The change in annual production of seaweeds in Japan is shown by species in Table 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 situation differs clearly from that in the other areas of the world. Japanese taste for "nori" (Undaria, Laminaria, Monostroma, etc.) is quite developed, and the shortage of its supply and resulting rise of its price have encouraged efforts to increase its production 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 Undaria (a member of Laminariaceae) has recently grown to an industry and the one for Laminaria 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 increased much from year to year. Little increase in Undaria production seems to come from overharvesting. Many efforts have been made to increase its production, but so far none has proved to be effective on the whole; though in some local grounds successful attempts have been reported-by setting stones to enlarge seaweed bed substrate, by blowing tip shallow beds with dynamite to lower their level, or by removing useless weeds which will otherwise occupy the substrate of the species being cultivated.
Another problem is found in the natural production. Sometimes, a local decay of seaweeds, often lasting more than several years, causes not only the decrease in the algal production, but also the decrease 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.
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, supplying 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 harvested, 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.
The nori harvest increased only gradually, amounting to 1 billion sheets-a sheet is a paperlike product of nori, of about 20 x 20 cm in size and about 3 g in weight-just before World War II.
Advances in the culture techniques were also poor. Old collectors (twigs from trees of oak, cherry, etc.) were replaced by bamboo twigs, promising more harvest than the old ones. Modern net collectors were found more effective to increase the harvest, but they were adopted only in limited localities because of the higher cost than the old collectors.
It should be mentioned here, that the nori cultivation in Korea had a rapid growth 10 years prior to World War II by introducing new techniques which produced about the same amount of nori as in Japan.
After World War II, nori cultivation in Japan made rapid progress. The amount of the harvest doubled in 1945, became four times in 1955, and is now six times that of the prewar level.
Social economic reasons for this abrupt rise are:
2) Innovation of fisheries systems after the War. Nori cultivators organized themselves in cooperative unions, which shut out the capital control of dealers and established a cooperative selling system that raised the rate of net income from about 30% in the prewar times to an income of 60-70%.
Rise of the market price of nori and increase of the net income made the nori cultivation the most profitable fishery. This was followed also by the rapid expansion of the industry throughout Japan, making strong demands on the advances of culture techniques.
3) Expansion of the nori grounds. Increase of population, fertilization of rice fields, and the progress of industry made the coastal waters richer in nutrients, making cultivation possible to spread away from areas adjacent to river mouths where nori often suffers from declining salinity during rainy weather.
2) Improvement of collectors. Old collectors were replaced by a net made of palm fiber string and then of synthetic fiber string of 2-3 mm in diameter. The strings are netted in a mesh of about 20 cm, and the standard size of a net is 18.2 x 1.3 m2. The nets are set stretched horizontally into the sea and are tied to bamboo poles set in two rows on the shallow sea. The net collector has many advantages over the old ones in rearing nori. It is far easier to deal with, surf resistant and more productive. The replacement made possible a wider culture, spreading from the limited waters near the mouth of rivers to deeper waters of rougher wave action, as the waters became more nutritious.
The net collector made possible the cultivator's control on the growth of nori. Elevating the net a little from its standard level slows the growth of nori but controls the growth of weeds, such as Enteromorpha and diatoms which may overcome the nori and decrease the harvest. Lowering the net accelerates the nori growth, but the nori often becomes weak by disease; Enteromorpha and diatoms grow vigorously on the net, displacing the cultured nori, if the weather in winter is calm and not too cold. Nori cultivators can then control the net level height as well as the nori growth, protecting against diseases and injurious weeds.
3) Seed control. Soon after-the findings of K. M. Drew on the "Conchocelis phase" in the life history of Porphrya, its whole history was made clear in Japan, being followed by the artificial control of nori spores. In 1955-60, nori producers cultured a necessary amount of Conchocelis for themselves through the summer and produced nori spores to start its culture. The technique removed the shortage of natural spores which had limited the growth of the cultivation especially in the western Japan.
It should be mentioned that a change of species in nori occurred with the change of culture techniques. P.yezoensis became dominate in place of P. tenera, the former seems to adapt more readily to higher salinities and to easier cultivation of spores. The change increased the harvest but produced a lowgrade product with decreased odor and hardening when tasted.
General View of Actual Nori Cultivation
At present, nori is cultivated in most bays and inland seas along the Pacific coast of Japan. Nori grounds are about 60,000 hectares in area, producing about 5-6 billion sheets of nori a year worth 70-80 billion yen. Fishermen's cooperative unions obtain prefectural government sanction to set nori grounds and manage them. About 60,000 fishermen set their own collectors, harvest grown nori on them, and produce dried paperlike products. The products are sold through the cooperative unions to the dealers.
