Experiments in Removing Red Tide Alga Phaeoecystis globosa from Zhanjiang by Algicides

Abstract:

Algicides, bromogeramine（B）and isothiazolone（I），were used for removing Phaeoecystis globosa in the experiments in containers of 450 ml seawater with 109 cells L^-1 of algae collected in April 2005 from Zhanjiang Seaport, Guangdong Province, where red tide had happened in January 2004. The results showed that LC50 of isothiazolone was 0.54 mg L^-1 for the algae treated for 72 hours, which was more effective than that of bromogeramine （LC₅₀=0.96 mg L^-1）. Alga-removal effects of both algicides used in combination showed synergistic action. The proportion ofbromogeramine to isothiazolone being 4.3 to 1 gave best result. Toxicity tests on little fishes （Mugil cephdus） showed that 2.0 mg L^-1 bromogeramine or 0.3 mg L^-1 isothiazolone were safe for fishes in the removal of algae in 72 hours.