TECHNICAL RESEARCH REPORTS
GAVINO C. TRONO, JR.
Marine Science Institute
University of the Philippines
Quezon City, Philippines
The world-wide increasing demand for seaweeds and seaweed products as items of food and raw material for the manufacture of industrial products as agar, carrageenan and alginate has been the main factor which has encouraged the development of production technologies of economic species of seaweeds. This paper is a brief review of the current production technologies for four tropical seaweed genera, namely, Eucheuma, Kappaphycus, Gracilaria and Caulerpa. The related production problems and needs are also described.
1. Mariculture of Eucheuma denticulatum/Kappaphycus alvarezii
Two species of carrageenophytes, namely, Eucheuma denticulatum and Kappaphycus alvarezii, are cultured in the Philippines, Indonesia, Western Central Pacific Islands and several other tropical countries. Both species are farmed using the same method of culture, the fixed bottom monoline and the raft method. E. denticulatum, however, is more strict in its farm ecology requirements than K. alvarezii. The latter can grow very well in sites where E. denticulatum are farmed. In contrast, E. denticulatum is not as productive in areas suited for K. alvarezii culture. A number of criteria are used in the selection of farm sites. These are water movement (current), water depth, bottom type (substrate), and presence of highly diverse marine communities where Eucheuma is present. Reef flats with good amount of water movement (current) which do not fully bare during extreme tides of spring characterized by high water transparency, and far from fresh water source are indicators that the area may be ideal sites for their culture. However, it is necessary that trial culture should be done first to determine the feasibility of the site for this purpose before any development of the area is done.
a. Fixed Bottom Monoline Method
The fixed bottom monoline method is the technique being used in the culture of the two species. It has many advantages over the other methods used in the past e.g. net method. It is cheaper and easy to install and maintain, although it is not as intensive as the net method. In this method, the stakes which are driven deep into the substrate are spaced 10 meters apart and at one meter interval in rows. The end of nylon monofilament line (180 lbs/test, about 10.5 meters long) is tied to one stake, stretched and the other end is tied to another stake in the opposite row. The monolines are constructed in such a fashion as to form plots or units of known sizes. Selected Eucheuma cuttings (50–100 gms) are tied to the monolines at 25–30 cm intervals using soft plastic tying material, i.e., soft plastic straw. The plants are allowed to grow to one kilogram or more in size before these are harvested. Depending on the growth rates, the crop may be harvested after two to three months. The whole plants are harvested and replaced by new cuttings.
b. Raft or Floating Method
In areas where space requirement for the monoline fixed bottom method is not available or where this method does not seem to work due to associated problems such as intense grazing and seasonality in growth, disease and changes in the degree of water movement brought about by monsoons the raft or floating method is used. The advantages of this method are: 1) grazing by bottom associated animals are minimized or eliminated because the plants are raised way out of reach of the grazers and 2) the plants, being near the surface of the water column, are exposed to more moderate water movement caused by waves. This method however is not recommended in sites exposed to strong waves.
The same principle used in fixed bottom monoline method is used except that the monolines to which the seedlings/cuttings are tied are attached to raft. Bamboo is the usual floating device used or if wood is used as frame of the raft, floatation materials such as pieces of styrofoam or empty plastic containers are used. In some areas, plastic bags filled with air are used as floating device. The raft is anchored to the bottom by means of nylon lines.
In order to maximize production per unit of raft, more intensive seeding is applied, i.e., the distances between lines and cuttings attached to monolines are closer. The size of the raft depends on the length of the frame materials. Aside from maximizing the number of plants on a raft, it has been observed that the adverse effects of more intense sunlight near the surface of the water column is offset by the slightly crowded spacing of the plants.
Eucheuma farming, like any other agricultural or fishery industry, has its share of problems which may adversely affect the productivity of the crop. The occurrence of these problems appears to be highly coincident with the seasonal changes in the ecological factors such as light intensity and water temperature regimes, nutrients and weather disturbances. These factors seem to be the predisposing conditions which result in the reduction or the complete loss of crops. Among these problems are “aging effect”, negative growth rates, the ice-ice disease, weeds and epiphytes, grazing, and crop loss due to typhoon. These problems may be minimized if the farms are ideally located.
“Aging effect” in Eucheuma is manifested by the slowing down of growth with time which appears to be directly associated with condition characterized by high light intensity regimes. Morphological changes such as the general thinning of the branches especially towards the distal portions of the plants, the production of fewer branches, the general paling of plants and roughening of the thallus surface are the signs of this problem. These indicators appear about a month or so after planting but plants may recover if no further complications develop. However, if this poor condition progresses further it may result in very slow growth and the advent of the ice-ice disease may completely result in total loss of the crop. This syndrome is characterized at its early stage by the general paling and later the development of discoloration on portions of the branches of the plants which ultimately become whitish in appearance. The tissue at the affected portions becomes soft and eroded. Breaking of the branches takes place at these infected parts. In farm areas characterized by strong water movement, the plants easily break into pieces and are carried away by current. Past studies have also shown that the occurrence of the “disease” is preceded by or coincides with the production of tremendous biomass of other associated seaweed species and epiphytes. The occurrence of these blooms seems to be contributory to the predisposing conditions which result in the development of “ice-ice.” In addition the incidence of this disease is preceded by low nutrient concentration. The tremendous amount of biomass (blooms) of associated species would have further depleted the nutrient supply available to the Eucheuma.
At present there is no known method in controlling the occurrence of ice-ice. To minimize loses, the crops should be harvested as soon as the disease appears. New batch of healthy plants should be used as starter seedstock. Weeding may help alleviate the effects of the predisposing condition of low nutrient supply to the crops but in instances where the other species develop tremendous biomass weeding becomes futile. Losses due to the effects of typhoons may be minimized by locating the farms in non-typhoon areas or reef areas not fully exposed to strong waves and currents during bad weather. In typhoon-prone areas, the crop losses may be minimized by harvesting these before the strong winds and waves hit the area. Thus a typhoon warning system is necessary. The effects of grazing may be minimized by the physical removal of the predators. However, it is impossible to control the seasonal grazing of big schools of rabbit fish (siganids). There is no known method of control for the predisposing conditions to “aging effect”. Fertilization may partly solve the effects of low nutrient supply but will be very expensive. The use of “fertilizer blocks” has limited beneficial effects in open water farm sites for Eucheuma.
