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Environmental Parameters and Estivation of Rhyacodrilus (Tubificidae, Oligochaeta) in Lake Suwa, Japan

Kaori Takada, Kenji Kato and Tokio Okino
Ecography
Vol. 15, No. 3 (Jul. - Sep., 1992), pp. 328-333
Published by: Wiley on behalf of Nordic Society Oikos
Stable URL: http://www.jstor.org/stable/3683165
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Environmental Parameters and Estivation of Rhyacodrilus (Tubificidae, Oligochaeta) in Lake Suwa, Japan
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Abstract

We confirmed that Rhyacodrilus spp. of Yasuda and Okino (1987) (Tubificidae, Oligochaeta) migrated entirely downward below 15 cm into the sediment from June to September in Lake Suwa, a shallow eutrophic lake in Japan. In October, Rhyacodrilus spp. began to return to the upper layer and immediately attained sexual maturity. They tended to show reduced body weight and respiratory activity during summer. The results indicate that an oligochaete of Rhyacodrilus spp. estivated in the deeper layer during summer. The estivation ostensibly occurred at 15°C and the species died off at 20°C, so it is evident that they must migrate from the surface to the deeper layer of sediment during summer in order to escape high temperature. Furthermore, physiological experiment suggested that this behavior is accelerated by low oxygen concentration with high temperature.

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