THE ARTIFICIAL CULTIVATION OF GRACILARIA
With the development of the agar-agar industry, the need for Gracilaria increased further. Experiments on artificial cultivation have been carried out in many countries in recent years. The stake-net culture of G. asiatica in the tidal zone was carried out by Ren Guozhong and others (Institute of Oceanology, Academia Sinica, 1984) in Qingdao; culture of G. sjoestedtii was carried out by Jiang Benyu and others (1984); stake-rope culture of G. domingensis was carried out by T. Mclachlan in Canada; pond culture and intensive production of G. lichenoides in Taiwan was reported by Jiang Yongmian; raft culture of G. tenuistipitata in the tidal zone and the culture of G. tenuistipitata v. liui in seawater ponds, salina reservoirs and salt pans were carried out by Liu Sijian in Zhanjiang, Guangdong Province. The studies described above reflect the importance of the artificial cultivation of Gracilaria.
China is the foremost country in Gracilaria culture. Remarkable achievements, especially along the southern coast of mainland and the western coast of Taiwan, have been reported. Two methods are chiefly used for artificial cultivation of Gracilaria in China. One is pond-scattering culture and the other is raft culture of stake-rope culture. The first method is most suitable for species from which sporelings are easy to obtain. G. tenuistipitata v. liui is an example, it propagates vegetatively and can be harvested from time to time during the whole growing period. G. parvaspora and G. blodgettii are other examples. They propagate through spores released now and then in spring, summer and autumn. In this method, sporelings are cultured in seawater ponds, saline lakes or wasted salt pans. The procedures are easy. The second method is used to culture species which have good quality and high agar content, such as G. asiatica, G. tenuistipitata, G. gigas and G. sjoestedtii, etc. They propagate only through spores.
Artificial cultivation of Gracilaria is carried out by taking into account its biological characteristics. Suitable sites must be selected and effective measures must be adopted in order to get good results.
A basic requisite in the selection of a site for the cultivation of Gracilaria is an understanding of the ecological factors required and culture method chosen. Generally, three types of cultivation sites exist, namely, areas inside bays, offshore regions, and ponds.
The shoal is flat and wide. Water remains during ebb tide so that the fronds will soak and grow there and not dehydrate and die due to exposure to air.
Hard, sandy clay bottoms are good for the growth of fronds. Unsuitable sites are muddy shores where the water becomes turbid and the growth bases will be buried easily.
Areas exposed to frequent typhoons, floods and strong waves should be avoided. Seawater should be clean and unpolluted. The rate of water exchange should be good.
A certain amount of freshwater should be let in. The seawater should be rich in nutrient salts and its nitrogen content should be above 100 mg per cubic meter of water.
The specific gravity range of the seawater should be 1.010 to 1.025.
The temperature should be above 0°C in winter and below 35°C in summer.
If the raft culture method is used on shoals inside a bay, the first two requisites mentioned above are of great importance, but the water depth during ebb tide should be maintained at 1.5 meters deep. If raft culture is carried out in the tidal zone, the first two requisites are very important.
The seawater is fertile. The nitrogen content is above 50 mg per cubic meter of water.
The water is calm so that equipment used would not be destroyed by wind or storm.
The water is clean and free from pollution. Water transparency is high.
The water is above 1.5 meters deep during ebb tide. Generally, in offshore sites, the raft culture method is used.
At present, ponds are used to culture G. tenuistipitata v. liui along the coast of South China and the western coast of Taiwan.
Some enclosed fields too salty for growing rice and too shallow for raising fish can be used to culture Gracilaria. Renovated salt pans and pools can also be used.
The water is 0.3–0.5 meters deep.
The optimum specific gravity is about 1.010. The suitable range is from 1.005 to 1.015. Growth will be hindered if it is above 1.020.
The optimum temperature ranges from 20°C to 30°C Gracilaria will stop growing if it is over 30°C or below 10°C and will rot and die if it is above 35°C.
The desirable pH value is about 8.0. If it is below 7, fronds die.
Sandy clay bottom is suitable. Muddy shores should be avoided because turbidity due to the high organic load of mud and silt will hinder the growth of the species cultured.
Production experience has proved that the criteria considered for selection of sites are not very strict. Areas from inside bays to offshore can be used for Gracilaria culture in most cases, but local geographical and sea conditions should be considered and suitable measures be taken accordingly.
Spore collection and sporeling culture methods were derived gradually with the development of production. Two methods are used, one is used in the open sea, the other indoor.
This method is simple and cheap but requires a great deal of labor. Various kinds of growth bases (attachments) and a certain amount of Gracilaria fronds are scattered on the shoal. Spores will be released naturally and germination follows. Then sporelings will be seen attaching on the growth bases. Sometimes, spore-filled water is used. The detailed procedure is as follows:
(i) Site selection
Farming sites are always selected in flat areas inside bays or offshore areas with a hard bottom, clean water and a good water current exchange. Specific gravity of the seawater should be from 1.010 to 1.025. At ebb tide, there should still be some remaining water. It is good if there are lots of shells, small stones and broken corallina on the bottom as they can be used as growth bases. Pools and crab ponds can also be used as sites to collect spores and culture sporeling because water depth and water exchange can be controlled in these ponds.
(ii) Preparation of growth bases
The kind of growth bases used depends on local conditions. Small stones, shells and broken corallina can be used. The surface of the growth bases should be clean and easy to be attached to by spores. About 500–600 tons of multi-angular stones weighing not more than 0.5 kg each are used per hectare. Shells of oysters, scallops, and clams, can be used; 180–210 tons of these shells are scattered over one hectare. The outer surface of the shell is turned upward if possible because it is rough and suitable for the spores to attach to. Broken corallina is also a good growth base and can be found in some places along the coast of South China. Sixty-strand (3×20) vinylon ropes and 33-strand (3×11) PVC ropes have been used since the 1960's; 15×15 cm mesh nets woven with these ropes are also used as growth bases.
Fronds are selected before spore collection. They must be strong, with luxuriant branches, intact, without damage, and with numerous sporangia on them. Cystocarps project outside the frond and are easy to be recognized. Numerous tetrosporia formed are seen as tiny red specks faintly visible inside the tetrasporophyte if observed against the sun. One must make sure only mature spores are collected. They can be identified from the characteristics of the sporangium.
Characteristics of the mature carposporangium. When carpospores are mature, cystocarps are seen projecting highly upwards. The apical part of the cystocarp is round and smooth like a steamed bun. The pore of the cystocarp is transparent and somewhat white in color. A big white spot with pores indicates that carpospores have already been discharged and the fronds can not be used. The plumpness of the spores can also be checked through a microscope.
Characteristics of the mature tetrasporangium. When the tetraspores are mature, they can be clearly seen as evenly distributed big red spots when viewed against the sun. The sporangium has a very clear and crossed groove when observed through a microscope.