Coastal waters of 0-5 m in depth are available for nori grounds of classic net systems, setting the nets by spreading them between two rows of bamboo poles. By the actual development of the new floating net system, cultivators have been able to turn waters 20-m deep into profitable grounds.
Usually a net, in a cultivating set, has a spread of 18.2 m x 1.3 m. Now 5 million sets are prepared for all the grounds. About 10 million nets are used per year, i.e., in a set two nets are spread one after another during a harvesting season, from November to next March or April.
Every fisherman has equipment for harvesting nori plants and also for manufacturing them into paperlike products. Generally the cooperative unions prepare cold storage for preserving nets with young buds in living condition. These unions sometimes have equipment for culturing Conchocelis and also for manufacturing nori products.
Paperlike products are gathered by unions and sold to the dealers, who preserve the products and sell them to consumers. Each Japanese eats an average of 50-60 sheets of nori per year. Nori is rich in vitamins, and two sheets of nori can supply one daily dose of them.
Processing in Actual Nori Cultivation
Seed.-Present cultivation depends completely on the spores from cultured Conchocelis. The culture is done by each fisherman or by his cooperative union. The culture begins at the end of the last season. Many cleaned oyster shells are spread on the bottom of shallow tanks filled with seawater. Cut pieces of mature nori plants are put on the water, so that the carpospores released from the plant will attach themselves to the shells and develop to the Conchocelis phase on them. Shells with Conchocelis are hung down in other tanks 0.5-1.0 m in depth, where they are kept throughout the summer. The water in the tanks is changed if it becomes dirty. Light in the tanks is controlled so that Conchocelis grows well without getting ill. At the end of summer, the Conchocelis matures and produces many spores which develop into nori buds.
In the fall, when the seawater temperature goes down below 24oC, fishermen prepare the cultivation. Twenty to forty nets are set in a layer in the sea. Shells with fertile Conchocelis are put into many vinyl bags, and these are hung just under the nets in order to have the spore find the collector as they come out of the bag. Sometimes the net layer is put into a large polyethylene bag with Conchocelis and left floating on the surface of the sea. This method prevents the cultivator from wasting spores and can also be done in deeper waters. After several days, when the spores have fixed themselves to the nets, these nets are taken out from the bag and are tied to the poles for spore development.
Bringing tip of young buds.-A set of 20-40 layered nets is separated into sets of 5-6 layered nets, which are then separated into single nets, as the buds grow. In the process of separation, when the buds are 5-50 mm in length, the necessary amount of nets with buds are taken out of the water, dried and stored in refrigerators set at -20oC. Here the buds are kept alive, preparing for the recovery of crops when the planted nori suffers from a prevailing disease or a heavy storm. Fishermen always control the level of nets as the climate and the tide changes, so that the buds do not suffer from severe drying out in low tide and also from growth of weeds and diatoms.
Rearing of nori plants and their harvest.-About 50 days after budding, nori plants grow to 15-20 cm in length and then are harvested. After the first harvest many buds remain on the nets, promising another harvest in 15-20 days. In this way harvesting can be repeated several times from a net throughout the nori season. But generally the crop decreases in repeating harvests; sometimes the crop may die from the diseases of nori or by some accident. Then, the cultivators replace these nets with the refrigerated ones that can replace the crop in 15-30 days.
Harvesting is done by using machines which make the labor at sea more comfortable and efficient.
Manufacturing paperlike dried products from cropped nori.-Cropped nori plants are cleaned by washing with seawater. Then they are chopped and spread on screens made of fine twigs of bamboo or of fine plastic rods and finally dried in a dryer with an old burner. Drying has to be done quickly at low temperatures, commonly in 2-3 hr with the temperature lower than 50oC. In these conditions nori is kept alive until the end of the drying procedure. This makes the product glossy, tasty, and sweet smelling, and retains all vitamins.
Recent Advances in Culture Techniques
Recent yearly changes of nori production is shown in Figure 1, with changes of numbers of cultivating sets, of nets used, and of nets stored in refrigerators. The overall nori production has increased year by year but show sharp fluctuations. In these days progress in culture techniques has tended towards 1) new methods on how to expand the nori grounds, 2) how to prevent sharp declines in the yearly production, and 3) how to reduce labor in cultivation and to make laborers more comfortable.
