Impact of whitefish on an enclosure ecosystem in a shallow eutrophic lake: selective feeding of fish and predation effects on the zooplankton communities |
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Authors: | Hanazato Takayuki Iwakuma Toshio Hayashi Hidetake |
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Institution: | (1) Environmental Biology Division, National Institute for Environmental Studies, Onogawa, 305 Tsukuba, Ibaraki, Japan;(2) Faculty of Science, Shinshu University, 390 Asahi, Matsumoto, Nagano, Japan |
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Abstract: | Bag-type enclosures (75 m3) with bottom sheets and tube-type enclosures (105 m3) open to the bottom sediment were stocked with exotic whitefish (Coregonus lavaretus maraena) to study their predation effects on the plankton community. The fish fed mainly on adult chironomids during the period of
their emergence (earlier part of the experimental period). Thereafter, the food preference was shifted to larvae of chironomids
and crustacean zooplankters. The predation effects on the plankton community were not evident in the bag-type enclosures where
zooplankton densities were consistently low. The fish reduced the crustacean populations composed ofBosmina fatalis, B. longirostris andCyclops vicinus in the tube-type enclosures where the prey density was high (above ca. 50 individuals 1−1). The results suggested that the intensity of predation depended on the prey density. Rotifers increased in the fish enclosure,
probably becauseCoregonus reduced the predation pressure byCyclops vicinus on rotifers and allowed the latter to increase. In the fish enclosures, no marked changes in species composition were observed.
Zooplankton predated by the fish seemed to be distributed near the walls of the enclosures. Problems of enclosure experiments
for examining the effects of fish predation on pelagic zooplankton communities are discussed. |
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Keywords: | whitefish Coregonus zooplankton community enclosure eutrophic lake |
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