Page 279 - Algae

262 Algae: Anatomy, Biochemistry, and Biotechnology

For cultivation, Laminaria must go through its life cycle, and this involves an alternation of
generations. Seedstock is produced from meiospores released from the sori of wild or cultivated
sporophytes, cleaned by wiping or brief immersion in bleach, and incubated in a cool, dark
place for up to 24 h. Released spore attach to a substratum within 24 h and develop into gameto-
phytes. Release of gametes, fertilization, and growth into sporophytes about 6 mm long require a
couple of months. In the original two-years method, seedstock was produced in late autumn,
when the sporophyte produce their sori, and was available for out-planting from December to
February, and the crop was ready to harvest in 20 months. In the forced-cultivation method, seed-
stock is produced in the summer, because sporophytes that spent 3 months in the autumn in the field
prior to their second growth season behaved as second-year plants. This method saves 1 yr.
Seedstock is reared on horizontal or vertical strings, placed in sheltered waters for about 10
days; after this period the strings are cut into small pieces that are inserted into the warp of the
culture rope. The ropes with the young sporophytes are attached to floating rafts, which belong
to two basic types. The first type is the vertical-line raft, consisting of a large diameter rope,
60 m long, kept floating by buoys fixed every 2–3 m. Each end of the rope is anchored to a
wooden peg driven into the sea bottom. The ropes with the young sporophytes attached hang
down from this rope at 50 cm intervals. The second type is the horizontal-line raft, consisting of
three ropes laid out parallel, 5 m apart. The ropes with the young sporophytes are tied across
two ropes so that they are more or less horizontal, and each of them has equal access to light.
In China, the largest region for Laminaria cultivation is in the Yellow Sea, which has been
found to be low in nitrogen fertilizer. Yields are increased when the floating raft areas, which
are usually set out in rectangles, are sprayed with a nitrate solution using a powerful pump
mounted in a boat. The plants take up the nitrate quickly and very little is lost in the sea. In
Japan, the cultivation is mainly in the waters between Honshu and Hokkaido islands and fertilizing
is not necessary. Harvesting takes place in the summer, from mid-June to early July.
The kelp is usually laid out in the Sun to dry and then packed into bales. In Japan, the whole
macroalgae is washed thoroughly with seawater, cut into 1 m lengths, folded and dried; the product
is suboshi kombu and is delivered to the local fisheries cooperative.
Laminaria species contain about 10% protein, 2% fat, and useful amounts of minerals and vita-
mins, though generally lower than those found in nori. For example, it has one tenth the amounts of
vitamins but three times the amount of iron compared with nori. Brown macroalgae also contain
iodine, which is lacking in nori and other red macroalgae. In China, haidai is regarded as
a health vegetable because of its mineral and vitamin content, especially in the north, where
green vegetables are scarce in winter. It is usually cooked in soups with other ingredients. In
Japan, it is used in everyday food, such as a seasoned and cooked kombu that is served with
herring or sliced salmon.
Another exploited kelp is Undaria sp., which together with Laminaria sp. is one of the two most
economically important edible algae. This alga has been a food item of high value and importance
in Japan since 700 A.D. Cultivation began in Japan at the beginning of this century, when the
demand exceeded the wild stock harvest, and was followed later in China. The Republic of
Korea began the cultivation around 1970 and today it is the largest producer of wakame/
quandai-cai from Undaria pinnatifida. This cultivation accounts for about 50% of the about
800,000 wet tons of edible macroalgae produced annually in this country. Some of this is exported
21
to Japan, where production is only about 80,000 wet tons yr . Undaria is less popular than Lami-
naria in China; by the mid-1990s China was harvesting about 100,000 wet tons yr 21 of Undaria
from cultivation, compared with 3 million wet tons yr 21 of Laminaria at that time.
U. pinnatifida is the main species cultivated; it grows on rocky shores and bays in the sublittoral
zone, down to about 7 m, in the temperate zones of Japan, the Republic of Korea, and China
(Figure 7.7). It grows best between 5 and 158C, and stops growing if the water temperature rises
above 258C. It has been spread, probably via ship ballast water, to France, New Zealand, and
Australia.