Gracilaria firma (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

1, habit; 2, cross-section of a thallus; 3, detail of 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 tetrasporangia; 8, cross-section of a male gametophyte with spermatangial conceptacles of the Verrucosa-type; 9, surface view of a detail of a male gametophyte, showing the ostioles of the spermatangial conceptacles.

Gracilaria firma C.F. Chang & B.M. Xia

Protologue: Studia Mar. Sin. 11: 143-144, 162-163, figs 38, 39 (1976).

Family: Gracilariaceae

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

Vernacular names

• Thailand: sarai woon.

Origin and geographic distribution

G. firma seems to have a fairly limited distribution. The type locality is Guangdong Province, China. In South-East Asia it has been recorded in eastern Thailand, Vietnam, Peninsular Malaysia and the Philippines.

Production and international trade

There is some production from phycoculture of G. firma in the Philippines and northern Vietnam, but exact data are not available. This alga is used in commercial production in the Philippines because of the good quality of its agar.

Properties

G. firma produces an algal galactan which can be extracted in hot water and gels at room temperature. Gel strength of agar of the non alkali-treated G. firma from wild populations in the Philippines is 765-876 g/cm². Melting point of this agar is around 94.6 °C, gelling point between 40 and 42 °C. Both melting temperature and gel strength are higher than those determined for other Philippine Gracilaria spp.

Description

• Thalli erect, 4-20 cm tall, terete, caespitose or solitary, robust and rigid, arising from a disklike holdfast; branches 1-4 mm thick; branching alternate to irregularly alternate, with marked constriction at the base, either few orders of branching with long, cylindrical branches, and blunt apices with or without some furcations, or many orders of branching with short last-order branches forming clusters with acute or blunt apices.
• Thalli in transverse section with medulla of many layers of cells, 230-360(-500) μm in diameter, with cell walls 10-20 μm thick; cortex only 1-2 cells thick; cell transition of medulla to cortex gradual.
• Tetrasporangia scattered over surface of thalli, ovoid to spherical, 18-38 μm in diameter; tetraspore with conspicuously pigmented stellate central body.
• Spermatangial conceptacles in cavities (Verrucosa-type), 35-60 μm wide and 50-80(-116) μm deep.
• Cystocarps conical or semiglobose, rostrate with or without constriction at base, 1-1.3 mm tall, 0.8-1.2 mm wide; gonimoblast filaments abundant, composed of small, dense and richly protoplasmic elongate cells; absorbing filaments scarce; pericarp 83-95 μm thick, 8-15 rows of undifferentiated cells with distinct cell walls.

Growth and development

G. firma 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 with material from Thailand (Trat), maximum daily growth rates (10.8%) occurred in July at seawater temperatures of 25-26 °C. At lower temperatures later in the year daily growth was much lower, while at higher temperatures (27-28 °C) later in the year daily growth was still considerable. The mean daily growth rate for G. firma in these outdoor tanks was 8.3 ± 1.5%, which was lower than for other tropical Gracilaria spp. Growth rates in the aquatron were much lower. Here, maximum daily growth rates for G. firma (0.9 ± 0.3%) occurred at 27 °C, and growth took place at all temperatures between 23-33 °C. The average daily growth rate for experimental outdoor rope cultivation in the Philippines was 8.7%.

Other botanical information

G. firma closely resembles G. blodgettii Harv. except for the difference in transition from medulla to cortex, size of medulla cells, presence of absorbing filaments, gonimoblast and stellate chromatophore in the tetraspore. The Malaysian specimens resemble those from the Philippines in plant form, size and branching. In some manuals it is stated that the name G. fisheri (B.M. Xia & I.A. Abbott) I.A. Abbott, C.F. Zhang & B.M. Xia is a synonym for G. firma. In Vietnam material of G. firma has previously been identified as G. blodgettii. However, the differences between G. firma and material of G. blodgettii from the Caribbean are listed in the original publication where G. firma is described.

Ecology

G. firma is found in similar habitats to those of G. changii (B.M. Xia & I.A. Abbott) I.A. Abbott, C.F. Zhang & B.M. Xia and G. salicornia (C. Agardh) E.Y. Dawson. It grows attached to shells, gravel, rock fragments in muddy areas and on fish cages, but also abundantly in its unattached form in brackish pools and lagoons.

Propagation and planting

Planting of G. firma in pond culture is usually by broadcasting, while bushes can also be grown attached to lines.

Phycoculture

G. firma may be cultured using vegetative methods in brackish pools and on monofilaments and rafts in open reef farming by use of methods also practised for other Gracilaria spp.

Diseases and pests

In outdoor tank growth experiments G. firma is often heavily grazed by isopods.

Harvesting

Wild growing populations of G. firma are gathered by hand.

Yield

The agar yield of G. firma from wild populations in the Philippines after non-alkaline treatment is 13.8-20% (dry weight).

Handling after harvest

Harvested plants of G. firma should be cleaned and dried, packed in bags and stored in a dry place.

Prospects

Because of its good quality agar, G. firma might be cultivated commercially before long.

Literature

• Abbott, I.A., 1988. Some species of Gracilaria and Polycavernosa from Thailand. In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds 2. pp. 137-150.
• 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.
• Ohno, M., Terada, R. & Yamamoto, H., 1999. The species of Gracilaria from Vietnam. In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds 7. pp. 99-111.
• Phang, S.-M., 1994. Some species of Gracilaria from Malaysia and Singapore. In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds 4. pp. 125-134.
• Yamamoto, H., Ohno, 0. & Nguyen Huu Dinh, 1994. In vitro life histories and spermatangial types of two Gracilaria species from Vietnam, G. heteroclada and G. firma (Gracilariaceae, Rhodophyta). Japanese Journal of Phycology (Sorui) 42: 331-333.

Sources of illustration

Xia, B. & Zhang, J., 1999. Flora algarum marinarum sinicarum, vol. 2, Rhodophyta, 5. Academiae Sinicae Edita, Beijing, China. Plate 3, fig. 2, no page number (habit), fig. 30, p. 51 (all other drawings). Redrawn and adapted by P. Verheij-Hayes.

Authors

• S.-M. Phang & K. Lewmanomont