報告書番号

V08039

タイトル（和文）

貯水池の水温、溶存酸素濃度および濁度がカワヒバリガイ幼生の発生動態に及ぼす影響

タイトル（英文）

Effects of water temperature, dissolved oxygen concentration and turbidity on population dynamics of larva of Golden Mussel Limnoperna fortunei in reservoirs

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究では、外来性汚損生物のカワヒバリガイの幼生発生と貯水池の水質（水温、溶存酸素濃度、濁度）との関係を明らかにするため、群馬県の大塩湖ならびに大塩湖の湖水が流入する竹沼湖において、幼生の発生状況と水質を調査した。幼生の発生期間はおおよそ6月末から9月末であり、発生開始時と終了時の水温はそれぞれ約17℃と約20℃であった。幼生密度は、竹沼湖に比べ大塩湖では約300倍も高かった。また、幼生は日中、深層部に分布が集中していた。大塩湖では、水質保全のための曝気循環装置により湖水が撹拌され、夏期に貯水池全体が水温20℃を超え、溶存酸素濃度も2mg/l以上であった。一方、竹沼湖では、夏期の成層形成により、深層部には10℃未満で0.5mg/l未満の貧酸素水塊が発生した。これらの結果から、大塩湖に比べ竹沼湖で幼生発生量が少ない原因は、成層形成後の低水温と貧酸素水塊による幼生供給の制限および加入幼生の死亡のためと考えられた。

概要 （英文）

Golden mussel Limnoperna fortunei is a freshwater bivalve that adheres to water intake facilities and produces several troubles by growing. Biofouling problems have been expanding recently in Japan, and the planktonic stage is considered to have an important role for their habitat distribution. However, little information has been obtained on the survival, growth, and reproduction of L. fortunei in lakes of Japan. We investigated population dynamics of larval L. fortunei in two reservoirs, Lake Ohshio and Lake Takenuma, which are connected by headrace channel. The L. fortunei larva occurred between late June and late September in the lakes. Larva were initially found on 18 June 2008 when water temperature (WT) was about 17 degree C. No larvae were found in autumn when WT was about 20 degree C in Ohshio lake. The larvae density in Lake Ohshio was more than 10,000 ind./m3 with maximum of 80,000 ind./m3 in summer of 2007 and 2008. The density in Lake Takenuma was much lower and maximum value was near around 200 ind./m3. The larvae were mainly distributed in deep area of the lakes during the day. However, it moved to near surface area with increasing turbidity. The WT and dissolved oxygen concentration (DO) were almost uniform regardless of water depth in Lake Ohshio because of destratification due to continuous aeration. Summer WT and DO in the lake were considered to be kept good for the survival and reproduction of L. fortunei. On the other hand, stratification was found for WT and DO in Lake Takenuma throughout the season. Low WT and DO in summer found in deep area of the lake were not considered to be acceptable for the survival of larva and adults of this species. Thus the population of L. fortunei larva differed extremely even in adjoining two lakes, and WT and DO are considered to be critical factors especially for their reproductions.

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