Gracilaria fisheri (PROSEA)
 |
Introduction |
Gracilaria fisheri (B.M. Xia & I.A. Abbott) I.A. Abbott, C.F. Zhang & B.M. Xia
- Protologue: Pacific Sci. 45 : 23 (1991).
- Family: Gracilariaceae
- Chromosome number: 2n= unknown
Synonyms
- Polycavernosa fisheri B.M. Xia & I.A. Abbott (1987),
- Hydropuntia fisheri (B.M. Xia & I.A. Abbott) M.J. Wynne (1989).
Vernacular names
- Thailand: sarai phom nang, sarai woon.
Origin and geographic distribution
G. fisheri seems to have a fairly limited distribution. It has been recorded in Thailand (especially Songkhla Lagoon and Pattani Bay), Vietnam and Peninsular Malaysia.
Uses
G. fisheri is the most common agarophyte in Thailand. It is sold in local markets in fresh or dry form and is eaten raw as a salad vegetable or cooked and mixed with other ingredients. The dried form is kept for sale at local markets in Thailand and nearby regions such as Kelantan (Malaysia), and exported to countries such as Japan and Taiwan for extracting agar. It is used experimentally in fresh form for abalone feed and for biological purification treatment of waste water from shrimp pond effluent.
Production and international trade
Reports are available from 1956 on for Thai export of dry Gracilaria (G. fisheri and G. tenuistipitata C.F. Chang & B.M. Xia). Although yearly data are not available until 1975, between 20 and 200 t (dry weight) were exported annually mostly to Japan, other Asian and European countries and the United States as well. The amount fluctuates as it is harvested from natural seaweed populations. G. fisheri and G. tenuistipitata have been cultivated since 1987 using the rope-inserting method at Songkhla Lagoon and by broadcasting in pond culture near Pattani Bay. This has resulted in consistently high production from 94-135 t per year. In 1994-1995, production increased to more than 500 t per year. This may be due to effluent from intensive shrimp farming in the area, supplying nutrients. Purchase of Thai produce by Malaysians is very common, especially during Ramadan. At present, Malaysia imports dried Gracilaria from Thailand for a small-scale agar extraction factory in Selangor. This factory processes 70 kg of dry Gracilaria daily, producing 8 kg agar per day.
Properties
G. fisheri is a good source of agar. Agar extracted by traditional methods from this alga showed gel strength of only 300-400 g/cm2. However, post-extraction alkali treatment increased gel strength to 700-1000 g/cm2.
Description
- Thalli 13-30(-45) cm tall, with many branches coming from a short stipe or from percurrent axis; branching alternate, 3-4 orders; branches cylindrical, 0.6-2.3 mm in diameter, usually less than 2 mm, constricted at their bases and tapering toward apices, often bearing short, hair-like, ultimate branches.
- Thalli in transverse section consisting of medullary cells, 220-620 μm in diameter, with thick layers of cortex; transition from medulla to cortex gradual.
- Tetrasporangia ovoid, tetraspores 20-25 μm in diameter.
- Spermatangia ovoid, covering the entire inner surface of single cavity conceptacle or of conceptacles with 2-3 cavities.
- Cystocarps conical, rostrate, unconstricted at bases, 0.3-0.7 mm × 1.0-1.3 mm; gonimoblasts consisting of many small cells; absorbing filaments lateral and upper; pericarp thick with inconspicuous cell walls and star-shaped contents.
- Carpospores rounded, 18-24 μm in diameter, or ovoid, 8-14 μm × 14-20 μm.
Growth and development
Maximum growth of G. fisheri is related to an optimum salinity range of 20-25‰. In Thailand this usually occurs during the period January-September. During the months of the year when no harvest occurs, the seaweed subsists either as very short left-over growth or seems to disappear. In Vietnam the specimens are usually smaller than those in Thailand. After the rainy season, when environmental conditions are suitable new growth appears quickly. G. fisheri 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, material from Thailand (Ko Yo) showed maximum daily growth rates of 14.3% in July at seawater temperatures of 25-26 °C; in August, at temperatures of 27-28.4 °C, daily growth was much lower, while at lower temperatures (23-25 °C) daily growth was considerable. The mean daily growth rate for this alga in the outdoor tanks was 13.8 ± 0.3%. Growth rates of G. fisheri were much lower in the aquatron, with a maximum daily growth rate of 2.6 ± 0.7% at 25 °C, which did not increase significantly at higher temperatures of 27-33 °C.
Other botanical information
In some manuals it is stated that the name G. fisheri is a synonym of G. firma C.F. Chang & B.M. Xia. Xia and Abbott described this alga as Polycavernosa fisheri from the type material purchased in a market near Kota Bahru (Kelantan), on the eastern coast of Peninsular Malaysia, which was said to have come from Pattani in Thailand.
Ecology
G. fisheri is commonly found growing on living mollusc or empty shells (Cerithium sp.) and on pebbles, polythene bags and fish cages, or existing unattached to the substrate in sandy muddy areas of turbid water. It occurs abundantly together with G. tenuistipitata in Songkhla Lagoon and Pattani Bay. It can tolerate a wide range of salinity, from 5-40‰. In low saline conditions during the rainy season its thalli become soft and pale and deteriorate after a long period of these conditions. During summer when salinity increases the thalli become short and brittle.
Propagation and planting
G. fisheri can be cultivated from tetraspores and carpospores. The number of carpospores produced from each cystocarp varies from about 6600 to nearly 7700 at 20 and 25‰ salinity respectively; the discharge period is 24 days. Vegetative propagation is simpler and more commonly used by local people in Thailand. Fragments of 5-10 g are prepared for either broadcasting or rope-inserting methods. Broadcast cultivation is used in Thailand in ponds at Pattani Bay and monoline culture in Songkhla Lagoon.
Phycoculture
The 2 best algae for cultivation in Malaysia and Thailand are G. fisheri and G. tenuistipitata. In Thailand, G. fisheri is the most abundant and readily cultivated Gracilaria sp.
Diseases and pests
In outdoor tank growth experiments G. fisheri is often heavily grazed by isopods.
Harvesting
G. fisheri and G. tenuistipitata usually occur together and it has been shown that the presence of agar from G. tenuistipitata does not materially affect the gel strength of agar from G. fisheri. G. fisheri can be harvested every 6-8 weeks, yielding weights approximately 8-10 times that of the seed material. In Thailand, raking and diving are the most appropriate methods for harvesting Gracilaria growing at the bottom of a pond; hand-collecting is used for monoline culture as well as for alga growing in fish cages.
Yield
The agar yield of G. fisheri from wild populations in the Philippines is (after non-alkaline treatment) 13.8-20% (dry weight). The agar content of G. fisheri in Thailand varies considerably, ranging from 12.9-26.7% of clean dry seaweed.
Handling after harvest
Sun-drying of G. fisheri near collection sites is the only method used. The dry seaweed is then packed into gunny sacks and stored in the warehouse ready for sale. Grinding the seaweed after initial boiling and thoroughly pressing it after boiling is completed, or cooking under steam tend to give higher yields.
Prospects
The demand for dry seaweed supplies for agar extraction is increasing. Harvest from natural populations is not enough and not constant. Without proper management the over-exploitation of G. fisheri will probably result in decreased yields. Research on appropriate cultivation methods is needed for the local coastal people to increase their production and income, and also to keep a constant and consistent supply of raw material.
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.
Sources of illustration
Original drawing of the authors Lewmanomont, K. & Phang, S.-M. Redrawn and adapted by P. Verheij-Hayes.
Authors
- K. Lewmanomont & S.-M. Phang
