• Ocean and Polar Research
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• v.26 no.2
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• pp.273-286
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• 2004

The effects of environmental forcing on autotrophic picoplankton distributional patterns were investigated for convergence ($5^{\circ}N$), divergence ($9^{\circ}N-10^{\circ}30'N$) and oligotrophic ($17^{\circ}N$) sites in the tropical eastern Pacific during 2001 and 2003 KODOS (Korea Deep Ocean Study) cruises. The distributions of picoplankton populations - Prochlorococcus, Synechococcus and picoeukaryotes algae - were determined by flow cytometric analyses. Latitudinal variations in abundance maxima, vertical profiles, integrated abundance (0-150 m), and estimated carbon biomass were contrasted for each site according to three hydrological conditions. Prochlorococcus showed consistently high abundance in the surface mixed layers of all sites at $1\;{\times}\;10^5{\sim}3\;{\times}\;10^5\;cells\;ml^{-1}$ and showed declining abundance below these layers. However, these decreasing rates were not particularly sharp showing considerably high abundance at $1\;{\times}\;10^4\;cells\;ml^{-1}$ or higher even at 100 m depth. Vertical profiles of Synechococcus and picoeukaryotes were generally parallel to each other in all sites. A clear abundance maximum was observed at divergence site at or slightly above the pycnocline depth. Higher abundance was observed at the surface mixed layer for convergence site but a sharp decrease was observed below the pycnocline. However, there was no significant abundance fluctuation with depth at more oligotrophic site ($17^{\circ}N$). Integrated cell abundance of Prochlorococcus was high in the oligotrophic site at $2.17\;{\times}\;10^{13}\;m^{-2}$, and low in the convergence site at $0.88\;{\times}\;10^{13}\;m^{-2}$. However, opposite pattern was observed for Synechococcus and picoeukaryotes where relatively high integrated cell abundance was shown in the convergence site. Estimated carbon biomass of Prochlorococcus contributed 30.4-80.3% of total autotrophic picoplankton carbon showing the highest contribution in the oligotrophic site and the lowest contribution in the convergence site. Synechococcus contribution of total autotrophic picoplantkon carbon biomass was lower than 5.8% for most of sites except the convergence site where Synechococcus contributed 23.2% of picoplankton carbon biomass. Carbon biomass of picoeukaryotes was 18.8-46.4% showing the highest carbon biomass at the convergence site. Overall, Prochlorococcus showed higher cell abundance and carbon biomass and exhibited different reaction to hydrological conditions when compare with the other two major autotrophic picoplankton groups.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.60 no.1
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• pp.37-46
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• 2024

This study was conducted to provide the basic information on environment effects on appearance of ichthyoplankton in the Yeongsan River Estuary in Spring and Summer from 2018 to 2020. Data were obtain from the database of 'Coastal Ecosystem' in "National Survey of Marine Ecosystem." Among the abundance ichthyoplankton species, the Gobiidae spp. dominated, accounting for 85% of the total abundances with the secondary dominant species being the Parablennius yatabei, representing 3% of the abundances. Cluster analysis results revealed a composition differentiated between spring and summer. The Yeongsan River Estuary is known to be significantly influenced by the opening and closing of estuarine gates. In this study, the fluctuation in the number of occurrence groups and abundance among the years and season is attributed to the phenomenon of high water temperature period and the freshwater discharge.

• Korean Journal of Ecology and Environment
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• v.54 no.4
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• pp.390-397
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• 2021

The time series data of rotifer community focusing on the species number and total density were collected from 29 reservoirs located at Jeonnam Province from 2008 to 2016 quarterly. The reservoirs had similar weather condition during the study period, but their sizes and water qualities were different. To analyze the temporal dynamics of rotifer community, the medians, ranges, outliers and coefficient of variation (CV) value of rotifer species number and abundance were compared. For the temporal trend analysis, time series of each reservoir data were compared and clustered using the dynamic time warping function of the R package "dtwclust". Small-sized reservoirs showed higher variability in rotifer abundance with more frequent outliers than large-sized reservoirs. On the other hand, apparent pattern was not observed for the rotifer species number. For the temporal pattern of rotifer density, COD, phytoplankton abundance fluctuation, and cladoceran abundance fluctuation have been suggested as potential factor affecting the rotifer abundance dynamics.

• The Korean Journal of Ecology
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• v.19 no.5
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• pp.393-402
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• 1996

Density fluctuations of soil microarthropods at the Piagol, Mt. Chiri was assessed on the basis of 113, 096 individuals collected from March 1993 to February 1994. Of 6 classes, and 18 orders, the Arachnida and Insecta were the most numerous members with abundance of 51.4% and 46.3%, respectively. The mean density of the Acari was $13, 310/m^2$ of microarthropods. The Acari were abundant in autumn and less found in winter and the density fluctuation of the Collembola followed a similar trend. The vertical distribution of the mesofauna revealed from the soil samples taken from the surface to 5 and from 5 to 10 cm in depths was as follows. In 5~10 cm layer. Collembola was numerous with abundance of 54.7%, followed by 40.1% fo Acari and the soil microarthropods reached the highest density peak in spring, while the lowest in winter. Populations concentrated in the 0~5 cm layer as much as 62.2% throughtout the season and 82.4% throughtout the altitudes. The Acari / Collembola (A/C) ratio in the 0~5 cm layer was higher than that in the 5~10 cm.

