V.S.K. Chennubhotla *
In India the Gulf of Mannar, Gulf of Kutch, Calh Bay, Hanshadweep and Bay islands are the important areas for seaweed culture owing to their considerable natural resources. The area stretches along the 6,100 km long coast line of the country.
About 680 species of seaweeds belonging to the groups Chlorophyta, Phaeophyta, Rhodophyta and Cyanophyta occur naturally in varying degrees of abundance in shallow bays, lagoons and coastal areas which offer suitable substrata for their growth and propagation.
Apart from their utility as a source of food, food derivatives, vitamins, proteins, etc., seaweeds provide the raw material for many agar-agar and algin based industries. The exploitation of carragenophyta such Hyphea, Acanthophora, Laurencia, etc. has yet to be done in the country. All these are available in sizeable quantities.
In view of the constant demand for seaweeds, research programmes on seaweed resources and their culture were taken up by the Central Marine Fisheries Research Institute and Central Salt and Marine Chemicals Research Institute at Mandapann at their Regional and Field Centre, respectively, and various other research organizations belonging to the state fisheries departments/universities. Seaweed farming experiments were mainly carried out with species of Ulva, Gelidiella acerosa, Gracilaria edulis, Gracilaria sp., Corhcata, Gelidiopsis variabilis, Gelidium pusillum, Hypnea musaformis, Acanthophora spicifera, Hormophyta triqueta, Cystoseira trinodis and species of Sargassum. The experiments were main conducted by the method of vegetative propagation. Some trials were made with spores as well. An appraisal of different techniques adapted is as follows:
II. Culture of Gelidiella acerosa
Bhanderi (1974) cultured the apical region of the Gelidiella acerosa by inserting these fragments in a string and suspended in a seawater aquarium at Port Okha, Gujarat. He observed a linear growth of 0.01 cm/day and an increase of 0.01 g/day in weight. Krishnamurthy et al. (1975) conducted some experiments with 2 cm fragments of G. acerosa in a lagoon on the southern side of Krusadi Island. After 4 months, the fragments grew to full sized plants of about 10 cm in length with 7 to 8 branches.
In the same area Subbaramaiah et al. (1975) carried out experiments on 2 cm length fragments of G. acerosa fastened to a nylon string at fixed intervals and the seeded string was wound around a rope kept submerged in coastal waters. The maximum growth attained was 6.6 cm and the rate of production was 3.13 g/m/month (wet). The total production of seaweed was 421 g/m (wet) in a year.
* Central Marine Fisheries Research Institute, Cochin-31, India.
Experimental field cultivation of G. acerosa using submerged coral stones as the substrata was done at Ervadi (Patel et al., 1979). An annual yield of 115.83 g/m2/day (dry) on overall basis was obtained which was 33 times over the seed material. Patel et al. (1980) reported a maximum yield of 122 g/m2 (dry) in one of their six monthly harvests made in January 1979 from the field cultivation of G. acerosa at Ervadi.
III. Culture of Gracilaria edulis
Raju and Thomas (1971) cultured G. edulis by long-line rope method in a sandy lagoon in Krusadi Island. Fragments of 1 cm and 2.5–3 cm length were used for planting and they grew to a length of 35–40 cm in about 5 months period. Three harvests were made at the end of 5,8 and 10.5 months and the total harvest during the year was about 3.5 kg per 1 m length of rope. Krishnamurty et al. (1975) carried out cultivation of G. edulis in a lagoon in the Krusadi Island. Fragments of 2.5 cm length were introduced in the twists of the ropes, which were tied to bamboo poles planted to the sea bottom. In about 5 months the plants attained a length of 30 cm and the average weight of plant was about 300 g. A total of 3 harvests were made in a 10-month period.
IV. Culture of other red algae
Bhanderi (1974b) recorded a linear increase of 0.02 cm/day and a weight gain of 0.07 g/day in his culture experiments on Gracilaria corticata in seawater aquarium. In experiment with Gelidiopsis variabilis he obtained a linear increase of 0.12 cm/day with an increase in weight of 0.04 g/day.
Mairh and Sreenivasa Rao (1978) cultured Gelidium pusillum in the laboratory under free floating conditions using nutrient enricher and obtained maximum fresh weight and full size within 3 to 4 months. Rama Rao and Subbaramaiah (1980) cultured Hypnea musciformis and obtained a four-fold increase in 25 days.
Thivy (1964) conducted culture experiments in ponds at Porbandar by attaching small plants of Sargassum cinctum, S. vulgare and S. wightii to coir nets tape. The plants grew to 15–52 cm from an initial 5–10 cm length within forty days. Bhanderi and Trivedi (1977) made an attempt to study the possibility of culturing Hormophysa triquetra by vegetative propagation in an aquarium. The fragments gained 7 times (fresh weight) over the initial weight at a rate of 0.333 g/day.
