Decline of afforested Ecklonia cava community by grazing of herbivorous fish Siganus fuscescens was studied on the coast of Hamaoka, Shizuoka Prefecture, Japan, during a period from May 1998 to November 1999. About 400 individuals of 3-years old E.cava were grazed their laminae during September to October 1999, and about 2,800 young individuals were grazed their laminae, only left their stipe from October to December. Because the fish bites basal parts of Ecklonia laminae, damage to the thallus is serious though the fish grazes small amount of plant body. Grazing by S. fuscescens was observed on and after June in 1998, while in 1999 grazing was seen on and after August. Rise of seawater temperature was earlier in 1998 than in 1999. This observation shows that grazing activity was affected by change of water temperature. Effect of grazing pressure by herbivorous fish on the growth of afforested E.cava community is clearly demonstrated from our observation.
