Abstract
As an urgent means suppression of red tides, we examined an application of ultraviolet rays for emergent treatment of Heterosigma akashiwo (Raphidophyceae). H. akashiwo was pre-cultured using f-2 medium for one month. Ultraviolet rays were applied directly to the sterilized petri dish, in which 2 ml H. akashiwo culture was added to 30 ml of f-2 medium. Ultraviolet rays were applied for about 30s (seconds), 60s, 120s, 300s and 900s. Ultraviolet ray strength were changed by 80μW, 400μW, 700μW and 1,500μW. In the counting of H. akashiwo, the living cell was distinguished by motility. Compared to the irradiation strength of ultraviolet rays, the cell growth was restrained in a condition of 80μW for 900 seconds, but the effect of ultraviolet rays on the cell growth was not recognized below the irradiation in cases of less than 900 seconds. Compared to the irradiation time of ultraviolet rays, the cell growth was restrainedin the case of 120 seconds with a condition of 700μW, but the restraining effect of the irradiation time was not recognized in the condition of less than 700μW. In irradiation time of 300 seconds or above in the case of more than 400μW, the cells do not multiply after irradiation. As a result, the relation between irradiation strength (X) and time (y) can be expressed as y=-202Ln (x) +1380 Irradiation strength of ultraviolet rays might influence the restraining effect rather than irradiation time, and its effect began to appear incases of more than 400μW.
