Boutique-Type Cultivation of Kappaphycus alvarezii (Doty) L.M. Liao in the Subtropical Waters of Tosa Bay, Shikoku, Japan

The red seaweed, Kappaphycus alvarezii, has been introduced to several countries (e.g., Brazil and Tunisia) outside of its origin in the Philippines, mainly for the extraction of the polysaccharide carrageenan. Unlike other countries, Japan started to cultivate the seaweed in 1991 in the subtropical waters of Tosa Bay, in Kochi Prefecture, to produce fresh seaweed to meet the demand from specialized gourmet restaurants offering seaweeds on their menus for phycogastronomy. Harvested biomass is also being used as a source of biostimulant for agricultural/horticultural applications. Initial research on K. alvarezii in Japan also discovered the seaweed as a source of lectin. Although relatively small in terms of production scale compared to other countries where K. alvarezii has been introduced, the innovation made on the culture of K. alvarezii developed by the local seaweed farmers in Tosa Bay involving over-wintering process in a land-based facility was able to sustain a niche market for this seaweed in Japan. The innovative method consists of placing small, palm-size fragments of the cultivars in plastic containers inside nursery tanks maintained at 23°C under natural light. This practically allowed the survival of the seaweed in Japan during cold winter months until the next growing season in the field. Given the name “nettai kirinsai”, or “tropical kirinsai”, to differentiate it from other kirinsai species in Japan, K. alvarezii is now cultivated in Uranouchi Inlet in Tosa Bay, from late spring in May, when surface seawater temperature (SST) begin to rise to 23 °C, doubling growth upon reaching 28–29°C in August. However, it suffers from ice-ice disease when the SST reaches an extreme of 32°C in the peak of summer and when the SST falls down again to below 23°C towards winter. The seaweed is planted by suspending the cultivars on horizontal lines which sink slightly (0.5–1.0 m) below the surface from a floating platform in which fish is co-cultured in net cages. The cultured seaweed not only supplies the gourmet market and the agricultural/horticultural sectors, but it also serves to bioremediate nitrogenous wastes released from fish culture in Tosa Bay.