Different methods used are as follows:
A certain amount of fronds is left during harvest for the seaweeds to flourish again. This method can be used in the place where Gracilaria is growing naturally. Growth bases are scattered. Spores discharged attach on the growth bases and germinate.
The fronds are dried and stimulated to release spores for collection. Strong and mature fronds are selected and washed clean with seawater and then dried in the shade or under the sun. If dried in the shade, fronds can be arranged on a bamboo mat or hung on a rack in bundles for 2 to 4 hours. Drying time varies according to the temperature, moisture, and air ventilation. When the fronds surface is dry and some irregular wrinkles start to appear, the treatment can be stopped. If dried under the sun, the fronds must be turned over now and then. Only a short time is needed. After the drying treatment, the fronds are cut into 2 to 3 long pieces. Generally, 15 to 20 kg fresh fronds of Gracilaria are needed per mu (1/15 or 0.066 ha). Fronds scattered in the farm site absorb water. This results in the rupture of the sporangium and subsequent release of spores. It has been reported that about 60,000 tetraspores or more than 40,000 carpospores are released from a Gracilaria plant (Mathieson, 1975). Spores set free sink slowly and attach on some stones and shells as growth bases. They subsequently germinate. A small disc forms in a week.
This method is suitable to be used in an area where not so many mature fronds of Gracilaria can be obtained. The work is carried out on a fine day and in the evening when the temperature is steady.
Mature fronds which had undergone the drying treatment are put into a clean big wooden bucket or a tank with sea water. They are stirred constantly with a stick in order to help set free the spores. The density of spores in the seawater is considered suitable when 30 to 40 spores are seen in a field through a microscope. The fronds are then removed to another bucket or tank for another collection of spores. Spores are set free continuously so that several buckets or tanks have to be prepared. The time of tide ebbs must be known beforehand so that the spore-filled water can be sent to the farm site and sprayed directly on the growth bases during ebb tide. The ability to attach becomes weaker and weaker with time. Spores lose the ability to attach 36 hours after they are set free.
Generally, the dried fronds start discharging spores 10 to 15 minutes after they are put into the seawater reaching a peak in 1 to 2 hours. Discharge of spores has a close relation with the water temperature. If the temperature is below 5°C no discharge occurs. Spores are set free in large quantities when the temperature is above 20°C.
The main advantage of the use of spore-filled water is that spore can be sprayed evenly and no mature fronds will be wasted. About 5–10 kg fronds are needed per mu and the fronds after discharging spores can be used as a raw material from which to extract agar-agar.
If nets and ropes are used as growth bases for collecting spores they can be put inside big wooden buckets or tanks and the spore-filled water is sprayed on them; 24 hours later, spores will attach firmly to these growth bases which are then put in the tidal zone where there is water remaining at ebb tide. The net can be fixed to the stakes or hung on a raft.
The method of spraying spore-filled water is similar to that of sowing seeds in agriculture. But plant seeds are visible to the naked eye and it is easy to control the density and check the result. The spores of the Gracilaria are too small to be seen except with a microscope. In order to check the density of the spores on the growth bases, several slides are put on them before they are sprayed with spore-filled water. A microscopic examination is done the next day after spraying the spore-filled water. If several spores can be seen in a field, the density is suitable. If vinylon nets are used, a piece of rope is cut and examined in the same way. If the density is too low, more spore-filled water must be added.
Spores are elliptical in shape immediately after being set free. After 10 minutes, they become round by absorbing water. The diameter is about 30 microns but it varies among species. For example, the carpospore of G. tenuistipitata is about 23–40 microns in diameter and the tetraspore is 24–56 microns. The shape of these two is exactly the same. There is a nucleus in the center of the spore and the chromoblast is stellate in shape and red in color, and lighter in the periphery.
Usually a spore after being set free from the parent will quickly attach on the growth base and then germinate. The spore is cleaved through the center into two equal parts. This is the first cleavage. If the spore is spherical, the cleavage takes place on the projected part first and two unequal parts are formed. The second cleavage will take place before long and is perpendicular to the first cleavage; four cells are formed. In some species, the second cleavafe is parallel to the first one so that 3–4 parallel cells are formed. After that, each cell divides irregularly and many small cells are formed.
In March 1978, an observation on the germination of G. tenuistipitata spore was made in Zhanjiang coast. It showed that the germination period of each spore is not the same; 24 hours after the attachment of the spores, some of them remain unchanged, some reached the two-cell stage, some the four-cell stage and some even reached the multicellular stages.
At the beginning, germination takes place inside the spore and spore diameter is nearly unchanged. Several days later, a small multicellular disc is formed. It attaches firmly on the growth base and gradually grows bigger. The diameter reaches 80–90 microns, and differentiation also begins to take place among cells. The pigment of the cells in the central part of the disc becomes darker than that of the cells in the peripheral part. The cells in the central part project upward. An erect body is formed. Generally an erect sporeling is seen a month later.
In the sea, collection of spores on growth bases and culture of the sporelings are carried out at the same site. Care should be taken so that:
Inspection is done regularly. If any pest like Enteromorpha prolifera, Ulva, Ectocarpus confervoides, diatoms or Amphipoda are found on the growth base, they should be removed immediately.
Silt deposited on the farm beds will suffocate the sporelings and must be removed in time.
There must be some remaining water at ebb tide to keep the growth base moist, otherwise the sporelings dry up and die. If pools and crab ponds are used to culture sporelings, water should be controlled to a depth of 50 cm.
The specific gravity must not be below 1.010. During the rainy season, if a great volume of freshwater enters the cultivation site, appropriate measures must be taken.
In North China, temperature drops greatly in winter. In South China, it rises to 35°C or higher in summer. During these periods the sporelings must be transferred to areas below the low tide level where the water is 1–2 meters deep.
An experiment on sporeling culture was carried out in April 1972 in the Haifeng Mariculture Farm in Guangdong. In a sea area named Gaoluo, vinylon nets were used to collect spores and culture sporelings which, by June, developed into numerous fronds that grew to 1 cm in length in July but stopped growing from August to September. In November the nets were collected, washed and hung on rafts in order to culture the sporelings evenly. In December most of the fronds were 5–6 cm or more in length and could be sandwiched for further culture. The experiment showed that it is feasible to use vinylon nets and PVC ropes for spore collection and culture. They are easy to manage, to wash clean of mud, to transfer from place to place if necessary, and require less labor.
When spores have been collected by using ropes or nets, they can be cultured on rafts in the sea using the same method used in culturing autumn seedlings of Laminaria. The most important work to be done is to keep away pests and silt or mud.
If rafts are used for sporeling culture, the water depth must be controlled according to the transparency of the sea water. It is reported that deeper positioning of the rafts in the water resulted in less fouling by organisms but poorer growth of the sporelings. On the other hand, culture of the sporelings in shallow water resulted in just the opposite.