Techniques to prevent sharp declines in the yearly production.-Of course, nori growth is affected by certain conditions, especially by the climate in the growing season. But the sharp drops in production were caused by severe outbreaks of diseases which occur successively in important grounds. It was found that the disease occurs in connection with overpopulation of the plants on the grounds-setting of too many nets for greater harvest. This finding led to the development of the techniques to get a far more stable crop by controlling the amount of nets to be set on a ground.
The technique to store live nori buds in cold storage was first applied in 1965, making it possible for crops to recover when the planted nori become severely damaged by disease or by some accident. Nets with young buds are dried until the water content of the nori comes down to about 20-30%, are packed in polyethylene bags, and are stored in refrigerators at about -20oC, in which buds can be kept alive for more than 6 mo and capable of recovering normal growth whenever they are returned to sea. Even wet buds can endure the cold storage for a short period, while many of the weeds and diatoms are killed. Also a parasitic fungus, which often causes disease on nori, loses its ability to reproduce by this treatment.
The number of nets with young buds stored in refrigerators has increased in the past 5 yr, as shown in Figure 1. This brought about new difficulties in bud rearing, because cultivators have to rear the buds with doubled amount of nets. In 1966-70, when too many nets are set during bud rearing, these nets often caused severe damage to the buds, resulting in a sharp decline in harvest. This problem is now solved by reducing the nets to a reasonable and manageable amount on each ground.
Techniques to expand nori grounds.-By using the net collectors, nori culture has developed the grounds in the new areas after the old grounds were destroyed by polluted waters and so on until 1965; after that the development and loss came into balance. However, nori grounds are still showing an overall increase by using a new rearing system, i.e., a floating-net system, which can make profitable grounds out of waters of about 20 m deep and with strong wave action.
Generally a square frame of synthetic rope is set floating on the surface of the sea with the help of buoys and anchors, and 20 nets with small buoys can be set in it. Waters with currents faster than 30 cm/sec or with somewhat strong wave action are convenient for rearing nori by this system. The frame systems can resist the impact of a wave 4 m in height without any damage to nori.
Mechanization of processes in nori cultivation.-Labor shortages and culture enlargement demanded the mechanization of each process of production. It turns culture labor into a comfortable and profitable one, keeping the young labor force from flowing out into land industries. This is an exception to the labor shortage situation for all fisheries. For instance, oyster culture appears more profitable in some localities than nori cultivation, but labor in oyster culture is far more severe and dirty, causing an outflow of young labor from the culture industry. This loss of labor is making the culture fall behind the nori cultivation.
Introducing engineering principles to make or to improve nori grounds.-From about 1965 engineering principles have been introduced in nori cultivation. For example, concrete or iron piles were set to decrease wave action in order to have nori culture possible behind them. On the grounds in shallow waters, water ways were dug to better the exchange of water and to increase the harvest, and now in several old grounds digging works are planned. Here the connection between the biological and engineering techniques have to collaborate closely to make the effort effective for production increment.
The demand for nori by consumers, which is supposed to increase year by year, was estimated at about 5-6 billion sheets a year in 1970. The import of nori from Korea is now politically limited to 200 million sheets a year, but it may increase to 1 billion sheets in the future. Cultivation in Japan produced 6 billion sheets in 1970, satisfying the amount of consumers' demand, and Japan is capable of increasing its supply with the increase of the consumers' demand, if the following technical problems are solved: 1) How to prevent a bad crop, and 2) how to improve the quality of the products.
There is another problem which has arisen, the spreading of industrial pollution. Coastal waters became polluted and nori products became contaminated with cadmium, mercury, etc. We are afraid we may need hygienic control in the future if pollution increases.
The most important problem in nori culture is found in its administration. Income of the cultivators increased more quickly than that of city laborers, but in recent years this is not so. The increase came from the rise in nori prices and also from the increase in the harvests. In the future the rise in the prices can be expected, but the increase in the harvest will cause oversupply. The mechanization of the culture processes is raising the cost of nori, especially in the case of small-scale operations.
The technique to store live nori buds in cold storage is also used for cropped nori plants. This will inevitably stimulate the development of factories which store cropped nori and make it into products far more efficiently than each fisherman can. Until now, the income of a cultivator was the sum of harvest plus manufacturing, and if the latter is removed, he must recover his loss by production increase.
In the near future nori cultivators will be divided into two groups, the majority going into mass production using the floating system and the minority going into small-scale operations producing nori of special quality.
