Gelidiella acerosa (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

1, habit (S = stichidia); 2, apex (schematic); 3, stichidium with tetraspores; 4, transverse section of stichidium; 5, detail of transverse section of sterile part.

Gelidiella acerosa (Forssk.) Feldmann & Hamel

Protologue: Rev. gén. Bot., Paris 46: 533 (1934).

Family: Gelidiellaceae

Chromosome number: 2n= 12

• Gelidium rigidum (Vahl) Grev. (1830),
• Gelidiopsis rigida (Vahl) Weber Bosse (1904).

• Indonesia: intipintip (Central Java), kembang karang (West Java: Banten), sangau (Lingga, Riau Archipelago)
• Philippines: culot (Ilocos Norte), gulaman, gayong-gayong, kulkulbot.

G. acerosa occurs in all tropical seas. In South-East Asia it is widely distributed in Burma (Myanmar), Thailand, Vietnam, Peninsular Malaysia, Indonesia, the Philippines and the southern coasts of Papua New Guinea.

G. acerosa is one of the chief algae collected in Malaysia, Indonesia, the Philippines and Vietnam for the preparation of agar forming hard gellies. In Java and the Philippines, hand-collected specimens are also eaten fresh or prepared as a salad vegetable, or they are cooked and eaten mixed with rice. Collection for agar preparation and human consumption also takes place in India, China and Japan.

Recent representative data for G. acerosa are not available for SouthEast Asia. In India 50-300 t dry G. acerosa are collected each year in the southeastern (MandapamCape Comorin) and the northwestern (Kathiawar Peninsula) parts. In 1976 world production of dried Gelidium (including Pterocladia and Gelidiella) was 5000 t. Around 1990, 350 t (dry weight) of G. acerosa was exported from India and China together. The only data available for the Philippines are from 1964, when a total of 200-300 t fresh G. acerosa was harvested. Production and international trade from SouthEast Asia mainly consists of sun-dried raw materials gathered from the wild. In 1977 dry Gelidium was valued at US$ 1000-1200 per t. Fresh or dried specimens are sold on the local markets and to traders.

G. acerosa properties differ considerably according to locality and extraction methods. Per 100 g dry weight it contains: protein 4-18 g, fat 8-12 g, carbohydrates 9-24 g; and per 1 g dry weight also: sodium 2-38 mg, potassium 30-60 mg, calcium < 2 mg, phosphorous up to 0.035 mg. Data from the literature also differ considerably for gel strength (usually given as "high") and sulphate content (usually given as "low"). In India, chromium, lead and cadmium contents are high (μg/g dry weight): 1.61, 1.77 and 0.83, respectively. Antiviral activity against Vaccinia virus and Hepatitus-B virus (HBV) has been shown in extracts of this alga, as well as haemagglutinating activity on goat blood erythrocytes.

Thalli caespitose, up to 5 cm tall, several tufted, entangled, cylindrical, sometimes arcuate axes rising from decumbent, arcuate cylindrical axis, up to 650 μm in diameter, arising from creeping holdfast or stolon, up to 750 μm in diameter, attached to substrate by clusters of unicellular rhizoids.

• Erect axes cylindrical or very slightly compressed, up to 700 μm in diameter, sometimes gradually tapering toward the apices, usually with 1-3 orders of sparse to frequent filiform, distichously arranged opposite, subopposite or partly secund branchlets, up to 30 mm long, generally shorter apically and frequently incurved abaxially.
• Apical cell conspicuous, lenticular.
• External cortical cells anticlinally elongated in transection, up to 4 μm broad and 7 μm long.
• Internal cortical cells more rounded, grading into a medulla of larger elongated cells, about 30 μm in diameter, without rhizines (= hyphae).
• Only tetrasporic thalli common.
• Tetrasporangia in apical portion of modified swollen, conical branchlets (stichidia), oblong, 40-50 μm long, 20-30 μm broad, cruciately divided, sparsely and often irregularly dispersed over the branch, lower ones usually in more advanced stage of development than those near apex.
• Cystocarps unknown; spermatangial sori in rounded, hemispherical swellings; only occasionally observed.

