• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.13 no.4
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• pp.308-319
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• 2008

Temporal variations in plankton assemblages and environmental factors in Asan Bay and their relationships were examined with the data collected from February till early June, 2005. Seawater temperatures showed typical pattern of temporal change observed in temperate waters. Salinity variation was minor. Phytoplankton biomass showed two peaks, one in February only in the inner part of the bay and the other in May in the whole bay. Phytoplankton succession was clearly shown with the increase of seawater temperatures. Diatom (Bacillariophyceae) dominated in February, diatom and cryptomonads (Cryptophyceae) prevailed in May, and dinoflagellates (Dinophyceae) was most abundant in June. Spring bloom in Asan Bay occurred about one month earlier than those observed in temperate seas. Among the inorganic nutrients (N, P and Si), only silicate concentration showed a significant negative correlation with phytoplankton biomass, indicating the sink of this nutrient in the bay to be the uptake by phytoplankton. Nitrate concentration seemed to be a limiting factor in this bay during the study period. Mesozooplankton abundances showed a significant positive correlation with seawater temperatures and a significant negative correlation with phytoplankton biomass. Increase of mesozooplankton abundance followed phytoplankton increase with the time lag of about two months. This increase of zooplankton seemed to be the result of increased seawater temperatures and food.

• Korean Journal of Ecology and Environment
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• v.41 no.3
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• pp.402-411
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• 2008

Grazing effects of two freshwater shellfish, Unio douglasiae (UNIO) and Cipangoplaudina chinese malleata (CCM), on the hibernal diatom communities in eutrophic water was examined in a laboratory. Two animals having different feeding types used in the study were collected from Keum River (Boryeong, Korea), acclimatized in the artificial management system in a laboratory over at least one month, and starved in a laboratory for 2 days before the experiment. Experimental waters, which dominated by Synedra ulna-Scenedesmus sp. (ca. 80%), was collected from eutrophic lake, Lake Ilgam (Seoul) in Feb., 19, 2008 at AM 10:00, and used in the study after the filtration with 1 mm Nylon mesh. Feeding experiments were largely divided into three kinds of animal treatments; five densities of UNIO (U0, U1, U2, U3, U4) and CCM (C0, C1, C2, C3, C4), and four combined densities of two shellfish (M0, M1, M2, M3). U0 and C0 were control (no addition of UNIO or CCM), U1 or C1 (each animal density at 0.5 ind. $L^{-1}$), U2 or C2 (1.0 ind. $L^{-1}$), U3 or C3 (1.5 ind. $L^{-1}$), and U4 or C4 (2.0 ind. $L^{-1}$), respectively. Four combined treatments were consisted of M0 (no animals), M1 (U1+C3), M2 (U2+C2), and M3 (U4+C1), respectively. Under the presence of animal, the concentration of Chl-a and algal abundance were clearly decreased with the increase of UNIO density and the treated time, while in combined group a strong decrease of algal density showed with the increase of UNIO density. Total phytoplankton density shifted as the similar patterns to that of Chl-a concentration (r=0.6527, p<0.0001), however, there showed the differences following a species. There were strong decreases of dominant species Synedra ulna, Scenedesmus sp., Ankistrodesmus falcatus in UNIO treatment group, Diatoma vulgare in combined group, while Cryptomonas ovata in high density of CCM increased about 20% in algal density. Grazing rates (GRs) based on the concentration of Chl-a was depend on the kind of shellfish and treatment time; a strong feeding of CCM showed in the initial stage, and four hours later, UNIO and combined group with high UNIO density showed the high GRs. Interestingly, faeces production of shellfish was highest in combined group with high density of CCM, while their size over 60 ${\mu}m$ was much higher in production magnitude than that less 60 ${\mu}m$. Collectively, these results suggest that two domestic shellfish and its combined treatment have a strong potential as an effective biological controller of diatom bloom in cold eutrophic waters.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.36 no.5
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• pp.515-521
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• 2003

