MARICULTURE OF SEAWEEDS AND ITS PROBLEMS IN JAPAN 



SHUNZO SUTO' 



D>4TRODUCTION 



The change in annual production of seaweeds in 

 Japan is shown by species in Tatile 1, where the 

 production from cultivation and harvest of wild 

 populations are mentioned separately. 



Japanese and people in East Asia consume most of 

 the seaweed harvested for human food, and its use in 

 industrial materials is comparatively less. The situa- 

 tion differs clearly from that in the other areas of the 

 world. Japanese taste for "norV (Undaria. 

 Lam'maria. Monostroma, etc.) is quite developed, 

 and the shortage of its supply and resulting rise of its 

 price have encouraged efforts to increase its produc- 

 tion from the natural beds and also the development 

 of its cultivation on the surface of the sea. 



Of course, the progress of cultivation depends on 

 social economic factors and the techniques to make 

 it profitable. Nori cultivation, it is said, started about 

 300 yr ago and harvested quantities are increasing 

 every year. The cultivation of [//z^/ana (a member of 

 Laminariaceae) has recently grown to an industry and 

 the one for Laininaria has just begun. Monostroma 

 has been cultivated for 30 yr, and in the past 10 yr, 

 the amount of its harvest has kept a constant level, 

 satisfying the consumers" demands. 



The amounts of Laminaria, Undaria, Gelidium, 

 etc. harvested from their natural beds have not in- 

 creased much from year to year. Little increase in 

 Undaria production seems to come from overhar- 

 vesting. Many efforts have been made to increase its 

 production, but so far none has proved to be effec- 

 tive on the whole: though in some local grounds 

 successful attempts have been reported — by setting 

 stones to enlarge seaweed bed substrate, by blowing 

 up shallow beds with dynamite to lower their level. 



' Mariculture Division. Tokai Regional Fisheries Research 

 Laboratory. .-Vrasaki. Nagai. ^okosuka. Kanagawa-ken, Japan. 



or by removing useless weeds which will otherwise 

 occupy the substrate of the species being cultivated. 

 Another problem is found in the natural produc- 

 tion. Sometimes, a local decay of seaweeds, often 

 lasting more than several years, causes not only the 

 decrease in the algal production, but also the de- 

 crease in the abalone catch, which feed on seaweeds, 

 and also affect the catch of coastal fish, owing to the 

 lack of production of juvenile fishes that grow 

 around the seaweed beds. The reasons why the 

 decay of seaweeds occur and why seaweeds cannot 

 recover soon are being studied at the present. 



NORI (PORPHYRA) 

 Cultivation of Nori 

 Historical Reviews 



The cultivation of nori started about 300 yr ago 

 around the coast of Tokyo Bay and developed 

 gradually in many localities on the bays facing the 

 Pacific coast of Japan, where this culture can find 

 protection from strong surf and an adequate tidal 

 range necessary for growth. 



Nori grounds were limited in those days to the 

 shallow waters around the mouth of rivers, on the 

 basin of which cities and rice farms developed, sup- 

 plying rich nutrients to nori grounds. 



Bundles of twigs of trees such as oaks, cherry, etc. 

 were set in rows on the ground in the fall as the 

 collectors, to which nori spores attach themselves 

 and grow. In the winter, grown nori plants are har- 

 vested, made into dried products similar to sheets of 

 paper, and are sold to consumers, mostly city 

 dwellers. 



The cultivators were mainly farmers in the coastal 

 regions. Gradually product dealers controlled and 

 exploited the cultivators, whose income was very 

 low, which in turn held back the industry from rapid 

 progress. 



