Phenology of Myagropsis myagroides, Brown Alge, in Tsuyazaki, Northern Kyushu, Japan

Abstract

Phenology of Myagropsis myagroides was studied in Tsuyazaki, northern Kyushu, Japan from January 1988 to January 1989. A plant of this species consists of holdfast, stem, and main branches. From the morphological characters, each main branch can be distinguished into three growth types: main short branch having leaves or no leaves (young branch), main branch having leaves and vesicles (buoyant branch), and main branch having leaves, vesicles, and receptacles (reproductive branch) . Distinct seasonal changes were found in the plant length and wet weight of plant, and their maximum length and wet weight were attained 400 cm and 1318 g during the period of egg release. The length and wet weight of holdfast with stem were very small compared with the plant length and wet weight of plant. These results clearly indicate that the seasonal changes in their plants were caused by the seasonal variation in main branches. The seasonal variations in buoyant and reproductive branches show that main branches form vesicles from summer to autumn and receptacles in winter, release eggs through winter and spring, and wither away in the following summer. The seasonal variation in young branch suggests that many main branches bud on the stem in summer.