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応用生態工学 6(2), 145-156, 2004

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原著論文 ORIGINAL PAPER

ECEロゴマーク

河川人工構造物が通し回遊性無脊椎動物の生息に与える影響について−河川間比較による検討−

井手口佳子・ 山平寿智*

九州共立大学工学部環境化学科 〒807-8585 北九州市八幡西区自由ヶ丘1-8

Keiko IDEGUCHI and Kazunori YAMAHIRA*: Effects of artificial structures in rivers on abundance of diadromous invertebrates: comparative studies among rivers. Ecol. Civil. Eng. 6(2), 145-156, 2004.

Department of Environmental Chemistry, Faculty of Engineering, Kyushu Kyoritsu University, 1-8 Jiyugaoka, Yahatanishi-ku, Kitakyushu 807-8585, Japan

Abstract:To detect factors affecting settlement, upward migration, and subsequent survival of diadromous organisms, the relationships between abundance of diadromous invertebrates (decapod crustaceans and a gastropod) and environmental features of various rivers (amount of flow and any artificial structures) was examined among 75 rivers in Fukuoka Prefecture, Japan. Field collection indicated that the shrimp Caridina leucosticta and the snail Clithon retropictus were more abundant in rivers with larger amounts of flow, while Caridina typus occurred only in rivers with smaller flows, suggesting interspecific differences in behaviors of settlement/upward migration. Further, C. leucosticta and C. retropictus were more abundant in rivers with dams, and C. typus was more abundant in rivers without floodgates, probably due to apparent effects by multiple correlations between the existence/non-existence of dams and floodgates and the amount of flow of each river. Effects of artificiality of riverbed/riverside and the amounts of vegetation on the abundance of each diadromous species were considerably different among species: C. leucosticta was more abundant in rivers having natural riverbeds and a water's edge with abundant vegetation, while C. typus, E. japonica, and C. retropictus were abundant in rivers with artificial riverbeds or shore protections. This interspecific difference is considered to reflect differences in ecology/behavior in freshwater areas. Neocaridina denticulata, a non-diadromous shrimp, was abundant in pools above dams. To assess the effects of artificial structures on diadromous invertebrates, one needs to focus not only on the direct effects of the structures (intercept of migration routes, etc.) but also on the indirect ones due to changes in biological environments (competition, predation, etc.).

Key words: amount of flow, dam, diadromous migration, floodgate, recruitment

摘要

福岡県内の75本の河川を対象に,流量および人工構造物(堰,水門,護岸など)の設置状況と,通し回遊性の甲殻類および貝類の生息状況(バイオマス・密度)の関係について調べ,通し回遊性無脊椎動物の着底と遡上,および生息に影響する要因について検討した.各河川の淡水域下限でそれぞれ定量採集・観察を行った結果,ミゾレヌマエビとイシマキガイは流量の大きな河川ほどバイオマスが高かったが,トゲナシヌマエビは流量の小さな河川に多く出現することがわかり,同じ通し回遊性生物でも着底・遡上の生態に種間差があることが示唆された.また,ミゾレヌマエビとイシマキガイは堰が無いより有る河川の方が,トゲナシヌマエビは水門が有るより無い河川の方が,それぞれバイオマスが高かった.これらは,堰や水門の有無と各河川の流量とが多重相関しているために現れる見かけの効果によると考えられた.河床の状態,護岸の有無,そして水際の植生量が各種のバイオマス・生息密度に与える影響は,種間で大きく異なっていた.ミゾレヌマエビは天然の河床で植生の豊富な河川に多く出現したが,トゲナシヌマエビ,モクズガニ,およびイシマキガイは人工的な河床や護岸が施された河川にも多く出現した.この種間差は,淡水域での生態の違いを反映していると考えられた.また,堰の上流の停滞域には,非通し回遊種(純淡水種)のミナミヌマエビが多く出現した.河川人工構造物が通し回遊性無脊椎動物に与える影響を評価するには,構造物による直接的影響(回遊経路の遮断など)以外に,生物的環境(種間競争や捕食圧)の変化による間接的影響にも焦点をあてる必要もあると考えられた.

line 2003年8月29日受付 2004年1月16日受理
* e-mail: yamahira@env.sc.niigata-u.ac.jp
* 現所属:新潟大学理学部自然環境科学科 〒950-2181新潟市五十嵐二の町8050番地
* Present address: Department of Environmental Science, Faculty of Science, Niigata University, 8050 Ikarashi-2, Niigata 950-2181, Japan line
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