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Exploring mixotrophy of dinoflagellate species is critical to understanding red-tide dynamics and dinoflagellate evolution. Some species in the dinoflagellate genus Karenia have caused harmful algal blooms. Among 10 Karenia species, the mixotrophic ability of only two species, Karenia mikimotoi and Karenia brevis, has been investigated. These species have been revealed to be mixotrophic; however, the mixotrophy of the other species should be explored. Moreover, although K. mikimotoi was previously known to be mixotrophic, only a few potential prey species have been tested. We explored the mixotrophic ability of Karenia bicuneiformis, Karenia papilionacea, and Karenia selliformis and the prey spectrum of K. mikimotoi by incubating them with 16 potential prey species, including a cyanobacterium, diatom, prymnesiophyte, prasinophyte, raphidophyte, cryptophytes, and dinoflagellates. Cells of K. bicuneiformis, K. papilionacea, and K. selliformis did not feed on any tested potential prey species, indicating a lack of mixotrophy. The present study newly discovered that K. mikimotoi was able to feed on the common cryptophyte Teleaulax amphioxeia. The phylogenetic tree based on the large subunit ribosomal DNA showed that the mixotrophic species K. mikimotoi and K. brevis belonged to the same clade, but K. bicuneiformis, K. papilionacea, and K. selliformis were divided into different clades. Therefore, the presence or lack of a mixotrophic ability in this genus may be partially related to genetic characterizations. The results of this study suggest that Karenia species are not all mixotrophic, varying from the results of previous studies.

The mortality rate of red-tide dinoflagellates owing to predation is a major parameter that affects their population dynamics. The dinoflagellates Ansanella granifera and Ansanella sp. occasionally cause red tides. To understand the interactions between common heterotrophic protists and A. granifera, we explored the feeding occurrence of nine heterotrophic protists on A. granifera and the growth and ingestion rates of the heterotrophic dinoflagellate Gyrodinium dominans on A. granifera as a function of prey concentration and those of Oxyrrhis marina at a single high prey concentration. The heterotrophic dinoflagellates Aduncodinium glandula, G. dominans, Gyrodinium moestrupii, Luciella masanensis, Oblea rotunda, O. marina, Polykrikos kofoidii, and Pfiesteria piscicida and the naked ciliate Strombidium sp. were able to feed on A. granifera. With increasing mean prey concentrations, the growth and ingestion rates of G. dominans feeding on A. granifera rapidly increased and became saturated or slowly increased. The maximum growth and ingestion rates of G. dominans on A. granifera were 0.305 d-1 and 0.42 ng C predator-1 d-1 (3.8 cells predator-1 d-1), respectively. Furthermore, the growth and ingestion rates of O. marina on A. granifera at 1,700 ng C mL-1 (15,454 cells mL-1) were 0.037 d-1 and 0.19 ng C predator-1 d-1 (1.7 cells predator-1 d-1), respectively. The growth and ingestion rates of G. dominans and O. marina feeding on A. granifera were almost the lowest among those on the dinoflagellate prey species. Therefore, G. dominans and O. marina may prefer A. granifera less than other dinoflagellate prey species. The low mortality rate of A. granifera may positively affect its bloom formation.

Noctiluca scintillans is a heterotrophic dinoflagellate that causes red-colored oceans during the day (red tides) and glowing oceans at night (bioluminescence). This species feeds on diverse prey, including phytoplankton, heterotrophic protists, and eggs of metazoans. Thus, many scientists have conducted studies on the ecophysiology of this species. It is easy to cultivate N. scintillans at a scale of 100 L because N. scintillans cells usually stay near the surface, while prey cells stay below the surface in large water tanks. To obtain mass-cultured N. scintillans cells, we developed an automatic system for cultivating N. scintillans on a scale of 100 L. The system consisted of four tanks containing fresh nutrients, the chlorophyte Dunaliella salina as prey, N. scintillans for growth, and N. scintillans for storage, respectively. The light intensities supporting the high growth rates of D. salina and N. scintillans were 300 and 20 μmol photons m-2 s-1, respectively. Twenty liters of D. salina culture from the prey culture tank were transferred to the predator culture tank, and subsequently 20 L of nutrients from the nutrient tank were transferred to the prey culture tank every 2 d. When the volume of N. scintillans in the predator culture tank reached 90 L 6 d later, 70 L of the culture were transferred to the predator storage tank. To prevent N. scintillans cells from being separated from D. salina cells in the predator culture tank, the culture was mixed using an air pump, a sparger, and a stirrer. The highest abundance of N. scintillans in the predator culture tank was 45 cells mL-1, which was more than twice the highest abundance when this dinoflagellate was cultivated manually. This automatic system supplies 100 L of N. scintillans pure culture with a high density every 10 d for diverse experiments on N. scintillans.

