筑後川上流（大山川）におけるダム湖由来の浮遊性藻類がアユの採餌環境に与える影響

抄録

Current researches indicate energy flow in river ecosystem is affected by an influx of planktonic algae from the upper dam reservoir. It seems that deposition of planktonic algae on river bed causes attached algae composition and its photosynthesis to change. Meanwhile, algophagous Ayu (Plecoglossus altivelis) are released into the Ohyama River (upper Chikugo River) where a few dams locate in the upstream. In this study, to investigate the effects of deposition of the planktonic algae on the feeding condition of Ayu in the Ohyama River, food web structure was analyzed by carbon and nitrogen stable isotope ratio among Ayu, omnivorous young fish, attached algae and planktonic algae. The results show that the effect of the planktonic algae on the feeding condition is not so large for Ayu, and the rate of it depends on fish species.