Porphyra (PROSEA)
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Introduction |
Porphyra C. Agardh
- Protologue: Syst. alg. XXXII: 190 (1824).
- Family: Bangiaceae
- Chromosome number: x= unknown; P. atropurpurea: 2n= 6 or 8, P. yamadae (as P. crispata):x= 3, P. suborbiculata: 2n= 6
Major species and synonyms
- Porphyra atropurpurea (Olivi) De Toni, Syll. alg. 4, Florideae, Sect. 1: 17 (1897), synonym: Ulva atropurpurea Olivi (1794).
- Porphyra suborbiculata Kjellm., Bih. Kongl. Svenska Vetensk.-Akad. Handlingar 23 (Afd. 2, 4): 10, pl. 1: figs 1-3; pl. 2: figs 5-9; pl. 5: figs 4-7 (1897). Accepted name is now (2016): Pyropia suborbiculata (Kjellman) J.E.Sutherland, H.G.Choi, M.S. Hwang & W.A.Nelson (2011).
- Porphyra vietnamensis Tak. Tanaka & P.H. Hô, Mem. Fac. Fish., Kagoshima Univ. 11: 34-36, figs 10, 11 (1962), synonym: P. marcosii Cordero (1976). Accepted name is now (2016): Pyropia vietnamensis (Tak.Tanaka & Pham-Hoàng Ho) J.E.Sutherland & Monotilla (2011).
- Porphyra yamadae T. Yoshida, Phycol. Res. 45: 166 (1997), synonym: P. crispata Kjellm. (1897). Accepted name is now (2016): Pyropia acanthophora (E.C.Oliveira & Coll) M.C.Oliveira, D.Milstein & E.C.Oliveira (2011).
Vernacular names
- Purple laver (En)
- Zicai (China)
- Nori (Japan)
- Philippines: gamet (name for dried products of all Porphyra spp., Ilocos Province), pedazo.
P. vietnamensis (as P. marcosii)
- Indonesia: huang isi, lumu lumu licin.
Origin and geographic distribution
Porphyra occurs usually in non-tropical areas, although some species occur in the tropics as well. In South-East Asia Porphyra has been recorded from Burma (Myanmar, P. yamadae, as P. crispata), Thailand and Vietnam (both P. vietnamensis and P. yamadae, as P. crispata), the Philippines (Luzon, all species) and eastern Indonesia (P. atropurpurea and P. vietnamensis, as P. marcosii). In many countries in South-East Asia dried Porphyra (nori) is imported from Japan, China or Korea.
Uses
The bulk of the Porphyra production as well as locally collected Porphyra is used as food in soups, sushi, and salads in Thailand, Vietnam, the Philippines and Indonesia. Several Porphyra spp. are also used for medical purposes, especially in Chinese herbal medicinal practice, where they are used to treat goitre and scrofula, cough, bronchitis, tonsillitis, asthma, urinary diseases and dropsy. Some Porphyra spp. are also applied as preventive medicine for hypertension. In northern Luzon (the Philippines) Porphyra ("gamet") is consistently the most popular edible seaweed. It is not generally available in southern Luzon. In Ambon (Indonesia) the locally available P. vietnamensis is sold at markets as dried sheets, prepared from many small thalli pressed together. In Halmahera and the Kai Islands (Indonesia) locally collected thalli are used to prepare sweetened jellies with coconut milk and the algae are also eaten in vegetable soup.
Production and international trade
Although Porphyra cultivation is one of the most economically important food industries in Japan, Korea and China, production in South-East Asia is rather limited and usually only of local importance. There are no data available on the extent of production and international trade of Porphyra in South-East Asia, while the annual production of cultivated Porphyra in China, Japan and Korea is about 1 million t (wet weight).