2. Production of Gracilaria
The production of agar producing seaweeds comes from three sources, namely, from gathering of drift materials and direct harvest from natural stocks, and cultivation. At present a large bulk of the seaweeds used for agar manufacture still comes from production from natural stocks. There is no available and accurate data on the contributions of agarophytes produced through culture but judging from the genera presently produced in different countries (Armisen and Galatas, 1987) which were imported by Japan in 1984, about 50% of the raw seaweeds processed into agar still comes from the production from natural stocks. The genera utilized in the international market for agar production are Gracilaria, Gelidium, Pterocladia, Gelidiella, Anhfeltia and Ceramium. Approximately 6,683 MT of agar were produced by 14 countries in 1984 (Armisen and Galatas, loc. cit.) about 48% of these amount were processed from Gelidium and Pterocladia, the other 52% from “other seaweeds” undoubtedly include other genera such as Gelidiella and Gracilaria. As far as we know today only the genus Gracilaria is being produced in commercial quantities through cultivation. In the first half of the 1980's, Chile, Brazil, Taiwan and the Philippines were the main suppliers of cultured Gracilaria to Japan. Recently, Vietnam, Indonesia, Thailand, Hawaii, etc. have applied culture techniques to Gracilaria production. Even at present a large portion of seaweeds produced by the Gracilaria producing countries still comes from local stocks. Gelidium and Pterocladia utilized mainly for the manufacture of bacteriological agar and agarose, so far as we are aware of, come from the gathering of natural stocks. Their commercial production through farming seems to be still a long way from realization. Thus, the production of most of these agarophytes is expected to be dependent still on their natural stocks for a long time to come.
2.1. Culture of Gracilaria
a. Considerations in the Selection of Species and Site for Culture
The following are important points to consider in the selection of species to be used and site for culture.
The species targeted for culture should have the following properties:
It must be a fast growing species which can be propagated utilizing vegetative propagules (cuttings) or spores. Species with large and robust thalli are preferred because these can produce large amount of biomass within relatively shorter cropping periods.
It must have high agar contents of good quality.
The above considerations therefore requires that the available species be screened. Comparative studies on their productivity should be conducted to determine the species to be selected. Because the properties of agar (gel strength, gelling and melting temperatures, amount of sulfate groups) differ among species it is terribly necessary that the correct name be applied. Thus the taxonomy of the species should be clarified. The names are indices to the kind and quality of agar the Gracilaria contains and are used as basis for determining the prices.
The selection of sites is a very important factor to consider in the pond and field culture because this could be the primary factor for success or failure of the farming venture. In general, areas that support natural stocks of species to be cultured are good sites. If culture will be done in an area where no stock of the species exists, then one should select sites which have comparable ecological conditions as the site where the stocks are found. This will need the gathering of data on various parameters such as salinity ranges, nutrient levels (NO-13, PO-34), turbidity, and type of substrate: other ecological parameters such as degree of exposure to waves, depth of the water and accessibility are also included in the evaluation of sites.
Natural Gracilaria stocks are generally found in areas which are characterized by calm water, high nutrient levels, shallow areas with sandy-muddy substrates. Sites for field culture should be located in areas which are generally protected from waves. Gracilaria has fleshy and fragile thalli and therefore easily removed or broken by waves. Species which are generally found in commercial quantities grow quite well in slightly brackish and highly fertilized waters thus protected bays and lagoons are areas generally preferred by most species. In tropical areas, Gracilaria species with high potentials for culture are also found on reef and sandy flats to sandy rocky and wave-exposed areas.
b. Production of Seeds
The term “seeds” here refers to both the vegetative propagules (cuttings) and spores which can be utilized as planting materials. The importance of the availability of local as source of seed materials is emphasized. These seedstocks may come from natural stocks or those from cultivation. Gracilaria exhibits triphasic alternation of the generation consisting of the gametophyte, sporophyte and carposporophyte. The latter, however, is microscopic and is parasitic on the female gametophyte. Thus, the large somatic stage consists of the gametophyte and the sporophyte. The results of the studies on the populations of these two generations have shown that the sporophytes are generally more dominant than the gametophytes, i.e., these are usually larger in size and the population makes up the bulk of the biomass. It has also been shown that under pond culture conditions (per. com.) the alga may not develop reproductive stages. These information are relevant in the selection of the type of “seeds” to be used in culture.
Vegetative (cuttings) propagules
Healthy stocks are selected for this purpose. The stocks should have thalli which are fleshy and elastic in texture, dark reddish brown color, robust well branched with smooth and shiny surfaces. In addition these must be clean, free from dirt and epiphytes. The preparation of the “seeds” vary depending on the type of culture used and these are described in appropriate sections of this paper.
Spores as seeding material
Two methods are being practices in the production of sporelings from spores: natural spore-recruitment and induced spore-shedding in hatcheries.
Natural spore recruitment
The use of spores as seeding materials for the production of sporelings for culture necessitates the availability of natural stocks. In the natural spore recruitment method artificial substrates such as ropes, rocks and netting materials are used. Ropes and netting materials are generally preferred. The use of ropes is a proven technique in the West Indies. The ropes are anchored or tied to wooden stakes among the dense populations of Gracilaria. These are left in the area for about two weeks to allow the naturally shed spores to settle on them. The sporelings developing from the spores become visible after 3 to 4 weeks. The seeded ropes are then transferred to the culture sites for outgrowing.
Hatchery production of sporelings from spores
The production of sporelings from spores requires some skills in recognizing fertile materials. Fertile materials are selected from available stocks. Recognition of the fertile female materials is quite easy because of the highly recognizable presence of cystocarps. These fertile structures appear as elevated mammillate “bumps” on the surface of the thalli with dark colored contents. Cystocarps which had already shed the spores (“empty”) are pale in color. In contrast the recognition of fertile sporophytic thalli is quite hard because the tetrasporangia are microscopic and do not form apparent recognised structures. The use of stereo-microscope is quite indispensable. The tetrasporangia appear as dark purplish microscopic spots on the surface of the thalli under low magnification. The presence of these structures, however, has to be counter-checked by the examination of sections of the suspected thalli under a compound microscope. The tetrasporangia are of the cruciate type and are embedded in the cortex of the thallus.
The hatchery production of sporelings requires land-based setup which may be sited some distance away from the outgrowing area. The setup was first used in Penang, Malaysia.
It is quite similar to those used in the seeding facilities for Porphyra and Laminaria although less sophisticated. It consists of a seeding tank with provision for control of water depth with an adjustable seeding material support structure. This structure consists of a wooden frame with monofilament netting material which can fit into the seeding tank. It is provided with mechanism so that its height from the bottom of the tank can be adjusted.
Various types of substrates can be seeded, e.g., pieces of gravel, shells or lines. These materials are placed at the bottom of the seeding tank. The use of lines as setting substrate requires additional structure, i.e., a frame which also fits the tank when laid flat on the bottom. The line may be monofilament nylon (90 lbs test as used in Malaysia) nylon braided ropes (ca. 3 mm diameter) or plastic tying materials. The “raffia line” is wound evenly to the raffia seeding frame. The frame with “raffia line” is then placed at the bottom of the tank.
Fertile material of Gracilaria are collected from natural stocks brought to the seeding facility. The moist materials are placed in containers such as styrofoam boxes provided with aeration holes to avoid stressing the materials which can affect the shedding and/or viability of the spores.