Water temperature affects plankton survival and growth. The dinoflagellate Shimiella gracilenta survives using theplastids of ingested prey, indicating kleptoplastidy. However, studies on the effects of water temperature on kleptoplastidicdinoflagellates are lacking. We explored the growth and ingestion rates of S. gracilenta as a function of water temperature.Furthermore, using data on its spatiotemporal distribution in Korean coastal waters during 2015–2018, we predictedits distribution under elevated temperature conditions of +2, +4, and +6°C. Growth rates of S. gracilenta with andwithout Teleaulax amphioxeia prey as well as ingestion rates were significantly affected by water temperature. Growthrates of S. gracilenta with and without prey were positive or zero at 5–25°C but were negative at ≥30°C. The maximumgrowth rate of S. gracilenta with T. amphioxeia was 0.85 d-1, achieved at 25°C, and 0.21 d-1 at 20°C without prey. The ingestionrate of S. gracilenta on T. amphioxeia at 25°C (0.05 ng C predator-1 d-1) was greater than that at 20°C (0.04 ng Cpredator-1 d-1). Thus, feeding may shift the optimal temperature for the maximum growth rate of S. gracilenta from 20 to25°C. In spring and winter, the distributions of S. gracilenta under elevated temperature conditions were predicted notto differ from those during 2015–2018. However, S. gracilenta was predicted not to survive at some additional stationsunder elevated temperature conditions of +2, +4, and +6°C in summer or under elevated temperature conditions of +6°Cin autumn. Therefore, global warming may affect the distribution of S. gracilenta.

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.

To explore the ecophysiological characteristics of the kleptoplastidic dinoflagellate Shimiella gracilenta, we determined its spatiotemporal distribution in Korean coastal waters and growth and ingestion rates as a function of prey concentration. The abundance of S. gracilenta at 28 stations from 2015 to 2018 was measured using quantitative realtime polymerase chain reaction. Cells of S. gracilenta were detected at least once at all the stations and in each season, when temperature and salinity were 1.7–26.4°C and 9.9–35.6, respectively. Moreover, among the 28 potential prey species tested, S. gracilenta SGJH1904 fed on diverse prey taxa. However, the highest abundance of S. gracilenta was only 3 cells mL-1 during the study period. The threshold Teleaulax amphioxeia concentration for S. gracilenta growth was 5,618 cells mL-1, which was much higher than the highest abundance of T. amphioxeia (667 cells mL-1). Thus, T. amphioxeia was not likely to support the growth of S. gracilenta in the field during the study period. However, the maximum specific growth and ingestion rates of S. gracilenta on T. amphioxeia, the optimal prey species, were 1.36 d-1 and 0.04 ng C predator- 1 d-1, respectively. Thus, if the abundance of T. amphioxeia was much higher than 5,618 cells mL-1, the abundance of S. gracilenta could be much higher than the highest abundance observed in this study. Eurythermal and euryhaline characteristics of S. gracilenta and its ability to feed on diverse prey species and conduct kleptoplastidy are likely to be responsible for its common spatiotemporal distribution.

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.

A small dinoflagellate, ~13 μm in cell length, was isolated from Jinhae Bay, Korea. Light microscopy showed that it was similar to the kleptoplastidic dinoflagellate Gymnodinium gracilentum nom. inval. rDNA sequences were obtained and its anatomy and morphology described using light and scanning and transmission electron microscopy. Phylogenetic analyses indicated that it belonged to the family Kareniaceae. However, its large subunit (LSU) rDNA sequences were 5.2-9.5% different from those of the other five genera in the family, and its clade was clearly divergent from that of each genus. Its overall morphology was different from those of the other five genera in the family and from Gymnodinium. Unlike Gymnodinium, this dinoflagellate did not have a horseshoe-shaped apical groove, nuclear envelope chambers, or a nuclear fibrous connective (NFC). It had an apical line of narrow amphiesmal vesicles and an elongated apical furrow crossing the apex. Cells were covered with polygonal amphiesmal vesicles arranged in 16 rows. Starved cells did not contain their own plastids, eyespots, pyrenoids, peridinin, or fucoxanthin. However, they could survive without added prey for approximately one month using chloroplasts from the cryptophyte prey Teleaulax amphioxeia, indicating kleptoplastidy. Because this taxon is genetically distinct at the generic rank from the other genera in Kareniaceae, it is placed in Shimiella gen. nov., and because G. gracilentum was invalid, the new bionomial S. gracilenta sp. nov. is proposed.

