1Department of Animal and Marine Bioresource Science, Graduate School, Kyushu University, Fukuoka, Fukuoka 812-8581,2Department of Animal and Marine Bioresource Science, Faculty of Agriculture, Kyushu University, Fukuoka, Fukuoka 812-8581, Japan
Seasonal changes in the vegetative morphology and reproductive state of Sargassum fusiforme (Harvey) Setchell were investigated over a 10-month period at Shikanoshima on the northern coast of Kyushu, Japan. The population was sampled at nearly monthly intervals, and the main branches from individual plants were weighed and divided into 5 dry-weight classes. The frequency of larger size classes increased from May to June, then decreased rapidly in August. Maximum plant dry weights were measured in June, minimum dry weights in September. Growth of new branches commenced in July and the frequency of branches within the smallest size class was highest in September. Reproductive activity was restricted to the period from June to August. Receptacles were present on all plants in July and August, when most of the larger branches and parts of the smaller branches were fertile. The proportions of male and female plants were approximately equal.