In 1973, spores of G. tenuistipitata and G. asiatica were collected with PVC ropes in the Zhanjiang coast. At the beginning, numerous sporelings could be seen and their growth was good. When summer came, the number of sporelings decreased until finally not enough sporelings remained for cultivation. The same thing happened in Haifeng Mariculture Farm in the 1970s. In 1987, an experiment on collecting spores with nylon ropes was carried out in Shangdong (Lee Xiuyen, Shandong Mariculture Farm). This farm also had no spare sporelings for other farm beds. In recent years, spores were collected by using growth bases like stones and shells in the tidal zone in Nansan Island, Tecun Island and the Longtouxia Area of Lianjian county, Zhanjiang, China. Especially since 1985, spores have been collected in the Shishi Area of Donghai Island, Zhanjiang. In autumn, during the cultivation season, sporelings cultured in each mu of shoal are sufficient for 10 mu cultivation. This method is simple, cheap, and easy to disseminate. In April 1985, spores were collected at the Shishi area of Donghai Island, Zhanjiang. Several big wooden buckets with seawater were prepared on the seashore. The mature fronds were scattered on the beach and dried in the sun. They were turned over and over until the frond surfaces were dry, then put into the bucket and stirred with a small bamboo pole. Numerous spores were released half an hour later. When 20 to 30 spores could be seen in a field through a microscope, the sporefilled water was ready and the fronds were taken to another bucket for another discharge of spores. The spore-filled water in the first bucket was sprayed on the shoal where there were lots of shells and small stones and there was water left at ebb tide. It took a week to finish the work. About 150 kg fronds were used to obtain spore-filled water for spraying a sea area of about 1 ha. In June, an examination showed numerous sporelings attached on the shells and small stones. Generally 30 to 40 0.5– 3 cm long sporelings can be found on a stone as big as a fist. On some of stones as muchn as 100 sporelings could be found. In August, another examination was done. Sporelings were almost 2–3 cm long. The apical part of some sporelings rotted away and the number of sporelings became less because some dried up under the sun during ebb tide. However, those attached near the sand were still alive. In November, the sporelings were 7–8 cm long. The bigger ones were about 20 cm long. These sporelings which were cultured in one hectare of sea area were sufficient for cultivation in 10 ha. Thus, the desired result was achieved.
|Facilities||Raw Material||Spec.||Quantity||Unit Value||Amount||Remarks|
|Headrope||polyethylene||3 × 40||90 kg||8.00 yuan/kg||720 yuan||For 3–4 years|
|Net rope||vinylon||11 × 2 × 3||330 kg||8 yuan/kg||2640 yuan|
|Bamboo float||small bamboo||1.2 m. long||2400 p||0.30 yuan/p||720 yuan||only 1 year|
|Stakes||tree trunk||1.0 m. long||600 p||0.20 yuan/p||20 yuan||only 1 year|
|Facilities||Raw Material||Specification||Quantity||Unit Value||The sum||Remarks|
|Floating rope||Polyethylene||3 × 40 strands||105 kg||8 yuan/kg||840 yuan||for 3 years|
|Seedling rope||Polyethylene||3 × 41 strands||112 kg||8 yuan/kg||896 yuan||for 3 years|
|Small bamboo||Small bamboo poles||1.2 m. long||2400 kg||0.30/m.||720 yuan||for 2 years|
|Stakes||Tree trunk||1.0 m.long||750 kg||0.20 yuan/m.||150 yuan||for 2 years|
|Others||Tread, nails||15 yuan|
To find a more scientific way of collecting spores and culturing sporelings, experiments have been carried out indoor since 1959.
Features of this method are as follows:
It is necessary to wash and handle the mature fronds carefully. Harmful organisms like diatoms, Protozoa and Annelida which attach on the fronds of Gracilaria will hinder the germination of spores and so must be kept away before spore collection is carried out.
The growth bases must be cleaned and disinfected. It is usually small and the water quality is not easy to be controlled, therefore growth bases must be brushed clean and the vinylon ropes must be soaked in seawater before hand.
The sea water used has been settled and filtered of diatoms, Protozoa, and other organisms that hinder germination of the spores.
Factors like temperature (20–25°C), light intensity (about 5000 Lux), content of nutrient salts (nitrogenous fertilizers about 1 ppm) and specific gravity (about 1.020) of the seawater can be controlled optimally indoor.
Spore collection has done indoor previously in some production stations. When the spores germinated and developed to the erect body stage, they were transferred to and cultured in the open sea. The sporelings were not cultured indoor because the seawater circulation inside the tank was poor so that the nutrient absorption and the metabolism of the erect bodies were not optimal. As a result growth was poor. Furthermore, the indoor method is costly. Since the method of collecting spores and culturing the sporelings in the sea can not meet the needs of large scale production, the indoor method must still be carried out but some problems must be overcome.
If the indoor method is used, a hatchery must be set up. The system's requirements are as follows:
A refrigeration system is needed in the hatchery. Temperature must be controlled to 20–25°C.
A water system with inlet and outlet must be set up. Facilities such as a tank for water setting, filter tanks, pumps, reservoirs, inlet and outlet pipes, etc. are needed.
About 40 cm deep rectangular tanks with inlets and outlets and white ceramic tiles on the sides and bottom are used. The volume of each tank is based on the actual need. The tanks are set in rows at different elevations so that seawater can flow through to support the growth of the sporelings.
Sporelings can be cultured in the hatchery after spores have been collected. The seawater is partially changed every day and kept flowing at a certain speed. The optimal light intensity is about 5,000 Lux. Some nutrients are added to keep the water fertile. The temperature is maintained at 20–25°C. The nets used for culturing sporelings must be kept clean.
In order to lower the expense, further studies are needed to verify if the fronds can be preserved at low temperature to delay the maturation till autumn when temperature is more suitable in South China.
It is clear that the method of collecting spores and culturing sporelings in the sea can be very suitably used in summer in North China. This method is economical and can be easily mastered by the people. The methods chosen for collecting spores or culturing sporelings must suit local conditions. For example, during harvesting of mature Gracilaria, some fronds can be left to flourish again. On the other hand, in places where there are no wild Gracilaria fronds, the methods of spraying spore-filled water, scattering, or cutting of dried fronds on the cultivation site are used. Shoal, pools or crab ponds can be used in the latter case. And to produce more sporelings to meet the needs of artificial cultivation, hatcheries must be put up so that spore collection and sporeling culture can be carried out indoor.
In order to raise the per unit area output of Gracilaria, the sporelings should be scattered for culturing when they grow up to a certain length. The starting time of scattering culture is different in various sea areas. Generally, the sporelings can be scattered for culturing when they grow to about 10 cm long. The scattering culture usually begins in mid November in Fujian, December in South China, and September-October in North China. At present, the following are some of the effective measures for Gracilaria culture in China:
Net preparation: The rope for knitting the 15 cm × 15 cm mesh 8 m × 1 m net is spun with 66 strands of vinylon thread. A 12 m long headrope, made of 120 strands of polyethylene threads (3×40) is tied on each side of the net. To keep the net suspended, a 1.2 m long floating bamboo pole is tied on each end of the net. 2–3 addi- tional bamboo poles are tied between the two poles.
