• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.5
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• pp.536-544
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• 2001

Three harmful algal bloom species with similar morphology, Cochlodinium polykrikoides, Gyodinium impudicum and Gymodinium catenatum have damaged to aquatic animals or human health by either making massive blooms or intoxication of shellfishes in a food chain. Eco-physiological and hydrodynamic studies on the harmful algae offer useful informations in the understanding their bloom mechanism by giving promising data for the prediction and modelling of harmful algal blooms event. Thus, we studied the abundance of these species in the coastal area of South Sea of Korea and their effects of temperature, salinity, irradiance and nutrient on the growth for the isolates. The timing for initial appearance of the three species around the coastal area of Namhaedo, Narodo and Wando was between Bate July and late August in 1999 when water temperature ranged from $22.8^{\circ}C\;to\;26.5^{\circ}C$ Vegetative cells of C. polykrikoides and G. impudicum were abundant until late September when water temperature had been dropped to less than $23^{\circ}C$. By contrast, vegetative cell of G. catenatum disappeared before early September, showing shorter period of abundance than the other two species in the South Sea. Both G. impudicum and G. catenatum revealed comparatively low density with a maximal cell density of 3,460 cells/L and 440 cells/L, respectively without making any bloom, while C. polykrikoides made massive blooms with a maximal cell density more than $40\times10^6$cells/L, The three species showed a better growth at the relatively higher water temperature ranging from 22 to $28^{\circ}C$ with their maximal growth rate at $25^{\circ}C$ in culture, which almost corresponded with the water temperature during the outbreak of C. polykrikoides in the coastal area of South Sea. Also, they all showed a relatively higher growth at the salinity from 30 to $35\%$. Specially, G. impudicum showed the euryhalic characteristics among the species, On the other hand, growth rate of G. catenatum decreased sharply with the increase of water temperature at the experimental ranges more than $35\%$. The higher of light intensities showed the better growth rates for the three species, Moreover, C. polykrikoides and G. impudirum continued their exponential growth even at 7,500 lux, the highest level of light intensity in the experiment, Therefore, It is assumed that C. polykrikoides has a physiological capability to adapt and utilize higher irradiance resulting in the higher growth rate without any photo inhibition response at the sea surface where there is usually strong irradiance during its blooming season. Although C. poiykikoides and G. impudicum continued their linear growth with the increase of nitrate ($NO_3^-$) and ammonium ($NH_4^-$) concentrations at less than the $40{\mu}M$, they didn't show any significant differences in growth rates with the increase of nitrate and ammonium concentrations at more than $40{\mu}M$, signifying that the nitrogen critical point for the growth of the two species stands between 13.5 and $40{\mu}M$. Also, even though both of the two species continued their linear growth with the increase of phosphate ($PO_4^{2-}$) concentrations at less than the $4.05{\mu}M$, there were no any significant differences in growth rates with the increase of phosphate concentrations at more than $4.05{\mu}M$, signifying that the phosphate critical point for the growth of the two species stands between 1.35 and $4.05{\mu}M$. On the other hand, C. polykrikoides has made blooms at the oligotrophic environment near Narodo and Namhaedo where the concentration of DIN and DIP are less than 1.2 and $0.3{\mu}M$, respectively. We attributed this phenomenon to its own ecological characteristics of diel vertical migration through which C. polykrikoides could uptake enough nutrients from the deep sea water near bottom during the night time irrespective of the lower nutrient pools in the surface water.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.6
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• pp.691-696
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• 2001

The first bloom of Cochlodinium polykrikoides was observed in the estuary of Nak-dong river near Pusan in Korea in 1982. Since then, there have been irregular blooms, sometimes spread over the adjoining .to Jinhae Bay even though it was confined to the bay and its vicinites until 1988. It had been outbroken frequently in the adjacent to Tongyeong, Geoje, Namhae and Yeosu coast since 1989. It became widespread along the coast of the South Sea to the East Sea of Korea in 1995. And in October in 1998 and 1999, the bloom had been taken place in Kunsan coast of Yellow Sea. According to the observations in situ, the frequency of occurrence has been increased year by year. The prevailing bloom season was from July to October with peak in September. The duration of the bloom became longer with the year, and sometimes lasted more than one month. The density of the bloom did not exceed 5,000 cells $mL^{-1}$until 1991, but it increased year by year to the highest of 43,000 cells $mL^{-1}$ in 1999. With respect to the assembleges of species in dinoflagellate blooms, C. polykrikoides was one of the important species with diatoms and the other dinoflagellates in 1980s. But since then, C. polykrikoides made an almost monospecific bloom. Based on two decadal observations of C. polykrikoides blooms, it became widespread throughout whole coast of the Korea, persistent for about one or two month long in some year, and monospecisc high density blooms. It was reported that significant fish mortalities were caused by this harmful dinoflagellate blooms especially in the fishfarms accomodating intensive fish cages such as Tongyeong, Namhae-do, Geoje, Yeosu and Geomun-do fishfarming yards. This widespread and persistent harmful algal blooms impede the development of marine aquaculture industries.

