In some Japanese coastal areas, seaweed beds have recently declined and changed into barren ground, so-called Isoyake. It is known that Isoyake in pacific coastal areas depends on the rout of Kuroshio Current, which is high water temperature and low nutrient concentration. An approaching of Kuroshio Current leads to a decrease of seaweed growth rate and an increase of herbivore grazing rate. At Muroto coastal area in Shikoku Island, many of seaweed beds have declined since over fifteen years ago. Deep ocean water (DOW) is low water temperature and high nutrient concentration. Thus DOW may leads to an increase of seaweed growth rate and a decrease of herbivore grazing rate. It has been reported that the DOW discharge may restore seaweed bed from Isoyake condition at Muroto coastal area. In this study, numerical simulations using a seaweed bed ecosystem model, which was based on the data of field surveys and biological experiments, were performed to clarify the mechanism of the recovery of seaweed bed. The results of numerical simulations showed that the nutrient concentration and grazing pressure, which depend on the deep ocean water content, are the important factors for the seaweed bed recovery.