Taking sporelings: When sporelings cultured indoor or in the natural sea grow to about 10 cm, the sporelings may be taken out for insertion into the mesh net. As Gracilaria is a top-growth seaweed, its growth is not influenced when the base of the fronds is cut. Therefore, after cutting, the sporelings can be transferred in a bamboo basket to the tidal zone for culture. In order to keep the sporelings viable, it is importnat to protect them from direct sunlight or drying in the air during transport.
Inserting sporelings: This procedure is usually carried out in the shade. Several groups of workers are organized. Some workers will separate the sporelings into tufts of several fronds; some will loosen the mesh knot; others will insert the sporelings into the mesh knot. Since Gracilaria is a top growth seaweed, its growth will not be influenced by gripping the middle part of the fronds. Usually, there are 180 tufts of sporelings gripped in a net. If 600 nets are placed in one hectare, the total count of the sporelings will be around 10,000 tufts. To prevent the sporelings from drying and get a good yield, the nets with sporelings should be immediately transported to the site for tying to the stakes stuck on the shoal.
Growout: When the net with sporelings is ready, it is transported to the shoal. Both ends of the floating rope of the net are tied to the stakes positioned in advance. The floating rope should be long enough for the nets of sporelings to be in a suspended condition during ebb tide. This way makes the fronds receive sunlight for photosynthesis. This is important for increasing yield. Before the stakes are stuck into the shoal, some factors (such as the direction of the tidal stream, the amount of remaining water during ebb tide, and convenience for routine management) should be considered. A certain space should be reserved between the nets for convenience in daily management. Usually, the distance between 2 nets is about 1 m. The buried depth of the stake should be determined according to the actual situation. Generally, about 50 cm is enough.
Routine management: After the nets with sporelings are set up on the shoal some workers must be put in charge of the daily management. This work is carried out on the shoal during ebb tide. With this method, 1,500 kg fronds dried weight can be harvested in about 3 months from one hectare. The output value would be about 7,500 yuan (US$ 1 = 4.75 Yuan at present).
This method is similar to the net culture method. The main difference is the meshing. In this method polyethylene ropes are used for gripping the sporeling. And the sporeling ropes are tied (10 cm apart) directly to the 1.2 m long floating bamboo at the two ends of the raft. Between the two ends of the raft, 2 more small bamboo stakes are added. The raft is 8 m long×1.2 m wide. The sporeling tufts are gripped every 10 cm along the polyethylene rope. Tied to each end of the floating bamboo is a 120-strand polyethylene floating headrope whose other end is tied to the stakes stuck on the shoal in advance. The advantages of this method is that the preparation of the net is unnecessary. Workers need not to loosen the knots of the mesh to insert the sporeling tufts which are easy to be gripped, so long as the rope is loosened at every 10 cm point. There are 750 tufts of sporelings on a raft, 800 rafts in a hectare, 30,000 tufts in one hectare.
Production cost: The principal materials used in raft
culture are polyethylene rope and small bamboo stakes, etc. The
cost of materials is shown in Table 2 (page 13).
The investment for one hectare in the first year is about 2,625 yuan. As the material can last for three years, the average cost for one hectare is about 800 yuan annually. There are no great differences between this method and the net culture method. In this method a worker may manage 2/3 of a hectare. After 3 months, 2,250 kg dried fronds can be obtained in one hectare. The value would be 11,250 yuan.
In 1960, some units in Haifeng and Fangcheng counties of Guangdong Provice used this method to culture Gracilaria. Cultured either horizontally or vertically, Gracilaria tenuis-tipitata grew to 1 meter or so, some to 2 meters. The fronds were full. On this basis the mariculture farm of Haifeng County conducted a further experiment and obtained a better result. The output per hectare was increased from 4,500 kg dried weight to more than 6,000 kg.
Since 1972, the mariculture farm of Haifeng County continued to improve the culturing method and designed a double raft device for culturing Gracilaria. Ecologically, the structure and the culturing density of the double raft are suitable for the culture of Gracilaria tenuistipitata. Two 28-meter long (3×6 strands) polyethylene ropes are used as headropes on the two sides of the raft, and 10-cm diameter, 2.2-meter long bamboo floats were tied on the two headropes every 4 meters. Fifteen sporeling ropes (3×4 polyethylene treads) were tied 14 cm apart on the floating bamboo pole. The length of the sporeling rope was 20 meters. In order to prevent the rope from getting entwined together, a small bamboo was tied on the sporeling ropes every 2 meters. The two ends of the headrope were fixed to the stakes which was stuck in the seabed. More floating bamboo poles could be added on the headropes according to the actual need.
The sporeling tufts were gripped every 10 cm; 200 tufts were gripped on a rope. There were 200×15, or 3,000, tufts in a raft. If 75 rafts were set on one hectare, then one hectare would have about 3,000×75, or 225,000 tufts. The density of sporelings cultured in the shallow sea was higher than the density of sporelings cultured in the tidal region so that the yield in the shallow sea was higher than in the tidal region.
There is little difference between raft culture in the tidal region and in the shallow sea except that in the latter method workers have to work on a boat. On average, a worker can only manage 1/3 hectare.
Specifications and cost of materials used in this method are given in Table 3.
|Facilities||Raw Material||Specification||Qty.||Unit Value||The Sum||Remarks|
|Heed rope||polyethylene||3 × 60 strands||37.5 kg||8 yuan/kg||300 yuan||used for 3–4 yr.|
|Seedling rope||polyethylene||3 × 14 strands||45 kg||8 yuan/kg||360 yuan||used for 3–4 yr.|
|Floating Bamboo||thick bamboo||2.2 m. long 10 cm. in dia.||450 p.||2 yuan/p.||900 yuan||for 2–3 year|
|Bamboo pole||small bamboo||small bamboo||825 p.||0.30 /p.||248 yuan||for 1 year|
|Stake||tree branches||1.0 m. long||225 p.||0.20 /p.||45 yuan||for 1 year|
|Thin rope||polyethylene||1.0 m. long||7 yuan|
As shown in Table 3, the cost of material, on the average, is cheaper with this method than with the raft culture and net tidal region. Moreover, the yield is higher than with the other methods.
As the cultivation techology improved more vertical sporeling ropes were hung on the headrope and the production increased further. (The length of the sporeling rope is 1.5 m the interval among ropes was 30 cm.)
Raft culture method in the shallow sea can also be used in the tidal region. The yield may also be increased further. The raft culture method is advanced and makes full use of the water area. The fronds are always immersed in seawater, but still get enough sunlight for their photosynthesis, so that they are able to grow rapidly. The yield is higher with this method than the other methods mentioned above.
As to management requirements of the various methods, two workers can manage 2/3 hectare using net culture and raft culture in the tidal region, and 1 worker can manage 1/3 hectare using the raft culture in the shallow sea. Assuming a unit output of 6,000 kg dried weight, the output value would be more than 12,000 yuan. After deducting the cost of the material and labour, the net income would be around 10,000 yuan.