In northern Luzon (the Philippines) Porphyra (most probably P. suborbiculata) is cultivated locally and the thalli are hand-picked and sold as dried sheets ("pedazo"). Dried Porphyra sheets are usually more expensive than other dried seaweed products. In the southern part of Thailand P. vietnamensis is exploited on a small scale. There, the total crop is less than 100 kg (dry weight) per year and no cultivation takes place. The slippery thalli are collected by hand in the upper littoral zone of exposed rocky coasts and reefs. In Thailand the larger thalli of P. vietnamensis are preferred to P. yamadae (as P. crispata); the latter is even considered to have no commercial value.
Properties
Most Porphyra spp. have a high content of digestible protein (20-25% of wet weight) and contain many free amino acids (especially glutamic acid, glycine and alanine), which are responsible for its specific taste. Its vitamin C content is similar to that of lemons, while it is also rich in the B vitamins. Porphyra is an excellent source of iodine and other trace elements.
Description
- Foliose thalli (blades) purplish-red, round, reniform, funnel-shaped or linear, usually attached by discoid holdfast and obscure stipe with rhizoidal cells, monostromatic; cells in surface view polygonal, in cross-section elliptical to rounded containing 1 stellate chloroplast, with or without microscopic serrations along margins of blades.
- Life cycle diplo-haplontic and triphasic.
- Foliose gametophytes large, forming sori of unicellular carpogonia (zygotosporangia, zygotospores) and spermatangia (spermatia).
- Vegetative cells forming monospores.
P. atropurpurea.
- Margins of leafy thalli without microscopic serrations.
- Although this species has been recorded as occurring and being utilized in South-East Asia, a recent reconfirmation is not available. Most probably, the name has been misapplied for one of the other Porphyra spp.
P. suborbiculata.
- Foliose thalli light pink or purplish-red, round, ovate, funnel-shaped, laciniate or caespitose, 1-10 cm tall, 25-50 μm thick, with undulate or inrolled margins and microscopic serrations, entire or deeply lobed, attached at one side by discoid holdfast, 0.8-1.2 mm in diameter, with obscure stipe.
- Vegetative cells rounded, polygonal or angular in surface view, 20-30 μm × 12-22 μm, quadrate with rounded angles in cross-section, slightly taller than wide, 20-32(-60) μm × 20-35 μm; rhizoidal cells angular, capitate.
- Fertile thalli monoecious, 35-50 μm thick, deep red female areas and yellowish male ones splashed, close to margins of thalli.
- Usually 32 zygotospores formed from each zygotosporangium and 64-128 spermatia from each spermatangium.
- Monospores usually on young gametophytic thalli only.
P. vietnamensis.
- Foliose thalli lanceolate to linear-lanceolate, basically branched, 3-27 cm × 0.3-3.6 cm, 20-32 μm thick, margins undulate, with microscopical denticulate processes, attached by small discoid holdfast.
- Vegetative cells angular with rounded angles in surface view, 9-15 μm in diameter, same form in cross-section, cells 13-22 μm tall; rhizoidal cells angulate-capitate to oblong capitate.
- Fertile thalli monoecious, pinkish female patches at margins and apical portions of thalli, pale male areas at other margins.
- Usually 8 zygotospores (12-15 μm in diameter) formed from each zygotosporangium and 64 spermatia (7 μm in diameter) from each spermatangium.
- Monospores (18-20 μm in diameter) on young gametophytic thalli only.
P. yamadae.
- Foliose thalli light red to black-purple, elliptical to reniform, often caespitose, 2-5 cm tall, 45-68 μm thick, margins often laciniate, with microscopic serrations, attached by discoid holdfast.
- Vegetative cells oblong-elliptical in surface view, longest dimensions 15-20 μm, in cross-section elliptical, half as tall as wide, (32-)55-60 μm × 20-27 μm; rhizoidal cells oblong capitate.
- Fertile thalli monoecious, brown-red female and yellowish male patches in separate areas along margins of thalli.
- Usually 32 zygotospores (8.8-14.8 μm in diameter) formed from each zygotosporangium and 128 spermatia (3-4.5 μm in diameter) from each spermatangium.
