostreopsis is an epiphytic and potentially toxic dinoflagellate. Here, we have provided the first report about the occurrence of Ostreopsis cf. ovata in Korean waters. In general, the morphology of the Korean strain of O. cf. ovata isolated from the waters off Jeju Island, Korea, was similar to the original description of O. ovata isolated from Japanese water. However, the cell length of the Korean strain was 20–30% smaller than that of the Japanese strain. In addition, the cingulum of the Korean strain was displaced and undulated in the ventral view, but that of the Japanese strain was not displaced. We have reported, for the first time, the presence of a line of small knobs on the Po plate. The plates of the O. cf. ovata Korean strain were arranged in a Kofoidian series of Po, 3′, 7″, 6c, 6s, V p , R p , 5‴, 1p, and 2⁗. When properly aligned, the small subunit (SSU) rDNA sequence of the O. cf. ovata Korean strain was 5.8% different to the O. cf. ovata Malaysian strain, which is the closest strain. In addition, compared to the south-east Asian, Pacific, Atlantic, and Mediterranean strains of Ostreopsis sp., O. ovata , and O. cf. ovata , the sequences of the internal transcribed spacer region (ITS1 and ITS2) plus 5.8S, D1–D3, and D8–D10 large subunit (LSU) rDNA of the O. cf. ovata Korean strain showed a difference of 3.6–16%, 15.8–19.7%, and 0–3%. Furthermore, in the phylogenetic trees based on D1–D3 LSU rDNA regions, the O. cf. ovata Korean strain was located in the basal position of the other O. ovata and O. cf. ovata clades. Therefore, we suggest that the O. cf. ovata Korean strain is genetically distinct among the O. ovata and O. cf. ovata strains reported to date.

Red tides by the ichthyotoxic dinoflagellate Cochlodinium polykrikoides have caused large scaled mortality of fish and great loss in aquaculture industry in many countries. Detecting and quantifying the abundance of this species are the most critical step in minimizing the loss. The conventional quantitative real-time PCR (qPCR) method has been used for quantifying the abundance of this species. However, when analyzing >500 samples collected during huge C. polykrikoides red tides in South Sea of Korea in 2014, this conventional method and the previously developed specific primer and probe set for C. polykrikoides did not give reasonable abundances when compared with cell counting data. Thus improved qPCR methods and a new specific primer and probe set reflecting recent discovery of 2 new ribotypes have to be developed. A new species-specific primer and probe set for detecting all 3 ribotypes of C. polykrikoides was developed and provided in this study. Furthermore, because the standard curve between cell abundance and threshold cycle value (Ct) is critical, the efficiencies of 4 different preparation methods used to determine standard curves were comparatively evaluated. The standard curves were determined by using the following 4 different preparations: (1) extraction of DNA from a dense culture of C. polykrikoides followed by serial dilution of the extracted DNA (CDD method), (2) extraction of DNA from each of the serially diluted cultures with different concentrations of C. polykrikoides cultures (CCD method), (3) extraction of DNA from a dense field sample of C. polykrikoides collected from natural seawater and then dilution of the extracted DNA in serial (FDD method), and (4) extraction of DNA from each of the serially diluted field samples having different concentrations of C. polykrikoides (FCD method). These 4 methods yielded different results. The abundances of C. polykrikoides in the samples collected from the coastal waters of South Sea, Korea, in 2014-2015, obtained using the standard curves determined by the CCD and the FCD methods, were the most similar (0.93-1.03 times) and the second closest (1.16-1.33 times) to the actual cell abundances obtained by enumeration of cells. Thus, our results suggest that the CCD method is a more effective tool to quantify the abundance of C. polykrikoides than the conventional method, CDD, and the FDD and FCD methods.

