Assessing chemical compounds for controlling predator ciliates in outdoor mass cultures of the green algae Dunaliella salina

Effects of different chemical compounds on ciliates grazing outdoor mass cu ltures of Dunaliella salina were studied. These taxonomically undetermined ciliates were capable of clarifying dense algal cultures within 2 days and tolerated a wide salinity range (up to 215 ppt). Treatments of micro-algal cultures with either formaldehyde, ammonia, hydrogen peroxide or metronidaz ole were inappropriate since lethal doses for the ciliate: also eliminated algal cells, However, the use of quinine sulphate rapidly destroyed ciliate s while keeping algal cells alive. A 24-h LC100 at 12-14 mg 1(-1) quinine s ulphate was found for the ciliate, whereas a 72-h EC50%, at 14.5 +/- 0.6 mg 1(-1) was found Tor Dunaliella. The application of a dose of 10 mg 1(-1) q uinine to contaminated outdoor algal mass cultures completely eliminated ci liates within a short time, and allowed the algal population to start recov ering. (C) 2001 Elsevier Science B.V. All rights reserved.