Growth and development
The immobile tiny spermatia of Porphyra, of which many (up to 128) are formed by each spermatangial cell, attach to papilla-like protrusions of the female cells (carpogonia) which, after fertilization, become zygotosporangia forming zygotospores. These spores are liberated and, when germinating on a calcareous substrate, form the microscopic and filamentous "Conchocelis" stage. These filaments later form rows of spores (known as tetraspores or conchospores) which are liberated and each can germinate to form a leafy gametophyte. Cells in young gametophytes may become vegetative monospores, which may form gametophytes again. In the northern Philippines (Ilocos Norte) and in Thailand gametophytes occur in the wet season, from November to February.
Other botanical information
Synonymy of P. suborbiculata and P. yamadae (as P. crispata) has recently been suggested. No clear differences could be observed between these taxa. Occasionally the thallus of P. yamadae (as P. crispata) is described as narrow, long, ribbon-like, up to 19-43 cm long, but probably this is a different species. The difference in form of the thalli and cells, as well as the number of spermatia formed by each spermatangium might be different enough to keep the taxa separated. The type of P. crispata is a green alga, hence the change of name to P. yamadae.
Synonymy of P. marcosii and P. vietnamensis has not yet officially been suggested. The differences in dimensions of cells, thalli and thallus form are not convincing.
Ecology
The leafy gametophytes of P. suborbiculata in the northern Philippines and southern Thailand are usually found in the upper intertidal zone on rocky, wave-exposed shores, while the microscopic "Conchocelis" phase occurs in calcareous substrates such as shells of molluscs (mainly Lamellibranchiates) and barnacles. Leafy thalli of P. vietnamensis also grow on rocks in the upper intertidal zone, exposed to strong waves. It seems to grow best when fully exposed, moistened by spray of the breaking waves, and it can be found during the wet monsoon season. In Thailand in that season water temperature drops from 27-30 °C to 24-27 °C and salinity from 31-33 ‰ to (11-)18-26 ‰. The "Conchocelis" phase of P. vietnamensis grows well in shells of Lamellibranchiates.
Propagation and planting
"Conchocelis" stages of P. vietnamensis can be cultured in shells at 25 °C, salinity 25 ‰ and a light intensity of 350-500 lux for 12 h/d. At lower temperatures growth is very slow, while at 35 °C the "Conchocelis" dies. Formation of conchosporangia occurs about 2 months after inoculation of the shells with zygotospores of Porphyra and is best at 30 °C, and somewhat lower salinity (20 ‰). Each filament starts formation of conchosporangia 10 days after the temperature change and produces 10-20 conchospores after another ten days of incubation. These conchospores release 1-4 days after lowering the temperature again to 25°C and salinity to 10-15 ‰, and raising the light intensity to 800-1000 lux. Young leafy fronds develop best at the same temperature (24 °C), somewhat higher salinities (20-25 ‰) and higher light intensities (1000-1200 lux). These young fronds need 40 days to grow to germlings of 1 mm tall, and a further 22-30 days to become mature and fertile.
Phycoculture
Local cultivation in northern Luzon (the Philippines) of P. suborbiculata and/or P. yamadae (as P. crispata) is based on erecting long and branched bamboo poles, set closely together in rows along the shore. They are suitable for collecting spores from the surrounding waters. In other parts of northern Luzon and in southern Thailand the entire crop comes from natural populations and no cultivation is conducted.
Diseases and pests
The list of known diseases of cultivated Porphyra in Japan is longer than for any other algal genus. It includes diseases caused by fungus-like protists (Pythium porphyrae causing red rot, and an Olpidiopsis sp. causing blight known as chytrid blight), bacteria (causing green spot disease or forming a filamentous bacterial felt), diatoms (forming a diatom felt) and many diseases caused by environmental conditions. In most cases the quality of dried nori sheets produced from diseased thalli is classified as inferior. Diseases also occur in the "Conchocelis" filaments, and at that stage of the life cycle mass cultivation is often very vulnerable to damage. Causes of "Conchocelis" diseases are pathogenic bacteria and fungi or fungus-like protists. Several weedy algae (especially members of the green algal genera Monostroma Thur., Enteromorpha Link, and Ulva L.) grow on the culture nets in between the Porphyra thalli. These weedy specimens can usually be killed by exposing the nets to the air for hours or even days, because the weed algae are more susceptible to desiccation than Porphyra. Grazing by herbivorous fish can also become a problem.