To understand interrelations between water quality and community structure of phytoplankton around the season of red tide outbreak, field surveys were conducted 10 times off the coast of Tongyeong from July to September in 2002. Because of heavy rain for 10 days, environmental conditions were changed and differed from the previous year, sustaining high nutrients and low salinity. During the surveyed period 48 species of 29 genera of phytoplankton were identified, and diatom and dinoflagellate was $51.8\%\;and\;38.0\%,$ respectively, At the time of bloom, cell counts of C. polykrikoides were outstanding but the number of species remarkably decreased. There were striking differences in dominant species among research stations before the bloom. Diatoms were the most dominant group in the whole study area in that period. Diversity and evenness index were highest just before outbreak of the red tides (2 Aug, 2002). During the bloom (4 Aug.), it decreased to the lowest value and then began to increase slowly. The result of PCA on water quality vs phytoplankton biomass showed that the land loads of nutrient may be the main cause of summer rally of phytoplankton biomass.

• Korean Journal of Ecology and Environment
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• v.41 no.2
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• pp.237-246
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• 2008

Filtration rates and fecal production of freshwater bivalve, Unio douglasiae on two kinds of hibernal diatom communities were measured simultaneously in a laboratory. One community is the Han River (HAN), which dominated by Asterionella Formosa. Stephanodiscus hantzschii (ca. 98% of total phytoplankton). The other community is the Ilgam Lake (IL), which dominated by Synedra ulna, Scenedesmus sp. Microcystis aeruginosa (ca. 82%). The HAN water has higher concentrations of nutrient (TN and TP) and chlorophyll $\alpha$ (Chl-$\alpha$), lower turbidity and conductivity than the IL water. Water sampling for the feeding experiment was conducted in the same day (Jan 15, 2008) and similar time (AM 10:00 for HAN, AM 11:00 for IL). Mussels with the similar size ($0.0{\pm}0.5\;cm$) were collected from the Gunsan and Okgu district (Jeonbuk), and starved in a laboratory for 2 days before the experiment. The experiment comprised CON (no addition of mussel), LOW (addition of mussel at 0.3 indiv. $L^{-1}$), MID (1.0 indiv. $L^{-1}$) and HIGH (2.0 indiv. $L^{-1}$), respectively. With the increment of mussel density and time, the concentration of Chl-$\alpha$ in two diatom communities were clearly decreased; Chl-$\alpha$ of HAN gradually decreased after 1 hour of mussel treatment, while that of IL decreased as soon as mussel introduction. In 7 hours of treatment, the former was removed finally up to about 90% of control, while the later was remained as about 50%. Under the presence of mussel, total phytoplankton density was shifted as the similar patterns to that of Chl-$\alpha$ (r=0.705, P<0.0001), however, there showed the drastic differences following a species. Based on the concentration of Chl-$\alpha$, filtration rate of U. douglasiae averaged 0.266 $L\;g^{-1}\;h^{-1}$ (0.115 to 0.442) on HAN and $0.577\;L\;g^{-1}\;h^{-1}$ (0.146 to 1.428) on IL water, respectively. There were no differences in feces production among the mussel density in the HAH water (ANOVA, P>0.5), while in IL water, including lots of seston, the HIGH mussel produced the higher fecal materials, over one hundred times of LOW. These results suggest that freshwater bivalve Unio douglasiae have the alternative potential, as a filter-feeder of seston in turbid lake, and a biological controller of diatom bloom in cold stream.

• Ocean and Polar Research
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• v.25 no.3
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• pp.303-314
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• 2003

The initiation of Cochlodinium polykrikoides blooming in the South Sea of Korea occurs in the sea near Naro-Do in late August. In this paper, the relationships of this annual occurrence with the environmental conditions are presented. In early summer, the winds in the sea near Naro-Do are southwesterly and the upwelling occurs in the near-shore area. The favorable winds to the upwelling are relaxed in August and the downwelling favorable northeasterly winds set in around late August. The change of wind direction causes the onshore transport of warm-and-fresh off-shore water into the sea near Naro-Do and a front between near-shore water and off·shore water is formed. Along the front, downwelling occurs and the environmental conditions for the diatom become unfavorable. When the typhoon and storm bring well-mixed East China Sea water into the sea near Naro-Do in September, the conditions for the dinoflagellates become unfavorable and blooming of C. polykrikoides disappears.

