Gracilaria blodgettii (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

1, habit; 2, cross-section of a thallus; 3, longitudinal section of a cystocarp; 4, longitudinal section of the pericarp of a cystocarp; 5, cross-section of a tetrasporophyte with tetrasporangia; 6, cross-section of a male gametophyte with spermatangial conceptacles.

Gracilaria blodgettii Harv.

Protologue: Nereis bor. amer. 2: 111 (1853).

Family: Gracilariaceae

Chromosome number: 2n= unknown

Synonyms

• Gracilaria cylindrica Børgesen (1920).

Vernacular names

• Indonesia: agar-agar gros, agar-agar biru, sango sango (Sulawesi).

Origin and geographic distribution

G. blodgettii is found along the tropical and subtropical coasts of the Atlantic Ocean (Caribbean, Florida), the Indian Ocean (Aldabra Islands, Seychelles, Mauritius, India, Sri Lanka, Andaman Islands, Australia) and the Pacific Ocean (China, Japan, Taiwan). In South-East Asia it has been recorded in Vietnam, Peninsular Malaysia, Singapore, Indonesia, the Philippines and Papua New Guinea. The type locality is Key West, Florida (United States).

Uses

The main use of G. blodgettii is as raw material for the agar industry. It is also consumed fresh as a vegetable (Sulawesi, Indonesia) and for making traditional jelly. In the Philippines it is used as human food, a source of agar, animal feed and fertilizer. It is used medicinally as a pectoral emollient and laxative, as well as for treating pulmonary complaints and stomach disorders.

Production and international trade

There are no statistical data on the total production of G. blodgettii from the South-East Asian countries where it occurs. Figures from Vietnam, where this alga was recorded as forming part of the production of Gracilaria Grev., indicated a total production of about 8000-9300 t/y (fresh weight). Of this, 70% was G. "verrucosa" (probably = G. vermiculophylla (Ohmi) Papenf.), 11% G. blodgettii (or G. firma C.F. Chang & B.M. Xia) and 19% other species. Other reports, from northern Vietnam, on G. "verrucosa" and G. blodgettii state that the total production of dried Gracilaria in that area was about 1500 t in 1987. By 1993 production had reached 3000 t, and an area of about 2000 ha was under culture.

Data on agar production in Vietnam are conflicting. In 1963 the Ha Long canning factory in Hai Phong started agar production on a small scale, using a simple method. For this canning factory it is stated that a capacity was reached of 120 t agar per year. Some other state-owned enterprises had a production capacity of 15-20 t agar per year. In addition, about 50 families produced 3-10 kg/day each. Total production of agar-agar in 1993 was stated to be about 250 t, mainly used in the food industry for the domestic market. Other reports, however, indicate that the agar industry in Vietnam did not start until 1974 and estimate the total annual production of quality agar at 80-100 t.

Properties

Gel strength of agar of G. blodgettii from Vietnam is 278 g/cm² when using alkaline treatment (2-4% NaOH) at 90-98 °C for 1-2 hours. The gel strength of material from Malaysia, using non-alkaline treatment is 344 and 440 g/cm² for 1.5% agar solutions. The melting point of this agar is 76-88 °C, and the gelling point 31-40 °C. For the Philippines an agar gel strength of 963 g/cm² has been recorded, which is the highest for the Philippine Gracilaria species that have been tested so far.

Description

• Plant up to 10 cm tall; thalli single, erect, attached to the substrate by a discoid holdfast, with cylindrical branches reaching a width of up to 2 mm; branching pattern variable, ranging from frequently dense to sparse and from irregularly alternate to a tendency to become secund; third and higher-order branches often beset with short branchlets, 3 mm × 1 mm; branchlets spindle-shaped or obtuse; according to some descriptions, branch bases distinctly constricted.
• Plant in transverse section composed of two rows of small cortical cells followed inwardly by 2-3 layers of medium-sized cells; medulla consisting of large, nearly uniform cylindrical to oval very thick-walled cells (to 26 μm thick).
• Spermatangia organized into shallow Textorii-type spermatangial sori.
• Cystocarps hemispherical to globose, not constricted at the base.
• Transverse-section through mature cystocarps with sterile gonimoblast bearing tubular nutritive cells reaching a well-developed pericarp of 10-15 layers of cells.

Growth and development

Average daily growth rates in farm culture for G. blodgettii in the Philippines can be as high as 9.0%.