The fertile Gracilaria are then placed on the seeding support structure submerged in water in the seeding tank. The distance of the seeding materials from the seeding substrates (rocks, stones or raffia in frames) should be adjusted to ensure the uniform distribution and density of the spores. The seeding materials are left in the tanks for 2 to 3 days to allow the shedding of the spores.
The seeded materials may be left in the tank for another 1 to 3 days to allow the spores to germinate and completely attached to the raffia or substrates. In the case of Porphyra, the seeded lines are transferred to a nursery ground where the spores are allowed to grow to sporeling size before transferring these to the outgrowing plots in the open sea. The immediate transfer of the seeded “raffia” to the nursery ground leaves the seeding tank free for immediate reuse.
The seeded rope is transferred to a holding tank or of a nursery area while waiting for the spores to develop into sporelings.
Production and selection of highly productive seedstocks
The utilization of highly productive species/strains with high quality natural product is always a factor in the successful farming of Gracilaria or any crop for that matter. In species where it is easy to manipulate the individuals to be improved hybridization utilizing the gametes may be the normal and logical way of improving the seedstocks. However, in Gracilaria and other species where the technique in the manipulation of the sexual process to produce hybrids is not well known other methods may be used in selection.
One of these methods is through species/strain selection. Different strains/species present in a natural populations are selected, e.g., different species, various colored strains, morphologically different thalli. These different strains/species are then multiplied through cloning. Comparative eco-physiological studies are then conducted using these stocks. In situ studies on seasonality and production capacities of the various strains/species relative to changes in ecological factors as salinity, temperature nutrients and water movement are important in determining the field conditions which determine the productivity of the various strains as well as the seasonal aspects of reproductive states and capacities of the various forms.
Physiological studies to determine the range in tolerance of the various species/strains to the changes in ecological factors can be determined through the use of manometric techniques using a respirometer where one can accurately control the various factors. The photosynthetic/respiratory responses can be monitored under varying conditions of stress.
Analysis of contents and agar quality of the various strains is also an indispensable tool in determining the qualities of the various strains or species as basis for the selection of seedstocks.
c. Methods of Culture
Pond Culture
Although several species of agarophytes belonging to the genera Gelidium, Pterocladia and Gracilaria have been reported to be commercially produced through some form of farming in several countries, such as Japan, China, Republic of Korea, Vietnam, India and the Philippines, it is in Taiwan where the production of Gracilaria through pond culture has achieved a high degree of success. Here an average of 12,000 tons per hectare per year of fresh (300 ha) Gracilaria has been produced during the past few years (Chiang, 1981).
The genus Gracilaria is characterized by the alternation of three somatic generations, the sporophyte, the gametophyte and the carposporophyte stages. The last stage is microscopic and it is parasitic on the female gametophytes, thus the gametophytic and sporophytic stages are the macroscopic forms which are used as planting materials in the pond culture. Although the reproductive potential of Gracilaria through spores is high, vegetative propagation by cuttings is presently used in the pond culture because of the very high regenerative capacity of the plant and the simplicity of the method. However, “hatchery produced” seedlings from spores have been demonstrated to be superior in the open field culture of Gracilaria (Doty, 1986).
Out of the several species of the genus presently used (e.g. Gracilaria chorda, G. tenuistipitata, G. edulis, G. “verrucosa”, G. lichenoides, G. compressa, and G. gigas), G. “verrucosa” is the most popular due to its ability to adapt to a wide range of ecological conditions in ponds, its higher production rates and better gel quality. The culture of Gracilaria started in 1962 in southwestern Taiwan. Production in ponds is primarily influenced by three ecological factors, namely salinity, light and temperature. High production is recorded during the months characterized by higher temperatures and growth is slow during winter. High light intensity experts adverse effects on the growth, therefore control of light conditions is practiced by adjusting the water depth in the ponds. Salinity of 15 to 24 ppt appears to be optimal for growth. The increase in salinity during the summer months is controlled by the addition of freshwater, thus farms need to be located near freshwater resources.
• Site Selection
The success in pond culture of Gracilaria is highly dependent on the selection of appropriate sites. The following criteria are recommended in the selection of sites for pond culture:
Gracilaria is a euryhaline species and can grow in brackish water under a wide range of salinity. A salinity range of 15 to 24 ppt have been found to be optimal. Salinity rises during the sunny months due to evaporation losses reaching values as high as 35 ppt or drops to as low as 8 ppt during the rainy season were shown to be detrimental to the crop. The maintenance of optimal salinity in the ponds requires readily available freshwater and seawater supply. The ponds should be located in areas protected from strong winds because there is a tendency for Gracilaria to accumulate on the leeward side of the pond. The formation of thick heaps of Gracilaria at one side of the pond has adverse effects on the growth due to shading.
Water management is greatly influenced by the tidal changes in relation to the elevation of the pond bottom. Ponds located in areas where the bottom is at or a little above the zero tide level can easily be managed as water exchange is easy.
• Culture Ponds
The average size of ponds for the culture of Gracilaria is about one hectare or smaller. Smaller ponds are easier to manage than larger ones because in large ponds Gracilaria used to accumulate at one side due to the influence of winds. Pond management is also easier when Gracilaria is polycultured with shrimp and/or crab. Provision of entrance and exit gates facilitate proper water management.
The depth of the ponds vary from 50 to 80 cm. The bottom generally is of clayish loam, silty loam or sandy loam. It was observed that Gracilaria easily gets buried in ponds with sandy bottom due to the effect of wind. This problem, however, could be resolved by increasing the depth of the water during windy periods. In larger ponds wind breaks consisting of bamboo slots are installed perpendicular to the direction of the wind to prevent the seaweed being transported to one side of the pond.
• Culture Method
The following method is generally followed in the pond culture of Gracilaria. The ponds are dried for several days, water is then introduced. Healthy stocks are selected as planting materials. These are generally characterized by their elastic feel to touch, reddish brown color, brittle texture, they must have stout and well branched thalli and must be free of dirt and extraneous materials. The planting material is transported from its source to the pond site early in the morning to prevent its exposure to the sun. During long-distance transport it is frequently sprinkled with seawater and perforated bamboo or plastic pipes are inserted into the bottom of the heap to provide aeration. The plants must immediately be placed in the water of the pond upon arrival. The planting material is then cut into pieces and is broadcasted uniformly on the bottom of the pond. In Taiwan, stocking is usually made with 5,000 to 6,000 kg chopped Gracilaria per hectare in April.
• Pond Management
The water is maintained at a depth when the surface is approximately 30 to 40 cm above the heap of the algae. However, the depth is increased to cover the algae by 60 to 80 cm during the warm summer months to prevent a significant rise in the water temperature. Water depth is also increased during the cold winter months to avoid temperature drops below 8°C which is lethal to Gracilaria.
Frequent exchange of water is necessary to maintain the optimum temperature of water in the ponds. The water is changed in every two to three days. About 50 to 75% of the pond water is drained and replaced with fresh seawater.