The number of cultivators has been kept at a level of 60,000 in the past 20 yr, but this level will decrease with the scale-up of each operation. Substitution of cultivators will occur, and cultivators who combine farming will decrease and ones who combine fishery will increase.
Under these changes of circumstances, the technical problems will be:
2) How to simplify each culture process? The present processes were developed for small-scale operations. They have to be modified to fit the need of a large-scale operation.
3) How to improve the qualities of the products? Development of an effective fertilizing technique will be expected.
4) Breeding of nori and introducing foreign Porphyra will be helpful for items 1-3-nori with more resistance to diseases, nori of higher productivity, perhaps of not maturing under winter's short-day conditions, and nori of higher quality, making the product more glossy, with more odor and better taste. A variety of P. tenera is highly productive and resistant to diseases but of lower quality.
5) Techniques for mass manufacturing of crop products.
"Wakame" is a seaweed peculiar to Japan and Korea, and 60,000 tons of this raw seaweed are landed annually, 10,000 tons in dry weight. Currently cultivation extends the seaweed industry to the northern areas, now including many districts all over Japan. The output from cultivation was over 60,000 tons in 1970.
The seaweed grows from beginning of winter to spring, then dies out after liberating zoospores. Within 20-40 days several hundred million spores come out from one plant. The spores germinate immediately to a microscopic filamentous alga, which lies dormant during the summer. In the fall, when the water temperature goes below 20oC, egg and spermatium are produced, germinate, and grow into the wakame plant. This seaweed grows to several millimeters long in 1 mo, 10 cm in 2 mo, and 1-2 m long in 3-4 mo. The temperature at the northern limit of distribution is 2oC in the winter and at the southern limit, 14oC.
In 1935 Kanda found that the life history of wakame was almost the same as that of Laminaria. Its cultivation started in the 1940's along the coast of southern Manchuria, together with that of Laminaria, where their natural growth is almost zero.
After World War 11, the industry was introduced into China which produced 30,000 tons of raw product a year, most of which is Laminaria. Meanwhile in Japan, the cultivation did not develop because of sufficient supply of natural products.
However, with increase in population, shortages in the supply of wild wakame occurred in the 1960's, stimulating the development of its cultivation. A new product, salted wakame, was developed and welcomed by consumers for convenience in cooking, and this product did a great deal for increasing consumption.
Under these circumstances wakame cultivation had an abrupt growth mainly in northern districts of Japan. The annual production was almost zero in 1963 and was over 60,000 tons in 1970, which exceeds the harvest from natural beds.
Processes in Cultivation
At the end of the season, wakame becomes mature and develops zoospores, at the time fishermen start to prepare the "seed strings" for the next season.
For collecting spores, strings of 2-3 mm in diameter made of synthetic fiber are used. The 100-m long strings are reeled over a frame made of vinyl plastic tube of 2-3 cm in diameter. A tank is filled with fresh seawater. Mature sporophylls of wakame are put into the tank after half drying. Enormous numbers of spores are released into waters, when the vinyl frames with strings are set in the tank so as to catch the spores. Several sporophylls are necessary for seeding a 100-m string. After 1-2 hr the frames are taken out and are put into culture tanks of about 1 m deep, where they are kept through the summer under controlled light intensity. It is desirable to keep the water temperature lower than 25oC. Favorable light intensity over them is 500 lux at 25oC and 1,000 lux at 20oC.
Germlings of wakame develop in the fall when the water temperature goes below 20oC. When young buds grow to about I mm in length, the frames with strings are put into the sea hanging from a raft, so as to accelerate their growth.
In northern waters, where invasion of fouling seaweeds and animals is less, the seeded strings are often cultured in the sea.
Management and Harvesting
The cultivation starts when the seawater temperature becomes 15oC and fouling organisms become scarce. A synthetic rope of 100 m long and of 8-10 mm in diameter is floated into the sea with the help of buoys and anchors. Often many branch ropes are hung from the rope. Seed strings with young buds of wakame are rolled up to the rope. Sometimes seed strings are attached to the ropes at 10-cm intervals after being cut into pieces of about 10 cm long.
in waters which are too rough or with many floating Sargassum plants, the rope is set at a depth of 1 m, where the buds can escape being damaged by wave action or by rubbing off by Sargassum.
Wakame grows quickly in winter. The optimum temperature for its growth may be about 10oC. The longer the period of lower than 15oC, the greater the harvest. However, temperatures lower than 5oC may injure the plant and may decrease the crop. Fast current and strong wave action are favorable for growth of the alga, if they do not damage the cultivation set.
