The green alga, Scenedesmus acutus, grows in culture in unicellular form, but it forms colonies (coenobia) when exposed for 48 h to a chemical released by the grazer Daphnia magna. The colony-forming response can be evoked only in growing cells. The Daphnia factor affects colony size but not algal growth rate. The minimum concentration of Daphnia factor that induces colony formation is equivale...

Lake restoration practices based on reducing fish predation and promoting the dominance of large-bodied Daphnia grazers (i.e., biomanipulation) have been the focus of much debate due to inconsistent success in suppressing harmful cyanobacterial blooms. While most studies have explored effects of large-bodied Daphnia on cyanobacterial growth at the community level and/or on few dominant species,...