Fertilization with either organic or inorganic fertilizers is done to enhance the growth of Gracilaria. In Taiwan, weekly application of three kilogram of urea per hectare was found sufficient. Fermented pig manure may be applied at a 160 to 180 kg per hectare dosage two to three days after the exchange of the water.
• Harvest and Post-harvest Activities
Under optimum conditions, the crop may be harvest 2 to 3 months after seeding. Cropping may be done every 30 to 45 days manually or by using scoop nets. The frequency of harvests is primarily dictated by the market price and the season. Approximately 30 to 40% of the biomass is harvested during each cropping. The crop is thoroughly washed in pond water to remove the silt, sand, pieces of shells and other extraneous materials, such as snails and other algae. The clean Gracilaria is spread uniformly on bamboo screens or plastic sheets for drying. An average wet to dry ratio of 7:1 is generally attained.
Standards set by the Bureau of Standards in Taiwan for the export of dried Gracilaria require that the product should not contain more than 1% of mud and sand, not more than 1% shells and not more than 18% other seaweed species. Moisture contents should not exceed 20%.
Dried Gracilaria is then packed into sacks of 100 kg weight for export or sold to local processing plants. Ten to twelve metric tons of dried Gracilaria are produced in a hectare of pond.
• Polyculture with Shrimp and/or Crab
Polyculture with shrimp (Penaeus monodon) and/or crab (Scylla serrata) is mainly done in Ping-tung prefecture in southwestern Taiwan. Stocking material for a hectare of farm consists of 4,000 to 5,000 kg of Gracilaria, 5,000 to 10,000 crab and 10,000 to 20,000 shrimp. Crushed trash fish and snails are generally used as feed for the crab. Crabs are harvested after three months, the shrimp often after four to seven months. Survival rates as high as 80% for crabs and 80 to 90% for shrimp has been documented making this polyculture one of the most profitable aquaculture method methods in Taiwan. The net income from polyculture has been proven to be three times as much as from monoculture.
In the Philippines a group of 40 fish farmers in Iloilo are also producing Gracilaria in their multi-crop fish farms. They also use cuttings as seedstocks. They do not use fertilizer as in Taiwan but only allow daily water exchange by tidal flow to ensure adequate nutrient supply for the seaweed. The ease in water management is enhanced by siting the bottom of the ponds at or just slightly above the 0 tide level. One of the main problems in the pond culture of Gracilaria is water management. Ponds are located away from both the fresh water and sea water sources and where the level of the bottom of the ponds is way above the 0 tide level, water changes becomes a major problem. In such ponds water can only be facilitated during extreme high tides. Maintenance of adequate nutrient levels as well as control of water temperature thus become a major problem. Another problem encountered in pond culture using large size ponds is the tendency of the Gracilaria to accumulate at the leeward portion of the ponds due to the influence of wind generated waves. The piling of a large of biomass is one portion of the pond results to shading. It also impedes the circulation of water which adversely affects nutrient supply. Provision of wind breakers as the “bamboo blocks” and “net blocks” in the ponds perpendicular to the direction of the prevailing winds, as practiced in Taiwan, has proven to be effective and cause increased production compared to ponds without them.
The development of blooms of other algae such as filamentous blue greens and greens is one of the major problems in the Philippines. These algae may totally displace Gracilaria or if not, they become so mixed with Gracilaria it becomes impossible to separate them resulting in a very low quality of the dried materials. The problem of blooms of epiphytes and other weeds has been placed under control by the introduction of grazers such as Tilapia and milkfish. However, the size and number of these grazers must be controlled otherwise these may consume the Gracilaria. The other countries at present engaged in pond culture of Gracilaria are Vietnam, Thailand, Indonesia, China (in Hainan Province), and Hawaii.
Field Culture
There are several methods now being utilized in the field culture of Gracilaria. The “seeds” used in these various methods are cuttings or sporeling produced from spores.
• Fixed bottom long line method
In this method of culture three-strand polyethylene ropes 5 to 8 mm in thickness and 5 meters long is generally used. Other materials such as coir or abaca ropes may be used as substitute. In the West Indies where the mariculture of sea moss (Gracilaria) is most successful the use of both sporelings produced from spores and cuttings are utilized as “seeds” in the fixed long line method as well as in the raft method.
The seeding of long lines using cutting consists of untwisting the rope and inserting bunches of cuttings between the strands of the rope, the seedlings passing twice or three times through the rope. This method insures that the cuttings are securely tucked in placed. The seeding of the ropes is done under the shade where the seedlings are placed in basin of sea water to prevent the cuttings from drying up.
The support system from the long line consists of wooden stakes driven into the ground. These are usually arranged in rows, the distance between stakes in the row is about one meter while the distance between rows of stakes would vary between 4 to 5 meters or longer. One end of the seeded rope is tied to a stake, stretched tightly and the other end tied to the opposite stake in the next row. In the West Indies two seeded ropes are usually tied to a pair of stakes.
The same technique is applied for ropes seeded with spores. In Malaysia, unbraided plastic raffia seeded with hatchery produced sporelings was used as long lines. In India longer ropes are used using additional stakes as support are provided to prevent the ropes from sagging to the ground. The distance of the seeded ropes from the ground vary depending on the depth and clarity of the water as affected by tidal changes. This method of field culture is being utilized in the West Indies, Burma, India, Brazil and Ceylon.
• Chilean method
The field culture method used in Chile is simple but has proven very successful. The anchoring system for the seedstocks (cuttings) consists of plastic bags one meter long, 0.1 mm thick and 4 cm in diameter. The plastic bag is filled with sand and the two ends are knotted. Five bunches of seedstock are tied to the same side of the sand-filled bags by rubber bands. The seeded bags are arranged in rows on the substratum and are positioned in such a way that the bag serves as an anchoring weight. The middle of the cuttings are weighted by the bag against the surface of the substrate with the tips of the cutting jutting free of the anchoring units.
The use of rocks as anchoring units for the cuttings was also found to be effective. However, both the use sand-filled bag and rocks as anchoring materials for cuttings was efficient in sites which are not exposed to strong surges or waves. Evaluation of the efficacy of this system showed that more than 60% of the biomass could be lost due to removal of thalli by strong surges. Using rocks as anchor system was observed to be more adversely affected than that using sand-filled bags; rock-anchored cuttings are easily dislodge from the substrate.
• Improvement of substrates
The method could only be utilized in areas where natural beds are found. The introduction of artificial substrates such as rocks, shells, bamboo or wooden stakes, etc. in the site provides additional favorable substrates for the spores to settle or fragments of thalli to attach. Most of the commercially important species of Gracilaria (beds) are found in shallow bays and coves where the substrate is generally particulate (sandy-muddy). The survival and success of spores to grow is greatly enhanced by the availability of solid substrates. Results of studies on the influence of solid substrate on biomass production had shown that production more than doubled in portions of the beds where solid substrates have been introduced.
