INTRODUCTION

1.     Outside a relatively small number of scientists, biologists and industrialists, the seaweed industry is perhaps one of the least understood sectors of the world's fisheries. Certainly, its economic and commercial aspects are among the most poorly documented. Yet it is an industry of considerable and, in many instances, rapidly growing proportions, with a total commercial value approaching some U.S.$ 1 000 million per annum; moreover, the products of its most dynamic section - the extraction of seaweed colloids - touch upon almost every aspect of modern society.

2.     The use of seaweeds for food and as medicines was recorded in China some thousands of years ago, and in parts of Asia seaweed and seaweed products have for many years been widely used, if not staple, food items. In the western world seaweeds have traditionally been valued principally for their properties as animal feed and fertilizers and, during the eighteenth and nineteenth centuries, as a source of soda, iodine and other chemicals.

3.     However, while seaweeds still remain of importance as a food supplement in the Far East, above all in Japan, the most notable trend over the last three or four decades has been the very significant growth in the output of seaweed colloids, notably agar, carrageenan and algin, of remarkably varied commercial application. This growth shows no signs of abating and most observers agree that, notwithstanding speculation regarding the potential of seaweeds as a direct source of protein and of drugs, the diverse demand for vegetable gums will be the major factor in influencing further exploitation of the world's resources of marine algae.

4.     The subject is one of considerable complexity, biologically, technically and commercially. As Woodward (1966) notes, there are such variations in seaweed species, in their habitats, accessibility and topography, in their chemical properties, availability and utilization and in the methods and costs of their harvesting and processing that it is quite impossible to consider the seaweed industry as a homogeneous entity. Moreover, a thorough review of the subject, at least its economic aspects, is seriously impeded by the relative lack of data and by the not unexpected secretiveness of the relatively few major commercial enterprises which dominate the highly competitive markets for seaweed colloids.

5.     Within these constraints, the present paper attempts, in as non-technical a manner as possible, to examine the various seaweed species and the products derived therefrom; to review recent trends in output, utilization and trade, and to identify possible opportunities, particularly in developing countries, for the greater economic exploitation of algaic resources.

Principal groups and species

6.     Marine algae are among the most primitive members of the plant kingdom. They occur in an incredible variety of life-forms, from uni-cellular species to giant kelp which may extend in length up to 40 m. The microscopic forms are seldom utilized and the smallest species eaten by man is believed to be the protein-rich Spirulina of Chad and Mexico, which consists of free-floating threads a quarter of a millimetre long. Some of the edible Codium species form soft pillows similar to mushroom caps clinging directly to the substrate. The green alga Ulva and the red Porphyra are formed of thin, tough membranes reminiscent of burst toy balloons, but most of the species used in large quantities take the form of cartilageous feathers, such as Gelidium, or are strong giants of the sea, like the brown algae classified as kelp and rock-weed. The latter have a differentiated plant body or “thallus” which consists of root-like “holdfast”, stem-like “stipe”, and the leaf-like “blade” or “frond”.

7.     The algae are generally classified into four main groups, largely upon the basis of pigmentation: green algae (the Chlorophyceae), blue-green algae (Cyanophyceae), red algae (Rhodophyceae) and brown algae (Phaeophyceae). Green and blue-green algae, while present in salt water, are more commonly associated with freshwater, and on land (for example, on tree trunks, in soil, etc.). Red and brown algae, on the other hand, are found almost exclusively in marine environments.

8.     Brown algae are the most familiar, conspicuous, largest and most abundant of the seaweeds, but in number and diversity are exceeded by the group of red algae of which there are some¹ 4 000 different species. The former are particularly abundant in cold northern waters and few species are found in tropical regions; red algae are present in all latitudes. The present study will concern itself mainly with members of these two groups which account for the majority of the algae of commercial importance.

¹ Dawson (1966)

9.     A list of the principal seaweeds presently used in the extraction of phycocolloids and an indication of their geographical distribution is presented in Table I. Certain of the seaweeds listed are also used as animal feed and fertilizers; for example, species of the Fucales order and Laminaria. Others, notably Laminaria, Nereocystis, Gracilaria and Gelidium, are used as direct food for man in various parts of the world, together with algae not included in the list, such as the red seaweeds Rhodymenia (“dulse”) and Porphyra (“laver”) and the green algae Ulva (“sea lettuce”) Enteromorpha and Caulerpa.

