Abstract
Seaweed forests of Eisenia bicyclis Setchell and Ecklonia cava Kjellman are broadly distributed along the rocky coastal area of central Honshu Island, Japan, facing the Pacific Ocean. We aimed to clarify a zonation of these plants and their causes. We measured irradiance at each depth of their habitat in a field and their photosynthetic rates in a laboratory. Seasonal changes of photosynthetic rates were higher in summer to fall and lower in winter. Initial slopes in Photosynthesis-Irradiance (P-I) curve of Ec. cava were higher than those of Ei. bicyclis at shallower depth. Daily compensation light quantity of Ei. bicyclis was higher than that of Ec. cava. This study showed quantitative facts that they were adapted to each photo-environment.