• Journal of the Korean Society of Marine Environment & Safety
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• v.16 no.4
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• pp.381-386
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• 2010

We have cultured the bluefin tuna in Yokjido, Tongyeong with floating cage which was vulnerable to harmful dinoflagellate, Cochiodinium polykrikoides. This study inspected a vertical migration of phytoplankton and Chl-a for reasonable sinking depth in floating cage. Furthermore, we analyzed the fluctuation of the phytoplankton including harmful dinoflagellates occurring in Yokgido for 6 years. Total cell density showed a significant monthly variation and the flora was predominated with diatoms. Gymnodinium sp. occurred 19 times, the greatest number of occurrence in all kinds of dinoflagellates during summer. In particular, the total number of occurrence at C. polykrikoides was 8, and harmful dinoflagellates such as Karenia brevis/Fibrcapsa japonica occurred. The relationship between Chl-a concentration/total cell number and sunset/sunrise was significant and reasonable sinking depth in floating cage was found to be at least 3m from the water surface, which was associated with massive fish kills caused by C. polykrikoides.

• Fisheries and Aquatic Sciences
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• v.11 no.4
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• pp.205-208
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• 2008

The mixotrophic dinoflagellate Cochlodinium polykrikoides was reported to be linked to major fish kills in Korea and Japan since the 1990s. Rapid and sensitive detection of microalgae has been problematic because morphological identification of dinoflagellates requires light microscopic and scanning electron microscopic observations that are time consuming and laborious compared to real-time PCR. To address this issue, a real-time PCR probe targeting the ITS2 rRNA gene was used for rapid detection and quantification of C. polykrikoides. PCR inhibitors in water column samples were removed by dilution of template DNA for elimination of false-negative reactions. A strong association between cell quantification using real-time PCR and microscopic counts suggests that the real-time PCR assay is an alternative method for cell estimation of C. polykrikoides in environment samples.

• ALGAE
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• v.21 no.2
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• pp.253-259
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• 2006

Organic substances are released from phytoplankton cells during all phases of growth. The type and amounts of organic substance excreted and the effects of nutrient limitation are often highly species-specific. Dinoflagellate, Cochlodinium polykrikoides grown in batch culture produced an exopolysaccharide. Exopolysaccharide and intracellular polysaccharide concentrations increased as C. polykrikoides cultures progressed from exponential phase, through stationary phase, to declining phase. In the exponential phase, the concentration of exopolysaccharide was relatively low, but in the stationary phase, it showed a rapid increase which seemed to coincide with the depletion of nitrate from the medium. Of the 20 amino acids analyzed, proline dominated in the organic matter of all cultures ranging from 48.2 to 79.9 nmol L–1, and constituting the 20-90% of total amino acids, and followed by histamine varying from 0.7 to 47.5 nmol L–1. Leucine and cysteine were also abundant in the stationary phase. The release rates of exopolysaccharide and intracellualr polysaccharide were higher the end of stationary phase than in the exponential phase. Exopolysaccharide concentration per cell was more than two times higher during the end of stationary phase than that in exponential phase. C. polykrikoides produced extracellular polysaccharide at a rate of 47.04 pg cell–1 day–1.

• Fisheries and Aquatic Sciences
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• v.3 no.2
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• pp.111-117
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• 2000

To clarify the ichthyotoxic mechanisms of a harmful dinoflagellate Cochlodinium polykrikoides, hematological responses of the flounder Paralichthys olivaceus and red sea bream Pagrus major exposed to this algal bloom were investigated. The mortality of red sea bream was considerably larger than that of flounder, and the threshold lethal density of C. polykrikoides to the test fish was approximately 3,000 cells/ml. Blood $PO_2$declined in proportion to the increasing density of algal cells. The blood $PO_2$ of moribund fish was about $40-60\% of control test fish. Particularly, the fishes began to be killed when the blood $PO_2$ fell below 30-40 mmHg. However, the blood pH dropped almost 1.0 unit just before fish kill. Hemoglobin and hematocrit levels of fish exposed to C. polykrikoides of 5,000 cells/ml for 24 h and of moribund fish did not show great difference. The concentrations of plasma $Na^+$, $K^+$ and $Cl^-$ were slightly elevated to different magnitudes except $Ca^{2+}$ and plasma osmolality was also increased in Cochlodinium-exposed fish. In the plasma cortisol level, these values of moribund flounder and red sea bream were 4- 5 times higher than those of control fish. These results suggest that the drop of blood $PO_2$ was may be one of the principal causes of fish kill by C. polykrikoides, and the changes of other hematological parameters were secondary responses elicited by the decrease in blood $PO_2$.

