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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.

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.

Marine plankton comprise the largest portion of the marine biomass, and play critical roles in the global carbon cycle. The carbon retention of marine-plankton communities is as important as their primary production; however, data on the annual carbon retention of marine-plankton communities based on daily sample analysis are limited. Using our published and unpublished data, we calculated the one-year integrated carbon retention of a marine-plankton community at an innermost fixed station in the highly eutrophic Masan Bay, Korea, collected daily from June 2004 to May 2005. The total one-year integrated carbon retention of all plankton taxa in the study period was 471 g C m−3 yr−1. The integrated carbon retentions by phytoplankton, heterotrophic protists, and heterotrophic bacteria were 344, 76, and 40 g C m−3 yr−1, respectively, whereas those by photosynthetic ciliates and metazooplankton were 9 and 2 g C m−3 yr−1, respectively. Among the plankton subgroups, the integrated carbon retention by the phototrophic dinoflagellates (109 g C m−3 yr−1) was highest, followed by raphidophytes (88), cryptophytes (73), diatoms (43), heterotrophic bacteria (40), and heterotrophic dinoflagellates (39). The total duration of the red tides by diatoms that grow using only photosynthesis (42 days), was considerably shorter than that of phototrophic dinoflagellates, raphidophytes, or cryptophytes, which can grow mixotrophically (56–135 days). The shorter duration of red tides by diatoms was primarily responsible for their lower carbon retention, although the maximum growth rates of the diatoms were considerably higher than those of the flagellates. The percentage of the 1-year integrated carbon retention of the heterotrophic protists relative to that of the phytoplankton was approximately 20%, similar to the mean-gross-growth efficiency of heterotrophic-protist grazers on phytoplankton, indicating a good balance between these two components in the planktonic food web. This study reported one-year integrated carbon retention of marine plankton at the species level, calculated based on daily samples, and thus gave an insight into which, and to what extent, species and groups contribute to the total carbon retention of plankton for one year in a highly eutrophic bay.

The genus Alexandrium often forms harmful algal blooms causing human illness and large-scale mortality of fish and shellfish. Thus, Alexandrium bloom dynamics are primary concerns for scientists, government officials, aquaculture farmers, and the public. To understand bloom dynamics, mortality due to predation needs to be assessed; however, interactions between many Alexandrium species and their potential predators have not previously been reported. Thus, feeding by five common heterotrophic dinoflagellates (Oxyrrhis marina, Gyrodinium dominans, Polykrikos kofoidii, Pfiesteria piscicida, and Oblea rotunda) and a naked ciliate (Strombidinopsis sp.) on 12 Alexandrium species was examined. Furthermore, the growth and ingestion rates of P. kofoidii on A. minutum CCMP 1888 (previously A. lusitanicum), A. minutum CCMP 113, and A. tamarense were measured as a function of prey concentration. The growth rates of P. kofoidii on the other Alexandrium species at single high prey concentrations were measured, at which the growth rates on A. minutum CCMP 1888 and A. tamarense were saturated. Feeding occurrence by these predators on 12 Alexandrium species could be categorized into 6 different prey groups. Each Alexandrium species was consumed by at least one predator; however, there was no Alexandrium species that was eaten by all six predators. Cells of A. minutum CCMP 1888, A. minutum CCMP 113, and A. tamarense were fed upon by four predators, but A. affine and A. pacificum by only one predator species, P. kofoidii or Strombidinopsis sp. Furthermore, A. minutum CCMP 1888 and A. tamarense supported high growth rates of P. kofoidii, but the other Alexandrium species did not support, but rather inhibited P. kofoidii growth. With increasing prey concentrations, the growth and ingestion rates of P. kofoidii on A. minutum CCMP 1888 and A. tamarense increased and became saturated, whereas those on A. minutum CCMP 113 continuously decreased. The maximum growth rates of P. kofoidii on A. tamarense and A. minutum CCMP 1888 were 1.010 and 0.765 d−1, respectively, and P. kofoidii maximum ingestion rates were 26.2 and 11.1 ng C predator−1d−1, respectively. In contrast, the growth rates of P. kofoidii on the other Alexandrium species at single high prey concentrations were almost zero (A. pacificum) or negative. Based on the feeding occurrence and growth and ingestion rates of predators on 12 Alexandrium species, it is suggested that common heterotrophic protistan predators respond differently to different Alexandrium species, and thus ecological niches of the Alexandrium species may be different from each other. These results may provide an insight into the roles of protistan predators in bloom dynamics of Alexandrium species.