• Korean Journal of Environmental Biology
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• v.21 no.4
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• pp.342-351
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• 2003

The southern rough shrimp Trachysalambria curvirostris (Stimpson) was monthly sampled from the coastal area of Yeosu, Korea from June 2000 to May 2001 and its stomach contents were investigated. Mysids and amphipods were the most dominant prey, comprising >40% of the diet in both % occurrence and % abundance. In particular, mysids were most important food without regard to seasons, size classes, or sexes. The abundance and occurrence composition of food items showed a seasonal fluctuation: mysids and amphipods were the predominant prey items in spring (33.8%), summer (41.1%), autumn (43.9%), and winter (49.2%). For small-sized shrimps (＞25 mm CL), mysids and amphipods consist of more than 45% of its food in both % abundance and % occurrence. For large-sized shrimps (>25 mm CL), these were clearly dominant. The quantities and items of food did not differ in both genders, which mainly fed on mysids and amphipods. The trophic diversity and equality of diet varied with seasons and size classes. The diet diversity for smaller shrimps was highest in spring, while that for the larger shrimp lowest in winter. Also, the mandibular structure of Trachysalambria curvirostris indicates that the species is carnivorous.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.26 no.5
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• pp.424-437
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• 1993

About three fourths of total variability of zooplankton in Asan Bay was associated with season and the difference between inner bay and outer bay was relatively small. However, the differences in percent compositions of major taxa at inner bay and outer bay increased gradually with time, suggesting the change of ecosystem in this bay due to the human exploitation such as reclamation. Seasons of maximum abundances were different among the taxa but consistent for each taxon throughout the three survey years. Calanus sinicus and Acartia bifilosa showed maximum abundance in spring. Sagitta crassa, Paracalanus parvus, A. pacifica, Tortanus spinicaudatus, Corycaeus affinis and Decapoda larva were most abundant in summer. Labidocera euchaeta and Bivalve larva appeared most abundantly in fall. But in winter no taxon showed maximum. In general, low abundance with many species in fall, low abundance and few taxa in winter, increase in both number of taxa and abundance in spring, and high abundance and many taxa in summer were observed. A hypothesis for the observed patterns was suggested although more evidences were needed to support this.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.43 no.4
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• pp.261-273
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• 2007

To analyze quantitative fluctuation in abundance and species composition in coastal waters of Dolsan, Yeosu, the fished were collected by gape net from March to November, 2000. The fish species caught by set net collected fishes were identified 63 species, 56 families, 42 orders, and the number of appearance and biomass was 2,230,297 individuals and 16,076.8kg. The most dominant orders were Perciformes, Clupeiformes and Tetraodontiformes which accounted for 71.4% of the total. The dominant species in number were Engraulis japonicus, Sardinops melanostictus, Trichiurus lepturus which accounted for 99.2% (2,211,642 individuals) of the total fishes collected. The dominant species in biomass were Engraulis japonicus which accounted for 79.7% (12,807g) of the total fishes collected. Temporal occurence of the dominant species such as the Engraulis japonicus, Sardinops melanostictus, Trichiurus japonicus, Ilisha elongata, Leiognathus nuchalis was closely correlated with water temperature, which is expressed as following regression equation, $y=0.0864x-0.2311(r^2＝0.3516)$. The species collected during the sampling yearly period were Engraulis japonicus, and migratory fish were Ilisha elongata, Trichiurus japonicus, Scomberomorus nipphnius, Scomber japonicus, Konosirus punctatus, Sphyraena pinguis, Pseudosciaena polyactis.

• Korean Journal of Environmental Biology
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• v.24 no.4
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• pp.372-379
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• 2006

In order to study temporal fluctuation and ecological characteristics of Noctiluca scintillans, its abundance was investigated in correlation with water temperature, salinity, precipitation, chlorophyll a concentration and copepods abundance in the coastal waters of Incheon from January 1999 to December 2000. N. scintillans was seasonally abundant during spring and autumn with temperature ranging from 10.3 to $21.5^{\circ}C$, but depleted in winter and summer. Low temperature below $4.5^{\circ}C$ in winter and low salinity due to high rainfall in summer led N. scintillans to disappear. A Cross Correlation Analysis (CCA) showed that chlorophyll a concentration was positively correlated with abundance of N. scintillans at the time lags of 10 days. This suggests that phytoplankton may be a contributing factor for increasing abundance of N. scintillans. During spring, eggs of Acartia hongi were found in 2.9 to 21.1% of individuals of N. scintillans. It was deduced that 1.2 to 49.5% of the eggs produced by A. hongi was preyed upon by N. scintillans. Therefore, N. scintillans may control the population size of initial developmental stage of A. hongi in the costal waters of Incheon.

• 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.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.43 no.4
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• pp.251-260
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• 2007

A species composition and population structure of fish, collected 16 times by bottom otter trawl in the coast of Geumo Island, from February 2002 to November 2005, was investigated. The fish species caught by bottom otter trawl from year 2002 to 2005 was entirely 72 species, 41 classes, and 12 orders, and the number of appearance and biomass was 5,999 individuals and 287,902.1g, respectively, being of the Perciformes(31 species and 19 classes; 43.1% in total number of species appeared) as a dominant species. 638 individuals of Leiognathus nuchalis which was 10.6% in total fish were appeared and 465 individuals of Konosirus punctatus(7.8%), 449 individuals of Engraulis japonicus(7.8%). biomass of Sebastes schlegeli was 33,258.7g as a dominant species(11.6% in total fish appeared) and 18,821.1g of Liparis agassizii(6.5%), 16,708.0g of Konosirus punctatus(5.8%). The diversity index of species per months of the collected by a small otter trawl in coastal water of Geumodo from year 2002 to 2005 was 2.860-3.639 and the evenness index was 0.825-0.887 in case of dominance index was 0.224-0.268 against the evenness index. The similarity of community structure per yearly was very high because of the relative difference(0.006), which was the least in 2004 and 2005.