Hydroclathrus (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Hydroclathrus tenuis - 1, habit. H. clathratus - 2, portion of a clathrate thallus; 3, cross-section of a clathrate thallus with plurilocular zoidangia; 4, cross-section of inrolled thallus, united by rhizoids; 5, detail of a prostrate microthallus with an unilocular and a plurilocular zoidangium; 6, zoid from a plurilocular zoidangium of a clathrate thallus, with an eye-spot (dark dot) and a pyrenoid (open dot); 7, zoid from an unilocular zoidangium of a prostrate microthallus, with eye-spot and pyrenoid.

Hydroclathrus Bory

Protologue: Dict. class. hist. nat. 8: 419-420 (1825).

Family: Scytosiphonaceae

Chromosome number: x= unknown

Major species and synonyms

• Hydroclathrus clathratus (C. Agardh) M. Howe, in Britton & C.F. Millsp. Bahama fl. 590 (1920), synonyms: Encoelium clathratum C. Agardh (1822), Hydroclathrus cancellatus Bory (1825).

• Hydroclathrus tenuis C.K. Tseng & B. Ren Lu, Chin. J. Oceanol. Limnol. 1(2): 187 (1983).

Vernacular names

• Philippines: lukot-lukot (Visayan), poko-poko, balbalulang (Ilokano). All names are mainly for H. clathratus .

Origin and geographic distribution

H. clathratus is the most common species and is widely distributed in most of the tropical warm waters of the world. In the South-East Asian region it is found in Burma (Myanmar), Thailand, Vietnam, Malaysia, Singapore, Indonesia, the Philippines and Papua New Guinea as well as tropical China, Japan and the western Central Pacific region. H. tenuis has only been recorded for the Philippines, Indonesia (Sulawesi) and the southernmost parts of China.

Uses

Both Hydroclathrus are used in human food, in salads after blanching in hot water or as a spicy ingredient. They are also applied as fertilizer, animal fodder and insect repellent, and are a good source of alginate and iodine.

Production and international trade

No production data for Hydroclathrus are available. It is not being cultured, the biomass being harvested from natural stocks.

Properties

Hydroclathrus generally contains alginate. It also contains iodine (1.4%), mannitol (17.3%), a fair amount of crude protein (9.0%), crude fat (1.0%) and crude fibre (1.8%), as well as growth regulators such as auxin (8400 μ auxin activity/g seaweed when an aqueous extract is tested on oat (Avena sativa L.)), gibberellin and cytosin. Fucoidin is also present in small quantities as well as vitamins such as folic and folinic acids. H. clathratus is occasionally cited as containing harmful "germs". This might be related to "curet", which are pinhead-sized poisonous crabs that breed in Hydroclathrus thalli. Infested thalli are reported to be deadly poisonous.

Description

• Round, cushion-shaped, clathrate mass when young, reticulate amorphous mass when mature; structure parenchymatous.
• Sporangia generally distributed over thallus surface.

H. clathratus.

• Thalli yellow-brown, attached by rhizoids when young, vesicular or irregularly ovate, becoming hollow with many small holes; mature thalli detached from substrate, developing into well-formed network with rounded holes 0.5-2 cm in diameter, margins around holes involute.
• Cross-section of network about 600-900 μm thick, composed of cortex and medulla; cortical cells small, cuboidal, 5-9 μm with chromatophore; hairs grouped in shallow depressions; medullary cells colourless, large, 100-130 μm.
• Life cycle heteromorphic.
• Plurilocular zoidangia at first biseriate, scattered over surface of saccate thalli, or occurring together with unilocular zoidangia on prostrate microthalli; mature plurilocular zoidangia on saccate thalli often broadly based, 33.3-41.6 μm × 10.0-11.7 μm.
• Unilocular zoidangia sessile or shortly pedicellate, 28.6-35.7 μm in diameter.

H. tenuis.

• Thalli yellow-brown, attached when young, vesicular, becoming hollow with perforations; mature thalli detached from substrate, developing into large reticulate network with rounded holes; reticulate thalli very thin, about 250-300 μm thick.
• Network consisting of cortex and medulla; cortex with small, quadrate, pigmented cells, 8-10 μm in diameter; medulla composed of several layers of large, colourless, parenchymatous cells, 70-30 μm in diameter; colourless hairs grouped in shallow depressions on surface of thalli.
• Plurisporangia biseriate, 22-25 μm × 6-9 μm, in groups on surface of thalli, associated with tufts of hairs.

Growth and development

Hydroclathrus alternates between macrothalli bearing plurilocular zoidangia and prostrate microthalli bearing both plurilocular and unilocular zoidangia. In plurilocular zoidangia each of the loculi of originally biseriate zoidangia often forms 4 smaller loculi, each containing a single plurizoid. Plurilocular zoidangia on prostrate microthalli are ectocarpoid, 36-36 μm × 14-15 μm, biseriate, somewhat spindle-shaped, occasionally branched, but usually simple, without a stipe. Plurizoids from both the microthalli and the macrothalli attach and form prostrate microthalli. Many unizoids are found together in unilocular zoidangia and always on microthalli. After germination they always form macrothalli. No sexual reproduction stage is known. In experimental tests, germlings of H. clathratus did not grow at temperatures of 5°C and below. This explains why the alga is not found on temperate coasts.

Ecology

H. clathratus and H. tenuis are very common on reef flats. Young thalli form reticulate clumps attached to coral rocks at the landward half of the reef crest and on the reef flat. The peak of abundance usually occurs during the sunny period of March-May/June when the alga forms thick blooms. The advent of the rainy season marks the start of the die-off stage of the bloom which completely disappears during the rainy months. H. clathratus is more abundant than H. tenuis.

Propagation and planting

Hydroclathrus is not known in phycoculture.

Harvesting

Hydroclathrus is hand-collected by local people.

Handling after harvest

Hydroclathrus is used and sold fresh or sun-dried.

Prospects

Unless commercial use of Hydroclathrus compounds is found, very few developmental prospects are likely in the future.

Literature

• Kogame, K., 1997. Life histories of Colpomenia sinuosa and Hydroclathrus clathratus (Scytosiphonaceae, Phaeophyceae) in culture. Phycological Research 45: 227-231.
• Montaño, N.E. & Tupas, L.M., 1990. Plant growth hormonal activities of aqueous extracts from Philippine seaweeds. SICEN Leaflet 2: 1-6.

Sources of illustration

Hori, T. (Editor), 1993. An illustrated atlas of the life history of algae. Vol. 2. Brown and red algae. Uchida Rokakuho Publishing Company, Tokyo, Japan. Plate 29, p. 58 (H. clathratus: cross-section clathrate thallus, prostrate microthallus, zoids); Trono, G.C. & Ganzon-Fortes, E.T., 1980. An illustrated seaweed flora of Calatagan, Batangas, Philippines. University of the Philippines Marine Science Center & Filipinas Foundation, Manila, The Philippines. Fig. on p. 45 (habit H. clathratus); Tseng, C.K., 1983. Common seaweeds of China. Science Press, Beijing, China. Plate 94, fig. 3, p. 187 (habit H. tenuis); Womersley, H.B.S., 1987. The marine benthic flora of Southern Australia. Part 2. Handbook of the flora and fauna of South Australia. Adelaide, Australia. Fig. 110A, p. 305 (cross-section of inrolled thallus). Redrawn and adapted by P. Verheij-Hayes.

Authors

• G.C. Trono Jr