We examined characteristics of bite scars left on thalli collected from three Ecklonia cava communities that were denuded by heavy browsing of Siganus fuscescens for a short period. In addition, leaflost Eisenia bicyclis that occurred in a Eisenia and Sargassum-mixed seaweed bed were compared betweenabrupt occurrence of leaf-lost thalli and usual constant browsing by S. fuscescens. Most of thalli collected from the three Ecklonia cava communities that were heavily browsed were stub-like with bare medullary layers of stems which were forced to be exposed by heavy browsing. A lot of scratch-like fine lines and/or linear grooves, the jaw tooth marks of S. fuscescens, were found in the stems of heavily browsed thalli and the whole surface of the stems were often covered with a great number of those bite scars. Characteristics of bite scars left on thalli of Lessoniaceae are discussed in relation to heavy browsing by a large school of adult S. fuscescens.