Abstract
In order to know the cause of the scarcity of flagellate red tide in the eutrophicated waters of Ariake Bay, acetone extracts were prepared from sediments for the analysis of chtorophyll in the sediments and for the bioassay of the growth inhibiting effects on Gyrodinium sp. For dissolvingthe acetone extracts in water, 40 ppm Tween 20 was used. The promotive and inhibitory effects were seen depending on the sampling points. The inhibitory effects were observed in offshore waters. When 2, 200 ppm DMSO which was confirmed to be safe was used, strong in-hibitory effects were revealed and the lowest lethal concentrations (LLC) ranged from 0.07 to 2.74 ppm, statistically 0.68±0.63 ppm. The causal substance was named as dinoflagellate growth inhibitor (DGI). If the potency of the acetone extract of 1 kg dried sediment inducing a certain quantity of liters of environmental water toxic to Gyrodinium sp. causing death is expressed as LLC equivalent, the contents of DGI in the sediments of Ariake Bay ranged from 333 to 14, 560, statistically 3, 867±3, 246 in LLC equivalent. Since chemical industrial wastes had been dis-charged for a long period in Ariake Bay, the waste components separated from the sediment in the vicinity of the outfall were subjected to the same bioassay. A certain fraction with the LLC of 0.4 ppm was found, but its yield was too small for the broad distribution of DGI in Ariake Bay. In Hakata Bay, where frequent diatom and occasional flagellate red tides occurred in summer and the inflow of the chemical industrial wastes were negligible, the distribution of DGI was also observed. The LLC of the acetone extracts ranged from 0.65 to 10.1 ppm, statistically 3.14±2.31 ppm. The contents of DGI in the sediments ranged from 231 to 1, 428, statistically 761±358 in LLC equivalent.