Harvest is done by cutting the weed which has grown to about 1 m in length. Most of it is dried under the sun or in a drier. Some of it is sold raw to meet local demands. The yield from 1 m of cultivating rope in a season is about 10 kg in wet weight in the northern areas and about 5 kg in warmer districts.
The amount of labor work in wakame cultivation is far less than that in nori cultivation. The set of the former is more resistant against rough waves than that of the latter. For these conditions the former is more profitable in northern open coast than the latter. However, the amount of consumption is now limiting progress of the industry.
With the spreading of the cultivation, new problems are occurring, i.e., damages caused by bacterial diseases and by the eating of young buds by isopods and gastropods.
Harvest of Wild Wakame
The amount of production changes every year primarily because of the variations in water temperature. The low temperature in the growing season, winter to spring, brings about a good crop except at the north limit.
Elimination of harmful seaweeds in wakame beds is found to be effective in increasing production during the season. The bed is likely to be taken over by other perennial weeds, Phyllospadix in the north and Sargassum and Ecklonia in the south. The best time to control the weeds may be during the germinating season of wakame buds.
We have never produced a favorite culture area by throwing stones into the sea, which is effective in the case of Laminaria and Gelidium. Limiting the amount of the harvest and transplanting mature plants were found ineffective for producing a better crop the following year.
Wakame is an annual plant and there is an enormous mortality in the microscopic phase in the summer. These conditions may cause the ineffectiveness of the foregoing techniques. However, after germination the plant grows to maturity with a little mortality. If some devices are used to plant young buds in large quantities, the efficiency will be quite reliable. Trials of this method are now underway.
Important species are Laminaria japonica and L. angustata. L. japonica is the best quality though not much is produced. Half of all Laminaria harvested is L. angustata var. longissima.
Laminaria mature in the fall. Some hundred million zoospores, each having two cilia, come out from a frond. A germling is a microscopic filiment. When the water temperature goes to 10oC or below in winter, the germling gives rise to spermatia and eggs. A fertilized egg germinates and grows into a Laminaria plant. The filaments do not fruit at water temperature over 10oC and for this reason Laminaria grows only in northern Japan.
Young plants are seen in early spring, then grow rapidly, but start to decay from the top of the frond in the autumn. In the second year, a growth at the top of the stipe develops and becomes a second year's blade. The growth in the spring is good at 5o-15oC, but never takes place at over 20oC in the summer. The second year's blades are the main parts of the plant harvested because the first year's blades are of unsuitable quality for consumption in Japan.
The harvesting season is from July to August. A drying process after harvesting is important to get an excellent product. Hokkaido is subjected to foggy days frequently; therefore, the drying by a drier is useful for increasing production and for improving quality.
Shinran-shonin, an old famous Buddhist priest, is said to have been the first to propagate Laminaria in 1718. At present a large amount of the national expenditure is invested in Hokkaido.
Throwing stones into the sea for propagation improvement has been practiced for many years with good results. The yield rate in the area where stones are thrown is roughly the same as the one in natural growing districts. The area in which this technique is used should not be one in which the bottom is altered by the movement of sands. Use of a short cylinder of concrete which was thrown into the sea was practiced on a large-scale basis at Nemuro, Hokkaido. The expense is supposed to be recovered in 7-8 yr.
The reefs which are too high to drain the even surface are dynamited so that Laminaria plants are able to grow. To eliminate harmful weeds such as Phyllospadix from the bed bottom explosives are also useful. An explosive equivalent to 150-300 g of dynamite has an effective area of about 4 m2.
China is said to produce 30,000 tons of Laminaria annually due to the recent progress in cultivation to produce a dietary balance.
In Japan the emphasis has been on increasing the production of Laminaria plants which grow naturally in the sea, because it supplied sufficient amounts for the demand of consumers. With increase of consumption and rise of market price, cultivation has been attempted.
There are some obstacles preventing a breakthrough in Laminaria cultivation, especially the fact that the plant takes 2 yr to grow into a desirable market product for Japanese consumers, i.e., 2 yr plants. Research is now going on to reduce this period.
The production of raw seaweeds for agar-agar in recent years has been 6,500 tons dry weight and 5,500 tons are imported. The latter, sold at a cheap price though not of good quality, replaced the ones raised in Japan. Agar output was 5,500 pounds in 1963. Korea which exported raw materials in prewar days is now producing more agar-agar every year and soon is going to exceed Japan's production.