Some Gracilaria such as G. tenuistipitata which multiply by vegetative propagation can be cultured with this method. After the sporelings of G. tenuis-tipitata are scattered into a pond, the fronds will grow naturally. When the growth fills up the pond, most of them may be harvested for sundrying or processing. Some are left in the pond to continue to grow so that the fronds can be harvested continuously. This method has been used for more than 10 years in the southwestern part of Taiwan. The area used for culturing Gracilaria in Taiwan is about 300 hectares. The yield is over 1,000 tons. The same method had been used for culturing G. asiatica, G. chorda or G. parvaspora, however, the culture of these Gracilaria are less efficient than culturing G. tenuis-tipitata. Now let us describe the method in detail:
The sporelings are transported to the site in spring (April-May) and scattered evenly into pond. 4,500 kg of sporelings are scattered in a hectare. Generally, this is carried out in the morning or evening or during a cloudy day, so that the sporelings will not be dried by direct sunlight. In order to prevent the fronds from being blown down by wind, some little bamboo poles should be stuck in the pond to support them. The water depth should be kept at 20–30 cm or so. In June, when temperature rises, the pond water depth should be increased to 60–80 cm. Some fertilizer should be spread in the pond as the fronds are growing. In Tainan country, 3 kg of urea is spread in a hectare every week. The effect is considerable. In some places, manure is put in the pond periodically. This is quite efficient too. The water should be changed every 2–3 days, and kept in good quality and be clear. Harmful seaweeds such as Enteromorpha, Ulothrix, Acanthophora, etc. should be removed from the pond.
Generally, 30–40 days after scattering the sporelings, the fronds will be ripe for the first harvest, some fronds should be left to flourish and continue the culture. The period of growing and harvesting could last for quite a long time. The harvesting can be from June to November. Normally, the fronds stop growing when the water temperature drops to below 8°C. December-March (because the temperature is too low then) is a low production period. However, in some places such as Pingdong Country, Gracilaria is cultured during December-July when the water temperature is favorable.
Production (with the use of advanced technology) in Taiwan Province reaches to 12 t/hectare per year in average. In the polyculture pond, in which shrimps, crabs and Gracilaria are cultured, the yield will be much higher. If managed properly, the unit output will be 1.5 t crabs, 9 t dried Gracilaria and 4.8 t shrimps per hectare per year. The output value is considerable.
After 1980, we found that G. tenuistipitata, G. parvaspora and G. blodgettii are suitable to grow in natural seawater ponds, saline lakes or wasted salinas in south China. The former is a vegetatively propagated seaweed and can be continuosly grown and harvested. G. parvaspora and G. blodgettii are sporiparous, multiply in spring, summer and autumn, and grow all year round. They all are excellent varieties for culturing in ponds. At present, the cultivated area of Gracilaria in south China has increased to 2,000 hectares. The annual output is about 2,000 t dried seaweed.
G. tenuistipitata grow on the bottom of calm ponds or natural seawater lakes in a semi-suspended condition. The optimum temperature range for their growth is 15–30°C. Below 10°C, growth is slow and over 35°C, growth stops, the fronds shrivel, turn dark, become twisted or rot at the tips, and all die finally.
Our experiment showed that G. tenuistipitata grows fastest in seawater of 1.010 specific gravity and that a specific gravity of 1.005–1.015 is suitable for the growth of the seaweed. When the specific gravity is too low, the fronds become yellow and flaccid. However, some fronds may survive in specific gravity lower than 1.002. In freshwater, they would all die after 20 days. When the specific gravity is above 1.020, they grow slowly, with the fronds turning dark and branches hardening.
The pH value of seawater may seriously affect the growth of Gracilaria. Our experiment revealed that the fronds die gradually when the pH value is less than 6.5. The pH value should be kept stably above 7.0. The optimum value is above 8.0.
A stronger light intensity is needed for the growth of G. tenuistipitata. Our experiment showed that the compensation point of photosynthesis of this seaweed is 20.3 μEM S. The saturation point of photosynthesis is 340 μEM S in its flourishing seasons such as autumn, winter or spring, and 95.9 μEM S in its decrepit season summer. The pure photosynthesis of the fronds is 0.72 mg O2/g fresh wt. per hr. and the latter is 0.30 mg O2/g fresh wt. per hr. The seawater should be kept clear and maintained at a depth of 20–30 cm in winter and spring so that there is enough sunlight for photosynthesis and the growth can be accelerated. In summer, the depth of the seawater should be kept above 50 cm. In this way, the temperature of the water will not rise rapidly, and the Gracilaria will be able to tide over the summer safely. The yield of Gracilaria will increase when the seawater is changed regularly and supplement of manure is provided. It is desirable to change the seawater and apply fertilizers such as (NH4)2SO4 or urea 1 g per cubic meter weekly. The sandy-mudy seabed is chosen for pond culture.
Gracilaria tenuistipitata is a perennial algae. Its propagational branches break off when they grow to over 10 cm in length. During harvesting, some fronds should be left in the pond to continue to flourish and reproduce a new crop for another harvest. The seaweeds grow in a state of semi-suspension and look like a carpet. A brownish-yellow surface is visible when new branches growing rapidly. As the illumination at the lower part of the fronds is weaker, the lower part may be darken. If the seaweed is turned over, the black branches on the surface will become green and throw out new branches.
To culture Gracilaria tenuistipitata a suitable site should be chosen for the production base. The main links in the production chain are scattering sporeling, daily management and harvest.
a. Site selection and the establishment of a production base. Generally, the natural seawater pond, wasted saline, or saline lake with sandy muddy bottom material are chosen for setting up the production base.
Construct the cofferdam system with gate (inlet) and drain (outlet) so that the seawater can be controlled at the depth of 20–50 cm. And the specific gravity can adjusted at about 1.010. The area of the pond is about 1 hectare normally.
Clear away harmful seaweeds. For this purpose, the seawater should first be drained and the pond dried by sun for days. Then plough and dry the bottom of the pond. If it is necessary, some slaked lime may be scattered to kill the weeds and adjust the pH value of seawater to about 8.2.
Let some amount of freshwater in and control the specific gravity of pond water at about 1.010. Apply growth promoting fertilizers.
b. Scatter sporelings. The sporelings (about 3.5 T/hectare) should be scattered as evenly as possible. The best density is about 0.5 kg sporelings/m2. After scattering, the Gracilaria will grow in a semi-suspended state. In order to prevent the fronds from being pilled up by wind, some little bamboo poles should be stuck in the pond for separating the fronds evenly.