Other botanical information

Material from Indonesia, identified as G. cylindrica Børgesen, has been described as the type of Polycavernosa vanbossae I.A. Abbott, later changed into Gracilaria vanbossae (I.A. Abbott) I.A. Abbott, C.F. Zhang & B.M. Xia. However, type material of G. cylindrica has been excluded from Polycavernosa vanbossae. When the species was renamed to G. vanbossae, the Indonesian material was excluded as well. Specimens named as G. blodgettii from South-East Asia often belong either to G. changii (B.M. Xia & I.A. Abbott) I.A. Abbott, C.F. Zhang & B.M. Xia or to G. manilaensis H. Yamam. & Trono, both species having branches that are markedly constricted at their bases. In some manuals G. cylindrica is cited as a direct synonym of G. changii. Material identified as G. blodgettii in Vietnam has often been re-identified as G. firma. Data for G. blodgettii and G. cylindrica are thus often also included in the data on other Gracilaria spp. In Harvey's original description of G. blodgettii, branches and branchlets are markedly constricted at their base of insertion and attenuated to an acute point; a medulla consisting of a few large thin-walled, irregularly polygonal cells and a cortex of vertically subseriate, very small, pigmented cells. This is not completely in accordance with the description given for South-East Asian material. Discussion on the correct identification and naming has therefore not yet been solved.

Ecology

Plants of G. blodgettii are found in tide-pools or in shallow subtidal areas, attached to rocks, pieces of shells or coral fragments. In Vietnam, it is found abundantly from October to July. It is commonly cultivated in brackish water swamps along coastal areas of Hai Phong and Cat Hai island.

Propagation and planting

Planting of G. blodgettii in pond culture in Vietnam is usually done by broadcasting. Plants are cultivated either as monoculture or polyculture with shrimp, fish and crab. Seeding density is 500-600 g/m². The size of monoculture ponds should be 0.5-5.0 ha, and for polyculture ponds 10-15 ha.

Phycoculture

Salinity is the most important factor for growth of G. blodgettii. The optimal range is between 12 and 24‰. Water exchange at high and low tide should be about 30-50% and water level is maintained at 35-45 cm depth, 40-50 cm during sunny months, with a maximum level of 60 cm. The pond should be supplied with organic fertilizer such as cattle manure or poultry manure at the rate of 3-4 t/ha 3-4 times a year. In the Philippines the best conditions for growth of G. blodgettii (as G. cylindrica) are found in areas with high salinity (above 33‰), clear water, high pH (about 8.0) and a firm substrate (coralline flat).

Harvesting

When a crop of G. blodgettii reaches over 1 kg/m² it can be harvested by hand or by rake and washed with pond water to remove sand, mud and dirt.

Yield

Phycoculture of G. blodgettii in South-East Asian waters can result in the production of 3-4 t/ha/y (dry weight). The agar yield of this alga from Vietnam (after alkaline treatment) is 26.5%. Non-alkaline treatment in Malaysia resulted in agar yields of 15-26.3% and 7.6-28.8% respectively for two different localities. Highest agar contents for this alga in Malaysia were found in January and June. Periods of low salinity do not correspond to high agar yields.

Handling after harvest

After washing G. blodgettii plants should be dried immediately to preserve quality. Dried material must be packed in bags and stored in a dry place.

Prospects

The potential for increased production of G. blodgettii is high in some countries, especially Indonesia and Vietnam, because there are large areas of brackish water for cultivation. It is quite possible that data for G. blodgettii in the Philippines refer to a different species from that found in Malaysia and Vietnam. The national and world demands for agar seem to be increasing due to rapid developments in the cosmetic, pharmaceutical, food and textile industries.

Literature

• Abbott, I.A., Zhang, J. & Xia, B., 1991. Gracilaria mixta, sp. nov. and other Western Pacific species of the genus (Rhodophyta: Gracilariaceae). Pacific Science 45(1): 12-27.
• Fredericq, S. & Norris, J., 1992. Studies on cylindrical species of western Atlantic Gracilaria (Gracilariales, Rhodophyta): G. cylindrica Børgesen and G. blodgettii Harvey. In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds 3. pp. 211-231.
• Khuong, D.V., 1995. Studies on taxonomy, ecology and processing technology of economic Gracilaria species. A country status report for final workshop of the Regional Study on the Taxonomy, Ecology and Processing of Commercially Important Red Seaweeds, Bangkok, Thailand. 14 pp.
• Phang, S.-M. & Vellupillai, M., 1990. Phycocolloid content of some Malaysian seaweeds. In: Phang, S.-M., Sasekumar, A. & Vickineswary, S. (Editors): Research priorities for marine sciences in the 90's. Proceedings of the 12th Annual Seminar of the Malaysian Society of Marine Sciences 1989. Kuala Lumpur, Malaysia. pp. 65-77.

Sources of illustration

Chang, J.F. & Xia, B.M., 1976. Studies on Chinese species of Gracilaria. Studia Marina Sinica 12: Fig. 28, p. 129 (habit), fig. 29, p. 130 (cross-section of thallus, sections of tetrasporophyte and male gametophyte), fig. 30, p. 131 (cystocarp, pericarp). Redrawn and adapted by P. Verheij-Hayes.

Authors

• K. Lewmanomont & S.-M. Phang