V. Seaweed culture experiments at Central Marine Fisheries Research Institute
The Central Marine Fisheries Research Institute at its Regional Centre at Mandapam, conducted culture experiments especially with Gracilaria edulis, and Gelidiella acerosa. In seawater aquaria Gracilaria corticata (Umamaheswara Rao, 1973) was cultured and showed an increase in length from 1.8 to 5.5 cm in 90 days. Experiments with Gracilaria edulis in 0.5 m2 coir net yielded very good results. The average height of the plants varied from 14 to 16 cm at the end of 2 months and the fragments gained a weight of 213 and 257 g respectively. Experiments conducted in 4 × 2 m size coir rope nets yielded 4.4 kg (fresh wt.) of seaweed per square metre in 80 days (Umamaheswara Rao, 1974a).
The culture experiments were conducted by introducing fragments of the seaweed into the twists of the coir ropes which in some cases were fabricated in the form of nets of different sizes. These were tied to wooden poles fixed in the coastal waters.
Experiments conducted in the submerged floating condition (Chennubhotla et al. 1978) proved to be more beneficial than that at sub-tidal level.
The cultivation was attempted at slightly deeper waters i.e. 3–4 m depth on HDP rope nets to avoid intensity of sedimentation and grazing by fish. The yield obtained was about 4 times the initial weight after 70 days. Chennubhotla et al. (1977c) cultured G. acerosa by tying small fragments along with substratum (coral piece) to the coir ropes in the net. One frame was introduced with 0.9 kg and the other with 1 kg seed material. A yield of 2.5 and 3 kg were obtained, respectively after 76 days.
Experiments conducted by keeping the G. acerosa seeded coral stones kept in cages were introduced in 2 and 4 metres depth. The growth of the seaweed was luxuriant.
The culture, which consisted of fastening fragments of G. acerosa to coral stones with the help of iron nails, reached harvestable size after 5 months, and 1 kg of seed material yielded 3.1 kg of fully grown plants.
Fragments of Sargassum wightii obtained from the basal portion of plants with holdfast were inserted in the twists of the coir ropes and cultured in inshore waters of the Gulf of Mannar at 1 m depth in mid water level. An average growth of 15.5 cm was recorded from an average initial length of 7.7 cm within 60 days. (Chennubhotla et al., 1976, unpublished)
Cultivation of Acanthophora spicifera was carried out on 2 HDP rope nets in 60 × 30 m sized ponds, which are connected through a feeder canal to the sea. An average yield of 22.615 kg (wet weight) was obtained after 45 days from the two nets which was found to be 3.6 times the initial seed material. The remnants were allowed to grow for the second harvest which was made after 35 days. An average yield of 14.4 kg was obtained in the second harvest (Chennubhotla et al., 1976, unpublished).
Experiments on Ulva lactuca, pre-treated with ascorbic acid were cultured in the seawater of different salinities in the laboratory. It was observed that the trials with 18% salinity boosted the production to 8 times in 92 days (Chennubhotla et al., 1976, unpublished).
VI. Culture of spores
The number of spores produced by an alga is enormous. In nature only a small number of spores grows to mature plants since viability, settlement and development of these spores are controlled by hydrobiological factors such as water movement, tidal-exposure, water temperature, competition for space and predators or grazing organisms. When the spores are raised into germlings on suitable substrata in the laboratory or nursery and then transplanted to the field, a high rate of germlings grows to harvestable size plants. Some work in this direction of culturing the spores of economically important seaweeds has been carried out in recent years.
Subbaramaiah et al. (1967) cultured germlings of Ulva lactuca. The germlings were kept growing in attached or in a free floating condition in petri-dishes containing sterile seawater which was changed once a week. In 2 months the germlings differentiated into cylindrical plants with 2–3 branches arising from the basal cells. The floating plants were found to be longer (1.25–1.7 m) and produced branches while the attached ones were shorter (0.75–0.83 m).
The effect of different culture media on growth and sporulation of laboratory raised germlings of Ulva fasciata was given by Oza and Sreenivasa Rao, (1977). Kale and Krishnamurty (1967) studied the effect of plain seawater, Erdschreiber seawater and artificial seawater medium (modified ASP-6) on the growth of germlings of Ulva lactuca var. rigida.
