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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 7099

Ohtaka Akifumi, Mori Naohito, and Saito Shoichi; Zooplankton Composition in the Tsugaru-Juniko Lakes, Northern Japan, with Reference of Predation Impact. Jap.J.Limnol. 57(1):15-26, 1996

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Species composition of zooplankton communities were investigated in all 30 lakes of the Tsugaru-Juniko Lakes in the Shirakami mountains, northern Japan. A total of 64 taxa was recorded, out of which 25 rotifers and two cladocerans were newly recorded in these lakes. Excluding several spring-fed ones, the present lakes were clearly classified into two groups on the basis of zooplankton composition. That is, in larger lakes with fish (Group A) rotifers predominated, especially Keratella cochlearis and Polyarthra spp., while crustaceans were much less abundant except for Bosmina longirostris. On the other hand, smaller lakes without fish (Group B) were inhabited by abundant Daphnia longispina and cyclopoid copepods, but rotifers and Bosmina longirostris scarcely occurred there. Distribution of larvae of a phantom midge (Chaoborus flavicans) was also restricted in the Group B lakes. Past records show that two large zooplankters, Daphnia longispina and Acanthodiaptomus pacificus, were abundant in the Group A lakes until 1940s. Predation by introduced fishes, especially the pond smelt Hypomesus transpacificus nipponensis, probably eliminated the large forms there. These facts suggest that predation is a major factor controlling the zooplankton community structure in the Tsugaru-Juniko Lakes.