• Raft method
The raft method is popularly used in West Indies in areas where bamboos are available. The raft generally measures 2 × 4 meters in size. The seeded long line are also utilized. One end of the seeded rope is tied to the shorter bamboo frame, stretch tightly and the other end fixed to the opposite side of the raft. The distance between ropes vary but about 12 to 14 lines may be planted to one raft.
In India the use of coir ropes fabricated into a network of 7 cm mesh size was used on a 2×2 m raft. The same method of seeding was utilized.
Variation from this method has been developed in China. Pieces of ropes about 70 cm long seeded with Gracilaria cuttings are hung horizontally on the low fixed raft or vertically along a long line floating raft.
2.2 Management of Natural Stocks
a. Important considerations in the utilization of natural stocks as source of biomass
The production of agarophytes from natural stocks is very much influenced by both the seasonal factors as well as by the harvest pressures exerted on them during the preceding cropping season. Because their growth cycles are highly influenced by environmental conditions and by man's exploitative activities their production is therefore unreliable. These are prone to over-exploitation. The need to manage and conserve their stocks is of prime importance in order to sustain or enhance further their productivity and prevent their over-exploitation.
The design of a sound management scheme for the natural stocks of commercial agarophytes depends primarily on the available information on the various aspects of their biology, such as reproduction and growth cycle, growth rates, their regeneration and recruitment capacities, productivity and the influence of environmental factors on the biomass production potentials of the stocks. The above information are necessary in the formulation of guidelines for the management of the natural stock of the target species. These information can provide answers to questions such as where the species is abundant, how much to harvest per unit area, when to harvest, how many times (cropping intervals) can the stocks be harvested in one season, what kind of harvest method is best for the species. The gathering of these basic information on the species to be managed requires basic skills in methodologies for field sampling and data gathering. Under management the production of stocks can be safely forecasted. This information is most important in quoted contracts which may be entered into by the farmer, fisherman, or exporter.
Thus, it is of prime importance that any plan to exploit natural stocks of seaweeds must be preceded by intensive biological studies to determine their seasonality in biomass production, reproduction, regeneration and recruitment. These information are necessary in determining the best possible time to harvest and the amount of harvestable stocks without diminishing their production capacities.
b. Requisite for the rational exploitation of natural stocks
Under a free-for-all situation, there is a tendency for the resource users to over-exploit the resources especially where there is a prevailing demand for the produce. The literature is replete with records of loss of the resource due to over exploitation. Thus, it is necessary that the commercial exploitation of natural stocks of seaweeds or any resource be preceded by biological studies which shall be the basis for their management. The following are the required biological studies which should be done in coming up with information as basis for the management of the stocks:
Inventory and assessment of stocks
The inventory and assessment of stocks are initial studies which should be done in areas where the exploitation of the stocks has not started, to know the kinds (species) potentially available for development, where and when these species are abundant, how much biomass is available for harvest and the behavior and responses of the stocks to certain degrees of exploitation.
The need to know the real identities of the different species is very important because unlike other resources, e.g., fish, crustaceans, etc., the kinds and quality of agar vary with species. Thus, it is very important that the taxonomy of the species comprising the stocks be known. In addition the quality of the hydrocolloid (agar) be defined, characterized or evaluated as the price of the produce is determined by the quality of the extractable agar from them. In the world market for agar the name of the species and in case of Gracilaria the information on the source of the dried raw material are important because these reflect the differences in the properties of these agar, e.g., there are the Gelidium, Pterocladia, and Gracilaria agar. The Gracilaria from Chile for instance is more high priced than Philippine Gracilaria because it contains high quality agar. Thus, the names applied to these produce serve as basis for the pricing of the produce. The price is generally based on the moisture content and purity and quality of the agar (gel strength, melting and gelling temperatures, viscosity and amount of sulfate group).
The information on the abundance and distribution of the resource in space and time may be gathered through biomass sampling of the stocks. There are available methodologies which have been applied and these may slightly differ depending on the behavior of the resource. However, the transect quadrant method is generally applied especially in situations where the stocks are not homogeneously distributed in space. The size of the bed is first delineated and permanent transects are marked. The orientation of the transects is generally related to certain ecological gradients, e.g., depth, wave exposure. Biomass sampling are generally done on a monthly basis along the transects; the size of the quadrant vary from 0.25 to 1.0 m2, and the number of quadrants to be sampled along the transects may also vary depending on the size and homogeneity of the bed, the time and efforts required but most important is the reasonableness of the amount and kind of data for statistical analyses i.e. the more samples to be gathered, the more reliable the data will tend to be.
The amount of loose (drift) biomass should also be monitored to come up with reliable data on the total biomass production of the bed.
Data on the biomass production recorded for a period of one year will indicate the annual productivity and seasonality in the production of the stocks. Additional year round of data will make the information on the stocks more reliable as basis for management. In most stock assessment works where the target species or group of species and their distribution are known the main concern in sampling is the production data.
The size of the bed must be known so that the potential total production of stocks can be determined. This information is vital in determining how much of the stocks should be harvested without unduly diminishing their productivity. Using the production data from the samples, total production of the bed may be projected/calculated by multiplying the biomass data (e.g., g/m2) by the size of the bed. The accuracy of the method is much improved if regular and repeated sampling on the stocks are done through time.
Additional source of information on the seaweed production in the area can be gained through interviews with market vendors and seaweed gatherers. Initial interviews may be done in local open markets where seaweeds are sold. Seaweed vendors are good source of information on the kinds of species, amount they sell, source of seaweed stocks, the supplier and the approximate number of gatherers. Seaweed gatherers are good source of primary data on production. They can be easily identified by inquiring from local officials in the area. Data on gathering sites, number of gatherers, the gathering season and output per unit effort, may be acquired from this source. Estimate of local production can then be made and counter-checked with the data on potential biomass production of the beds or collecting area.
The seasonal variation in the reproductive/fertility states of the stocks should also be known. The fertility of the stock may be determined by randomly collecting 50 or more thalli and the number of the vegetative and fertile thalli are determined. This is usually expressed as % fertility. This information is relevant in the scheduling of harvesting/cropping periods. The recruitment capacities of stocks is generally influenced by their states of fertility especially for those species where recruitment is largely dependent on the production of reproductive cells (spores). Cropping or harvesting should be scheduled some time before or after the peak of fertility of the stocks in order not to unduly interfere with the recruitment process. This, however, may not be relevant on species where production is mainly based on vegetative means (cuttings, fragments). Some stocks of Gracilaria, for instance, have been reported to be purely vegetative (Rueness et al., 1987). Pond cultured Gracilaria in Northern Philippines have been observed to be purely vegetative the whole year round (per. comm.). In cases where recruitment is primarily based on vegetative means certain amount of the seedstocks is retained in the bed for next season's cropping. This amount may be equivalent to the amount of biomass produced in the bed during it's lowest production period.
