• Ecology and Resilient Infrastructure
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• v.4 no.3
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• pp.130-141
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• 2017

We evaluated the field application feasibility that biologically derived substances (Naphthoquinone derivate: NQ 2-0) can be used for the eco-friendly mitigation of natural harmful cyanobacterial blooms in freshwater. We conducted a 30 ton scale mesocosm experiment to investigate the effects of NQ 2-0 on biotic and abiotic factors in water collected from Gi-heung reservoir. In the mesocosm experiments, the abundance of Microcystis sp. was continuously increased in the control. However, the Microcystis sp. cell density was sharply decreased on the $10^{th}$ day. In the treatment, NQ 2-0 showed the strong and selective algicidal activity toward the target cyanobacteria (Microcystis sp.). Accordingly, the algicidal activity of NQ 2-0 compound increased gradually until $10^{th}$, $15^{th}$ days and algal biomass was decreased to 99.4 and 100 %, respectively. NQ 2-0 compound was not only selective algicidal activity but also the growth of other phytoplankton and increased the Shannon-Wiener diversity index of phytoplankton. In the mesocosm experiments, the dynamics of biotic (bacteria, heterotrophic nanoflagellate, ciliates, zooplankton) and abiotic (water temperature, dissolved oxygen, pH, conductivity, nutrients) factors remained unaffected. These results suggest that NQ 2-0 could be a selective and ecologically safe algicide to mitigate harmful cyanobacterial blooms. In addition, it is believed that NQ 2-0 will play a major role in forming a healthy aquatic ecosystem by facilitating habitat and food supply of aquatic organisms.

• Korean Journal of Environmental Biology
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• v.28 no.3
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• pp.172-178
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• 2010

The bloom of the genus Stephanodiscus was gradually extinguished after 18 April. Counts of bacterial population were increased as the diatom bloom was disappeared. Numbers of the heterotrophic nanoflagellates and ciliates were also increased during the disappearance of the bloom. The densities of the mesozooplankton, the major predator of the diatoms, started to increase in April. However, their growth was suppressed during the bloom period of the diatoms (from January to March). During the bloom period of the diatoms, the monthly average value of the basic productivity amounted up to 11,765.7 mgC $m^{-2}day^{-1}$, which is relatively high value considering the low temperature and light during that period. The growth rate of phytoplankton in March, when the bloom was beginning to be supressed was 0.007. The growth rate of phytoplankton was negative value in April when the decreasing of the algal density was started.

• 한국해양학회지
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• v.30 no.5
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• pp.413-425
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• 1995

Abundances and bacterivory of heterotrophic and mixotrophic nanoflagellates were investigated fourtimes between October 1993 and March 1995 in an estuarine system of the Mankyung and Dongjin rivers to understand distributions of nanoflagellates and ecological significance of bacterivory of nanoflagellates. Bacterivory of nanoflagellates were measured with fluorescently labeled bacteria (FLB). Heterotrophic and autotrophic flagellates showed a rage of 438-4,159 cells ml/SUP -1/ (mean of 2,145 cells ml/SUP -1/, n=20) and 971- 4,935 cells ml/SUP -1/ (mean of 2,2226 cells ml/SUP -1/, n-20), respectively. These two groups of nanoflagellates generally showed similar distributions of abundance. Abundances of heterotrophic nanoflagellates, known as major grazers of bacteria, and those of autotrophic nanoflagellates with chloroplasts showed statistically significant correlations with bacterial abundance (respectively, r$^2$=0.51 and r $^2$=0.47, p>0.05). Mixotrophic nanoflagellates seemed to comprise at least 4-23% of autotrophic nanoflagellate populations. Individual predation rates of heterotrophic nanoflagellates ranged from 2.2 to 14.2 bacteria flagellate/SUP -1/ h/SUP -1/ (mean of 4.9 bacteria flagellate/SUP -1/h/SUP -1/, n=16), and those of mixotrophic nanoflagellates from 1.6 to 9.7 bacteria flagellate/SUP -1/ h/SUP-1/ (mean of 3.7 bacteria flagellate /SUP -1/ h/SUP -1/, n=16). Bacterivory by mixotrophic nanoflagellates comprised from 30 to 69% of total nanoflagellates grazing on bacteria, indicating the significant role of mixotrophic nanoflagellates as grazers on bacteria in the study area. The ratios of grazing rates on bacteria to bacterial secondary production ranged widely from 0.06 to 1.23. In June, when abundances of total nanoflagellates were low, removal of bacteria by bacterivory of nanoflagellates was also a small fraction (0.08${\pm}$ 0.01, n=4) of bacterial production. In other seasons, nanoflagellates usually grazed on bacteria in significant fraction (0.06${\pm}$0.37, n=9) of bacterial production. Both heterotrophic and mixotrophic nanoflagellates appear to be major grazers on bacteria, and might transfer bacterial secondary production to higher trophic level in an estuarine system of the Mankyung and Dongjin rivers.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.8 no.1
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• pp.44-57
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• 2003

