A field test of porous carbonated blocks used as artificial reef in seaweed beds of <Emphasis Type="Italic">Ecklonia cava</Emphasis>

Marine forests are the main primary producer in coastal waters, supplying food to fish and shellfish as well as providing their spawning and growing sites. It is important to conserve marine forest in order to protect coastal marine environments. A “Marine Block” comprised of steelmaking slag particles combined by CaCO₃ has several merits: (1) solidification of CO₂, (2) stability and safety, (3) porous materials covered with CaCO₃, (4) harmony with the seabed environment, (5) recycling of iron by-products, and (6) the ability to be mass produced in coastal ironworks. The objectives of this study were to observe the algal succession, the growth of Ecklonia cava and other attached organisms on Marine Blocks and concrete blocks compared to natural seaweed beds. In November 2001, five 1 m³ Marine Blocks and five 1 m³ concrete blocks were installed close to E. cava beds around the coastal frontage of Jogashima at the mouth of Tokyo Bay. Scuba-diving observations were continued until April 2006. In the field, a large number of seaweed and animal species were observed on the Marine Blocks, and it was found that the speed of succession, the plant length and the wet weight of E. cava were greater on Marine Blocks than on concrete blocks. The main advantages of Marine Blocks are considered to be the recycling of steelmaking slag, the absorption and solidification of atmospheric CO₂, and the conservation of coastal environments.