Porphyra washarvested for food in China beginning in at least 533 A.D. and in Japan as early as 1000 A.D. A form of aquaculture developed where rocks were cleared of all competing organisms to encourage the growth of Porphyra. Another form of crude aquaculture developed in Japan where bundles of thin strips of bamboo (“hibi”) were placed in the shallow areas of bays in Porphyra habitatto collect “seeds.” Kathleen Drew discovered the conchocelis portion of the life history of Porphyra, and Japanese workers were the first to domesticate Porphyra following her discoveries. The Chinese soon followed, and they began massive, government-backed, commercial cultivation. Each year on Drew’s birthday, there is a festival in Japan in the primary Porphyra culture area that honors the “Mother of the Sea”.
Porphyra yezoensis (“nori”) mariculture is practiced by seeding nets with either conchospores or asexual spores (archeospores) in land-based facilities (e.g. greenhouses). Nets are then transferred for grow-out to coastal waters. Such nets typically consist of one line with three twisted components: polyethylene thread, for spore attachment; and two polypropylene threads, to increase strength. The nets are manufactured in a number of sizes depending on the style of mooring to be used, but the most common sizes are 1.7 m x 20 m and 1.7 m x 1.7 m nets with a 20 cm sq.mesh size.
Nori farms can be either intertidal or moored in deeper water. Typically, intertidal nori farms are fixed on poles or to a floating support system that allows drying of nets to occur during each tidal cycle; this reduces epiphytes. In a floating system, nets have to be periodically dried through other means that include drying the nets on poles, shore-based drying racks, or by turning the nets. Mature thalli are usually harvested with a mechanical harvester but hand-harvesting is still used in some Chinese farms. The wet material is processed onshore, and the final product usually consists of machine-dried sheets of chopped, pressed Porphyra.