In daily management, the most important job is to observe the growing situation of the seaweed. If the color of the fronds is abnormal, this should be analyzed to see if it is indicative of lack of fertilizer, inadequate light intensity, or unsuitable specific gravity, and apply appropriate corrective measures promptly. Harmful seaweed such as Enteromopha, Ulothrix, Acanthophora and diatom etc. in the pond should be removed. Otherwise, they will proliferate, assimilate the nutrients, scramble for the space, and adversely influence the growth of Gracilaria. Generally, after a heavy rain, the manager has to pay special attention to the change of the specific gravity of the water. If it is too low, some fresh seawater should be introduced into the pond for adjusting it to the desired value. If the bottom material is acid, and the pH value is too low, the water in the pond should be changed or some slaked lime should add to adjust the pH value. In order to accelerate the growth of the seaweed, attention should be paid to the depth of the pond water and make sure sunlight reaching the plants is of proper intensity. To lower the high temperature in summer, some trees could be planted beside the pond for shading the water.
In order to increase the unit output value, scientists and mariculturists recommend the polyculture shrimps and crabs in Gracilaria pond or Gracilaria in shrimp and/or crab ponds. In the former case, Gracilaria cultured mainly and a certain number of post larvae of crabs or shrimps are scattered in to pond. The ammonia decomposed from the bottom material and purification of the seawater because the residual feeds were absorbed by Gracilaria. Moreover, when growing, the seaweed go on with a by product of photosynthesis (oxygen) was used by the shrimp for respiration. Data from the trial showed oxygen content in the polyculture pond was 5.82 mg/1 while in monoculture pond it was 4.58 mg/l.
As Gracilaria parvaspora thrives in water of specific gravity of about 1.020, the reservoir of high salinity or brine pond in a normal saline are ideal sites for the cultivation. The seaweeds can release their spores in spring, summer and autumn. The spores can germinate, grow and multiply themselves continuously. It is unnecessary to breed the sporelings for this Gracilaria.
G. blodgettii has similar ecological characteristics. The Woods Hole Oceanographic Institution USA, (Laponate & Ryther 1978) reported that scientists culturing G. tikuahial with flowing seawater could reap continuously while the seaweeds were growing if NH4-N or No3-N are supplied sufficiently. Every day, they could harvest 34.8 g (dried wt.)/m2 /ha per year. They used a 6 m. long, 0.4 m. wide semi-cylindrical polyethylene tank to culture the seaweed. Various tubes installed at the bottom of the tank kept the seawater circulating. Some air stones were on the bottom for aeration. The illumination was natural sunlight; the range of temperature was 12–34°C annually; the salinity range was from 20–34%. Nutrients were supplied sufficiently. The content of nutrient salts were 50 um/1 NaNO3, 5 um/l NaH2PO4. The initial culturing density of the seaweed was 2 kg/m2 surface. Harvesting was once a week. The production cycle of this culture was 2 months. This is enlightenment for us. Organizations with the facilities should consider Gracilaria farming on a large industrial scale.
The methods for cultivating Gracilaria have been described above. However, the unit output of Gracilaria is much less than that of the kelp (Laminaria) because the fronds are smaller and its growth cycle is shorter. More studies on increasing the output of Gracilaria are needed. At present, the effective increment approach is adopted or is being studied, by some units in regard to four aspects:
In the natural seawater, some broken fronds of Gracilaria can continue to grow. This reveals that Gracilaria possess a strong regenerative ability. In the spring of 1973, scientists of the South China Sea Oceanographic Institution, Chinese Academy of Science, conducted a cutting trial with 40 of over 10 cm long Gracilaria tenuistipitata fronds in Zhanjiang port. In the experiment, only the 10 cm long base of the fronds was cultured. About one month after cutting the fronds grew to cover 10 cm again. The average growth rate was about 0.6 cm/day. The result was remarkable. From the winter of 1973 to the spring of 1974, a further experiment on cutting increment was conducted in our mariculture farm showed that if the base of the fronds for cultivation is too short after cutting, the growth of the seaweed will be retarded. The growth of the fronds with 1/4–1/2 been cut off was compared with that of the controls not cut. Cutting off 2/3 resulted in obviously slow growth. On the whole, the yield of Gracilaria can be increased by cutting. The seaweed was cultured in rafts in shallow sea. The polyethylene sporeling ropes were tied on the floating bamboo. The tufts of fronds were gripped every 10 cm on the rope. We cut the fronds when they were growing, and measured the weight, and calculated the ratio of the increment. Raju and Thomas of India reported an experiment of the culture of G. edulis carried out in the east shore of Krusadia Island from January, 1967-May, 1968. Usually this seaweed is found under the lowest tidal line. When they grow up, their fronds will reach to 50 cm. Their sporelings appear during June-July and December - February. Their mature period is from May-June. At the beginning of the trial, the top part (1 cm long) of the frond was gripped in a nylon threads at 5 cm intervals. Then the threads were twisted on a coir rope. The rope with sporelings was kept about 30 cm under the surface of the water and fixed on stakes stuck on the seabed. In the later experiment, the sporelings were gripped on coir ropes directly. The harmful seaweeds were cleared away every 1/2–1 month.
The result showed that, in the first month, the length of the fronds ganged between 4.4–6.0 cm, the fresh weight ranged between 0.5–0.7 g, and dry weight ranged between 0.025–0.030 g. From the second to the fifth month the fronds grew faster. At last, the length ranged between 35–40 cm, fresh weight ranged between 25.5–30 g and dry weight between 1.5–30 g and dry weight between 1.5–2.0 g. After five months of culturing, the fronds could be reaped. When reaping, the base of the fronds should be reserved for replanting. The second harvest was in 30 months after the first reaping. During the period of the second and the third harvest, the seaweeds grew more flourishingly and the yield was increased. The unit output in a 1 meter long rope could reach to about 3.5 Kg fresh weight. The result of the one year trial is shown in Table 4.
|Date||ave. length (cm) at harvest||ave. fresh wght at harvest (g)||ave. dry wght at harvest (g)||unit output/1 m rope fresh weight (g)|
|Item||original length (cm)||final length (cm)||ave. growth rate (cm)/day||orig. wt. per tuft (g)||final wt. per tuft (g)|
This Gracilaria can grow throughout one year in India. The gripping sporeling culture and periodical cutting method are certainly meaningful approaches.
G. encheumoides is also a tropical perennial seaweed. The cutting increment approach could be used with this seaweed also.
According to the report by Yamasaki of Japan, in their experiment, the Gracilaria was cut in 12 cm lengths, and cultured with the sporeling gripping method. The fronds were gripped in a rope for culturing. 15 days after culturing the fronds grew to about 30 cm long. After one month they reached to 50 cm. After culturing for 2 months, the weight of the fronds increased to more than forty times the original weight.
As a forementioned, the yield of Gracilaria can be promoted by using the cutting increment approach. If the cuts from the original fronds are used for reproduction, the increment result will be much better because the growth at the tip of the seaweed is faster.
Gracilaria grow well in the natural seabed where the fresh fertile seawater comes in. If the seaweed is cultured on barren seawater, application of fertilizers is a useful approach for increasing growth. In South China, some units considered the seawater is fertile, so fertilization is unnecessary.
