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We studied the population dynamics of epriphytic chironomid larvae in the vegetated areas of Lakes Suwa and Kitaura. We quantitatively collected chironomid larvae from samples of the 4 species of angiosperms present in the lakes: the emergent plants phragmites australis (a reed) and Zizani latifolia; the floating plant Nymphoides peltata; and the submerged plant Potamogeton malaianus. Collections were made from all 4 plant zones in Lake Suwa from April 2000 to November 2000 and from the reed zone in Lake Kitaura from April 2000 to March 2001. In both lakes the most abundant chironomid Larvae on the reed stems from late May to September were Chironominae (especially, Dicrotendipes pelochloris and Glyptotendipes tokunagai). On the leaves of submerged and floating plants in Lake Suwa, Orthocladinae larvae (especially, Cricotopus trifasciatus) dominated during the sampling period. On the reed stems in Lake Suwa, mean larval density was 0.4 ind cm⁻² and biomass of epiphytic chironomids was 12.9μgcm⁻²; these values were 23% and 22%, respectively, of those in Lake Kitaura. The differences in chironomid abundance observed in the lakes seemed to be caused by differenes in food availability (i.e., abundance of algae attached to reed stem). The average of diversity index (1/λ,λ:Simpson's index) of chironomid larvae on each plant was 2.7-3.3 on reed and Z.latifolia. 1.8 on N. Peltata and 1.8 on P. malaianus from June to August. The differnces in diversity index may be correlated with the conditions of DO concentration during this period., Article, 信州大学山地水環境教育研究センター研究報告 2: 111-115(2004)

In outdoor experimental ponds, where overwintering individuals of zooplankton had been controlled with an insecticide, the following events were observed during winter and the following spring : (1) Daphnia survived through the winter as free-living individuals; (2) Daphnia ceased egg production in mid-winter, but restarted it in late winter or early spring; (3) the spring peak of the Daphnia population established by overwintering free-living individuals appeared nearly a month earlier than that by individuals hatched from resting eggs. Although resting eggs are often thought to play an important role in establishing spring populations of Daphnia, the experimental results suggest that overwintering free-living individuals can also contribute to it. The significance of the overwintering stages in Daphnia population dynamics is discussed., Article, 信州大学理学部紀要 35(1): 31-42(2000)

The pattern of diel vertical migration (DVM) of Daphnia galeata was analyzed in summer in Lake Kizaki (a small mesotrophic lake) with maximum depth of 29.5 m. Juveniles, small adults and medium-sized adults stayed the whole day at 4-8, 8 and 14 m depths, respectively, and did not perform DVM, while large adults showed DVM between 14 m and near the bottom layer (26-27.5 m). Smaller adults had larger clutch sizes relative to their body size and allocated more energy to reproduction than larger adults. They might have compensated for loss due to predation by producing abundant offspring in the epilimnion where the food level was higher. On the other hand, the larger adults performed DVM to reduce mortality due to predation at the cost of reduced reproductivity induced by environmental factors in the hypolimnion (low concentrations of food and oxygen). The study thus demonstrated that even a single population of Daphnia can show different DVM patterns depending on body size (life stage)., Article, 信州大学理学部紀要 32(2): 77-88(1998)