Seasonal variations of bacterial abundance and production, heterotrophic nanoflagellate (HNF) abundance and HNF ingestion rates on bacteria using FLB together with environmental variables were investigated at intervals of a month in Kyeonggi Bay from December 1991 to November 1998. Bacterial abundance and production ranged from 0.38$\times$10$^{9}$ ~ 3.25$\times$10$^{9}$ cells 1$^{-1}$ (average 1.19$\pm$0.69$\times$10$^{9}$ cells 1$^{-1}$ ) and from 1.51 to 20.4 cells 1$^{-1}$ h$^{-1}$ (average 6.04$\pm$ 1.88$\times$10$^{6}$ cells 1$^{-1}$ h$^{-1}$ ), respectively. Bacterial abundance and production showed no differences at the high tide and low tide, and bacterial abundances were not different with depth, but bacterial production decreased with depth. Seasonal variation of bacterial abundance showed almost similar fluctuation pattern to those of DOC (dissolved organic carbon). HNF abundances ranged from 388 to 4,374 cells ml$^{-1}$ (average 1,344$\pm$130 cells ml$^{-1}$ ), were high in March, April, July and August. HNF abundance showed no difference between the high tide and low tide, and was not different with depth. The ingestion rates of HNF on bacteria were 1.0 to 6.3$\pm$10$^{6}$ bacteria 1$^{-1}$ h$^{-1}$ (average 3.12$\pm$0.55$\times$10$^{6}$ bacteria 1$^{-1}$ h$^{-1}$ ), resulting ingestion rates of HNF removed 19.4 to 141.4 %(average 62.3$\pm$12.0%) of bacterial production. Ingestion rates and grazing pressure of HNF on bacteria showed high correlation with HNF abundance. Although we cannot exactly discussion about seasonal variation of bacteria community in this study area where physical and chemical parameters were very complex, the results indicate that bacterial abundance and production were mainly controlled by resources supply as dissolved organic carbon and chlorophyll-a(bottom-up) except March which bacterial abundance and production uncoupled chlorophyll-a because of low dissolved organic carbon and low temperature, and were controlled by HNF grazing pressure(top-down) in the warm seasons except the winter.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.8 no.2
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• pp.78-93
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• 2003

To investigate seasonal variation and structure of the microbial community in Kyeonggi Bay, abundance and carbon biomass of nano-and micrzooplankton were evaluated in relation to size fractionated chlorophyll-a concentration, through the monthly interval sampling from December 1997 to November 1998. Communities of nano-and microzooplankton were classified into 4 groups such as heterotrophic nanoflagellate(HNF), ciliates, heterotrophic dinoflagellates(HDF) and zooplankton nauplii. Abundance and carbon biomass of HNF ranged from 380 to 4,370 cells ml-1(average 1,340$\pm$130 cells ml-1) and from 0.63 to 12.4 $\mu\textrm{g}$C 1-1(average 4.35$\pm$0.58 $\mu\textrm{g}$C 1-1), respectively. Abundance and carbon biomass of ciliates ranged from 331 to 44,571 cells ml-1(average 3,526$\pm$544 cells ml-1) and from 1.3 to 119.7 $\mu\textrm{g}$C 1-1(average 13.7$\pm$3.0 $\mu\textrm{g}$C 1-1), respectively. Abundance and carbon biomass of HDF ranged from 88 to 48,461 cells 1-1(average 9,034$\pm$2,347 cells 1-1) and from 0.05 to 54.05 $\mu\textrm{g}$C 1-1(average 6.9$\pm$2.4 $\mu\textrm{g}$C 1-1), respectively. Abundance and carbon biomass of zooplankton nauplii ranged from 5 to 546 indiv. 1-1(average 83$\pm$15 indiv. 1-1) and from 0.17 to 43.2 $\mu\textrm{g}$C 1-1(average 6.3$\pm$1.2 $\mu\textrm{g}$C 1-1), respectively. Eash component of microbial biomass was not different from tidal cycle except tintinnids group. Depth integrated nano-and microzooplankton biomass ranged from 124 to 1,635 mgC m-2(average 585$\pm$110 mgC m-2) and was highest in March and May. The relative contribution of each component to the nano-and microzooplankton showed difference according to seasons. Community structure of nano-and microzooplankton was dominated by planktonic ciliate group. During the study period, carbon biomass of nano-and microzooplankton was strongly positively correlated with size fractionated chlorophylla-a. It implied that prey-predator relationship between microzooplankton and phytoplankton was important in the pelagic ecosystem of Kyeonggi Bay.