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In the coastal waters of Kochi, Ecklonia cava formed dense beds until the 1980’s. However, these beds have declined rapidly since the 1990’s. The reasons for the decline of E. cava are the rise in seawater temperature along with grazing by sea urchins and marine herbivorous fish. Many researchers have conducted marine afforestation of E. cava beds. There are three main afforestation methods. The first is transplantation using adult plants or young plants cultured from fertilized eggs in indoor tanks. The second is to use a spore bag. The last method is to use a net cage for protection from grazing by herbivorous fish. Marine afforestation of E. cava using the spore bag method was tried at an Isoyake (barren ground) area in autumn. Many young sporophytes appeared around the spore bags in the following spring. However, several years later these plants completely disappeared due to grazing by marine herbivorous fish and sea urchins. In another afforestation attempt using a net cage, most of the E. cava were destroyed by high temperatures during summer, even though they were protected from fish. Although some afforestation attempts failed, others succeeded. Namely that is the afforestation using artificial reefs with seedlings. This results in constant growth and reproduction of E. cava. E. cava beds, which though small are similar to natural beds, have been formed around the artificial reefs now. This area maintains low seawater temperature and the grazing pressure from sea urchins and marine herbivorous fish is also low. Thus, it is important to select a suitable site for marine afforestation of Eclonia cava beds.