円山川水系(兵庫県)の水生生物群集 IV : 中・下流域における底生昆虫の分布

抄録

The present paper deals with the results of ecological investigations on the benthic insects of Maruyama River especially in its middle and lower parts. The survey was carried out from 1956 to 1959,and 109 species of aquatic insects belonging to nine orders were collected. Of these insects, 63 species were found in the headstream and springs, 56 in the torrential part of the river, 41 in the middle part and seven in the lower part. Orders found in each part are shown in Table 6. Some species of caddisworms as Stenophylax ondakensis, Limnocentropus insolitus, Uenoa tokunagai and some stonefly nymphs as Nogiperla sp., Nemoura(Nemoura)sp. were found only in the headstream. On the other hand, sand-dwelling mayfly nymphs as Potamanthus kamonis were charactyristic in the middle parts. According to the typological classification of life forms, the netspinning form was dominant in most parts of the river. The standing crop of the benthic insects of each part of the river was found to be as : middle part>torrential part>headstream>lower part. The constitutions of the communities and the standing crops varied with different river beds even at the same part. Generally, the Hayase-rapid showed the largest standing crop in the middle part. The standing crops were greatly controlled by the presence or absence of the net-spinning caddisfly larvae belonging to the Stenopsychidae. From the viewpoint of the blological production of the river beds, this stenopsychid larvae seemed to be of the most important. The lower limit of distribution of the stenopsychid worms in Maruyama River seemed to be restricted by the conditions of substratum, and the upper limit by the water temperature. In addition to these factors, water pollution in the lower parts and the continuity of the water surface which was the important element to the migration of ovipositing female in the upper parts were proved to be the factors influencing the distribution.