Restoration of seaweed bed was challenged at a block (10×10m) of Diadema barren on the northwestern coast of Izu Peninsula. Monthly removal of Diadema was started in April 2007 and followed by repeated enclosures using sand bag curtain, gill nets and plastic sheet or rolled gill nets. Seaweeds (but no Sargassum) grew on the barren boulders from winter to spring. When the nets were fouled, bended or broken, Diadema often invaded the enclosures. In the enclosure, Sargassum horneri juveniles (20cm high) fixed on mid-layer floats on December 2008, grew up to 6m in height and matured in February 2009. S. horneri recruited on the seafloor (boulders) in late May 2008, but were grazed by invaded D. setosum and gastropods. S. horneri juveniles transplanted in October 2008 were browsed by herbivorous fish in a month. However, S. horneri juveniles (covered with honeycombed PET) and S. pilutiferum juveniles transplanted in December 2008 could grow and mature. To supply more abundant juveniles, S. piluliferum was installed in the mid-layer net and suspended at a height of 1m from the sea bottom. As the result, the matured S. piluliferum could supply hundreds of germlings around the net.
