白神山地・津軽十二湖湖沼郡の河川における底生動物の群集構造と食性

概要

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Species composition and food habits were surveyed for zoobenthos in all nine streams on a chain-lake system inthe Tsugaru-JITniko Lakes, Shirakami Mountains, northern Honshu, Japan, in 1998 and 2001. The number of zoobenthictaxa increased in streams at the middle course of the water system. The total density and biomass of the zoobenthosincreased markedly in the lake outlet streams, in accordance with the increase in the chlorophyll-a concentration in thewater, where filter-feeding trichopterans, amphipods, and gastropods dominated. Analyses of stomach contents indicatethat in the lake outlet streams, algae and detritus derived from upper-located lakes are used as food not only by filter- anddeposit feeders, but also by primary grazers and even predators. On the other hand, filamentous green algae occurringabundantly on stream beds were not ingested very frequently by every invertebrate. The abundance of zoobenthosdecreased in the lower streams during summer and autumn. This may be partly due to the decrease of algal production inthe upper lakes or to the occupation of stream beds by sponges.