Mairh and Krishnamurty (1968) observed 100% germination of spores of Cystoseira and 94% survival. The germlings survived and grew to young and healthy plants under experimental conditions. Chauhan and Krishnamurty (1967) cultured the oospores of Sargassum swartzii in petri-dishes lined with filter paper. They developed into germlings and some of them grew for a period of 5 weeks. Experiments were also conducted using different substrata such as coral pieces, shells, granite stones, nylon threads and rough stones. Some of the oospores attached to the substrata developed in to healthy germlings while a large number did not survive. Continuous illumination of the culture experiments with a light intensity of 600–800 lux, 23–26 °C temperature and circulation of a thin stream of filtered seawater were found favourable for healthy growth of germlings. Chauhan (1972) observed the survival of germlings in Sargassum swartzii for about 6 months under controlled laboratory conditions. Of the eight different substrata used, concrete blocks, bricks and filter paper were found to be good substrata as they retained 84.55%, 78.42% and 62% of the germlings, respectively. Filtered seawater and enriched seawater were found to be most suitable culture media for the growth of germlings. The use of media like ASP-6 and SP-12 did not give good growth of germlings. Continuous illumination was found to be more beneficial than 18 hours photoperiod.
Raju and Venugopal (1971) made an attempt to allow the oospores of Sargassum plagiophyllus to settle on a concrete substratum with a view to finding out the time required for the appearance and growth. The concrete cylinders were lowered in Sargassum beds. Observations revealed that the appearance of Sargassum germlings on the cylinder took 10 months and another 8 months to grow to maturity. Observations after one year revealed that there was a number of new plants which had germinated from the spores within the year and some had regenerated from persisting holdfasts. There appears to be potential for regeneration for a third year in a few plants. Umamaheswara Rao and Kaliaperumal (1976) maintained the oospores of Sargassum wightii in a medium of seawater enriched with agar-agar and found that 47.6% of germlings were healthy at the end of 60 days. Krishnamurthy et al. (1969) raised the germlings of Gracilaria edulis and G. corticata on a nylon fabric from carpospores under laboratory conditions. They were then transferred to the sea. After four months, young plants appeared and they took another four months to attain maturity and develop reproductive structures. Chennubhotla et al. in 1977 (unpublished) conducted laboratory culture experiments on the viability, germination, and growth of germlings of Turbinaria ornata and Gracilaria edulis under controlled temperature of 18+/-2 °C and light intensity of 4 R lux. The spores of T. ornata were found to be viable even after a period of 2 months, but growth of germlings was not satisfactory. Carpospores of G. edulis were allowed to germinate and parenchymatous stage of development was noticed.
The UNDP/BOBP programme at Madras has embarked on the culture of seaweeds by tetraspores in Mandapam-Vedalai area. This may throw light on the aspect of spore culture in the natural environment.
VII. Environmental factors in relation to seaweed culture
In the Central Marine Fisheries Research Institute, culture experiments were conducted in different seasons of the years from 1976 to 1985 continuously. Although there were variations with respect to the quantity of seed material introduced, the yield rate showed fluctuations during certain seasons. In order to understand these variations, relevant environmental data were collected from the inshore waters where culture operations were carried out.
The average values of each environmental parameter such as surface temperature, salinity, O2 and nutrients during each culture operation were compared in relation to biomass increase and duration of culture period. (Table 1). It was observed that no single environmental parameter could be pin-pointed as responsible for variation in production. At best it could be inferred that a complexity of environmental factors operating in a dynamic inshore area may be responsible for seasonal variation in the yield of seaweeds. The Gulf of Mannar and Palk Bay experience contrasting seasonal changes in wind velocity and direction. The solar radiation in the region, rainfall, transport of inorganic and organic material into the region are some of the factors other than those observed parameters.
VIII. Survey of seaweed resources
Surveys conducted in various maritime states of India have revealed that the resources of seaweeds along the coasts can be placed at around 100,000 tonnes. The quantities by area are as follows:
|Station No.||Area||Annual yield in tonnes (fresh wt)||References|
|I||Tamil Nadu||22,044||Subbaramaiah et al., (1979a)|
|II||Gujarat||20,000||Chauhan & Krishnamurty (1968)|
Bhanderi & Trivedi (1975)
Sreenivasa Rao et al., (1964)
Chauhan & Mairh (1978)
|III||Maharashtra||20,000||Untawale et al., (1979b)|
|IV||Lakshadweep Islands||8,000||Subbaramaiah et al., (1979b)|
|VI||Kerala||1,000||Chennubhotla et al., (1987)|
Table 1. Data on seaweed production and related environmental factors in the Gulf of Mannar and Park Bay, south east coast of India.
|Year||No. of days of culture operation||Initial weight of seed material|
|Ave. gain of seed|
|Mean values of hydrological data||pH|
|Surface Temperature (°C)||Salinity|
|Gulf of Mannar||30||1.00||4.30||0.1100||27.7||32.79||4.65||0.45||0.53||8.25||8.2|
Gulf of Mannar
Gulf of Mannar
Gulf of Mannar
Gulf of Mannar
The seaweeds along the Indian coasts are harvested by small and large scale industrialists by engaging divers. Seaweed collection is a profession by itself and offers employment to rural people. There are a number of agents who deal with the collection and supply of seaweeds to the industries. The method of collection of seaweeds are very crude at present. Extension work is essential to educate the people on the collection and management of natural beds in a judicious way.
