Abstract
Environmental factors and macroinvertebrates in riverside pools were investigated in the Urano River, a tributary of the Chikuma River. The pools were maintained by spring water and characterized by their small area and low temperatures in May and June, and were generally low in dissolved oxygen and poor in inorganic nutrients. The occurrence of very high water levels in the Urano River in July caused many pools to disappear or be greatly changed. Gammarus and some species of Coleoptera such as Laccotrephes japonensis and Appasus japonicus were distributed only in the riverside pools, and there were fewer Trichoptera compared with those in the main stream. Oligochaeta, Chironomidae, Ephemeroptera and Odonata were abundant both in pools and the main stream. The total number of invertebrates in May was high in pools rich in dissolved oxygen and extensive in area; in September, they were found only a short distance from the main stream and large areas. However, important environmental factors differed between the invertebrate groups. Riverside pools in small rivers are important for invertebrates that require clear still water and/or spring water, and their conservation is necessary.
