Gracilaria changii (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 Verrucosa-type of spermatangial conceptacles; 7. cross-section of a male gametophyte of which the adjacent spermatangial conceptacles coalesc to form Polycavernosa-type spermatangial conceptacles.

Gracilaria changii (B.M. Xia & I.A. Abbott) I.A. Abbott, C.F. Zhang & B.M. Xia

Protologue: Pacific Sci. 45(1): 23 (1991).

Family: Gracilariaceae

Chromosome number: 2n= unknown

Synonyms

• Polycavernosa changii B.M. Xia & I.A. Abbott (1987),
• Hydropuntia changii (B.M. Xia & I.A. Abbott) M.J. Wynne (1989).

Vernacular names

• Malaysia: sarer (known collectively with other Gracilaria spp.) (Malay, Kelantan)
• Thailand: sarai kao kwang.

Origin and geographic distribution

G. changii seems to be restricted to southern Asia. It is widely found in Malaysia and the eastern part of Thailand. It is also recorded from Burma (Myanmar), Vietnam and the central Philippines.

Uses

Coastal communities, especially in Kelantan and Terengganu (eastern coast Peninsular Malaysia) and Selangor (western coast Peninsular Malaysia), collect G. changii for food. After washing, the seaweed is blanched in boiling water and served together with onions, chilli, grated coconut and lime juice, as an appetizer. In Thailand, large quantities are collected from the eastern coast of the Gulf of Thailand for food, agar extraction and abalone feed.

Production and international trade

There is no known commercial cultivation of G. changii, but in Malaysia it is cultivated on an experimental scale.

Properties

G. changii is an agarophyte with an agar content of 26-39% (dry weight) and an agar gel strength of 344-500 g/cm², when extracted after 7 days of cold alkali pretreatment with 4% NaOH and then soaked for one hour in 0.2% acetic acid. The agarose yield ranges from 13.4-16.3% while the agarose gel strength ranges from 737-950 g/cm². Acid and alkali pretreatment can increase the agar gel strength from 423 to 626(-650) g/cm² and decrease agar yield from 11 to 26%. Ash content of the agar ranges from 8.1-14.2%, while the gelling temperatures range from 32-45 °C, and melting temperatures from 82-89 °C.

The gel strength of G. changii from Thailand without pretreatment with alkali at room temperature was 714 g/m², with a sulphate content of 0.07%. For Philippine G. changii agar sulphate contents of 0.022-0.028% have been recorded. The separation of agarose directly from the seaweed gave a better yield than when its agar was used for fractionation. The gel strength of the agarose obtained ranged from 747-950 g/m² of a 1% gel concentration with a sulphate content from 0.17-0.4%, which is comparable to the sulphate values of commercial agarose. In conclusion, G. changii can be considered as producing good food-grade agar as well as agarose.

Description

• Thalli 6-20 cm tall, robust, purplish-brown to dark brown when dry, with one to many axes, 1.0-3.5 mm in diameter, arising from a disk-like holdfast or from a percurrent axis; branching of two to four orders, irregular, alternate or secund; branches turgid, cylindrical, 0.3-2.5 mm in diameter, abruptly constricted at the base forming a slender stipe, slightly swollen distally, tapering towards the tip.
• Fronds in transverse section consisting of large rounded medullary cells (350-570 μm) with thick walls (7.5-20 μm), and 2-3 layers of small, pigmented cortical cells; transition of cells abrupt.
• Tetrasporangial and gametophytic plants similar in size and branching pattern.
• Tetrasporangia ovoid to elongate, densely scattered over frond surface, cruciately divided.
• Spermatangia covering the entire inner surface of conceptacles with multiple cavities or with oval to globose, solitary conceptacles.
• Cystocarps conical or semiglobose, up to 1.4 mm in diameter, slightly rostrate, not constricted at base; gonimoblast consisting of many small cells; basal absorbing filaments few, connecting inner and outer pericarp.
• Carposporangia rounded or ovoid, 18-32.5 μm in diameter; pericarp thick consisting of two kinds of tissue, the outer 5-6 rows of rounded to oval cells and the inner 7-9 rows of compressed cells.

Growth and development

Recordings from the standing biomass of G. changii populations in two mangrove areas in Selangor, western coast of Peninsular Malaysia ranged from 58-98 g/m² (dry weight). In the Philippines, Iloilo (western Visayas) biomass in the dry season (January-June) ranged from 3-32.4 g/m². Culture trials in Selangor gave average growth rates of 1.7-3.3% per day when cultured on monofilaments in shallow mangrove ponds, 3.0-3.6% per day in shrimp ponds, and 2.5-8.4% per day in irrigation canals at the shrimp farm. In Malaysia G. changii is found producing carpospores and sporelings throughout the year. In Thailand, male and female gametophytic plants are found in similar proportions throughout the year but tetrasporic plants are usually in greater numbers.

Other botanical information

G. changii has often been misidentified as G. blodgettii Harv. or its synonym G. cylindrica Børgesen, because of the similar constriction at the base of the branches at the point of insertion. This is also often the case in herbarium voucher specimens. Some data reported for G. changii are still confused with those on G. blodgettii. Some specimens also resemble G. manilaensis H. Yamam. & Trono.

