The Effect of Temperature and Density on the Amplitude of Vertical Migration of Daphnia Magna

Abstract

The effects of thermal stratification (temperature and density changes) on the amplitude of vertical migration of Daphnia magna were studied under controlled conditions in acrylic tubes. Vertical migration was inhibited in thermally stratified columns. Changes in water density alone did not affect vertical movement. Abolition of the descending blue dance could not explain the results because of the use of a light source with a spectrum shifted to the red region. The magnitude of vertical migration may be reduced by an avoidance reaction to large but commonly observed differences in temperature encountered in temperate lakes during summer stratification