Harvesting

10.     The seaweed industry has often been described as a “cottage” industry and whilst such an aphorism cannot justly be applied to the modern processes involved in the extraction of phycocolloids, the methods employed in harvesting and drying of seaweeds still in general remain small-scale, traditional and primitive. To a certain extent, this situation is unavoidable as the variety in the size, type, habitat, location and abundance of marine algae is such that their collection and handling is often extremely difficult to mechanize. The harvesting methods used (or, rather, which it is possible to use) thus depend primarily upon the physical properties and natural environment of individual seaweed species or species groups. In general, the red algae are much smaller in size and occur in deeper waters than the brown algae; consequently their harvesting is slower, more difficult and more costly. Although many species yield fluctuating harvests of cast-weed, torn loose during seasonal storms and deposited on beaches and rocks, red algae are generally collected by harvesting the beds by hand or by using rakes or grapnels.

11.     Gelidium, for example, which grows on rocks in the intertidal zone and beyond, is gathered by hand between tides, by means of long-handled rakes in shallow waters and by divers from the deeper sublittoral regions where the best quality plants are normally to be found. In Japan, a major producer of Gelidium, the greater part of the harvest is obtained by divers, traditionally women, who, using goggles, can only work down to a depth of some 10 m. Whilst labour-intensive and costly, harvesting by divers can give excellent yields. Aberdein (1968) estimated that an experienced diver can collect between 120 and 250 kg (dry weight basis²) of Gelidium per day; according to Okazaki (1971) the Japanese women divers are said to harvest up to 300 kg daily, whilst Chapman (1970) reported that in Baja California a diver, working from a boat in conjunction with a boat operator and life-line tender, can collect as much as 1.5 tons of fresh Gelidium in a single working day, although harvests of much less than this are more normal.

² Three to four kg of fresh Gelidium yield about one kg of dry weed

Table I

Principal Seaweeds in Present Commercial Use and Their Geographical Distribution¹

¹ After Chapman (1970), Whistler (1973), Firth (1969), Dawson (1966) and Kim (1970)
² Of which the main genera are Fucus, Ascophyllum and Sargassum

12.     The collection of Gracilaria, the other major seaweed used in agar production, is relatively easier. It is a very prolific species found in considerable abundance in many countries. Rather larger than Gelidium, Gracilaria grows in shallow water, up to a depth of about 7 m and is readily harvestable by hand, by means of grapnels or rakes or through the use of nets or fences placed across channels formed by tidal currents. A description of the varied methods of harvesting Gracilaria employed by a fishery cooperative in the Maullín River estuary, Chile, was given by Cable (1974), who noted that the most common method is the use of long-handled rakes to rip the plants from their surface of attachment; quantities are also hand-gathered in shallow water at low tide or direct from the beach after winter storms. Cable observed that two fishermen working from a 10-m motorized launch can collect and, with the help of their families, dry around 500 kg (dry weight) of weed daily. Depending upon the species, between six and ten tons wet Gracilaria are required to produce one ton of dried weed; in the case of the Maullín River fishermen, therefore, two men were estimated to harvest up to five tons of fresh algae per day. It is interesting to compare the yield from the above traditional method with that of a specially designed trawl-grapnel, used in New South Wales, Australia, with which it is reported up to eight tons of wet weed can be collected in one week by a crew of three men.¹ The difference in the “harvest-per-unit-of-effort” between these two methods probably reflects relative abundance of weed rather than absolute efficiencies of harvesting methods.