Survival of free-living and symbiotic dinoflagellates ( Symbiodinium spp.) in coral reefs is critical to the maintenance of a healthy coral community. Most coral reefs exist in oligotrophic waters, and their survival strategy in such nutrient-depleted waters remains largely unknown. In this study, we found that two strains of Symbiodinium spp. cultured from the environment and acquired from the tissues of the coral Alveopora japonica had the ability to feed heterotrophically. Symbiodinium spp. fed on heterotrophic bacteria, cyanobacteria ( Synechococcus spp.), and small microalgae in both nutrient-replete and nutrient-depleted conditions. Cultured free-living Symbiodinium spp. displayed no autotrophic growth under nitrogen-depleted conditions, but grew when provided with prey. Our results indicate that Symbiodinium spp.’s mixotrophic activity greatly increases their chance of survival and their population growth under nitrogen-depleted conditions, which tend to prevail in coral habitats. In particular, free-living Symbiodinium cells acquired considerable nitrogen from algal prey, comparable to or greater than the direct uptake of ammonium, nitrate, nitrite, or urea. In addition, free-living Symbiodinium spp. can be a sink for planktonic cyanobacteria ( Synechococcus spp.) and remove substantial portions of Synechococcus populations from coral reef waters. Our discovery of Symbiodinium ’s feeding alters our conventional views of the survival strategies of photosynthetic Symbiodinium and corals.

The marine phototrophic dinoflagellate Gymnodinium smaydae n. sp. is described from cells prepared for light, scanning, and transmission electron microscopy. Also, sequences of the small (SSU) and large subunits (LSU) and the internal transcribed spacer region (ITS1-5.8S-ITS2) of ribosomal DNA were analyzed. This newly isolated dinoflagellate possessed nuclear chambers, nuclear fibrous connective, an apical groove running in a counterclockwise direction around the apex, and a major accessory pigment peridinin, which are four key features for the genus Gymnodinium. The epicone was conical with a round apex, while the hypocone was ellipsoid. Cells growing photosynthetically were 6.3-10.9 μm long and 5.1-10.0 μm wide, and therefore smaller than any other Gymnodinium species so far reported except Gymnodinium nanum. Cells were covered with polygonal amphiesmal vesicles arranged in 11 horizontal rows, and the vesicles were smaller than those of the other Gymnodinium species. This dinoflagellate had a sharp and elongated ventral ridge reaching half way down the hypocone, unlike other Gymnodinium species. Moreover, displacement of the cingulum was 0.4-0.6 × cell length while in other known Gymnodinium species it is less than 0.3 × cell length. In addition, the new species possessed a peduncle, permanent chloroplasts, pyrenoids, trichocysts, pusule systems, and small knobs along the apical furrow, but it lacked an eyespot, nematocysts, and body scales. The sequence of the SSU, ITS1-5.8S-ITS2, and LSU rDNA region differed by 1.5-3.8%, 6.0-17.4%, and 9.1-17.5%, respectively, from those of the most closely related species. The phylogenetic trees demonstrated that the new species belonged to the Gymnodinium clade at the base of a clade consisting of Gymnodinium acidotum, Gymnodinium dorsalisulcum, Gymnodinium eucyaneum, etc. Based on morphological and molecular data, we suggest that the taxon represents a new species, Gymnodinium smaydae n. sp.

To investigate heterotrophic protists grazing on Symbiodinium sp., we tested whether the common heterotrophic dinoflagellates Gyrodinium dominans, Gyrodinium moestrupii, Gyrodinium spirale, Oblea rotundata, Oxyrrhis marina, and Polykrikos kofoidii and the ciliates Balanion sp. and Parastrombidinopsis sp. preyed on the free-living dinoflagellate Symbiodinium sp. (clade E). We measured the growth and ingestion rates of O. marina and G. dominans on Symbiodinium sp. as a function of prey concentration. Furthermore, we compared the results to those obtained for other algal prey species. In addition, we measured the growth and ingestion rates of other predators at single prey concentrations at which these rates of O. marina and G. dominans were saturated. All predators tested in the present study, except Balanion sp., preyed on Symbiodinium sp. The specific growth rates of O. marina and G. dominans on Symbiodinium sp. increased rapidly with increasing mean prey concentration < ca. 740–815 ng C/ml (7,400–8,150 cells/ml), but became saturated at higher concentrations. The maximum growth rates of O. marina and G. dominans on Symbiodinium sp. (0.87 and 0.61/d) were much higher than those of G. moestrupii and P. kofoidii (0.11 and 0.04/d). Symbiodinium sp. did not support positive growth of G. spirale, O. rotundata, and Parastrombidinopsis sp. However, the maximum ingestion rates of P. kofoidii and Parastrombidinopsis sp. (6.7–10.0 ng C/predator/d) were much higher than those of O. marina and G. dominans on Symbiodinium sp. (1.9–2.1 ng C/predator/d). The results of the present study suggest that Symbiodinium sp. may increase or maintain the populations of some predators.