• Journal of Environmental Science International
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• v.16 no.10
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• pp.1119-1125
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• 2007

We examined the horizontal distribution of salinity and the concentrations of DIN and DIP after heavy rain-fall events in coastal areas of South Korea from Yeoja Bay to Narodo and from Gwangyang Bay to Geomodo to determine whether fresh water actually flows into areas of Cochlodinium polykrikoides red tides and to observe its effect on the growth of this organism after heavy rainfall. Following heavy rainfall (155 mm) in the Yeosu and Suncheon regions, the average salinity was 21 and 29 psu at Yeoja Bay and in the coastal waters of Narodo, respectively. After 126 mm of rainfall, the values were 19 and 25 psu in the coastal waters of Yeosu and Geomodo, respectively. This may have been caused by an influx of fresh water, after the rainfall event, into the open sea coastal areas around Narodo and Geomodo from the Dong and Seomjin Rivers, which are about 3540 km away. After the rainfall, the concentrations of $NH_4-N,\;NO_2-N$, and $PO_4-P$ were slightly increased; however, the concentration of $NO_3-N$ was greatly increased and diffused throughout the coastal areas of Narodo and Geomodo, which frequently experience C. polykrikoides blooms. The influence of $NH_4-N,\;NO_2-N$, and $PO_4-P$ on the occurrence of C. polykrikoidesred tides in coastal areas around Narodo and Geomodo after heavy rainfall does not appear to be great. Instead, the occurrence C. polykrikoides red tides in the coastal areas of Narodo and Geomodo seems to be facilitated by $NO_3-N$.

• Journal of Fisheries and Marine Sciences Education
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• v.28 no.6
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• pp.1662-1672
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• 2016

To address physicochemical factors of yellow clay for removing Cochlodinium polykrikoides blooms, the correlation of removal efficiency with mineralogical characteristics of yellow clay collected from various areas was surveyed. Yellow clay from different localities showed the wide range of chemical compositions $SiO_2$ : 43~71%, $Al_2O_3$ : 13~26%, $Fe_2O_3$ : 5~14%, MgO : 0.4~1.8%, $K_2O$ : 0.6~3.3%, L.O.I.(Loss of Ignition) : 4.5~15%. The mineral compositions of yellow clay were mainly consisted of quartz and feldspar including small amounts of kaolinite, chlorite, and Fe-oxides. The result of size analysis showed that $6{\Phi}(31{\sim}16{\mu}m)$ and $7{\Phi}(16{\sim}8{\mu}m)$ were dominated sizes. The zeta-potential were in the range of -4.1~-20.7mV(average -13.7). As increasing removal efficiency of C. polykrikoides, contents of $Al_2O_3$, $Fe_2O_3$ and L.O.I. in yellow clay increased, whereas $SiO_2$ content decreased. Furthermore, the amounts of silt mineral and small particle were high when the removal efficiency was high. According to factor analysis using principle component analysis, two components of factor 1 and factor 2 showed 79% of the total variance, which is related to cohesion and adsorption. Inducing cell lysis of C. polykrikoides by cohension and adsorption between C. polykrikoides and yellow clay.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.24 no.3
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• pp.422-428
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• 2019

Fish killing dinoflagellate Cochlodinium polykrikoides has been separated into four genetically differentiated subpopulations globally based on large-subunit (LSU) ribosomal RNA gene, and two subpopulations have been found in the South Sea, Korea. In this study, distributions of the East Asia and Philippines ribotypes were surveyed in the South Sea for 3 years (2014~2016) using quantitative real-time PCR (qPCR). The East Asia ribotype was detected in all sampling stations of the South Sea (Tongyeong~Wando) by 40~100% positives for 2014~2016, whereas the Philippines ribotype was detected in some areas of Tongyeong~Goheung by 1~2% positives for only 2016 when the Tsushima Warm Current (TWC) was particularly strengthened. These results indicate that the East Asia ribotype is the dominant subpopulation in the South Sea, also some of C. polykrikoides swimming cells might be transported from offshore to the South Sea via TWC.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.6
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• pp.674-680
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• 2020

Quantitative real-time polymerase chain reaction (qPCR) was applied for the early detection of red tides in the coastal areas of South Gyeongsang in 2019. Cochlodinium polykrikoides (Dinophyceae) was detected at very low cell densities (0.0015~0.0058 cells mL^-1) in early June, but its cell density increased by up to 0.163 cells mL^-1 in mid-August. Higher cell densities were detected mainly in Namhaedo using both qPCR and microscopy (maximum 24 cells mL^-1) in late-August. Accordingly, a red tide alert was issued on September 2 (maximum 200 cells mL^-1) on this island. C. polykrikoides cell density in Namhaedo peaked on September 11 (12,000 cells mL^-1). Our results indicate that C. polykrikoides was detected at very low cell density in Namhaedo prior to bloom, which occurred in the same area. Therefore, qPCR is a useful tool to detect even at very low cell densities of C. polykrikoides for early warning of blooms.