In most locations in the tropics G. acerosa occurs all year, with maximum occurrence and thallus size when temperatures are submaximal for the locality. In the Philippines (Ilocos Norte) it is most frequent in the dry season (November-April). After periods of maximum growth, formation of stichidia can occur and shedding of tetraspores takes place. 5000-10 000 tetraspores can be formed per g fresh weight. In India, however, reproduction is almost exclusively by vegetative propagation, while, in some populations in the Philippines, tetrasporic thalli predominate over vegetative thalli during some months of the year. Probably, maximal occurrence of tetrasporic thalli is in August, while the minimum is thought to be in the period November-February. Usually, tetrasporic plants are uncommon in G. acerosa from tide pools and upper intertidal habitats, while they are often common in the subtidal area. During the warmest periods, thalli begin to bleach and start dying. The mode of germination of tetraspores is of the Gelidium type, a type that has not been found in any red alga outside the Gelidiales. Sexual thalli appear to be lacking in the natural populations, although circumstantial evidence of a triphasic life cycle is provided by the haploid and diploid nuclear DNA levels obtained from plants in culture and derived from tetraspores.

In pre-1970 literature from India this alga is often cited as Gelidium micropterum Kütz. This is a misidentification; Gelidium micropterum also occurs in India but has no economic importance. Occasionally the name Gelidium rigens (C. Agardh) Grev. ex Kütz. is used for material belonging to Gelidiella acerosa. This is a misidentification and is probably mainly due to misspelling of the name. The correct name for Gelidium rigens is probably Caulacanthus ustulatus (Turner) Kütz., an alga that is not known to have economic value. Gelidioid algae is a designation used for all Gelidium-like algae, being seaweeds that are often harvested for high-quality agar production. Although quantities of commercial agar produced from other agarophytes (Ahnfeltia and Gracilaria spp.) are higher on a worldscale, the gel strength of these agars is not of the same quality as in the Gelidioid algae. Most gelidioid algae belong to the order Gelidiales .

The important economic species of gelidioid algae in most parts of the world belong to the genera Gelidium J.V. Lamour. and Pterocladia J. Agardh. In South-East Asia, however, the most common gelidioid agarophyte is Gelidiella acerosa.

G.acerosa occurs in the algal turf on surf-exposed and moderately wavesheltered rocks and reefs in the eulittoral and sublittoral zone. It is also found in tide pools at higher levels on the shore and occasionally on shell fragments in shallow water. Tide pool G. acerosa plants are taller and bushier than intertidal and subtidal ones, but intertidal plants are better adapted to high light regimes. Usually, plants are covered with silt or occur underneath foliose seaweeds and can be characterized as "shade adapted". Full sunlight can be tolerated without much bleaching, but reversible photo-inhibition has been demonstrated. The alga can survive emersion and desiccation, but this results in lowering of the biomass, especially when coupled with exposure to strong sunlight. Some water movement is needed for growth, but highest water movement values in Hawaii are limiting. In the Philippines high gel strength is associated with seasonal high intensity water movement. Optimum growth in specimens from rock pools and from the shallow intertidal zone takes place in salinities of 35-40‰. It can survive short-period fluctuations of between 10-80‰. Upper intertidal plants especially tolerate low salinities (22-28‰) very well, but higher salinities (34-40‰) less well. For specimens from the northern Philippines, the optimum temperature for growth is 28 °C; tetrasporic specimens show greater tolerance to temperature fluctuations than vegetative ones.

Cultivation of G. acerosa is mainly still in an experimental stage. In India apical fragments have been grown in constant-depth plantings (attached to ropes and nets) and in constantlevel plantings (attached to cement pipes and coral stones). In all cases growth was between 5-265 mg/g per day during the growth seasons. In 6 months the fragments had grown up to 7 times their original weight and the maximum population density became 129 g/m² wet weight. In natural populations a maximum growth of 131 g/m² per 6 months has been observed. Better growth and/or proliferation occurs after addition (under laboratory conditions) of 200-225 mg/l NaNO₃, or about 30 mg/l NaH₂PO₄, or 70-85 mg/l indoleacetic acid (IAA) or an increase in pH to 8.2-9.2.

