大塩貯水池および竹沼貯水池におけるカワヒバリガイの生態について: 現地調査と飼育実験による解析

摘要

分布域の拡大やそれにともなう通水阻害等の発生が懸念されている特定外来生物カワヒバリガイLimnoperna fortunei）は、浮遊幼生期を持ち（中井，2001）、発生から付着可能な幼生（付着期幼生）に成長するまでに10~20日（水温によって変化）を要することが知られている（Cataldo et al.,2005）。そのため、大陸に比較して急峻かつ流域長が短く滞留時間が短い我が国の多くの河川では、河川内で産卵・受精しても、付着期に達する前に海まで流下してしまうと考えられる。%In this study, we investigated the density of the golden mussel {Limnoperna fortunei) that were attached to the channel walls and the population dynamics of its larvae in lakes Ohshio and Takenuma. We also examined the effect of temperature on the survival of L. fortunei. The density of attached mussels at a given site in the channel decreased as the distance between the site and the lake increased. In Lake Ohshio, larvae were detected in June 2008 when the water temperature increased to 17℃. L. fortunei larval densities in Lake Ohshio were more than 10,000 individuals m~(-3) for 1 month from mid August to mid September 2007. By contrast, larval densities were very low in Lake Takenuma (max: ca. 200 individuals m~(-3)) during the same period. A comparison of the two lakes showed that water temperature and dissolved oxygen concentration greatly influenced the survival and breeding of L. fortunei. The survival rate of the mussels was independent of the temperature from 5 to 30℃. On the other hand, the survival rate was much lower at 35 ℃ during the 114-day rearing experiment, although it was initially unaffected for 20 days. Half of the mussels died after 309 days of rearing at 5°C. These results suggest that L. fortunei can survive under a wide range of temperatures, and is able to inhabit most lakes and ponds in Japan.