Mixotrophic dinoflagellate species with low or moderate growth rates but diverse prey cause red tides globally., Microalgae fuel food webs and biogeochemical cycles of key elements in the ocean. What determines microalgal dominance in the ocean is a long-standing question. Red tide distribution data (spanning 1990 to 2019) show that mixotrophic dinoflagellates, capable of photosynthesis and predation together, were responsible for ~40% of the species forming red tides globally. Counterintuitively, the species with low or moderate growth rates but diverse prey including diatoms caused red tides globally. The ability of these dinoflagellates to trade off growth for prey diversity is another genetic factor critical to formation of red tides across diverse ocean conditions. This finding has profound implications for explaining the global dominance of particular microalgae, their key eco-evolutionary strategy, and prediction of harmful red tide outbreaks.

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

Gymnodinium smaydae is a fast-growing mixotrophic dinoflagellate. This study investigated whether light intensity (0–346 µmol photons m−2 s−1) and temperature (5–35 °C) affect the autotrophic or mixotrophic growth rate or ingestion rate of Gymnodinium smaydae GSSH1005. At all light intensities tested, G. smaydae GSSH1005 showed negative autotrophic growth rates, but positive mixotrophic growth rates when feeding on Heterocapsa rotundata. However, both autotrophic and mixotrophic growth rates were significantly affected by light intensity. The mixotrophic growth rates at 0–6 µmol photons m−2 s−1 were 0.67–0.72 day−1; they increased up to 1.28 day−1 at 58 µmol photons m−2 s−1, but became saturated at higher light intensities. The ingestion rates were also significantly affected by light intensity. The maximum ingestion rate of 2.3 ng C predator−1 day−1 was achieved at 58 µmol photons m−2 s−1. Although the autotrophic growth rates were negative at all temperatures tested, the mixotrophic growth rates were positive at 10–32 °C. Both autotrophic and mixotrophic growth rates were significantly affected by temperature. The maximum mixotrophic growth rate of 1.55 day−1 was noted at 25 °C. The ingestion rates were also significantly affected by temperature. The maximum ingestion rate of 4.2 ng C predator−1 day−1 was noted at 32 °C. Therefore, both light intensity and temperature can affect the population dynamics of G. smaydae GSSH1005.

The mixotroph Yihiella yeosuensis is a small- and fast-swimming dinoflagellate. To investigate its protistan predators, interactions between Y. yeosuensis and 11 heterotrophic protists were explored. No potential predators were able to feed on actively swimming Y. yeosuensis cells, which escaped via rapid jumps, whereas Aduncodinium glandula, Oxyrrhis marina, and Strombidinopsis sp. (approximately 150 μm in cell length) were able to feed on weakly swimming cells that could not jump. Furthermore, Gyrodinium dominans, Luciella masanensis, and Pfiesteria piscicida were able to feed on heat-killed Yihiella cells, whereas Gyrodinium moestrupii, Noctiluca scintillans, Oblea rotunda, Polykrikos kofoidii, and Strombidium sp. (20 μm) did not feed on them. Thus, the jumping behavior of Y. yeosuensis might be primarily responsible for the observed lack of predation. With increasing Yihiella concentration, the growth rate of O. marina decreased, whereas that of Strombidinopsis did not change. However, with increasing Yihiella concentration (up to 530 ng C/ml), the ingestion rate of Strombidinopsis on Yihiella increased linearly. The highest ingestion rate was 24.1 ng C per predator per d. The low daily carbon acquisition from Yihiella relative to the body carbon content of Strombidinopsis might be responsible for its negligible growth. Thus, Y. yeosuensis might have an advantage over its competitors due to its low mortality rate.

The newly described phototrophic dinoflagellate Alexandrium pohangense, APPH1409, fed only on the dinoflagellate Margalefidinium polykrikoides among 16 potential algal prey species tested. To explore the ecophysiology of A. pohangense, its growth and ingestion rates with and without added M. polykrikoides prey were determined as a function of light intensity (0–346 µmol photons m−2 s−1) and temperature (10–35 °C). Both the autotrophic and mixotrophic growth rates of A. pohangense fed on M. polykrikoides were significantly affected by light intensity. In the darkness, A. pohangense did not grow under either mixotrophic or phototrophic conditions. The compensation light intensity for the growth of A. pohangense under mixotrophic conditions (2.7 µmol photons m−2 s−1) was lower than that under autotrophic conditions (11.7 µmol photons m−2 s−1). Growth inhibition due to light stress did not occur at the tested light intensities. A. pohangense grew between 15 and 30 °C, but did not grow at 10 °C or ≥ 32 °C. Both the autotrophic and mixotrophic growth rates of A. pohangense fed on M. polykrikoides were also significantly affected by temperature. At the same light intensity or temperature, the mixotrophic growth rate of A. pohangense was generally considerably greater than the autotrophic growth rate, with a few exceptions. Therefore, light intensity, water temperature, and prey accessibility may affect the population dynamics of this species.