In India, industrial production of agar from G. acerosa started around 1965. The Horizontal Single Rope Floating Raft method has had good results in India. It allows the growth and yield characters of the plants to vary according to the level at which the algae grow. This technique, however, is still not often used and harvesting is mainly done from natural stock. The growth rate in laboratory conditions has been increased by adding nitrate, phosphate, vitamins, or hormones. Although all results are promising, quantities needed differ considerably according to these experiments, as is also the case for the suitable N:P ratio. NH₄NO₃ was found to be more effective than urea, NaNO₃, or (NH₄)₂SO₄. Addition of vitamin C also promotes growth, as well as tetraspore production. Tolerance of G. acerosa to low salinities suggests that lowering the salinity in culture tanks could be used to eradicate other algae, such as dinoflagellates or filamentous green algae.

In the northern part of the Philippines, grazing by fish and marine invertebrates has an insignificant effect on the biomass of G. acerosa, although in Indonesia (South Sulawesi) mono-line cultivation trials had to be interrupted because all specimens had been gnawed off by fish.

Hand-collection during spring tides or by divers is the current method of harvesting. Mechanical collection has not been successful up to now. In the Philippines, harvest is by hand-picking at rocky shores during summer. In the northern part of the Philippines, the best harvesting period has not yet been established. One set of experiments suggested the dry season month of April, when biomass is optimal, agar extractable from the plants is of average quality, and gel qualities (gel strength, viscosity, gelling and melting temperatures, sulphate content and 3,6-anhydrogalactose or 3,6-AG percentage) are characteristically high. However, another set of experiments in the same geographic area resulted in the rainy months between July and September being selected as the best harvesting period, when yield is high and gel strength is maximal. In general the best harvest season for natural populations will be just after shedding of the tetraspores.

Quantitative data on the agar contents of G. acerosa differ considerably, depending on the calculation methods used. Published data range between 12.6-50% (dry weight). Agar content and quality varies considerably during the seasons of the year, and this is usually associated with variations in water temperature, light intensity, photoperiod, and geography. There are also significant differences in yield and properties of agar of vegetative and tetrasporic thalli, with the highest agar yield and gel strength occurring in the vegetative thalli.

G. acerosa to be sold fresh on the local market should be transported without delay. The harvested material is rinsed in clean sea water. If needed, the alga is bleached by repeated soaking and drying until the pigments are removed. Most specimens are sundried immediately after harvest and then sold. Dried ones used for future consumption are reconstituted to nearly fresh condition by blanching in boiling water for 2 minutes. Several different methods and procedures are used to extract the phycocolloids. In some areas in India agar is prepared by soaking sun-dried seaweed in 1% KOH solution for 12 hours, this is then washed free of alkali and boiled in water of 30-40 times its volume containing 2 ml/l acetic acid for 3-4 hours. Precipitated CaCO₃ is then added to achieve pH 6.5 and the product is filtered and gelled. Firm gel is sliced and frozen between -12 °C and -18 °C. After thawing, the shreds are soaked in 1% bleaching solution and exposed to the air (for 4 hours). Bleached shreds are washed free of chlorine with SO₂ and dried. This results in a pearlwhite agar with a gel strength of 300 g/cm² in a 1.5% agar solution. If no freezing equipment is available agar can be flocculated by treating the filtrate with 90% industrial alcohol. The alcohol used can be redistilled. Another manufacturing method, also developed in India, involves the following steps: the dried seaweeds are subjected to cold strong acid pretreatment, followed by thorough washing with tap water, sorting out all contamination. They are given further pretreatment with hot alkali solutions. The algae are boiled at atmospheric pressure till the agar goes completely into solution. The solution is then filtered to remove insoluble impurities. The filtrate is gelled in trays and frozen for long periods. The agar is separated from the frozen water by thawing. Then the agar film is bleached with hypochlorite solutions, the residual impurities are chemically treated, the agar is sterilized and dried in hot-air ovens, then sliced into agar strips for use in the food market, or cut, ground and blended for pharmaceutical agar powder. Further chemical treatments are given to obtain pure grade agarose-rich agar. In food grade agar production Gracilaria spp. are mixed with G. acerosa.