In addition to these basic biological studies harvesting experiments should be carried out to determine the production capacities and the effects of different harvest pressures and methods on the regeneration of the stocks. The information in the capability of the stocks to regenerate to their former level of production after trial cropping/harvesting shall be the basis for determining the harvest schedules during the cropping season.
Development and application of management scheme for the stocks
The application of a management scheme on natural stocks has been shown to significantly improve the total production of the beds. In Chile, the annual production of the Gracilaria in Lenga Cove located in San Vicente Bay increased from 80 MT to 600 MT after the application of a management programme (Poblete and Inostroza, 1987). It is apparent from their studies that the strict application of a management scheme, had improved the production ecology of the bed resulting in a 7.5-fold increase over normal production.
In general the formulation and application of a management scheme for the natural stock of seaweeds may follow the following stages/steps. Variation from this scheme may be necessary to suit certain biological characteristics of the species. The basic considerations include:
• The seasonal changes in the annual productivity of the stocks
The information on changes in the annual productivity of the stocks are derived from the monthly biomass measurements done on the bed. It provides information on the total amount of biomass available for cropping and the season when cropping/harvesting may be done. In addition to the information on the annual productivity of the stocks, the seasonal variation in the amount of agar contained in the crop is also considered in the scheduling of the harvest. High quality crop is obtained when cropping is done during periods when its agar contents is high.
• Determination of the amount of biomass to be left after cropping
The amount of biomass left after the first cropping is very important in determining the amount of biomass available for the next cropping season. It is a rule of thumb that this minimum amount to be left in the bed to serve as “seeds” for the next cropping season should not be less than lowest biomass recorded during the year. The amount of biomass available for harvest will be the difference between the total amount of biomass available in the bed during its peak production period and the minimum biomass during its depressed period of growth.
• Determination of the harvest schedule
How often should the harvest be done during the peak production season of the stocks? The harvest regimes can be determined from information on the regenerative capacity of the stocks, e.g., from the results of studies on different trial harvest pressure. The schedule of subsequent harvests is determined by the period within which the stock can recover its original biomass after the first harvest.
• Control of the amount of biomass to be harvested
The amount of biomass to be harvested during each harvest regime should not exceed the amount of biomass available for cropping. The amount of biomass available for cropping is the difference between the maximum amount of biomass during its peak production period and the minimum amount of biomass during the stress period of growth. Thus, it is necessary that the number of fishermen should be limited and the amount of crop each should be allowed to harvest must not exceed his share of the available biomass for cropping during each of the cropping period.
• Protection of the recruitment and regeneration processes
This is a very important consideration because the continuity of the stocks depends on these processes. The approach may differ depending on the biological characteristics of the species. For stocks which depend on the regeneration of biomass through vegetative structures such as holdfast, cuttings or fragments, and underground thalli, the protection of these structures may be done by the application of harvest methods which would cause the minimum harm to these regenerative structures. For those stocks where recruitment and regeneration processes depend on both the reproductive cells and the vegetative structures, the timing of the harvest so as not to impede or adversely affect recruitment and the method of harvest which will have minimal destructive effects on the regenerative structures are important considerations. Thus, harvesting should not be done during peak fertility of the stocks.
• Socio-economic consideration in managing the resources
The fishermen/seaweed gatherers should be organized into production groups such as cooperative. Only the bonafide members have the right of access to the resource and the amount of harvest each of the member is allowed to crop is determined by his fair share of the available biomass for cropping. The legal basis for enforcing these regulations can be easily achieved through the rules promulgated by the local government or by the cooperative's established rules/regulations. Peer pressure among the members is a strong factor which may be applied to the members. The management of the cooperative is done by the selected members. A portion of the earnings of the members is channeled back to the cooperative for management support. Technical assistance should be extended to the cooperative by the concerned government agencies.
3. Production of Caulerpa
3.1. Pond Culture
The development of a new area into Caulerpa ponds consists of several stages, namely, site selection, pond construction, planting of the ponds, maintenance of the culture, harvest and post-harvest activities. Fishponds with marginal production are usually preferred because initial investment for their conversion to Caulerpa ponds is low and usually the location of these unproductive fishponds generally fits the ecological requirements of Caulerpa culture, that is, they are far from sources of freshwater and pollution sources.
a. Site Selection
The success in the culture of Caulerpa depends primarily on the selection of a good site. The following ecological factors have to be considered when electing sites for pond culture of Caulerpa.
The site must be far from sources of freshwater such as rivers and streams. Caulerpa is a purely marine stenohaline alga and will die even in slightly brackish seawater. The salinity should not be lower than 30 ppt.
The elevation of the pond bottom must be at or just a little above the zero tidal level. This is necessary in order to enhance proper water management in the ponds. Frequent water change is necessary for the growth and development of Caulerpa.
The site must be protected from the destructive effects of wind and waves. A buffer zone of mangroves and/or coral reef is necessary.
The substrate must be loamy-muddy. However, very deep, soft mud must be avoided.
Sites with acidic soil should be avoided. Caulerpa will not grow in areas characterized by low pH.
The area must be near an unpolluted source of seawater supply. Caulerpa is consumed fresh, thus it must be grown in areas free from both domestic and industrial pollution. Bacterial contamination of the crop should be avoided. Caulerpa may also absorb pollutants such as heavy metals and toxic chemicals which it can accumulate with deleterious effects to the consumers.
Existing saltwater ponds can be used for Caulerpa culture. Some framers stock milkfish in Caulerpa ponds as a secondary crop.
b. Pond Construction
The maintenance of good water quality necessary for good growth of Caulerpa through proper water management is dependent on the proper design of the ponds. The traditional layout of ponds for milkfish and shrimp production does not provide the necessary water exchange required in Caulerpa culture.
Caulerpa ponds may be divided into compartments of 0.10 to 0.25 hectare and should incorporate a flow-through design; each of the compartments should be provided with individual entrance and exit gates positioned in such a way that the water could easily be changed and circulated during the draining and flooding process. The flow-through design is important to facilitate frequent and complete water change necessary in maintaining high nutrient level in the seawater required by the seaweed for rapid growth and development. Peripheral or diversion canal may also have to be provided to divert runoff water from the ponds during rains to avoid drastic lowering of salinity in the ponds which is detrimental to the crop.
c. Planting of the Ponds
The ponds should be drained to a depth of 0.3 meters to facilitate planting. During the early development of the culture, broadcasting was used to “seed” the ponds with Caulerpa cuttings. However, this technique was found to be inefficient because the “seeds” were not uniformly distributed on the pond bottom and resulted in the uneven growth of the crop.
Planting is done by burying into the mud one end of a handful of Caulerpa cuttings at about one meter interval. Uniform planting is facilitated with the use of lines as guide or the planted spots are marked by pieces of bamboo. After planting, the ponds should be flooded to a depth of about 0.5 to 0.8 m. Flooding should be done slowly to prevent the newly planted cuttings from being uprooted and carried away by the current. The newly planted ponds must be inspected a day or so after planting and the unplanted areas should be planted to ensure uniform growth. The pond water should be changed only several days after planting to make sure that the cuttings are already well rooted and could not be carried away by water currents.
