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ISSN : 2288-1115(Print)
ISSN : 2288-1123(Online)
Korean Journal of Ecology and Environment Vol.32 No.1 pp.16-23
DOI :

Environmental Studies of the Lower Part of Han River IV. Zooplankton Dynamics

Sewha Kim*, Jin Hwan Lee1
Department of Life Science, Yong-In University, Yongin 449-714
1Department of Biology, Sangmyung University, Seoul 110-743
Corresponding author: Tel: 0335) 330-2778, Fax: 0335) 337-1503, E-mail: swkim@eve.yongin.ac.kr

Abstract


Seasonal distribution of zooplankton was studied at seven selected stations in the lower part of the Han River during the period from June 1995 to June 1996 at two month intervals. Among 70 taxa of total zooplankton occurred, 60 taxa were identified to species, viz., three protozoans, 25 rotifers, 18 cladocerans, 13 copepods and one polycheat. In June 1995, a prosperity in species number was observed between 10~27 taxa through seven stations and became poor drastically just after a flood in July 1995.



Spatially upper waters showed a prosperity in species number when compared with lower ones. Maximum abundance of 44,317 indiv./m3 was recorded at station 7 in June 1996, while no zooplankters were observed at the same station in July 1995. Seasonal distribution showed the high abundance in June both in 1995 and 1996, and low abundance in July and January. Three cladoceran species (Daphnia galeata, D. pulex and Bosmina longirostris) and three copepod species (Canthocamptus carinatus, Cyclops vicinus and Thermocyclops hyalinus) dominanted zooplankton community with high abundance. Maximum population density of 16,964 indiv./m3 was recorded by the single species of D. galeata (station 2 in June 1996). D. pulex (9,375 indiv./ m3), B. longirostris (7,250 indiv./m3), T. hyalinus (6,714 indiv./m3) and C. vicinus (5,772 indiv./m3) also established dense populations, respectively. Spatial and temperal variation in the species diversity index indicated that the higher values of indices the upper stations except May and June 1996.



한강하류의 환경학적 연구 IV. 동물플랑크톤의 동태

김 세화*, 이 진환1
용인대학교 생명과 학과
1상명대학교 생물학과

초록


1995년 6월부터 1996년 6월까지 한강 하류 7개 정점에서 6회에 걸친 현장조사를 통하여 동물플 랑크톤의 계절적 변동에 대하여 연구하였다. 조사기간중 출현한 동물플랑크톤은 총 70분류군 (taxa)으로 원생동물 3종, 윤충류 25종, 지각류 18종, 요각류 13종, 다모류 1종 등 60종이 종준위까 지 동정되었다. 계절별로는 1995년 6월에 전정점에서 10~27분류군이 출현하여 가장 다양한 출현 양상을 보였으며 홍수 발생 직후인 1995년 7월에 가장 빈약하게 출현하였다. 정점별로는 상류에서 하류보다 많은 종류가 출현하는 경향을 보였다. 동물플랑크톤의 최대출현량은 입방미터당 44,317 개체(1996년 6월, 정점 7)를 기록하였으나 같은 정점에서 1995년 7월에는 전혀 출현하지 않았다. 계절별로는 1995, 1996년 모두 6월에 높은 출현량을 기록하였으며 7월과 1월에 출현량이 급격하 게 감소하였다. 우점종으로는 지각류인 Daphnia galeataD. pulexBosmina longirostris와 요 각류인 Canthocamptus carinatus, Cyclops vicinus, Thermocyclops hyalinus 및 요각류 유생이 출 현하였다. 단일종으로 D. galeata가 최대 입방미터당 16,964개체의(1996년 6월, 정점 2) 농밀한 개 체군을 형성하였으며 D. pulex, B. longirostris, T. hyalinus, C. vicinus도 각각 입방미터당 9,375 개 체, 7,250개체, 6,714개체 및 5,772개체의 개체군이 관찰되었다. 동물플랑크톤군집의 종다양성지수 는 1996년 5, 6월을 제외하고는 상류역인 정점 1~4에서 하류역인 5~7보다 높게 나타났다.