Especially in the Philippines, many experiments have been carried out on methodologies of agar extraction in G. acerosa. Gamma-irradiation and pressure cooking both result in increased agar yields, but this agar is of lower quality, especially because of a decreased 3,6-AG percentage. The highest agar yield in the Philippines from G. acerosa (about 30%), with the highest gel strength (about 680 g/cm²) was obtained by 0.5% acetic acid treatment for 1 hour at 16-20°C and extraction using steam pressure. The obtained agar is of bacteriological grade quality.

World demand for agar, and in particular for gelidioid agar, is higher than what the available seaweed can supply. This has often resulted in overharvesting of known seaweed populations which, in turn, has reduced subsequent harvests. As a consequence, the price of food grade agar increased out of proportion, causing a rapid decline in sales. Cycles occur every few years, discouraging the commercial producer as well as the consumer. If the future production of high quality agar is to be based on wild sources only, the fluctuating cycles will result in customers becoming discouraged by the undependable source. Thus the controlled cultivation of seaweed is essential to the future of the agar industry. If no satisfactory cultivation methods become available, hand-collecting of wild sources for the local market will remain the main way of utilizing G. acerosa. In all cases, a comprehensive management model, based on seasonal changes in the yield and quality of agar, should precede intensive harvesting and exploitation of these slow-growing agarophytes.

• Ganzon-Fortes, E.T., 1994. Gelidiella. In: Akatsuka, I. (Editor): Biology of economic algae. SPB Academic Publishing BV, The Hague, The Netherlands. pp. 149-184.
• Ganzon-Fortes, E.T., 1997. Photosynthetic and respiratory responses of the agarophyte Gelidiella acerosa collected from tidepool, intertidal and subtidal habitats. Hydrobiologia 398/399: 321-328.
• Kapraun, D.F., Ganzon-Fortes, E.T., Bird, K.T., Trono Jr, G.C. & Breden, C., 1994. Karyology and agar analysis of the agarophyte Gelidiella acerosa (Forssk.) Feld. et Hamel from the Philippines. Journal of Applied Phycology 6: 545-550.
• Mairh, O.P., Ramavat, B.K. & Rao, P.S., 1990. Nutrition, growth and tetraspore induction of Gelidiella acerosa (Forssk.) Feld. et Hamel (Gelidiellaceae, Rhodophyta) in culture. Botanica Marina 33: 133-141.
• Melo, R.A., 1992. A note on the absence of hyphae (rhizines) in the thallus of Gelidiella acerosa (Forsskål) Feldmann et Hamel (Rhodophyta). In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds 3. pp. 173-181.
• Roleda, M.Y., Ganzon-Fortes, E.T. & Montaño, N.E., 1997. Agar from vegetative and tetrasporic Gelidiella acerosa (Gelidiales, Rhodophyta). Botanica Marina 40: 501-506.
• Roleda, M.Y., Ganzon-Fortes, E.T., Montaño, N.E. & de los Reyes, F.N., 1997. Temporal variation in the biomass, quantity, and quality of agar from Gelidiella acerosa (Forsskål) Feldmann et Hamel (Rhodophyta: Gelidiales) from Cape Bolinao, North-West Philippines. Botanica Marina 40: 487-495.
• Santelices, B., 1997. The spermatangial sorus of Gelidiella acerosa (Gelidiellaceae, Gelidiales). In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds 6. pp. 77-87.
• Subbaramaiah, K. & Banuthi, R., 1991. Growth and reproductive biology of the red alga Gelidiella acerosa (Rhodophyta) in the Mandapam region, east coast of India. Indian Journal of Marine Sciences 20: 61-66.
• Villanueva, R.D., Montaño, N.E., Romero, J.B., Aliganga, A.K.A. & Enriquez, E.P., 1999. Seasonal variations in yield, gelling properties, and chemical composition of agars from Gracilaria eucheumoides and Gelidiella acerosa (Rhodophyta) from the Philippines. Botanica Marina 42: 175-182.

Westphal, E. & Jansen, P.C.M. (Editors), 1989. Plant resources of South-East Asia. A selection. Pudoc, Wageningen, The Netherlands. Fig. on p. 135. Redrawn and adapted by P. Verheij-Hayes.

• W.F. Prud'homme van Reine, A.M. Hatta & P. Gronier