An initial stocking rate of 1000 kg per hectare under favorable weather conditions can produce a good crop in about two to three months.
d. Water Management
Proper water management is a key factor in the successful pond culture of Caulerpa. Ideally, the pond water must be changed every three to four days at the start of the growing period in order to avoid strong water currents which may uproot the seedlings. The frequency of water changes should be increased to every other day at about the third week after planting especially when the plants start to form a thick growth on the pond bottom. Frequent water exchanges provide fresh supply of nutrients for the normal growth and development of Caulerpa, thus, it will eliminate the need for fertilizer application.
In general the water in the ponds must be maintained at a depth where the Caulerpa is visible from the surface of the water. Thus, the depth of the water in the pond would vary depending on the transparency of the pond water to provide enough light for photosynthesis. However, adjustments in water depth should be made to avoid perimeter dikes from collapsing during spring tides when the tidal amplitudes are extreme. During rainy days the pond water should also be maintained at a slightly greater depth to reduce the possibility of a dilution below 30 ppt. Caulerpa will die when the salinity goes below this level and the entire crop may be lost. After heavy rains the pond water should be immediately drained and replaced by fresh seawater to ensure that the salinity is maintained at or above 30 ppt.
Fertilization may not be necessary as long as frequent water exchange can be made. However, fertilizer has to be applied especially one or two weeks before the harvest, when a large crop has already been produced and when the plants appear to be pale in color (that is light green or yellowish). The sufficient rate of fertilization is about 16 kg per hectare. Nitrogenous fertilizers have produced very good results. The plants regain their healthy green color a few days after application. The fertilizer may be broadcasted, but past experience has shown that wrapping the fertilizer in many layers of gunny or plastic sacks and suspending these in strategic places in the pond at a level where the bags are just about half submerged in water, produces very good results. The fertilizer should be applied right after water in the pond has been changed for several days after the fertilizer has been applied.
Weeding is an important activity which should be done regularly to remove other seaweed species and associated organisms growing in the pond. Weeds compete with Caulerpa for space, light and nutrients. The weeds and the associated organisms should be removed before they take over as dominants. The presence of the weeds results in decreased production and low quality of the product and adds extra labor cost to sort them out before the product is sold in the market.
The dikes and gates of the ponds must be continuously maintained to effect efficient water management. This is especially critical during the monsoon season when strict and efficient water management is required to avoid extreme dilutions due to heavy rains.
e. Harvesting and Post-Harvest Activities
Depending on the growth rate of the plants the crop may be harvested two months after the initial planting, when the plants had already formed a relatively uniform carpet on the pond bottom. The plants at this stage are of high market quality, light grass-green in color, soft and succulent in texture. Older plants though high in biomass are of lower quality because they are tougher in texture and their basal portions are pale or colorless. The paling of the basal portions of the fronds are caused by self-shading when the plants became older and form very thick carpet.
Harvesting is done by uprooting the plants from the muddy pond bottom. More crops can be produced during a growing season if partial harvesting is done leaving a sizeable amount of 20–25 percent of the crop in the pond to serve as seedstock for the next crop. Harvesting should be done in such a way that the leftover of the crop is more or less uniformly distributed in the ponds. Large vacant areas of the pond bottom should be replanted to ensure uniform crop stand. This practice has drastically reduced production costs by savings made in labor costs for replanting. The sizeable amount of seedstock left in the pond also results in a much shorter growing period and the farmers in Mactan, Cebu claim they can harvest every two weeks after the first harvest during the optimal growing season (dry season). Studies have shown that the algae could triple its initial weight after two months (Trono & Denila, 1987).
Harvested seaweeds are thoroughly washed in seawater to remove the mud and other debris. They are then sorted, unsuitable thalli and other seaweed species are removed. The clean seaweed is placed in bamboo baskets lined with banana leaves or other seaweeds such as Sargassum. The baskets are filled with clean seaweeds, then topped with leaves or Sargassum and finally covered with plastic sack which is secured by lacing its margin to the basket. The baskets are placed under the shade where they are allowed to drip before transporting them to the market. The product can stay fresh for four to five days.
Caulerpa for export to other countries (such as Japan) is shipped as a fresh product or in brine-cured or salted form. The seaweed is first thoroughly washed several times in seawater. Then thalli of good quality are selected. The clean seaweed is first completely drained of water, packed in styrofoam boxes provided with aeration holes on the upper side or cover of the box, taped and sent to its destination by air cargo. A large portion of Caulerpa exported to other countries is either brine-cured or salted. The latter two forms can be kept for longer periods and may be transported by surface cargo.
3.2. Open Lagoon Farming
Open lagoon farming of C. lentillifera have been successfully tried in some parts of the Philippines. The selection of the site for the farm is a primary consideration which would determine the success or failure. Several criteria are considered in the selection of sites for farming. Caulerpa is a stenohaline marine alga. It can not survive or successfully colonize brackish areas where salinity is lower than 28 ‰ so that lagoons located away from sources of fresh water are preferred. The water depth must be at least 1–2 feet during low tides. Shallow lagoons are usually characterized by turbid waters, thus areas which are deep should be avoided because light may become the limiting factor to growth. Sites characterized by good amount of tidal flushing is preferred because renewal of nutrients is facilitated as well as minimize sedimentation which may cover the plants cutting off of light needed for photosynthesis. The presence of a rich algal community is a good indicator that the site can support Caulerpa farming. Sites with barren substrates should be avoided. The substrate should be loamy muddy although areas with very deep soft bottom should be avoided.
The area should first be partly cleared of other seaweeds and seagrasses before planting. The method of planting follows that applied to pond culture. One end of a handful of Caulerpa cuttings are buried into the muddy lagoon bottom. The seedlings are planted at 0.5 m intervals or closer. The development of the seedlings are monitored at the start to ensure that these are not covered or overgrown by other seaweeds species. Weeding will thus give them a headstart to colonize the area.
Harvest may be done after a month or so when the stocks has developed 50% cover on the substrate. Thinning or partial harvest is done to provide enough stocks for the succeeding crops.
References
Armisen, R. and F. Galatas. 1987. Production, properties and uses of agar. In D. J. McHugh (ed.) Production and utilization of products from commercial seaweeds. FAO Fish. Tech. Pop. (288): 1–57.
Barrales, H. and A. Pizarro. 1986. Field Assessment of Two Methods for Planting the Agar-Containing Seaweed, Gracilaria, in Northern Chile. Aquaculture: 59: 31–43.
Bird, K.T. 1987. Gracilaria Cultivation in the Caribbean. Paper Presented at the 1987 Caribbean Aquaculture Trade Expo. in Puerto Rico. 8 pp.
Bird, K.T. 1988. Agar Production and Quality from Gracilaria sp. strain G-16: Effects of Environmental Factors. Botanica Marina 31: 33–39.