Harvesting
In northern Luzon (the Philippines) and southern Thailand Porphyra thalli are hand-picked from bamboo poles and from submerged boulders and coastal rocks.
Handling after harvest
The locally produced Porphyra thalli in northern Luzon (the Philippines), southern Thailand and Ambon (Indonesia) are sold fresh or are prepared for the market by washing in freshwater, bleaching and sun-drying. In the Philippines this results in sheets 100-150 cm × 100 cm in size and about 5 mm thick. In Thailand and on Ambon, the dried sheets are circular and about 25 cm in diameter.
Breeding
In Porphyra cultivation improvement is done by selecting better producing strains.
Prospects
Because Porphyra includes the most highly domesticated marine algae, the state of understanding of its biology is quite advanced. Recent scientific advances in genetics, physiology, and biochemistry are quickly being applied in new production techniques and in the near future considerable progress is expected on the genetics of Porphyra. Vegetative propagation of the leafy gametophytes via protoplasts could help in eliminating the need for the expensive step of "Conchocelis" cultivation and will possibly bring genetic stability to the blades in cultivation.
Literature
- Cordero Jr, P.A., 1976. Phycological observations II. Porphyra marcosii, a new species from the Philippines. Acta Manilana, series A, 15 (24): 14-24.
- Fujita, Y., 1990. Diseases of cultivated Porphyra in Japan. In: Akatsuka, I. (Editor): Introduction to applied phycology. SPB Academic Publishing bv, The Hague, The Netherlands. pp. 177-190.
- Kumar, C.A. & Panikkar, M.V.N., 1997. Indian species of Porphyra (Rhodophyceae, Bangiales). Feddes Repertorium 108: 419-423.
- Lewmanomont, K. & Chittpoolkusol, O., 1993. Life cycle of Porphyra vietnamensis Tanaka & Pham-Huang Ho from Thailand. Hydrobiologia 260/261: 397-400.
- Llana, E.G., 1990. Status of production and utilization of seaweeds in the Philippines. FAO/NACA report on the regional workshop on the culture and utilization of seaweeds. Cebu City, The Philippines. pp. 124-149.
- Masuda, M., Ohno, M., & Trono Jr, G.C., 1991. A taxonomic assessment of Porphyra suborbiculata Kjellman, a food species from the Philippines. Japanese Journal of Phycology 39: 375-380.
- Tseng, C.K. & Chang, C.F., 1984. Chinese seaweeds in herbal medicine. Hydrobiologia 116/117: 152-154.
Sources of illustration
Cordero, P.A., 1976. Phycological observations 2. Porphyra marcosii, a new species from the Philippines. Acta Manilana, ser. A, 15 (24): fig. on p. 21 (details P. vietnamensis); Cordero, P.A., 1979. Phycological observations 9. Acta Manilana, ser. A, 18: fig. 1, p. 29 (habit P. yamadae), fig. 2, p. 31, (habit P. vietnamensis), fig. 3, p. 33 (habit P. suborbiculata); Kumar, C.A. & Panikkar, M.V.N., 1997. Indian species of Porphyra (Rhodophyceae, Bangiales). Feddes Repertorium 108: fig. 2, p. 421 (habit P. vietnamensis); Tanaka, T., 1952. The systematic study of the Japanese Proptoflorideae. Memoirs of the Faculty of Fisheries, Kagoshima University 2(2): fig. 16, p. 32 (details P. suborbiculta), fig. 17, p. 35 (detail P. yamadae). Redrawn and adapted by P. Verheij-Hayes.
Authors
- W.F. Prud'homme van Reine
