• Korean Journal of Ecology and Environment
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• v.37 no.4 s.109
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• pp.385-393
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• 2004

The herbivorous rotifers community (Brachionus spp.) and population dynamics of the predator rotifer (Asplanchna spp.) in three tributaries (Kumho R., Nam R., and Hwang R.) of the Nakdong River were evaluated on biweekly intervals from Jan. 2001 and Dec. 2002. High abundance of the herbivorous rotifers (peak density: - ca.>1000 Ind. $L^{-1}$) was observed from two tributaries (Kumho R. and Nam R.) during the spring and fall seasons, respectively. The high peaks of herbivorous rotifers were not evident in one tributary (Hwang R.). Among the herbivorous rotifers, brachionid rotifers (Brachionus spp. consisting of 7 species) were the characteristic rotifer community in this study. Brachionus spp. tended to occur together with the other perennial species, Asplanchna. Asplanchna was also present while two species of B. angularis and B. calyciflorus were highest in density. Subsequently, two populations (B. angularis and B. calyciflorus) rapidly declined, becoming rare after high peaks of Asplanchna occurred, except in one tributary (Hwang R.). We found community shifts in rotifer groups in mid-spring and mid-fall at the study site. The Asplanchna population could be appeared to play an important role in regulating the rotifer community and total plankton biomass in spring and fall at high trophic levels.

• Korean Journal of Ecology and Environment
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• v.39 no.1 s.115
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• pp.52-61
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• 2006

The aim of this study was to analyze the seasonal patterns of zooplankton community dynamics in the lower Nakdong River (Mulgum, RK; river kilometer; 27 km from the estuarine barrage), with a Self-Organizing Map (SOM) based on weekly sampled data collected over ten years(1994 ${\sim}$ 2003). It is well known that zooplankton groups had important role in the food web of freshwater ecosystems, however, less attention has been paid to this group compared with other community constituents. A non-linear patterning algorithm of the SOM was applied to discover the relationship among river environments and zooplankton community dynamics. Limnological variables (water temperature, dissolved oxygen, pH , Secchi transparency, turbidity, chlorophyll a, discharge, etc.) were taken into account to implement patterning seasonal changes of zooplankton community structures (consisting of rotifers, cladocerans and copepods). The trained SOM model allocated zooplankton on the map plane with limnological parameters. Three zooplankton groups had high similarities to one another in their changing seasonal patterns, Among the limnological variables, water temporature was highly related to the zooplankton community dynamics (especially for cladocerans). The SOM model illustrated the suppression of zooplankton due to the increased river discharge, particularly in summer. Chlorophyll a concentrations were separated from zooplankton data set on the map plane, which would intimate the herbivorous activity of dominant grazers. This study introduces the zooplankton dynamics associated with limnological parameters using a nonlinear method, and the information will be useful for managing the river ecosystem, with respect to the food web interactions.