Growth of Main Branches of Sargassum siliquastrum at Tsuyazaki, Japan

Abstract

In this study, the main branches of S. siliquastrum found at Tsuyazaki were divided into leaved, buoyant, and reproductive branches. Leaved branches had leaves, buoyant branches formed vesicles and leaves, and reproductive branches bore receptacles, vesicles, and leaves. The seasonal changes in the number and length of these main branches were investigated from February 1988 to February 1989. Leaved branches were short during the study period. From autumn to winter, the number of leaved branches increased and remained constant until spring. Subsequently, their number decreased rapidly in summer when many buoyant branches appeared. The buoyant branches elongated rapidly until autumn, and then their number and length were reduced in winter when reproductive branches appeared. The reproductive branches released eggs in spring and withered away in autumn. These results indicate that many main branches bud from autumn to winter and scarcely elongate for 5 to 10 months until vesicles are formed in summer, and that main branches elongate, release eggs, and finally wither, during about 1 year from the initial formation of vesicles.