and warm current are located and where the trans- 

 parency of the water is high which enables G. ainan- 

 sii to grow. In the Izu Islands, plants do not appear 

 in large amounts in the region directly washed by 

 the warm current, but grow in good amounts in the 

 waters with an upweiling of bottom water. They al- 

 so do not grow in muddy water, or on rocks covered 

 with fouling organisms, but grow well on rocks on 

 sandy bottom. 



G. (iiminsii reach 10 cm high in 1 yrand 20 cm in 2 

 yr. The span of the lifetime of a plant seems to be 2 

 yr. but a holdfast remains several years and pro- 

 duces new plants. The crop largely depends upon the 

 plants that developed from these holdfasts. 



The plants are able to grow in densities up to 1 

 kg/m- at Izu Peninsula, the most favorable bed. At 

 harvesting, plants up to 0.2 kg/m^ are usually left to 

 grow because these plants grow back to 1 kg/m- 

 within 2 mo after harvesting. Harvesting is done 

 three times in a season, the yield per square meter is 

 well over 2 kg. 



Sometimes in vast areas most algae except 

 Surgassum disappear and calcareous algae take 

 over. The cause of this phenomenon, "Isoyake" in 

 Japanese, is still obscure. All trials, such as adding 

 stones and transferring plants, to bring about recov- 

 ery of the vegetation have been unsuccessful. 



Harvest 



Harvest is done under the control of a 

 Fishermen's Cooperative Association that manages 

 the ground. A rest period is required during the 

 harvesting season to save labor and increase yield in 

 the fruitful years. Plants remaining at the end of the 

 fishing season do not thrive the next year. There- 

 fore, the plants should be cropped as many times as 

 possible. 



Culture Techniques 



Gcliiliiini is a perennial with a slow rate of growth. 

 The most reliable technique for propagation is to 

 produce more places in favorable areas by throwing 

 stones into the sea. The elimination of harmful 

 weeds, such as Eckloiiki and Eisenia that grou in 

 Gi'liJinni beds, is effective for 1 or 2 yr. 



Cultivation is not an efficient way for increasing 

 production because the spores take 2 yr to grow and 

 reach harvesting size. Branchesof plants attached to 

 a rope, which is hung into the sea. grow well. How- 

 ever, the costs of plants for seed are high, and the 



cost of the large labor force, which is needed for 

 setting seed plants on the rope, leaves little for profit. 



In order to expand the growing area, stones should 

 be placed on the sandy bottom in and around the 

 growing areas. Stones weighing 20-100 kg are used 

 since they are not moved by wave action and do not 

 embed into the sand. Soon after calcareous algae 

 such as Lithotluimnion appear on the stones and 

 spores of Gelidium grow on them. 



It does not make much difference if the stones are 

 set at the best time so far as production is concerned, 

 but does make a big difference whether it is a suitable 

 place or not. Production on new substrate provided 

 along the Izu Peninsula is almost the same as that of 

 natural populations, i.e., 1-2 kg/m-. The expendi- 

 tures for setting stones is recovered in 4 yr. In re- 

 gions where production is less than 0.3-0.4 kg/m^ it 

 is not recommended that stones be added because 

 the costs cannot be recovered. 



Introduction of a gradually dissolving lump of fer- 

 tilizer into the bed is said to be effective in restoring 

 both color and growth during the summer. It has not 

 been clear whether it is profitable or not. 



CONCLUSION AND PROBLEMS 



There are two different ways to increase seaweed 

 production: 1) to increase harvest from its natural 

 ground and 2) to cultivate in or near the surface 

 being completely independent from its rocky natural 

 ground. 



Problems in Propagation Protection 



Many attempts to increase natural crops by in- 

 creasing the size of the seaweed bed by setting 

 stones or concrete blocks on sandy bottoms around 

 the seaweed ground have proved to be quite effec- 

 tive. Annual growth on these stones was the same as 

 the ones grown nearby on natural substrate. 



Expenditures for setting stones is recovered 

 within 4-5 yr with Gelidiiim and in 5-8 yr with 

 Liiniinaria on the most favorable grounds. Regions 

 of low production cannot be recommended for set- 

 ting stones in the sea. Fov IriJaea andClionclnis. the 

 period of cost recovery would be 20 yr: therefore, 

 this attempt for habitat improvement is not a profita- 

 ble one. 



In Porphyra. a concrete cover on rugged rocks 

 increased their harvest. This investment is recov- 

 ered in 3-4 yr on profitable beds. 



15 