Takayama helix is a mixotrophic dinoflagellate that can feed on diverse algal prey. We explored the effects of light intensity and water temperature, two important physical factors, on its autotrophic and mixotrophic growth rates when fed on Alexandrium minutum CCMP1888. Both the autotrophic and mixotrophic growth rates and ingestion rates of T. helix on A. minutum were significantly affected by photon flux density. Positive growth rates of T. helix at 6-58 μmol photons · m-2 · s-1 were observed in both the autotrophic (maximum rate = 0.2 · d-1 ) and mixotrophic modes (0.4 · d-1 ). Of course, it did not grow both autotrophically and mixotrophically in complete darkness. At ≥247 μmol photons · m-2 · s-1 , the autotrophic growth rates were negative (i.e., photoinhibition), but mixotrophy turned these negative rates to positive. Both autotrophic and mixotrophic growth and ingestion rates were significantly affected by water temperature. Under both autotrophic and mixotrophic conditions, it grew at 15-28°C, but not at ≤10 or 30°C. Therefore, both light intensity and temperature are critical factors affecting the survival and growth of T. helix.

The dinoflagellate genus Scrippsiella is known to cause red tides. Mortality due to predation should be assessed in order to understand the population dynamics of Scrippsiella species. However, predation has been explored only in a few species. In this study, we examined feeding by common heterotrophic dinoflagellates Oxyrrhis marina, Gyrodinium dominans, Polykrikos kofoidii, Oblea rotunda, and Pfiesteria piscicida, and a ciliate Strombidinopsis sp., on four Scrippsiella species, of similar size, namely Scrippsiella acuminata, Scrippsiella donghaiensis, Scrippsiella lachrymosa, and Scrippsiella masanensis. All the heterotrophic protists tested could feed on all the four Scrippsiella species. However, the numerical and functional responses of P. kofoidii to the mean prey concentration were apparently different between the Scrippsiella species. With increasing prey concentration, the growth and ingestion rates of P. kofoidii on S. lachrymosa increased rapidly, and then saturated similar to those on S. acuminata, as previously reported, but those on S. donghaiensis continuously decreased. The cells of S. donghaiensis lysed P. kofoidii cells. In contrast, the growth and ingestion rates of P. kofoidii on S. masanensis were not significantly related to the prey concentration. At similarly high mean prey concentration, the growth and ingestion rates of G. dominans were significantly different between the four Scrippsiella species Therefore, differences in the growth and/or ingestion rates of G. dominans and P. kofoidii on the four Scrippsiella species might result in different ecological niches of both the predator and prey species.

In this paper, the loading methods of EOTS for an exploratory developing fighter were analysed by the technical characteristics of it`s operation, maintenance, engineering technology and development cost. By the analysis of operational ability evaluation, the internal type had the merits of stealth function, but the external loading type was preferable to certificate the accessibility, install/detach, compatibility and interoperability with the existing fighter aircraft. From the results of 17 items of technology and development cost evaluation, we found out that the internal type had the advantage of small sizing lightweight, but the external type was highly estimated in the field of application of domestic technology, cost reduction and technical stability for achievement of performance.

The dinoflagellate Alexandrium spp. have received much attention due to their harmful effects on diverse marine organisms, including commercially important species. For minimizing loss due to red tides or blooms of Alexandrium spp., it is very important to understand the eco-physiology of each Alexandrium species and to predict its population dynamics. Its trophic mode (i.e., exclusively autotrophic or mixotrophic) is one of the most critical parameters in establishing prediction models. However, among the 35 Alexandrium species so far described, only six Alexandrium species have been revealed to be mixotrophic. Thus, mixotrophic ability of the other Alexandrium species should be explored. In the present study, whether each of three Alexandrium species (A. andersonii, A. affine, and A. fraterculus) isolated from Korean waters has or lacks mixotrophic ability, was investigated. When diets of diverse algal prey, cyanobacteria, and bacteria sized micro-beads were provided, A. andersonii was able to feed on the prasinophyte Pyramimonas sp., the cryptophyte Teleaulax sp., and the dinoflagellate Heterocapsa rotundata, whereas neither A. affine nor A. fraterculus fed on any prey item. Moreover, mixotrophy elevated the growth rate of A. andersonii. The maximum mixotrophic growth rates of A. andersonii on Pyramimonas sp. under a 14:10h light/dark cycle of 20μEm-2s-1 was 0.432d-1, while the autotrophic growth rate was 0.243d-1. With increasing mean prey concentration, the ingestion rate of A. andersonii increased rapidly at prey concentrations