Excreta of the grazer Daphnia magna increase the frequency of coenobia in the green alga Scenedesmus obliquus of various physiological ages

Exponentially growing (2 days), early stationary (7 days) and late stationary phase (14 and 22 days old) Scenedesmus obliquus were exposed in a standard biotest to filtered water from a Daphnia culture. Although growth rates were gradually decreasing with age of the test algae, in the biotest when exposed to the 'Daphnia incubation water' all algae formed colonies, whereas the controls remained unicellular. No difference was detected between algae that had been previously exposed to Daphnia incubation water and control algae that had not. As long as the algae are capable of growth and division, regardless their physiological state and history, exposure to Daphnia excretory products will result in the formation of colonies.