The experiment showed that the growth rate of the fertilized groups, in which the sporeling ropes were dipped in fertilizer for 24 hours, was higher than that of the controls. The group fertilized with urine and manure grew most rapidly. The average growth rate reached to 2.34 cm/day. While the growth rate of the group fertilized with urine was 2.26 cm/day, that of the control was only 1.13 cm/day. The total increment in length of the fronds in the group fertilized with urine and manure was 82.84 cm total, 0.97 cm/day in average. The length of the group fertilized with urine increased by 58.3 cm, 0.68 cm/day in average. The controls increased by 43.88 cm in total, 0.51 cm/day in average. This showed that by dipping the sporeling rope into organic manure before gripping, the growth of Gracilaria may be increased obviously. By dipping the ropes into fermented urine and manure, the effect of the fertilizer lasted for a longer of time and the result was much better. This was a preliminary trial. In this approach, less labor is needed, the organic manure is easy to obtain, and the cost is low, and is a simple and effective way to increase the yield of Gracilaria in some regions.
This approach is similar to fertilizing with barnyard manure in agriculture. The effect of the fertilizer can last for a long time. Since the concentration of the manure is very high, the gripped sporelings should be transferred to seawater as soon as possible. Otherwise, if the sporelings were kept on shore for some time the water in the epidermal cells of the fronds will be easily lost; the fronds will dehydrate, and die soon after culturing in the seawater. This is worth paying attention to.
The effect of fertilizing is also proved by the experiment conducted by the Shandong Mariculture Farm in 1959. After culturing for more than four months, the length of the fronds fertilized was 14% more than that of the controls. The results are shown in Table 5 (on page 35).
This experiment clearly showed that supplementary fertilization of Gracilaria in fertile seawater is still effective. The only job in this fertilizing method is to fertilize the sporeling ropes before gripping. Little labor is needed. Therefore this method is easy to spread for mass production.
Growth hormone is a material which actively influences growth of plant. Its function is to promote the extension of the plant cells. It is reported that the hormone increases the respiration of the plant cell first, then increases the asparagine fiber and other material forming the cell wall. These rapidly increases the volume and respirator intensity of the cell and the soluble material. Osmotic presure causes the cell to absorb a certain quantity of water so that the cell length and volume become large. As a consequence, the plant's growth is accelerated. Growth hormones have such aforementioned effects on Gracilaria growth.
In 1962, we conducted an experiment on the effect of growth hormone on the growth of Gracilaria tenuistipitata. The preliminary result indicate that, some plant growth hormones can promote the growth and increase the yield of Gracilaria.
d. Removing harmful organisms: Harmful organisms (mainly Enteromorpha, Ectocarpus, Calothrix, Cladophora, Polysiphonia etc.), they establish a foothold, they multiply in large numbers and attach to the Gracilaria and hinder nutrient assimilation and the photosynthesis of Gracilaria so that the growth, yield, and quality are very adversely affected. The preventive approach is to keep harmful seaweeds away from the growing fronds. The culture pond should first be drained of water, after which the bottom should be dried by sunlight and ploughed. Slaked lime should be scattered on the ploughed bottom. Fresh seawater is induced to the culture pond only after harmful organism have been removed. As Gracilaria growth is hampered by attaching mud, the fronds should be flushed frequently. Some fishes and shellfish may bite and break the fronds and cause a certain loss.
Clearing away harmful seaweeds is complicated work. According to our experiment, Ectocarpus and Polysiphonia separate themselves from Gracilaria automatically as temperature rises and so has little effect on the culture Gracilaria. Tightly attaching diatoms on the fronds of Gracilaria are hard to remove. The quality of harvested fronds is influenced badly by these organism. These attaching organism can be flushed away after the fronds are dipped into 1/20,000 formalin solution. And the Gracilaria can continue to grow. To clear away Enteromorpha, a solution of 3–6% paraquat is sprayed on the seaweeds after ebb tide. When flood tide comes Enteromorpha, will become white gradually and die and separate themselves from the net. In pond culture, the seaweeds should be drained dry, then paraquat solution can be sprayed on the seaweeds. In this way the harmful seaweeds can be cleared away.
The history of Gracilaria culture is only several decades. With the development of science and the industry and agriculture, the culture of Gracilaria will continue to develop as well.
Some species of Gracilaria such as Gracilaria tenuis-tipitata v. liui, G. parvapora, etc. culture in ponds can be reaped while they are growing. It is desirable to harvest on a clear day so that the fronds can be dried by sunlight. A part of the fronds should be left in the pond for them to flourish and develop in to a new crop for harvest. After reaping, the fresh fronds be washed clean and then put on a grass lawn for drying by sunlight. In moderate condition, the ratio of dry weight to fresh weight is 10.0%–12.5%.
Gracilaria Asiatica, G. tenuistipitata, G. gigas and G. sjoestedtii etc. can be harvested after 3–5 month cultivation. In South China, harvest starts from March. The last harvest should not be later than mid April. The harvest season in Fujian is one month later than in Guangdong. In North China harvest takes place in June-July. When harvesting, the fronds are just picked up by hand, washed clean of mud and weeds and then sundried. In the past, it was necessary to wash and dry the algae several times and bleach the algae till they become yellowish in sunlight. Normally, the ratio of dry weight of fresh weight is 6–7%.
At present, Gracilaria is used to make agar. The agar content in various species are different. The agar content in G. tenuistipitata, G. asiatica, G. gigas and G. sjoestedtii are more than 25%, that in G. parvaspora and G. blodgettii are about 20%, while that in G. tenuistipitata v. liui is only or so. According to analysis the agar content in the tender part of the fronds is lower than that in the mature part of the fronds. When the dry algae are stored, attention should be paid to keep the storehouse dry and well ventilated. The dry algae should not be exposed to humid air otherwise they become mildewed, or the agar content will be affected.
Gracilaria, a widely distributed seaweed, is an important raw material in agar-agar production. With the development of the agar industry, its economic value is continuously increasing. But at the same time, the natural resources of Gracilaria are destroyed in varying degrees in different parts of the world because no conservation measures are adopted. At present, the annual global output of Gracilaria is about 30,000 tons (dry wt). The yield is not stable and cannot meet the needs of the agar industry. The natural resources of Gracilaria must be conserved and exploited rationally, at the same time artificial cultivation of Gracilaria should be widely carried out.
Gracilaria is a group of warm water seaweeds distributed widely in every part of the world except the polar regions. Gracilaria has been recorded not only in offshore islands where the salinity is high, but also in estuaries where the salinity is low and in the open sea as well as in enclosed pools and ponds. Most of them are distributed throughout the tropic, subtropic, and temperature regions. As for the vertical distribution, Gracilaria is distributed from the high tide zone to the low tide zone or below.