Raw seaweeds for producing agar belong to the families of Gelidiaceae and Gracilariaceae. Of these, Gelidium amansii is the most important species. It grows between low tide level and 20- to 30-m depth. They are found in areas which are influenced by warm currents. More than 60% of the total production comes from Izu Peninsula and Izu Islands, where the rock of the andesite, clear water, and warm current are located and where the transparency of the water is high which enables G. amansii 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 upwelling of bottom water. They also do not grow in muddy water, or on rocks covered with fouling organisms, but grow well on rocks on sandy bottom.
G. amansii reach 10 cm high in 1 yr and 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 produces 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/m2 at lzu Peninsula, the most favorable bed. At harvesting, plants up to 0.2 kg/m2 are usually left to grow because these plants grow back to 1 kg/2 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 Sargassum 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 recovery of the vegetation have been unsuccessful.
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. Therefore, the plants should be cropped as many times as possible.
Gelidium 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 Ecklonia and Eisenia that grow in 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. Branches of plants attached to a rope, which is hung into the sea, grow well. However, 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 Lithothamnion 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/2. The expenditures for setting stones is recovered in 4 yr. In regions where production is less than 0.3-0.4 kg/m2, it is not recommended that stones be added because the costs cannot be recovered.
Introduction of a gradually dissolving lump of fertilizer 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.
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.
Many attempts to increase natural crops by increasing the size of the seaweed bed by setting stones or concrete blocks on sandy bottoms around the seaweed ground have proved to be quite effective, 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 Gelidium and in 5-8 yr with Laminaria on the most favorable grounds. Regions of low production cannot be recommended for setting stones in the sea. For Iridaea and Chondrus, the period of cost recovery would be 20 yr; therefore, this attempt for habitat improvement is not a profitable one.
In Porphyra, a concrete cover on rugged rocks increased their harvest. This investment is recovered in 3-4 yr on profitable beds.
However, even in a good ground, a project of setting stones or a concrete cover could not be an object of investment from a private enterprise. In Japan, the privilege to harvest seaweeds is reserved for Fishermen's Cooperative Association, who in return is responsible to manage and protect this resource by means of propagating seaweeds and enlarging their substrate. This association has worked on substrate enlargement by stone setting with government aid of 100 million yen per year, an amount too small to improve their total production.
Other attempts to improve the production from natural beds are found to be not so effective. Elimination of injurious weeds may sometimes improve production in I to 2 yr. Also, trials to recover from decreased production in "Isoyake" waters by stone setting proved to be ineffective.
On the seaweed grounds, the fauna and flora have interrelations with each other depending on environmental conditions. Due to the difficulties in changing the environment with a limited budget, the way to increase production or recover from production declines is to change the succession mechanisms of flora and fauna.
For instance, in waters where seaweed population has decreased by some accident, starved abalones, top shells, and other gastropods may eat up and consume the young seaweed buds, decreasing the flora recovery. Therefore, to protect these buds, it is necessary to put a large amount of transplanted seaweeds sufficient enough to feed gastropods and other grazers, preventing the ingestion of buds needed for the vegetation to recover.
In cultivation, seaweeds grow on a net, a rope, or a raft set or floating at or near the surface of the sea. This means the cultivation is done free from the bottom conditions, on which natural growth of seaweeds largely depends. The cultivation can be done anywhere on any species, if techniques and water conditions make it profitable. The problems are:
2) How many water areas can be made into profitable grounds.
However, the cultivation of Gelidium, Gracilaria, Iridaea, and Chondrus has yet not developed, because it is not profitable. This stems from the fact that these crops are too small or that their cultivation requires too much labor. Here an epochal improvement in techniques is expected in making their cultivation practical.
In the already industrialized cultivation of Porphyra and so on, the problems are:
2) How to change water areas of rough waves into profitable grounds; that is to say, how to improve the culture apparatus to make it more resistant to waves and how to reduce wave action by some engineering techniques.
3) How to protect cultivated plants from diseases, which cause large fluctuations in yearly production.
4) How to improve the quality of products, especially in Porphyra, to meet better the consumers' demands. An effective fertilizing technique is expected to develop.
5) Breeding is expected to be useful to answer some of these problems. Looking for more favorable species abroad will be of consequence in the breeding.
1Mariculture Division. Tokai Regional Fisheries Research Laboratory. Arasaki, Nagai, Yokosuka, Kanagawa-ken, Japan.