• Ocean and Polar Research
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• v.34 no.2
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• pp.125-135
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• 2012

To evaluate the algicidal impact of a newly developed algicide thiazolidinedione derivative, TD49, on dinophyceae Akashiwo sanguinea in aquatic ecosystems, tentative culture experiments for the target species were conducted in small (SS), middle (MS), and large scale (LS) culture vessels. When TD49 was introduced at the final concentration of $2{\mu}M$ in SS and MS, as well as $1{\mu}M$ in LS, the abundance of A. sanguinea decreased significantly in all the treatments. On the other hand, total phytoplankton abundance, except A. sanguinea in the TD49 treatments, gradually increased with culture time, which implies that a cell destruction of A. sanguinea by TD49 is a major cause of the population growth by other phytoplankton species. Also, A. sanguinea was easily destroyed, which was likely to be a source of extracellular substances. In particular, a pH decrease was significant in the treatments than in the control, which indicates that the water in the treatments has been acidified, due to an increase in the heterotrophic metabolisms of bacteria and degradation of A. sanguinea cells. Our results indicate that the TD49 substance is the potential agents for the control of A. sanguinea in the enclosed and eutrophic water bodies.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.20 no.3
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• pp.151-157
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• 2015

Recent laboratory studies have documented that mixotrophic dinoflagellates Dinophysis spp. and heterotrophic dinoflagellate Oxyphysis oxytoxoides share a common prey, i.e. the mixotrophic ciliate Mesodinium rubrum. Nonetheless, very little is known about the population dynamics and species interactions among these protists in natural environments. To investigate the interactions between the dinoflagellate predators and their ciliate prey in the field, we took the samples twice a day from 26 July to 28 August, 2011 at a fixed station in Masan Bay and analyzed their abundances. During this study, salinity was highly variable, ranging from 5 to 28, due to the periodic input of rainfalls to the sampling station. Water temperature was on average $26.5^{\circ}C$ until 20 August and thereafter was about $21^{\circ}C$ by the end of the sampling period. The ciliate M. rubrum occurred persistently throughout the sampling period, ranging from 13 to $492\;cells\;mL^{-1}$. Cell densities of D. acuminata and O. oxytoxoides ranged from undetectable level to $19,833\;cells\;L^{-1}$ and from undetectable level to $100,333\;cells\;L^{-1}$, respectively. The high abundance of D. acuminata mostly followed the blooming of the ciliate M. rubrum, but it often did not peak even during heavy blooms of the prey, probably due to sensitivity to large salinity fluctuation and also presumably overlapped grazing by other mixotrophic dinoflagellates. The abundance of O. oxytoxoides was detected only when water temperature was lower than $24^{\circ}C$, indicating that water temperature is an important environmental factor to control the population dynamics of the dinoflagellate species.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.6
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• pp.920-926
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• 1998

To investigate the effects of yellow loess on the microbial community after applying into C. polykrikoides as a red tide centrol method during decomposition process, we conducted this study using microcosm experiments, which consisted of sediment collected from Jinhae and Masan bay. The composition, number of bacteria and respiratory electron transport system activity (ETSA) were analyzed. The number of heterotrophic bacteria examined in the samples of both stations reached maximum value within 12 hrs with $10^7$ cells/dry g, independent with the yellow loess applied. In addition, a differenee in the variation of heterotrophic bacterial composition was not observed by adding the yellow loess, and Vibrio spp. always appeared during the culture periods, However, in day 8 culture, the sulfate reducing bacteria was $3.8\times10^7$ cells/dry g in Masan bay and $5.5\times10^6$ cells/dry g in Jinhae bay samples without yellow loess, and these were 120, 350 fold-and 160, 420 fold-increased when yellow loess was added (1 : 1, 1 : 2). The average ETSA was 6.8$\~$7.6 $\mu$g formazan $h^{-1}$ dry $g^{-1}$ independently with yellow loess in aerobic condition for both samples, but activity was decreased by addition of yellow loess in anaerobic. Thus the addition of yellow loess to marine sediment seems to have an effect to inhibit the anaerobic decomposition process and growth of sulfate reducing bacteria which lead to the bad condition of marine environments.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.7 no.2
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• pp.78-86
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• 2002

