The outbreaks of ice–ice disease since 1999 at various seaweed culture in Indonesia were still very high with
significant losses. Moreover, very scanty of the research on the cause and control methods has been developed.
Meanwhile, Mangrove leaf extract (Sonneratiaalba) contained bacteriostatic that might potentially effective to
combat a such disease. This research was aimed to demonstrate the performance of mangrove leaf extract
to control bacteria causing ice–ice disease. Mangrove leaf (S. alba) was extracted by methanol. Nine bacterial
collection from the ice–ice were then in vitro-exposed to mangrove extract at concentration of 2500, 5000 and
10,000 mg/l respectively. Research results demonstrated that mangrove leaf extract at all concentrations tested
were able to prevent the growth of 9 bacterial strains associated with ice–ice disease. The diameter of clear zone
was between 7.47 and 16.17 mm after 24 hours incubation. Thus, it can be concluded that alkaloid, saponin,
tannin, triterpenoid/steroid, and flavonoid in the mangrove leaf at concentration as low as 2500 mg/l was able
to prevent the growth of 9 bacterial associated with ice–ice disease