• Proceedings of the Korea Society of Environmental Biology Conference
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• 2003.11a
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• pp.103-107
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• 2003

Spatial distribution of phytoplankton was investigated in the southwestern sea of Korea in May 2000 in terms of phytohydrography. The sampling was done at the 0m, 30m, 50m of 15 selected stations, and permanent slides of each samples were prepared by QPS method for quantitative and qualitative analyses. Phytoplankton standing crops ranged from 3.23${\times}$10$\^$-4/ to 1.09${\times}$10$\^$-7/ cellsㆍ$\ell$$\^$-1/ in the study area. Dominant species comprised of 9 diatoms and 2 phytoflagellates, showing higher dominance of diatom and most predominance of Skeletonema costatum in all layers of most stations. Phytohydrographic results indicate that the study area might be divided into 4 categories, that is, I area is designated as neritic area where occurrence of terrestrial and coastal species is frequent, II area as intermediate area, III area as offshore area where oceanic species dominate, and IV area as other's. Especially in the II area, Skeletonema costatum was most predominant at both surface and 30m layer in most stations and represent an characteristic of northward expansion with spring massive bloom.

• Korean Journal of Ecology and Environment
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• v.41 no.3
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• pp.338-347
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• 2008

Grazing rate (GR) and feces production (FP) of freshwater snail Cipangopaludina chinensis malleata on two hibernal diatom communities were examined in a laboratory. Snail with the similar size (4.2$\sim$5.8 cm) were collected from the Gunsan and Okgu district (Jeonbuk), transferred to the artificial management system in laboratory, and starved for 3 day before the experiment. The feeding experiments were conducted at various conditions such as passage of time (0, 1, 4 and 7 hr), snail density (0.0, 0.5, 1.0, 2.0 and 4.0 ind. $L^{-1}$) and kinds of prey (cold lake and stream water). One prey used in this study is the water of Lake Ilgam, the other is that of Han river. Lake Ilgam water was dominated by Synedra ulna (69.1%) and Scenedesmus sp. (6.6%), while Han river was by Asterionella formosa (69.4%) and Diatoma vulgare (27.7%). With the increment of snail density and time, the Chl-a concentration of two experimental waters were clearly decreased. Chl-a of Han river rapidly was decreased after 1 hour of snail treatment, while that of Ilgam lake was decreased after 4 hour. On the passage of time, a highest GR (1.94 L $g^{-1}\;h^{-1}$) showed at 1 hr, and then, decreased gradually to 0.04 L $g^{-1}\;h^{-1}$ by 7 hr. The highest FP (0.11 mg $L^{-1}$) showed at 7 hr. These results indicate that native snail Cipangopaludina chinensis malleata may be applied as a potential bio-filter to control diatom blooms in the cold lake and stream.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.2
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• pp.93-102
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• 2001

Biomass and species composition of phytoplankton and zooplankton along the salinity gradients in the Seomjin River estuary were investigated in March, July, September and November, 1999. The locations of sampling sites were set based on the surface salinity during each cruise rather than geographic locations. A total of 96 phytoplankton species were identified with 60 diatom species in the study area. The species number of green algae was relatively high in low salinity region while the number of dinoflagellates increased in high salinity areas. Monthly mean of phytoplankton biomass ranged from 183 cells/ml to 833 cells/ml. There was a diatom bloom of Skeletonema costatum in November at the 5-15 psu salinity region and sharp decrease of biomass in very low salinity region occurred in March. During the rainy season in July with the salinity less than 8.1 psu, the green algae dominated in most of the study areas. Chroomonas spp. were highly dominant in March and September and the biomass increased towards the high salinity regions. A total of 83 zooplankton taxa were identified with 72 marine and 11 freshwater taxa. Major group of marine form was copepods with34 taxonomic groups. Most freshwater taxa were aquatic insects. Threshold salinities of freshwater zooplankton appearance were 8.1 psu in July, 4.7 psu in September, and 0.2 psu in November. The number of taxa appeared and abundances of zooplanktons were minimal in the middle of salinity gradients in this estuary.