IX. Economics of seaweed culture
In view of the importance of marine algae as a source of food, fodder fertilizer and pharmaceutical compounds, augmentation of this resource by different methods has to be undertaken. The economics worked out by the Central Marine Fisheries Research Institute indicate that at least a minimum of Rs 500/- per month accrues to the farmer by taking up cultivation in one hectare area.
Culture experiments conducted in the inshore coastal waters from 1972 to 1986 in the Gulf of Mannar and in Palk Bay have shown that on the culture frames the agarophyte Gracilaria edulis reaches maximum length (harvestable size) within three months while in nature it takes 4 to 5 months time).
These studies have further indicated that the minimum period for the seed material to reach harvestable size is 2 months for G. edulis and that the length of the algae at the time of harvest would be 20 to 25 cm. The suitable period for carrying out the culture operations are October to April in Gulf of Mannar and May to September in Palk Bay.
Harvesting is done by hand picking or by cutting the crop with sickles leaving the basal portions to the net for regeneration. One kg of seed material of G. edulis yields an average of 3 kg/m2 of net after 60 days of growth. In one ha area of nets (i.e. 1000 nets) 30 tonnes of fresh G. edulis could be harvested. Based on the above studies, the economics of culture of G. edulis has been worked out for a hectare area. Details are given below:
For the cultivation of G. edulis in one ha, 1000 coir nets of 5 × 2 m size. 2000 casuarina poles of 1.5 m height and 10,000 kg of fresh seed material (for initial introduction) are required. The cost of 2000 casuarina poles is Rs 6000/- (approximately) and the cost of 1000 coir rope nets is Rs 33,000/- including charges for fabrication. The seed material will be collected for the initial introduction from the natural beds and from the cultured crop for subsequent seeding. Wages for seeding harvesting and maintenance of the farm for 4 persons at the rate of Rs 10/- per day for 360 days work out to Rs 14,400/- the total expenditure for one year would be Rs 54,000/- including a miscellaneous expenditure of Rs 600/-. The estimated cost is arrived at on the assumption that a minimum of four harvests could be made in a year. A total of 120 tonnes (fresh weight) of crop could be obtained from the four harvests in a year when the yield is 3 kg/m2. If the seaweed is dried (75% moisture) and marketed at a rate of Rs 2000/- per ton, the net profit would be Rs 6000/- for one year.
If the harvested seaweed is dried and processed into agar-agar, the profits will reach around Rs 100,000.
At Mandapam, the culture frames were often the target of attack by certain fishes like Siganus javus and S. canaliculatus. The crabs Thalamita crenata and T. integra caused extensive damage to growing parts of the seaweeds by merely clipping them with their claws (James et al., 1980). The problem of predators can be solved to a great extent by enclosing the cultivation area with latticed fence or a net of a suitable mesh size.
XI. Effects of hormones on seaweed growth
Studies on this aspect are limited. Oza (1971) has found that low concentrations of IAA progressively stimulated the growth of Gracilaria corticata while higher concentrations were found lethal. Raju (1971) conducted experiments on the effect of hormones and fertilizers on the photosynthetic carbon assimilation in Ulva fasciata, Sargassum sp and G. corticata. The photosynthetic uptake of C14 was found to be maximum in G. corticata followed by U. fasciata treated with gibberellic acid. In Sargassum maximum effect on photosynthetic C14 assimilation was observed in plant supplied with ammonium sulphate. Tewari (9175) found that Chlorflurenol in hormonal range increased the fresh weight and the number of proliferations. But the elongation growth was found to be inhibited. Chauhan and Joshi (1979) reported that Indole-3-acetic acid at the concentration of 105 proved a better stimulant on the growth of Sargassum swartzii germlings than the other concentrations tried. The 10-3 to 10-6 M concentration of Gibberellic acid helped in increasing the length of pseudophylls of the sporelings.
XII. Conclusions and recommendations
Simplify the seaweed culture technology to reduce cost of production and make the technology economically viable.
The seaweed farmer and his family members or some families jointly undertake, on cooperative basis, the cultivation of seaweeds and to extract agar-agar.
Find out the methods of controlling the grazing of the crop by fish and other predators.
To enable the fishermen or landless laborers to undertake seaweed cultivation, the Government or some funding agencies may offer credit facilities with subsidies under the programmes such as IRDP, DPAP, etc.
More studies on the use of hormones and fertilizers.
Development of hybrid varieties of seaweeds by genetical methods may be given due consideration.
Transplantation of commercially important exotic species like Eucheuma and Caulerpa lentillifera should be tried in Indian waters in suitable locations.
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