Development of Regeneration Technology for a Seaweed Bed

Reduction of seaweed beds in coastal areas, called isoyake in Japanese, is a serious problem in Japan, which results in the disappearance of habitats for many fishes and the decline of coastal fisheries. Many factors may contribute to the reduction of seaweed beds, including seawater temperature rising, grazing by herbivores, deficiencies of nutrients (nitrogen, phosphorus) and iron, among others. We examined fertilization by selected some nutrients and minerals, with a particular focus on iron, and developed a fertilizer, VivaryTM Unit. VivaryTM Unit is a 1:1 (v:v) mixture of the steelmaking slag and humus soil. Steelmaking slag, which is a by-product of the steelmaking process, is a source of iron, and artificial humus soil contains chelators such as humic acid. To establish a regeneration technology for seaweed beds, we verified the role of iron in seaweed growth and the bioavailability of VivaryTM Unit with several experiments in various scales. In vitro culture was used to demonstrate the synthesis of chlorophyll a in Pyropia yezoensis thalli and the requirement of iron in gametophyte maturation in Saccharina japonica var. religiosa. The effects of VivaryTM Unit were demonstrated through two experiments. (1) a cultivation test of P. yezoensis in a mesocosm facility, (2) a field test in Hokkaido, Japan. In the cultivation of P. yezoensis the elution of nitrogen, phosphorus, silica and iron from VivaryTM Unit were revealed, and P. yezoensis grew only in the mesocosm with VivaryTM Unit. In the field test in Hokkaido, seaweed beds, especially S. japonica var. religiosa, were restored following fertilization via a buried VivaryTM Unit. We indicated the effect of dissolved iron supplied by the buried VivaryTM Unit by examining the correlation between EC (electrical conductivity) and dissolved iron compared with the correlation between EC and dissolved silica.

Keywords: Chlorosis, Converter slag, Fertilizer, Humus soil, iron, isoyake, Mesocosm, Pyropia yezoensis, Reduction of seaweed beds, Saccharinales, Saccharina japonica var. religiosa, Seaweed bed restorations, Steelmaking slag, VivaryTM Unit.