Dinoflagellates are a major component of marine ecosystems, and very cold and hot water may affect their survival. Global warming has amplified the magnitude of water temperature fluctuations. To investigate the molecular responses of dinoflagellates to very cold and hot water, we compared the differentially expressed genes of the phototrophic dinoflagellate Biecheleriopsis adriatica grown under optimal temperature and cold and heat stress. The number of genes upregulated or downregulated between optimal temperature and cold stress was twice than that between optimal temperature and heat stress. Moreover, the number of upregulated genes was greater than that of the downregulated genes under cold stress, whereas the number of upregulated genes was less than that of the downregulated genes under heat stress. Furthermore, among the differentially expressed genes, the number of genes upregulated under cold stress and with unchanged expression under heat stress was the highest, while the number of the genes downregulated under cold stress, but not under heat stress, was the second-highest. Facilitated trehalose transporter Tret1 and DnaJ-like subfamily B member 6-A were upregulated and downregulated, respectively, under cold stress; however, their expression remained unchanged under heat stress. In contrast, Apolipoprotein d lipocalin and Troponin C in skeletal muscle were upregulated and downregulated, respectively, under both cold and heat stress. This study provides insight into the genetic responses of dinoflagellates to climate change-driven large water temperature fluctuations.

Phytoplankton blooms can cause imbalances in marine ecosystems leading to great economic losses in diverse industries. Better understanding and prediction of blooms one week in advance would help to prevent massive losses, especially in areas where aquaculture cages are concentrated. This study has aimed to develop a method to predict the magnitude and timing of phytoplankton blooms using nutrient and chlorophyll-a concentrations. We explored variations in nutrient and chlorophyll-a concentrations in incubated seawater collected from the coastal waters off Yeosu, South Korea, seven times between May and August 2019. Using the data from a total of seven bottle incubations, four different linear regressions for the magnitude of bloom peaks and four linear regressions for the timing were analyzed. To predict the bloom magnitude, the chlorophyll-a peak or peak-to-initial ratio was analyzed against the initial concentrations of NO3 or the ratio of the initial NO3 to chlorophyll-a. To predict the timing, the chlorophyll-a peak timing or the growth rate against the natural log of NO3 or the natural log of the ratio of the initial NO3 to chlorophyll-a was analyzed. These regressions were all significantly correlated. From these regressions, we developed the best-fit equations to predict the magnitude and timing of the bloom peak. The results from these equations led to the predicted bloom magnitude and timing values showing significant correlations with those of natural seawater in other regions. Therefore, this method can be applied to predict bloom magnitude and timing one week in advance and give aquaculture farmers time to harvest fish in cages early or move the cages to safer regions.

The phlorotannin compounds, dieckol and phlorofucofuroeckol (PFF), extracted from Ecklonia cava, have been suggested to exhibit anti-inflammatory, anti-adipogenic or anti-tumorigenic activity. However, role of dieckol or PFF in LPS/TLR-4 signaling that regulates cancer development still remains to be determined. Here we report that dieckol or PFF blocked lipopolysaccharide (LPS)-induced migration and invasion of human breast cancer MCF-7 or MDA-MB-231 cells by about 50% (p

Heterotrophic dinoflagellates are major grazers of microalgae in marine food webs. The feeding of the newly described heterotrophic dinoflagellate Gyrodinium jinhaense was explored by providing 19 common microalgal prey species and the ciliate Mesodinium rubrum as prey. Furthermore, the specific growth and ingestion rates of G. jinhaense feeding on the chlorophyte Dunaliella salina were determined as a function of prey concentration. Cells of G. jinhaense were able to feed on microalgae of sizes ≤ 26 μm with the exception of the dinoflagellate Karenia mikimotoi. In contrast, G. jinhaense did not feed on microalgae > 26 μm with the exception of the dinoflagellate Lingulodinium polyedra. With increasing mean prey concentration, both the specific growth and ingestion rates of G. jinhaense feeding on D. salina rapidly increased at mean prey concentrations