2018 Volume 11 Issue 1+2 Pages 1-10
For last three decades, the distribution of temperate Sargassum species has declined, and that of tropical Sargassum species has increased along the coast of Kochi Prefecture, southwestern Japan. However, little is known about the ecological and physiological characteristics of tropical Sargassum species in Kochi Prefecture. In the current study we performed culture experiments to understand how the growth of a tropical Sargassum species, S. ilicifolium, is affected by seawater temperature. We also conducted a 31-month field study to understand the seasonality of this species. The culture experiments showed that the relative growth rates of S. ilicifolium thalli sharply increased from 11 ℃ to 12 ℃ and gradually increased from 12 ℃ to 15 ℃. From 14℃ to 30 ℃, the relative growth rates of the tropical S. ilicifolium were higher than those of temperate species. The relative growth rates of the germlings were optimal between 25℃ and 30℃, while the germlings at 10℃ had almost no growth. The results of the field study indicated that S. ilicifolium formed macroalgal beds steadily every year. We proved that this species has the ability to grow, even during winter along the coast of Kochi Prefecture.