The grazing of Eisenia bicyclis and several species of Sargassaceous and Cystoseiraceous seaweeds by Siganus fuscescens in relation to the differences of species composition of their seaweed beds

Abstract

We investigated the annual grazing of tagged thalli of Eisenia bicyclis, Sargassum ringgoldianum subsp. coreanum and Myagropsis myagroides and random-selected thalli of several Sargassum species by Siganus fuscescens in a Sargassum bed including a mixed-stand of E. bicyclis and S. ringgoldianum subsp. coreanum and in amono-specific bed of E. bicyclis. E. bicyclis in the mixed-stand was only slightly grazed, whereas S. ringgoldianum subsp. coreanum was so heavily grazed that almost all of its branches and blades were lost in December. In contrast, E. bicyclis in its mono-specific bed had fish bite scars on its blades in July and about twenty percent of the tagged thalli lost almost all of the blades in November. M. myagroides had fish bite scars on its thalli in August and lost most of its thalli in November. In contrast, S. siliquastrum was only slightly grazed and showed noticeable growth of its thalli in November. Thus, the grazing greatly changed according to the feeding preference of large brown macroalgae and the differences of species composition of their seaweed beds.