Gracilaria salicornia (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

1, habit of a plant found in clear and relatively calm waters; 2, habit of a plant found in turbid water, exposed to moderate to strong water movement; 3, cross-section of a thallus; 4, longitudinal section of a thallus; 5, longitudinal section of a cystocarp; 6, longitudinal section of the pericarp of a cystocarp; 7, cross-section of a tetrasporophyte with tetrasporangium and large gland cells; 8, cross-section of a male gametophyte with spermatangial conceptacles of the Verrucosa-type; 9, portion of a thallus of G. salicornia with the adelphoparasite Congracilaria babae.

Gracilaria salicornia (C. Agardh) E.Y. Dawson

Protologue: Bull. S. Calif. Acad. Sci. 53: 4 (1954).

Family: Gracilariaceae

Chromosome number: 2n= possibly 48, a number found for severalGracilariaspp. and in agreement with the assessment of nuclear genome size for Philippine material of the present species

Synonyms

• Sphaerococcus salicornia C. Agardh (1820),
• Corallopsis salicornia (C. Agardh) Grev. (1830),
• G. minor (Sond.) Durair. (1961).

Vernacular names

• Indonesia: agar-agar, bulung buku, sango sango (Sulawesi)
• Philippines: susueldot bay bay (La Union Province, for G. crassa), canot-canot, lagot
• Thailand: sarai kaw
• Vietnam: rau cau chung vit (for G. crassa).

Origin and geographic distribution

G. salicornia is found along most tropical coasts of the Indian and Pacific Oceans. In South-East Asia it occurs on the coasts of all countries.

Uses

In Indonesia (Java, South Sulawesi), the Philippines, Thailand and Vietnam G. salicornia is collected by coastal communities and used fresh as a salad or blanched with hot water and mixed with onion, chilli, dried shrimp, sugar, fish sauce and lime juice. It can be used to produce home-made jelly and for agar extraction, but the gel strength is not as good as that of most other Gracilaria spp. It is used for abalone feed and is a food source for the green turtle. It is also applied as fertilizer, insect repellent, and in traditional medicine.

Production and international trade

No commercial cultivation of G. salicornia is known to exist. Occasionally it is sold fresh on the local market.

Properties

G. salicornia is an agarophyte. When collected from intertidal rocky shores in Thailand it has a low agar yield, ranging between 4.4-10.0% (dry weight). The average gel strength obtained is 345 g/cm². The melting and gelling temperatures range from 76-89 °C and from 42-48 °C respectively. It was determined that G. crassa gave an agar yield of 23%, a gel strength of 140 g/cm², and melting and gelling temperatures of 84 °C and 48 °C respectively. The agar contains 3.3-3.7% sulphate, 0.09-0.11% pyruvate and 26.5-35.1% 3,6-anhydrogalactose. Dried plants of G. salicornia from Sri Lanka contain per 100 g: water 13.7-15.5 g and ash 14.3-15.9 g (sulphate 2.4-4.2%, sodium 7.8-9.0%, potassium 11-19.3% and calcium 2.5-2.8%). The phycocolloid contains per 100 g: water 14.1-16.8 g and ash 14.3-14.5 g (sodium 3.6-5.4%, potassium 3.0-8.5% and calcium 1.9-2.6%). Data on quantities of constituents of normal G. salicornia and its supposed growth form "G. crassa" often differ.

Description

• Plant up to 15 cm tall, greenish-purplish to orange; all axes, branches and branchlets with more or less distinct claviform articulations; with or without main axes, regularly or irregularly branched, forming tightly entangled masses or low prostrate caespitose clumps.
• Fronds cylindrical, brittle and fleshy, cartilaginous and succulent when fresh. Branching irregular to dichotomous, trichotomous, tetratomous and divaricate; branches blunt, truncated or with a somewhat acute apex.
• Thalli with large medullary cells, 250-600(-720) μm in diameter in transverse section, with cell walls 2-15 μm thick.
• Transition of cells to cortex (10-15 μm × 20-30 μm in diameter) gradual or abrupt, with frequent roundish gland cells, 30-35 μm in diameter; cortex cells irregularly shaped, oblong, ovate or rounded, in 2-3 layers.
• Tetrasporangial and gametophytic plants similar in size and branching pattern, segments in tetrasporophytes often slightly larger.
• Tetrasporangia scattered over the surface of thalli, numerous, cruciately divided, sphaerical to oblong, 30-50 μm in diameter.
• Spermatangia covering the entire inner surface of deep pot-shaped conceptacle, 26-50 μm × 85 μm in longitudinal section.
• Cystocarps nearly globose, prominently protruding, usually with a distinct beak, constricted at base or not, 1-2 mm in diameter, irregularly disposed on the branches.
• Gonimoblast with large thin-walled central cells, connected to the pericarp by many absorbing filaments.
• Pericarp 180-265 μm thick, with 2 layers of tissue: elongated cells in outer layers and brick-like cells in inner layers.
• Carpospore globose, 23-30 μm in diameter, produced in chains.