• ALGAE
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• v.20 no.3
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• pp.207-216
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• 2005

Myrionecta rubra, a mixotrophic ciliate, is a cosmopolitan red tide species which is commonly found in neritic and estuarine waters. M. rubra had long been listed as an “nculturable protist”until 2 different laboratory strains were finally established in 2 research groups at the beginning of this century, enabling us to perform initiative investigation into various aspect of the live M. rubra strains (Gustafson et al. 2000; Yih et al. 2004b; Johnson and Stoecker 2005). Field sampling was carried out on high tide at 2 fixed stations around Kunsan Inner Harbor (St.1 near the Estuarine Weir and St.2 off Kunsan Ferry Station) every other day for 4 months from mid-February 2004 to understand detailed figure of the recurrent spring blooms of M. rubra following the onset of the water gates operation of the Keum River Estuarine Weir on August 1994. With its maximum abundance of 272 cells mL$^{-1}$ in St.1, fluctuation pattern of the M. rubra population at the 2 stations was strikingly similar. Notable growth of M. rubra population started on late April, to cause M. rubra red tides during one month from mid-May in which “xceptionally low salinity days”without its red tide were intermittently inserted. High abundance of M. rubra over 50 cells mL$^{-1}$ was recorded at samples with their water temperature and salinity higher than 15${^{\circ}C}$ and 4.0 psu, respectively. During pre-bloom period when salinity fluctuation is moderate and the water temperature is cooler than 15°C, Skeletonema costatum, a chain-forming centric diatom, was most dominant. Cyanobacterial species such as Aphanizomenon flos-aquae and Phormidium sp. replaced other dominant phytoplankters on the days with “xceptionally low salinity”even during the main blooming period of M. rubra. To summarize, M. rubra could form spring blooms in Keum River Estuary when the level of salinity fluctuation was more severe than that for the dominant diatom Skeletonema costatum and milder than that for the predominance by freshwater cyanobacteria. Therefore, optimal control of the scale and frequency of freshwater discharges might lead us to partially modify the fluctuation pattern of M. rubra populations as well as the period of spring blooms by M. rubra in Keum River Estuary. Sampling time interval of 2 days for the present study or daily sampling was concluded to be minimally required for the detailed exploration into the spring blooms by M. rubra populations in estuaries with weirs like Keum River Estuary.

• Ecology and Resilient Infrastructure
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• v.2 no.3
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• pp.224-236
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• 2015

We conducted the algicidal activity screening tests using 10 L microcosm to investigate the possibility of the field application of naphthoquinone derivative Nq 4-6 compound as an algicide. We determined its application range to assess its algicidal effects on the phytoplankton and to evaluate the response of the planktonic community and the water environment to this chemical. From results of the microcosm experiments, Nq 4-6 compound showed high algicidal activity on the centric diatoms such as Stephanodiscus hantzschii and Cyclotella meneghiniana, but it had no effect on other phytoplankton. The abundance of S. hantzschii continuously increased in the control, but its cell density decreased 1 day after the Nq 4-6 treatment. In particular, Nq 4-6 showed algicidal activity of 94.4% against S. hantzschii 7 days after the treatment. The dominance index of phytoplankton community was lower in the treatment than in the control. The diversity index, richness index and evenness index of phytoplankton community was higher in the treatment. Environmental factors and biological factors did not show specific changes after the Nq 4-6 compound treatment. Therefore, the results of this study demonstrates that Nq 4-6 is an effective agent for the control of S. hantzschii blooms, and that the microcosm tests play a crucial role when assessing field application.