Ecology

G. changii grows abundantly on intertidal mudflats and attached epiphytically to mangrove tree roots, shells, pebbles, plastic debris and fish cages. It is also found on rocky-sandy substrates in water depths of 0.5-2 m, that can be exposed to strong waves during the wet season (June-October) in the Philippines. Salinity, rainfall, temperature and duration of sunshine together with nutrient levels in the water may affect the growth and development of G. changii. Salinity in the mangroves where much G. changii is found ranges 27-35‰. However the plants appear to have adapted to low salinities of 15-18‰ in culture ponds at Ban Merbok, Perak (Malaysia). G. changii standing biomass is higher during the warmer, drier months in Selangor (Malaysia) and this is also the case in natural populations in Iloilo (the Philippines). Better growth rates in Malaysia were exhibited by plants attached to monofilaments near the water surface than those submerged 20 cm below the water surface, in a shrimp pond and irrigation canal. Also the lower turbidity of the irrigation canal compared to the shrimp pond (Secchi disk readings of 36-43 cm in the pond versus 46-59 cm in the canal) produced better growth in the former. Light availability is therefore an important factor influencing growth.

Propagation and planting

G. changii can be propagated vegetatively by cuttings or by tetraspores and carpospores. Average number of sporelings on raffia fibres set out amongst thalli in the mangroves in Morib (Malaysia) ranged between 7-55 per m raffia. In pond culture, monofilaments with attached thalli are best placed within the top 10 cm of the pond surface.

Phycoculture

In experimental pond cultures in Malaysia, G. changii is cultivated in an integrated polyculture system with shrimps. When grown on monofilaments in shallow mangrove ponds, shrimp ponds and irrigation channels in the shrimp farm, maximum daily growth rates were 3.3%, 3.6% and 8.4%, respectively. In larger (0.5-1 ha) experimental ponds, 0.6-1.3 m deep, with a reduced salinity of 15-18‰ and in polyculture with the shrimps Panaeus monodon and Lates calcifer, the stock density on rafts of G. changii of 1-5 kg/m² doubles in 1 month. Best results are achieved at a stocking density of 2 kg/m². In pond culture, 1-2 daily water changes (up to 40% of total volume) are advisable.

Diseases and pests

In integrated culture of G. changii with shrimps, the high nutrient content (in particular of N and P) in the ponds encourages heavy epiphytization of the thalli by other algae including Chaetomorpha, Cladophora and Hypnea spp. Rabbit fish are common grazers on Gracilaria spp.

Harvesting

Plants of G. changii can be harvested after 1-2 months. Ponds have to be drained partially and plants are harvested manually from the floating rafts and monofilaments.

Yield

The highest yield of G. changii obtained from a 0.5 ha pond is 8 t wet weight after one month of growth. During hot weather periods slightly higher agar yields are produced, although gel strength increases during periods of rainfall. Gelling and melting temperatures of agar of G. changii change little with the seasons.

Handling after harvest

Harvested plants of G. changii should be cleaned and sun-dried on raised platforms, packed in bags and stored in a dry place.

Prospects

There is a large market for agar, especially high quality agar and agarose, because of increasing use in biotechnological research. In Malaysia there is a large domestic market as shown by the imports of 189 t of agar in 1991. G. changii produces excellent food-grade agar and agarose, and is highly tolerant of harsh conditions and a wide range of salinities, as found in the mangroves. These characteristics make it a potentially interesting species for commercialization.

Literature

• Abbott, I.A., Zhang Junfu & Xia Bangmei, 1991. Gracilaria mixta, sp. nov. and other Western Pacific species of the genus (Rhodophyta: Gracilariaceae). Pacific Science 45(1): 12-27.
• Chirapart, A., Lewmanomont, K. & Ohno, M., 1992. Seasonal variation of reproductive states of the agar-producing seaweed, Gracilaria changii (Xia & Abbott) Abbott, Zhang & Xia in Thailand. Bulletin of Marine Science and Fisheries, Kochi University 12: 9-16.
• Doty, M.S., Santos, G.A. & Ong, K.S., 1983. Agar from Gracilaria cylindrica. Aquatic Botany 15: 299-306.
• Jahara, J. & Phang, S.-M., 1990. Seaweed marketing and agar industry in Malaysia. In: Gracilaria production and utilization in the Bay of Bengal. Bay of Bengal Programme. BOP/REP/45. pp. 75-86.
• Phang, S.-M., Shaharuddin, S., Noraishah, H. & Sasekumar, A., 1996. Studies on Gracilaria changii (Gracilariales, Rhodophyta) from Malaysian mangroves. Hydrobiologia 326/327: 347-352.
• 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.
• Pondevida, H.B. & Hurtado-Ponce, A.Q., 1996. Assessment of some agarophytes from the coastal areas of Iloilo, Philippines. I & II. Botanica Marina 39: 117-127.
• Shaharuddin, S., Phang, S.-M. & Sasekumar, A., 1994. Agar quality of Gracilaria changii extracted under various acid and alkali treatments. In: Phang, S.-M., Lee, Y.K., Borowitzka, M.A. & Whitton, B.A. (Editors): Algal biotechnology in the Asia-Pacific region. University of Malaya, Kuala Lumpur, Malaysia. pp. 64-69.

Sources of illustration

Original drawings of the authors Phang, S.-M. & Lewmanomont, K. Redrawn and adapted by P. Verheij-Hayes.

Authors

• S.-M. Phang & K. Lewmanomont