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Kim Farming

Seaweed was first consumed in Japan at least 1500 years ago, according to early written records. During the Asuka Era (600-700 AD) and Nara Era (700-800 AD) seaweed was only consumed by the Japanese aristocracy. Until the Middle Ages there was only wild seaweed, which limited it as a food source. During the Tokugawa Era (1600-1800 AD), Ieyasu Tokugawa, the Shogun of the time, ordered fishermen in the small town of Shinagawa (now part of the Tokyo metropolitan area) to bring him fresh fish everyday. The fishermen built an offshore fence and started a fish farm. They also found that seaweed preferred growing on this fence. Thus was seaweed cultivation born.

Seaweed cultivation takes many forms but there is a kind of evolutionary process through which it develops, the rate of which is market-driven. If demand is low and natural resources adequate, cultivation is unnecessary. As demand increases, natural populations frequently become inadequate and attempts are made to increase production by resource management techniques such as improving harvesting techniques, removing competing species, adding artificial habitats and seeding cleared areas. Such techniques are most highly developed in Japan, China and south-east Asia.

Should such management prove to be inadequate, the use of artificial structures to grow seaweeds becomes inevitable. Fragments of adult plants, juvenile plants, sporelings or spores are seeded onto ropes or other substrata and the plants grown to maturity in the sea. To do this, intimate knowledge of both the biology and life history of the plants is critical. For example, kelps cannot be grown from fragments as there is a high level of specialization and fragments of sporophytes do not regenerate. On the other hand, many red algae do not have this degree of specialization and can easily be grown from portions of the adult plant. Knowledge of the life history is critical in many cases and on-land cultivation of particular life history phases is often necessary for seeding. A considerable amount of technology has gone into the development of reliable methods for the cultivation of seed-stocks and their improvement.

The penultimate development in seaweed cultivation is the growing of plants in artificial impoundments on land. This involves the use of either tanks or ponds into which seawater is pumped and the seaweeds are grown detached and at very high densities. This necessitates the careful study of the growth parameters of the seaweeds involved and the development of special strains, preferably with high growth rates, but more importantly, adapted to the artificial conditions. In some instances, the cultivation of seaweeds in association with animals has been attempted, which is often referred to as "polyculture".

The ultimate development of seaweed cultivation will probably be the growth of genetically-improved strains in fermenter-like reactors, in which all environmental factors will be computer-controlled and artificially-compounded seawater-like growth media used. It is likely that such strains will be developed by means of biotechnological techniques.

Production systems

Due to its complex life cycle, the farming system for Porphyra can be divided into 5 distinct phases: conchocelis culture; collection of conchospores; ongrowing in open sea; harvesting; and processing. Seed supply Rearing conchocelis As described earlier in this fact sheet, the farming of nori occurs in two stages. The first occurs indoors, from May to October, where the conchocelis stage is cultivated and conchospores produced. The second stage occurs from October until April or May; in this phase farmers focus on the cultivation of the thalli in the field In early and mid-May, Asiatic hard clam (Meretrix meretrix) are seeded by desiccating the conchocelis to release the conchospores; a suspension of them is then sprayed onto the substrate, or the substrate is submerged in the suspension. Cultivation occurs in large elongated shallow tanks filled with 20-30 cm of seawater that has been subjected to sedimentation and to which nitrogenous and phosphate nutrients have been added. At this stage, the temperature is not controlled and is allowed to fluctuate with ambient air temperature. However, optimal growth occurs between 20-25 °C. The carpospores develop into the conchocelis phase. In mid-May to early June, the water temperature is raised to 22-23 °C, to encourage vegetative growth of the conchocelis phase. In July, the light intensity is reduced to encourage the formation of conchosporangia, which will eventually release the conchospores. From early July to late August, the water temperature is gradually raised to reach 27-28 °C by mid-August. After this, the water temperature is gradually decreased again. By late August to late September, the water temperature has been lowered to 23 °C; during this period of the conchosporangia form. The light intensity is held at the same level to encourage the formation of the conchospores in the conchosporangia but the day length is reduced to 8-10 hours. Conchospores are present by late September but mass discharge occurs in early and mid-October. Once the conchospores are released, they are seeded onto special cultivation nets which are placed in the tanks. When 50 000 spores are being released per day, the light intensity is increased slightly to encourage thallus germination. The water in the tanks is also agitated to distribute the spores evenly and ensure their contact with the cultivation nets. This procedure of collecting conchospores is called "collecting seeds". About 50 percent of laver farms rear the seeds by themselves, while the rest buy culture nets from seed suppliers. Ongrowing techniques There are three main farming methods: (a) on floating, (b) semi-floating; and (c) fixed nets. A fourth technique is known as "freezing nets" (see below). Three methods farming Porphyra spp. Floating system This method has been used in Japan and has recently been widely adopted by Chinese farmers. The nets are attached to buoys floating on the surface of the sea, so the nori thalli would be constantly soaked in water. With this method it is possible to cultivate the thalli even in areas outside shallow bays, in depths of 10-20 m. Semi-floating system This method is a mixture of the floating and fixed net systems. At high tide the nets float on the surface, in the ebb tides, the system stands on the land. This combines the advantages of fixed net and floating systems, so it has been widely adopted in China. Fixed nets In this system, also known as the "pole system", the nori nets are hung between poles. During ebb tides, the nets are exposed to air and become dry. Intertidal pole cultivation is often preferred over floating or semi-floating cultivation in deep water, because it ensures periodic exposure of the proper duration, which helps to reduce the incidence of disease and the growth of competitive (weed) species, especially epiphytic diatoms. However, this type of cultivation is restricted to the inner portions of bays, with shallow, sandy bottoms Freezing nets This method has two advantages: preventing diseased nori, and improving the quality of the final product. The procedure for processing freezing nets is as follows: When the young thalli reach 1 to 3 cm long, they are brought back from the culture area, together with the nets. The nets are dried in the air until the moisture content of the thalli decreases by 20-40 percent, which usually requires 2 to 3 hours. Dried nets are put into vinyl bags. Dried nets are stored in a freezer at -20 ºC. When required, the nets are taken brought back to the nori fields for rearing. Harvesting techniques After rearing in the open sea for 40 or 50 days in the case of Porphyra haitanensis and P. yezoensis respectively, the first harvesting phase begins. Harvesting activities can last for 5 months. The interval of harvesting is every 10-15 days; therefore, the crop is harvested 10-12 times annually. Two methods are used, namely manual and machine harvesting, as shown in the images gallery. Handling and processing The harvested thalli are cut into pieces and processed by drying into a traditional form - a thin, rectangular flake, each 21 x 19 cm in size and weighing about 3 g. The procedure consists of selecting the wet nori; washing in seawater; washing in freshwater; cutting; softening; making into flakes; dehydrating; drying; grading; and packing. Dried nori can be refined into seasoned products that can be directly consumed; these items have become as popular as sweets (candy). Production costs Production costs vary geographically; no information supplied.

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