DISTRIBUTION AND STANDING CROPS OF CHIRONOMID-LARVAE IN SHIOZU BAY OF LAKE BIWA

This paper is the report on the distributional pattern and the standing crops of chironomid-larvae which were investigated at Shiozu Bay of Lake Biwa. We investigated by a bottom sampler four times through the year; April, August, October, 1968 and January, 1969. In our study, Phaenopsectra sp. B, Phaenopsectra sp. C, Procladius sp. B and so on were dominant species next to Chironomus plumosus. Most species lived in the mud, some of them in gravel, and are distributed in the bottoms shallower than 30m. In the sand botom we failed to find any species during this investigation. On the other hand, Phaenopsectra sp. B is very widely distributed from the lake-side to a depth of about 60m. According to our count, the number of investigations for sampling by a bottom sampler are 2.3 to 3.8 times for Chironomus plumosus and are 46.2 to 66.3 times for Phaenopsectra sp. C, in 50% confidence limits respectively. If we request more correct answer, a large number of investigation are necessary. We presumed that the values of individual numbers and the standing crops in whole Shiozu Bay is as shown in Table 7. Chironomus plumosus was dissected for the examination of food habit. In the five examples, some algae were recoginized in the alimentary canal.