Page 278 - Algae

Algae and Men 261

FIGURE 7.6 Frond of Laminaria japonica.

can grow up to 10 m in favorable conditions. It requires water temperatures below 208C. Laminaria
was originally native to Japan and the Republic of Korea, where it is cultivated since 1730. It was
introduced accidentally to China in 1927 probably by the importation of logs from Hokkaido in
Japan. Prior to that, China had imported its needs from the naturally growing resources in Japan
and the Republic of Korea. In the 1950s, China developed a method for cultivating Laminaria;
sporelings (“seedlings”) are grown in cooled water in greenhouses and later planted out in long
ropes suspended in the ocean. This activity became a widespread source of income for large
numbers of coastal families. By 1981, 1,200,000 wet tons of macroalgae were being produced
annually. In the late 1980s, production fell as some farmers switched to the more lucrative but
risky farming of shrimp. By the mid-1990s, production had started to rise again and the reported
annual harvest in 1999 was 4,500,000 wet tons. China is now self-sufficient in Laminaria and
has a strong export market. In the Republic of Korea, the demand for Laminaria is much lower
and most is now provided from cultivation. Kombu is the Japanese name for the dried macroalgae
that is derived from a mixture of Laminaria species. These include L. longissima, L. japonica,
L. angustata, L. coriacea and L. ochotensis. These are all harvested from natural sources, mainly
on the northern island of Hokkaido, with about 10% coming from the northern shores of
Honshu. The first three of the above are the main components of the harvest. The plants grow
on rocks and reefs in the sublittoral zone, from 2 to 15 m deep. They prefer calm water at tempera-
tures between 3 and 208C. The naturally growing plants are biennial and are ready for harvesting
after 20 months. Harvesting is from June to October, from boats. Hooks of various types are
attached to long poles and used to twist and break the macroalgae from the rocky bottom. As
demand grew in the 1960s, attempts were made to develop artificial cultivation methods, but the
2 yr cycle meant the costs were too high. In the 1970s, forced cultivation was introduced, reducing
the cultivation period to 1 yr, similar to the system developed in China in the early 1950s. Today,
about one third of Japan’s requirements come from cultivation, with the remaining two thirds still
coming from natural resources.