    INTRODUCTION

    Zooplankters play an important role in transferring primary production to higher trophic levels, i.e., ichthyoplankton and aquatic insects, etc. Thus zooplankton dynamics is affected by biological environments (structure of aquatic fauna and flora around them) as well as physical ones (water temperature and diunal length) (Raymont, 1984). Due to these characteristics, zooplankters have generally been used as indicator organisms for the water quality assessment (Hanazato and Yasuno, 1990;Nam, 1996).

    The Han River is the one of major rivers in the Korean Peninsula, and flows westward to reach the Yellow Sea. Flowing through the capital city, Seoul, the river is the sole resource for the industrial and drinking water supply in metropolitan area.

    Because of this necessity of the river, a number of studies has been carried out to understand about the zooplankton dynamics in the Han River, and a monographic study has recently been compiled (Lim, 1992). Water quatily of the Han River has been deteriorated gradually due to the increasing sewage input. Moreover the construction of underwater dams, and the lin- earization and adjustment of riverside disturbed the ecosystem of the lower part of the Han River seriousely.

    The objective of the study was to clarify the spatial and temporal distribution of zooplankton in waters adjacent to Yˇoˇuido and Chungjido of the lower part of the Han River. This study has been carried out as a part of study which assessed the impact of thermal discharge of Seoul thermal power plant on surrounding waters such as water quality (Hahn et al., 1997), phytoplankton dynamics (Lee and Chang, 1997), sediments (Hahn et al., 1997), and benthos and fishes (cf. KORDI, 1996).

    MATERIALS AND METHODS

    Zooplankton samples were collected six times in June, July, October 1995, January, May and June 1996 at seven selected stations in the lower part of the Han River (Fig. 1). The upper most station, station 1 was located beneath the Map’o bridge, stations 2 and 3: the front of the intake and discharge of Seoul thermal power plant, station 4: below the Tangsan bridge, station 5: the enterance of Saetkang, station 6: below the Sungsan bridge and station 7: off the Kayang water supply.

    Samples were vertically collected from the bottom to surface (4~12 m depth) with Kitahara net (mouth diameter: 24 cm, mesh aperture: 0.1 mm), and were fixed with 4% neutralized formalin with borax on board. Samples were moved to the laboratory and examined within 48 hours.

    Zooplankters were examined and counted under a dissecting microscope (Mag. X40~80) (cf. Omori and Ikeda, 1984). Protozoans, rotifers, cladocerans and copepods were identified to species under a compound microscope with higher magnification (X100-400). Identification was carried in accordance with Shen (1979), Chang and Kim (1986) for copepods, Chiang and Du (1979) and Kim (1988) for cladocerans, and Mizuno and Takahashi (1991) for protozoans and rotifers, and Kim (1991) for rotifers. The number of each species was converted to number per cubic meter of water by using calculated volume of water through the net.

    Species diversity index (Shannon and Weaver, 1963) as an ecological index was caculated with the computer program in statistical ecology (cf. Ludwig and Reynolds, 1988) at each station and compared with other stations.

    RESULTS

    Among 70 taxa of zooplankton observed in the study waters, 60 taxa were identified to species and consisted of three protozoans, 25 rotifers, 18 cladocerans, 13 copepods and one polycheat (Table 1). Rotifers showed a prosperity in species number which consisted of 35.7% of total zooplankton taxa, followed by cladocerans (25.7%) and copepods (20.0%).

    Table 2 showed the seasonal change in the species number of dominant zooplankton taxa, consisted of rotifers. cladocerans and copepods. In May 1996 and June 1995, rotifers showed a prosperity in species number (14 and 18 species) while cladoceran and copepod species were observed to be somewhat constant during the study period.

    Taxa number was recorded to be maximum (10~27 taxa) in June 1995 at all stations except station 6 (Table 3). Just after a flood in July 1995, zooplankton species decreased drastically. Zooplankton species were more or less constant at station 2, whereas other stations showed to be variable with varying season.

    Maximum abundance (44,317 indiv./m3) was recorded at station 7 in June 1996, while no zooplankter was observed at the same station in July 1995 (Table 4). Zooplankters were found to be abundant in June both in 1995 and 1996, and low abundance in July 1995 and January 1996.