Abundance, carbon biomass and chlorophyll a concentration of each size-fractionated plankton on the basis of trophical level were investigated in terms of spacial and temporal distribution, and interactions between each biological parameter and environmental factors in Jungmun coastal waters of Jeju Island from July 1999 to June 2000. Heterotrophic picoplankton (HPP) abundance averaged 1.4${\times}$$10^{6}$ cells ${\cdot}$ $ml^{-1}$ at of offshore and 8.3${\times}$$10^{5}$ cells ${\cdot}$ $ml^{-1}$ at inshore, while autotrophic picoplankton (APP) abundance 9.9${\times}$$10^{4}$ cells ${\cdot}$ $ml^{-1}$ at of offshore and 7.1${\times}$$10^{4}$ cells ${\cdot}$ $ml^{-1}$ at inshore. They were more abundant at of offshore than at inshore, and also more abundant than the other areas of Korean waters. On the other hand, heterotrophic and autotrophic nanoplankton (HNP, ANP) were more abundant at inshore than at of offshore. Microplankton (AMP) abundance was affected by diatom (r=0.962, P${\le}$0.001) at inshore and by dinoflagellate (r=0.868, P${\le}$0.001) at of offshore. However correlations between each plankton group in terms of size and trophic level were not significant. Carbon biomass showed as same as the distribution pattern of abundance, but composition percentage of each biomass of plankton group were quite different from that of abundance, representing the highest percentage in ANP. Seasonal fluctuation of chlorophyll a were different according to size class, showing the highest with 0.42 ${\mu}g$CHl-${\alpha}$${\cdot}$$1^{-1}$(57.9%) of APP in March 2000, 1.42 ${\mu}g$CHl-${\alpha}$${\cdot}$$1^{-1}$(74.7%) of ANP in May 2000, and 1.51 ${\mu}g$CHl-${\alpha}$${\cdot}$$1^{-1}$(81.8%) of AMP in July 1999. Correlation between biological parameters and environmental factors by principle component analysis revealed that the first factor as main explanation is the increasing of phosphorus and silica and the increasing of the at both of offshore and inshore. The N:P ratio were 36.4 at inshore and 32.6 at of offshore, showing the lack of phosphorus. Thus we suggest that phosphorus might be a main limiting factor to affect phytoplankton community in the study area.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.5 no.1
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• pp.37-46
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• 2000

We investigated the temporal and spatial variations in heterotrophic dinoflagellates (hereafter HTD) and ciliates from June to September 1997 in the waters off Kohung, Korea where red tides dominated by harmful dinoflagellates had occurred from August to October since 1995. We took water samples five times from 5-7 depths at 3 stations in this study period. A total of 17 HTD species were present and of these species in the genus Protoperidinium were 11. The species number of tintinnids (hereafter TIN) present totalled 15 and several naked ciliate (hereafter NC) species were observed. The species numbers of HTD and TIN rapidly increased between August 1st and 21st and then reached to the maximum numbers of 13 and 10, respectively, on August 27 when red tides dominated by Gyrodinium impudicum were first observed in the study area. However the species numbers drastically decreased on September 22. The maximum densities of HTD, TIN, and NC were 45, 39, 57 cells $ml^{-1}$, respectively. ADAS, calculated by averaging the densities of a certain species in the all samples collected from all depths and stations at a sampling period, most increased between August 1st and 21st and then reached to the maximum density of f cells $ml^{-1}$ on August 27 for HTD, while did between August 21st and 27th and up to 7 cells $ml^{-1}$ for TIN. Unlike ADAS of HTD and TIN, that of NC did not change much with the maximum of 8 cells $ml^{-1}$ on August 27th. The pattern of the temperal variation in the species number and ADAS of HTD was similar to that of diatoms and the distributions of Protoperidinium spp. and diatoms had a strong positive correlation. This evidence suggests that HTD, in particular Protoperidinium spp. be a grazer on diatom. In general, the densities of HTD, TIN, and NC decreased with going to stations located in the outer bay. Therefore, the availability of suitable prey and distance from the coastal line might be responsible for the distribution of HTD, TIN, and NC. The results of the present study provide a basis for further experiments for the feeding by dominant HTD, TIN, and NC on dominant phytoplankton including red tide species and for understanding food webs in the planktonic community before, during, and after the red tide outbreak.