Abstract
The authors previously reported the usefulness of deep seawater (DSW, known as clean, cold and nutrient-rich seawater pipelined from a depth of 397 m in Suruga Bay, central Pacific coast of Japan) in seed production of brown algae Eisenia arborea and Ecklonia cava and the effects of light intensity and water temperature on their juvenile growth. In the present study, juvenile sporophytes of the two species were cultured at four flow rates (0.5-9.4cm sec-1) of DSW and surface seawater (SSW, pipelined from a depth of 24m) in a transparent pipe to determine the best flow rate condition. The culture was conducted under the natural light condition at a water temperature of 14°C for 24 days in E. arborea and at 18°C for 16 days in E. cava. As a result, no significant difference was found in the relative growth rates (in blade length) of the two species in the examined range of flow rate (but data was not obtained at 9.4cm sec-1 in E. arborea) when cultured in DSW. However growth rates of E. arborea and E. cava increased with the flow rate in SSW [E. arborea: y = 0.40Ln (x) + 4.47 (r2 = 0.99); E. cava: y = 0.84Ln (x) + 7.99 (r2 = 0.99)], attaining each maximum, 5.4% day-1 and 9.7% day-1, respectively. These results indicate that juvenile sporophytes of E. arborea and E. cava can grow in DSW faster than in SSW regardless of the flow rate. Use of DSW may result in the decrease of unevenness of juvenile growth in the culture tank.
