Laminaria Cultivation

Laminaria japonica Areschoug (commonly called 'kelp') is the most widely cultivated species that is primarily cul tivated in China, Korea, and Japan. According to the FAO, 4 074 415 mt (wet weight) of Laminaria were har vested globally in 2004, mainly through cultivation. China is the largest producer of Laminaria, contributing over 4.0 billion kg wet weight. L. japonica grows well on reefs or stones in the subtidal zone, at a depth of 2-15 m (sometimes up to 30 m). They prefer sheltered and calm seas, rather than open waters. The thalli of the edible kelp L. japonica are large, up to 2-5 m in length, but sometimes may grow up to 10 m. The life cycle of Laminaria is well understood. It consists of an alternation of generations between a microscopic gametophytic phase and a very large macroscopic sporophytic phase. In the field, the frond (the sporophytic phase) usually matures during spring and late autumn. The sporophyte releases the zoospores that settle down on a substratum. They immediately germinate and grow into microscopic male and female gametophytes in equal ratios. Upon reaching maturity, the filamentous male gametophyte releases motile biflagellate sperm (from an antheridium) that fertilize a large nonmotile egg that is extruded from the oogonium. Within 15-20 days, young sporophytes develop, thus completing the life cycle. In nature,

L. japonica is a biennial, and the frond reaches a harvest able size in about 20 months after germination. The cultivation period can be reduced to as little as 8-10 months through a technique called 'forced cultivation'. As with Undaria (another species of kelp), the cultivation of Laminaria consists of four phases: (1) collection and settlement ofzoospores on seed strings; (2) production of seedlings; (3) transplantations and outgrowing of seed lings; and (4) harvesting (Figure 6).

Traditionally, the collection ofzoospores is carried out in spring or in some cases in early autumn when fertile thalli are available and the water temperature increases or decreases to about 15 °C, depending upon the season. The Chinese technique of intermediate nursery culture is employed to bring the plants to a size of 5-10 cm before transplanting to the nursery grounds (Figure 6f). The seed string (after 30-60 days) may then be transferred to the sea and fixed to rafts consisting of a series of bamboo segments anchored to the bottom by ropes or long lines (50 m). Another major enhancement in the cultivation of L. japonica has been the raising of sporelings via the mass culture of gametophyte clones. Female and male gameto phyte clones are mass cultured individually, followed by the induction of gametogenesis for each phase. With reared clones, mass quantities of sporelings (with desired traits) can be successfully produced, thereby reducing the need for long term cultivation in temperature controlled greenhouses or environmentally controlled rooms. The sporelings are transplanted to the seed string and then inserted within the braided long lines that are usually 50-100 m long (Figure 6a). Raft supported long line sys tems are of two types, namely the single line (bamboo or rubber tube) and the double line raft system (Figures 6a and 6b). Thirty or more sporelings (attached to the polye ster seed string) are transplanted to a 2 m (or shorter) piece of rope. One end of the growing rope (containing the seed string with sporelings) is attached at regular intervals (50 cm) to the main support rope of a raft or long line system so that the culture rope hangs vertically (the stan dard Japanese drop line system; Figure 6b).

Aside from light and water temperature, nutrients (especially NO3 -N) were found to be a limiting factor in the culture of Laminaria. Traditional culture was often limited to waters that were highly fertile, such as those found in bays. As culture systems were moved away from near shore bays to offshore sites, the introduction of commercial fertilizers (using porous fertilizer cylinders that release nutrients gradually) has significantly extended the kelp growing area to these deeper oceanic waters. Harvesting of L. japonica takes place during late April to June depending on oceanographic conditions (Figures 6d and 6e). The blades are cut from the cultiva tion ropes and washed in seawater to remove diatoms, hydrozoans, and other attached organisms. Afterward, the blades are dried naturally in the sun for several days on

Figure 5 Aspects of Gracilaria, Eucheuma, and Kappaphycus cultivation on ropes. (a and b) Gracilaria attachment and insertion in rope culture. (c) Open water cultivation of Kappaphycus and Eucheuma on monofilament long lines. (d and e). Open water cultivation and harvesting of Kappaphycus. Courtesy of T. Chopin.

Figure 5 Aspects of Gracilaria, Eucheuma, and Kappaphycus cultivation on ropes. (a and b) Gracilaria attachment and insertion in rope culture. (c) Open water cultivation of Kappaphycus and Eucheuma on monofilament long lines. (d and e). Open water cultivation and harvesting of Kappaphycus. Courtesy of T. Chopin.

any available surface. When weather conditions are unfa vorable for natural drying, oil powered dryers may be used.

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