At present, about 100 Gracilaria species are reported in the world. According to Ekman (1953): 20 in the America-Pacific warm water sub-area, 17 in the Malaya sub-area, 9 in the Japan subtropical sub-area, 24 in the Indian Ocean sub-area, 18 in the America-Atlantic warm water sub-area, and about 10 in the eastern coast of North Atlantic. It is clear that most of them are in tropical and subtropical areas. Along the coast of China, 21 species are found. They are mostly distributed over the South China Sea and 17 species are distributed in Hainan Province alone.
The geographical distribution types of the major species of genus Gracilaria are as follows:
a. Tropical species which are only distributed over the tropical areas.
1. Gracilaria cacalia (J.Ag) Dawson
Distribution: Indian ocean, Indonesia, islands in the middle of the Pacific, tropical waters of Australia, north Pacific up to Okinawa of the Ryukyu Islands (about 128°E-26°30'N), Hainan, China.
2. G. salicornia (Ag.) Dawson
Distribution: Siam Bay, the Philippines, south point of Okinawa (about 127°40'E-26°5'N), southeastern part of Guangdong and Hainan Provinces, China.
3. G. minor (Sond.) C.F. Chang et B. M. Xia
Distribution: From Guam Island in the Pacific Ocean (about 144°40'E-13°20'N) to Cape York Pen at the north point of Australia and Hainan Province, China.
4. G. crassa Harv
Distribution: Indian ocean, Red Sea, Indonesia, vietnam, Okinawa Island of the Ryukyu Islands group, Guangdong and Hainan Provinces, and Taiwan Island, China.
5. G. purpurascens (Harv.) J.Ag
Distribution: Sri lanka, Okinawa Island of the Ryukyu Islands group and southern part of Taiwan, China. A variety f. spinulosa (Okam.) Yamada is found in Indonesia.
6. G. coronopifolia J. Ag
Distribution: Okinawa and other place of the Ryukyu Islands, Hawaii, Hainan and Taiwan, China.
7. G. constricta C. F. Chang et B. M. Xia and G. hainanensis C. F. Chang et B. M. Xia
Species peculiar to Hainan Island, China
b. Subtropical species which are widely distributed over the subtropical areas.
1. G. punctata (Okam.) Yamada
Distribution: from Shirahama of Wakayama Honshu, Japan (about 135°20'E–33°45'N) to Ryukyu Islands and north part of Taiwan, China.
2. G. gigas harv
Distribution: along the coast of Japan up to Susaki of Chiba (about 139°45'E-34°55'N) which is in the middle of the eastern coast of Honshu. This species is also found in the east part of Guangdong, China.
3. G. parvaspora (Gmel.) Silva
Distribution: England, Mediterranean Sea, Indonesia, Island in the middle of the Pacific, Caribbean Sea, Japan, Fujian, China, Guangdong, China, Hainan, China, etc. The adaptable temperature range of this species is wide.
4. G. tesengiana C. F. Chang et B. M. Xia
A species peculiar to the continental coast of the South China.
5. G. tenuistipitata
Distribution: Coast of South China and Hainan, China. A variety G. tenuistipitata v. liui is found in Hainan, Guangdong, and Guangxi autonomous region, China.
c. Tropical species adaptable to a wide range of temperature, and spreading northwards to subtropical areas.
1. G. arcuata Zahard
Distribution: Mediterranean Sea, Red, Indian Ocean, Tongs Island, Indonesia and up to Susaki (about 133°15'E–33°20'N) and Hakushima (about 132°35'E–32°45'N) in the north, which are in the south part of Shikolu, Japan. In China, it is found in Hainan, Dongsha Islands, and Xisha Islands.
2. G. blodgettii Harv
Distribution: Caribbean Sea, Indonesia Sea, south coast jawa Island and up to Susaki Japan in the North. In China, it is distributed from Jinmen Island (near Xiamen, Fujian Province) in the north to Hainan Island and the west coast of Taiwan in the south.
3. G. corticata J.Ag
Distribution: Red Sea, Indian ocean, Korea, and Peru.
d. Temperate zone species. Their adaptable temperature range is the widest of all. They are distributed not only over the temperate regions but also northwards and southwards.
1. G. asiatica
Distribution: Yellow Sea, East China Sea, north part of South China Sea, Japan, and Korea.
2. G. foliifera (Forssk) B.rg
It is a widely distributed species with different shapes. The standard type is distributed from New Hampshire, U.S.A. in the north, through the Caribbean Sea, Brazil to West Atlantic coast of Uruguay, southern part of England, Red Sea, Hawaii, south and north part od Indian Ocean and Yellow Sea, China. The variety with broad leaves f. textorii is found in the California peninsula, California Bay, the east and south coast of the Australia, the east of Jawa, Indonesia, places between Chiba and Akai, Japan and places from Ninriaku Bay of Hokkaido in the north to Kumamoto of Kyushu, Japan in the south. In China, it is found in the Yellow Sea and in the north part of the south China Sea.
There are still others of this species which are distributed in different places of the world.
Gracilaria is mostly used to yield agar-agar. Many species of this genus have already been exploited. The annual yield of agar at present is about 7,000 tons in the world, with most of it made from Gracilaria as raw material. The content of agar in many species (dried is about 20 to 30%, or even more, and the quality is good. It has been clearly shown that many Gracilaria species have not been exploited yet. Further effects are still needed to fully and rationally exploit these natural resources.
With the development of the agar industry, the need and price of the raw material Gracilaria increases day by day. Some people only care for their immediate interests and do not care about the preservation of the natural resources so that great damage has been done. Fronds of wild Gracilaria in the sea are collected whenever needed. No spores and new plants are reproduces if fronds are collected before maturation. In the end, the natural resources become less and less. It is regrettable that not enough attention has been paid so far to the matter of conservation of these natural resources. How to preserve the material resources of Gracilaria and what measures must be taken to ensure the normal development of the agar industries become important problems that must be paid attention to. Some suggestions are offered below:
1. First of all, the artificial cultivation of Gracilaria must be widely carried out. Except in China where Gracilaria is cultured artificially on a certain scale, no artificial cultivation has been done (or only on an experimental scale) in other places of the world. The annual global yield of cultured Gracilaria is less than 5,000 tons of dry material in the world, and only a few species are being cultured.
2. Species of Gracilaria must be fully exploited as raw material yielding agar.
3. Some species which propagate through spores must be harvested only when they are mature. Fronds are used to release spores. The spore-filled water is sprayed into the sea so that new plants are reproduced.
4. Strengthen studies on biology, genetics, breeding, bioengineering, culture techniques, etc. of Gracilaria in order to provide scientific basis for artificial cultivation and to provide improved breeds of Gracilaria.
5. Strengthen the work of introducing fine varieties. Some species whose sporelings are easy to obtain and whose culture techniques have been well-developed should be introduced and spread. Various culture methods must be carried out to get higher economic benefits.
In summary, great attention must be devoted to the exploitation and conservation of the natural resources and the artificial cultivation of Gracilaria by various methods. This could promote the production of adequate raw material for producing agar and further develop the agar industry.