Abstract
Diel vertical movement of Neomysis intermedia population in Lake Kasumigaura, a shallow hyper-eutrophic lake, was investigated. N. intermedia tended to concentrate more near the lake bottom during the daytime and to disperse throughout the whole water column at night. This behavior was observed at all growth stages, and the timing of this movement closely corresponded with sunset and sunrise. Diel vertical movement of N. intermedia may be initiated by a critical light intensity encountered at certain times of sunset and sunrise.