Growth and development

The standing crop of G. salicornia on an intertidal rocky shore at Pantai Dickson, Negeri Sembilan, western coast of Peninsular Malaysia was estimated to be between 1.5-4 g/m² (dry weight). There are two forms of growth: one which exhibits articulations and three phases of reproduction, and the other which forms an entangled mat producing sterile or tetrasporangial plants. Spores from the mat-type of plants, when cultured under laboratory conditions, produce all stages of the life cycle, showing that the mat habit is dependent on environmental conditions like strong waves. G. salicornia can be grown in outdoor cultivation tanks with flowing seawater as well as in indoor closed-recirculating systems (aquatron). In outdoor experimental cultivation tanks in Japan using algal material from the Philippines (Manila Bay), maximum daily growth rates (12.7%) occurred in July at sea water temperatures of 25.2-26.2 °C, although daily growth rates were still considerable at all temperatures from 23-28 °C. The mean daily growth rate for these days in these outdoor tanks was 11.0 ± 0.9%, which is higher than for G. firma C.F. Chang & B.M. Xia, but considerably lower than for other tropical Gracilaria spp. Growth rates were much lower in the aquatron. Maximum daily growth rate for G. salicornia (0.9 ± 0.2%) occurred in the aquatron at 27 °C, and the growth rate was considerably less at other temperatures of 23-33 °C. When cultivated in the intertidal zone or in semi-enclosed ponds in the Philippines, daily growth rates of 1.3-2.8% have been recorded.

Other botanical information

Not all specialists agree upon whether all names in the list of synonyms are conspecific. Especially G. canaliculata (= G. crassa) is often considered to be different enough to be a separate species.

Ecology

G. salicornia grows on various substrates: rocks, gravel, shells and mangrove roots. It is usually found in protected portions of reef flats away from the impact of wave action, or in waters exposed to moderate to strong water movement, attached to small rocks or pieces of dead coral or shells, or on sandy-rocky substrate. Occasionally it is also found in shallow pools in intertidal terrigenous mudflats and between seagrasses. Temperatures exceeding 30°C are lethal to G. salicornia.

Phycoculture

G. salicornia grows well in fish ponds.

Diseases and pests

A commonly found parasite on G. salicornia is Congracilaria babae H. Yamam. This parasite is of the adelphoparasite type, which closely resembles the host. There are no rhizoids but the parasite connects to the host tissue by means of pit connections. Other adelphoparasites probably also occur on G. salicornia.

Yield

The G. salicornia plants at Pantai Dickson (Malaysia) peaked in biomass with the return of sunny conditions after the rainy season. The agar content appeared to be negatively correlated to biomass. Biomass was positively correlated to salinity while the reverse was true for the agar content. The agar yield of dried G. salicornia varies widely according to the locality. Published data include 4.4-10% for Thailand, and 21.7-27.6 for the Philippines (in Ilocos Norte, however, an agar yield of 40.1% has been recorded). Outside South-East Asia an agar yield of 14-35% has been obtained from dried G. salicornia from Taiwan and Micronesia, and 47.2% (for G. canaliculata) from Hawaii.

Handling after harvest

For effective extraction of agar from G. salicornia a strong alkaline pretreatment is advised.

Prospects

The low and unpredictable agar yield and gel strength make G. salicornia an alga with very little potential as an agar source, and thus not a likely candidate for commercial cultivation.

Literature

• Chirapart, A. & Ohno, M., 1993. Growth in tank culture of species of Gracilaria from the Southeast Asian waters. Botanica Marina 36: 9-13.
• Lewmanomont, K., 1994. The species of Gracilaria from Thailand. In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds 4. pp. 135-148.
• Phang, S.-M., 1994. Some species of Gracilaria from Peninsular Malaysia and Singapore. In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds 4. pp. 125-134.
• Tarlochan Singh, 1992. Agar and agar production. Infofish Technical Handbook 7. 26 pp.
• Xia Bangmei, 1986. On Gracilaria salicornia (C. Agardh) Dawson. Chinese Journal of Oceanology and Limnology 4(1): 100-106.
• Yamamoto, H., 1986. Congracilaria babae gen. et sp. nov. (Gracilariaceae), an adelphoparasite growing on Gracilaria salicornia. Bulletin of the Faculty of Fisheries, Hokkaido University 37: 281-290.
• Yamamoto, H., 1991. Life-history of Gracilaria salicornia (C. Agardh) Dawson (Gracilariaceae, Rhodophyta) in vitro. Japanese Journal of Phycology 39(1): 55-56.

Sources of illustration

Trono, G.C. & Ganzon-Fortes, E.T., 1988. Philippine seaweeds. National Bookstore, Manila, The Philippines. Fig. 121, p. 172 (habits); Xia, B. & Zhang, J., 1999. Flora algarum marinarum sinicarum, vol. 2, Rhodophyta, 5. Academiae Sinicae Edita, Beijing, China. Fig. 40, p. 67 (sections of thallus and tetrasporophyte), fig. 40a, p. 68 (sections of cystocarps and spermatangia); Congracilaria babae is in an original drawing of Phang, S.-M. & Lewmanomont, K. Redrawn and adapted by P. Verheij-Hayes.

Authors

• W. Moka, R. Sutijanto & P. Gronier