Colony formation in planktonic algae induced by zooplankton culture media filtrate

Grazer induced colony formation was examined using the cyanobacterium Microcystis aeruginosa Kutzing and the green alga Scenedesmus dimorphus (Turpin) Kutzing. Algae were cultured in a medium with or without filtered water taken from cultures of Daphnia magna Straus or Moina macrocopa Straus. Exposure to the zooplankton culture media filtrate (ZCMF) promoted colony formation in both S. dimorphus and M aeruginosa, with the magnitude of this response being directly proportional to the relative volume of ZCMF that was added to the culture medium. However, the degree of colony formation of M aeruginosa was weakly influenced by ZCMF by comparison to that for S. dimorphus. The mean number of cells per colony and mean particle biovolume of the two algal species increased significantly from 8 hr to 72 hr for the D. magna-CMF treatment and the M macrocopa-CMF treatment (p < 0.001), most likely due to the influence of chemicals released from D. magna or M macrocopa. Such info-chemicals could act as signals on trigger to induce colony development.