天竜川における水生昆虫群集の構造, biotic indexおよび季節変動

Abstract

Ecological studies were made of the aquatic insect communities in the Tenryu River, Central Japan, in the summer of 1967, with special reference to their composition, the biotic index calculated according to BECK-TSUDA's method. During the years from 1968 to 1969, the seasonal change of aquatic insect communities and the biotic index were studied in the area of polluted water by wastes from the KP pulp plant located in the upper reach. The results are as follows 1. In July, 1967, the aquatic insect fauna was poor in the Tenryu because of various reasons. The net-spinning caddis-worm Hydropscyche ulmeri was dominant at most stations there. 2. The aquatic insect communities were composed of 20 to 29 in the number of species, of which the maximum numbers attained in May, the minimum in July, at the station Tatsuno-A (relatively clean water) in the samples by using a quadrat (50×50cm). The number of species at Tatsuno-B (150 meters down from the KP pulp plant) was 2 to 4, and that at Shinmachi (2 kilometers down from the same plant) was 8 to 14. 3. The individual numbers and standing crops of many species of aquatic insects became minimum in summer in quadrat samples at Tatsuno-A, and increased from autumn till winter. 4. The seasonal change of the biotic index was 37 to 53 at Tatsuno-A, 3 to 7 at Tatsuno-B, and 12 to 25 at Shinmachi.