    Three cladoceran species (Daphnia galeata, D. pulex and Bosmina longirostris) dominanted zooplankton community with high abundance (Table 5). Three copepod species (Canthocamptus carinatus, Cyclops vicinus and Thermocyclops hyalinus) also dominated with seasons and stations. Maximum population density of 16,964 indiv./m3 was recorded by the single species of D. galeata (station 2 in June 1996). D. pulex (9,375 indiv./m3), B. longirostris (7,250 indiv./m3), T. hyalinus (6,714 indiv./m3) and C. vicinus (5,772 indiv./m3) also established dense populations, respectively. The proportion of dominant zooplankton species to total zooplankton abunadance was recorded in Table 5. D. galeata consisted of more than 85% of total zooplankton abundance at station 5 in October and C. vicinus also recorded to be 80% of zooplankton abundance at station 6 in July.

    Fig. 2 showed the spatial and temperal variations in the species diversity index in the lower part of the Han River. Except stations 6 and 7, all the stations were oberved to fluctuate between 0.6 and 2.2. Spatial and temporal variation in the index seemed to show little correlation with the environmental change.

    DISCUSSION

    Zooplankton dynamics has often been used to interpret the water quality and aquatic ecosystem (Hynes, 1966;Waterman, 1960). For example, biological mornitoring system has been developed by using of Daphnia magna for watching the pollutant input into aquatic habitats (Knie and Puzicha, 1991). Recently, a number of studies has been performed for revealing the influence of various pollutants on aquatic habitat on the basis of toxicity test by using a freshwater cladoceran Moina irrasa in Korea (Kim et al., 1994, 1996; Yoo and Nam, 1996;Yoo et al., 1998).

    Daphnia galeata was revealed to be the predominant species in the lower part of the Han River. Although rotifers showed the prosperity in species number, their abundance was lower than cladocerans and copepods.

    Lower number of zooplankton taxa (70 taxa) observed during the study when compared with Lim , s result (115 taxa) (1992) seems to be due to our study water being confined to the lower part of the Han river while Lim had covered from the P , altang Lake to Haengju Bridge. Despite the defiency of intensity of our filed work when compared with Lim , s study, we found somwhat interesting results which was not mentioned by Lim, viz., the influence of flood. The flood due to the heavy rain fall in early July 1995 appeared to sweep the ichthyofauna (Cyprinus carpio and Carassius auratus) of study waters to the river mouth of the Yellow Sea while only an upper water fauna (Siniperca scherzeri and Lepomis macrochirus) was observed to be dominant at the same waters (KORDI, 1996). Zooplankton also seemed to be drifted away to the downstream because no zooplankters were found at station 7 in July 1995. No such a phenomenon was ever reported in the Han River.

    We found a carnivorous cladoceran Leptodora kindti establishing a large population at station 4 in June 1995 (1,200 indiv./m3). According to Lee and Chang (1997), stations 1 and 4 were recorded to be higher than other stations in phytoplankton standing crop in June 1995. High primary production might cause the prosperity of herbivorous zooplankton, e.g, Polyarthra vulgaris and Daphnia galeata, and in turn might give a preyrich enviroment to L. kindti (Herzig, 1995). A lack of aquatic plants at this station possibly let L. kindti relieve food competition with ichthyoplankters (Reede and Ringelberg, 1995).

    During the study, hybrid individuals in cladocerans were ignored. The occurrence of hybrid form in cladocerans remains to be studied in zooplankton dynamics more precisely in Korean inland waters.

    ACKNOWLEDGEMENTS

    We thank to Dr. S.-J. Hwang of Kyonggi Development Institute for critical reading which improved the manuscript. Thanks are also due to Drs. M. Chang and S.K. Yi of KORDI for their management of the project. The study was supported partially by Seoul thermal power plant of KEPCO (Project No. BSPI 00213-943-3) and KRF(Project No. 1998-015-D00231).

    Figure

    KJL-32-1-16_F1.gif

    Map showing the sampling stations in the lower part of the Han River

    KJL-32-1-16_F2.gif

    Spatial and temperal variation in the species diversity index in the lower part of the Han River.

    Table

    List of zooplankton observed in the lower part of the Han River

    Seasonal change in the species number of dominant zooplankton taxa in the lower part of the Han River

    Seasonal distribution in the taxa number occurred in the lower part of the Han River

    Seasonal distribution in the zooplankton abundance in the lower part of the Han River

    Seasonal variation in the proportion (%) and abundance (indiv./m3) of dominant zooplankton species in the lower part of the Han River

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