Bird, K. T., M. D. Hanisak and J. Ryther. 1981. Chemical Quality and Production of Agar from Gracilaria tikvahiae Grown in Different Nitrogen Enrichment Conditions. Botanica Marina 24: 441–444.
Chiang, Y. M. 1981. Cultivation of Gracilaria (Rhodophycophyta, Gigartinales) in Taiwan. Proc. 10th Intl. Seaweed Symp.: 569–574.
Daugherty, B. and K. T. Bird. 1988. Salinity and Temperature Effects on Agar Production for Gracilaria verrucosa Strain G-16. Aquaculture 74: 1–9.
De Zaixso, A.L.B. 1987. Gracilaria verrucosa in Golfo Nuevo, Chubut, Argentina. Biological parameters and environmental factors. Hydrobiologia 151/152: 239–244.
Doty, M. S. 1986. Estimating farmer returns from producing Gracilaria and Eucheuma on line farms. Monografias Biologicas, 4: 45–62.
Doty, M. S. and V.B. Alvarez. 1973. Seaweed Farms: An Approach for the U. S. Industry. In: Marine Technology Society 9th Annual Conference Proc: 701– 708.
Doty, M. S. and V. B. Alvarez. 1975. Status, problems, advances and economics of Eucheuma farms. J. Mar. Technol. Soc. 9(4):30.
Guerin, J. M. and K. T. Bird. 1987. Effects of Aeration Period on the Productivity and Agar Quality of Gracilaria sp. Aquaculture 64: 105–109.
Guerrero, R. D. 1989. Producing Gulaman in Ponds for Export. Fishbites. Agribusiness Weekly. July 14–20: 12. Lin, M. N., G. Y. Lin and T. L. Huang. 1979. Preliminary Report on the Improvement of Gracilaria Farming. Agriculture 2(3): 22–31.
Naylor, J. 1976. Production, trade and utilization of seaweeds and seaweed products. Fisheries Tech. Paper No. 159. FAO, Rome.
Neisch, A.C. 1978. Developments in the culture of algae and seaweeds. pp. 395–402. In. T.V.R. Pillay and W. A. Dill (eds.). Advances in Aquaculture. Fishing News Books Ltd., Farnhein, Surrey, England.
Poblete, A. and I. Inostroza. 1987. Management of a Gracilaria natural bed in Lenga, Chile: A Case Study. Hydrobiologia 151/152: 307–311.
Raju, P.V. and P.C. Thomas. 1971. Experimental Field Cultivation of Gracilaria edulis (Gmel.) Silva. Botanica Marina. 14: 71–75.
Rueness, J., H. A. Mathisen and T. Tananger. 1987. Culture and field ovservations on Gracilaria verrucosa from Norway. Botanica Marina 30: 267– 276.
Santelices, B. J. Vasquez, U. Ohme and E. Fork. 1984. Managing wild crops of Gracilaria in Central Chile. Hydrobiologia 116/117: 78–89.
Sijian, L. 1986. Experiments of Picking Spore and Raising Seedling of Gracilaria tenuistipitata. Jour. Zhanjiang Fish. Coll. 1: 31–34.
Sijian, L., L. B. Bensong, Z. Shufang, L. Bingsin and J. Zhenying. 1986. The Experiment of Gracilaria tenuistipitata fixed to Sporeling Rope with Float Raft in Tidal Zone. Jour. Zhanjiang Fish. Coll. 1: 35–38.
Smith, A. 1986. A guide to seamoss cultivation in the West Indies. Carribean Conservation Association Publication. 19 pp.
Smith, A. H., Nichols, K. and McLachlan, J. 1984. The cultivation of seamoss Gracilaria in Sta. Lucia, West Indies. Hydrobiologia 116–117: 249–251.
Tachanavarong, S. 1988. Gracilaria Culture in Thailand. In: Report on Training Course on Seaweed Farming. ASEAN/SF/88/GEN/6: pp. 136–141. FAO Publication.
Thomas, P. C. K. Rama Rao, and K. Subbaramaiah. 1975. Changes in natural growth of Gelidiella acerosa (Forsskal) Feldmann et Hamel in an exploited population. Botanica Marina 18: 241–243.
Trono, G. C. Jr. 1974. Eucheuma farming in the Philippines. Univ. of the Philippines Natural Science Research Center Publication. 13 pp.
Trono, G.C. Jr. 1981. The Present Status of Production and Utilization of Seaweeds in Asia. In: G.C. Trono, Jr. and E.T.G. Fortes (eds.) Report on the Training Course on Gracilaria Algae. SCS/GEN/81/ 29: 44-44. FAO Pub., Manila.
Trono, G.C. Jr. 1981. Field Culture of Gracilaria and other Species. In: G.C. Trono, Jr and E.T.G. Fortes (eds.) Report on the Training Course on Gracilaria Algae. SCS/GEN/81/29: 51–56.
Trono, G.C. Jr. 1981. Natural production of commercially important seaweed species. In. G.C. Trono, Jr. and E.T. Ganzon-Fortes (eds.) Report on the training course on Gracilaria algae. SCS/GEN/ 81/29: 45–46.
Trono, G.C. Jr. 1986. Seaweed Culture in the Asia-Pacific Region RAPA Publication 1987/8. Regional Office for Asia and the Pacific. FAO of the United Nations, Bangkok Thailand. 41 pp.
Trono, G.C. Jr. 1986. Seaweed Culture in the Asia-Pacific Region. RAPA Publication 1987/8: 15–18. FAO, Bangkok.
Trono, G.C. Jr. 1987. Studies on the pond culture of Caulerpa. Phil. Jour. Sci., Monogr. 17: 83–98.
Trono, G.C. Jr. 1988. Production of Economically Important Seaweeds through culture and Harvesting of Natural Stocks. In: Report on the Training Course on Seaweed Farming. ASEAN/SF/88/GEN/6: 59–70. FAO Publication.
Trono, G.C. Jr. and E.T. Ganzon-Fortes. 1988. Philippine Seaweeds. 330 pp. National Bookstore Inc., Metro Manila, Philippines.
Trono, G.C. Jr. (1989, in press). Inventory and assessment of natural stocks of marine macrobenthic algae. In: Proceedings of Seaweed Research Training and Workshop for Project Leaders. 6 pp. Jointly sponsored by the Marine Science Institute, College of Science, University of the Philippines at Quezon City, and the Philippine Council for Agricultural Resources Research and Development, Los Banos, Laguna, Philippines.
Uyenco, F., L.S. Saniel and G.S. Jacinto. 1981. The “ice-ice” problem in seaweed farming. Proc. International Seaweed Symposium 10: 625–630.
FAO. 1983. World Seaweed Industry and Trade. Joint ADB/FAO (SCS-INFOFISH) Market Studies. Vol. 6. 30 pp. SCS/DEV/83/26. FAO, Manila.