¹ Chapman (1970)

13.     Time-tested, labour-intensive collection methods still account for almost the entirety of the harvest of Chondrus crispus or “Irish moss”, the principal raw material used in the production of carrageenan. The plant, small (about 60–150 mm) and bushy, is found at the extremity of the tidal zone, normally attached to rocks from just above low-water level down to a depth of some 6 to 7 m. Harvesting is carried out during the summer months, May to September, and is possible only during the 3 to 4 hours of the ebb tide. The principal harvesting areas are the eastern seaboard of Canada and the U.S.A., and parts of western Europe. In the former, conditions permit the widespread use of long-handled rakes manipulated from a small boat; in Europe, the irregular character of the rock surfaces and the admixture of Chondrus with other seaweeds necessitates slower, more selective hand collection methods.

14.     The manner in which harvesting methods are determined principally by the habitat and accessibility of the plant species was clearly illustrated by MacFarlane (1964) in a description of the seaweed industry of the Maritime Provinces of Canada. In southwest Nova Scotia the gentle slope of the shore, the high tides, rapid currents and adequate shelter create excellent conditions for both harvesters and plants; on the peninsula's Atlantic-facing coasts the continuous ocean swell and steep slope limit both plant growth and the days when harvesting is possible. By contrast, in Prince Edward Island and the Northumberland Strait, the substratum is chiefly of very friable sandstone; holdfasts are readily torn off and the greater part of the harvest is from storm-cast material; raking, the most common hand-gathering method in the rest of the area, is made very difficult by a heavy sediment, which, stirred by the wind, seriously lowers visibility.

15.     Expertly used, the long-handled rake is in effect a “combing” device and does not injure the holdfasts; with proper setting of the teeth on the crossbar, the rake removes only the larger plants, leaving the smaller plants to be collected to greater advantage at a later harvest. Depending upon the ecological, tide and weather conditions, and the collector's skill and experience, as many as 400 to 500 kg (fresh weight) of Chondrus can be harvested per tide; however, most commentators agree that, on average, a good collector normally harvests about half of such an amount.

16.     The other main seaweeds used in the extraction of carrageenan - Eucheuma, Hypnea and Iridea - are generally harvested by hand when their intertidal habitats are exposed by low tides, although considerable quantities of Eucheuma are collected as castweed after seasonal storms. Between 90 and 135 kg of wet weed have been reported² as a normal harvest of Iridea by one man during one low tide period.

² Tseng, C.K. (1947)

Fig. 1 Gelidium sp. (R)	Fig. 2 Gracilaria confervoides (R)
Fig. 3 Chrondrus crispus (R) “Irish Moss”	Fig. 4 Furcellaria fastigiata (R)

17.     The red seaweed Furcellaria, which since the mid 1940s has become the basis of an important phycocolloid industry in Denmark, grows at somewhat greater depths than most other Rhodophyceae and separates from the substratum to float in the sea, sometimes accumulating in the centre of circulatory currents. Considerable quantities of unattached weed used to collect in the central part of the Kattegat and were harvested by trawlers using dragnets; daily yields per trawler of up to 100 tons (fresh weight) being obtained. Harvesting was carried out the year round, although the cold winter months are preferred, the algae then being less liable to decomposition. By the end of the 1960s it became obvious that the resources in this locality were being overexploited and in recent years harvests have been deliberately restricted by the industry in an attempt to protect and conserve the resources. Attention has also turned to the exploitation of cast Furcellaria upon Danish shores (4 000 to 5 000 tons wet weight per year) and of Furcellaria from the north shore of Prince Edward Island (Canada), where the species grows in mixed beds with Chondrus.

18.     Whilst also used for fertilizer and as an animal feed supplement, the brown seaweeds are valued chiefly for the alginic acid present in most species.¹ The abundance, habitat and size of the largest species - the giant kelp, Macrocystis - have permitted a fairly high degree of mechanization in harvesting practices. The individual plants have a perennial “holdfast” attached to the ocean bed at depths of from 7 to 25 m, from which grow numerous gas-filled fronds spreading out at maturity to 7 m or more (Silverthorne and Sorenson 1971).

¹ It should also be noted that very considerable quantities of certain species of brown (and red and green) algae are cultivated, for human food purposes, in Japan, the Korean Peninsula and China

19.     Mechanized harvesting has been most fully developed in California where Macrocystis grows in large beds, up to a mile in width and several miles in length. Specially built, power-driven barges equipped with reciprocating underwater mowers are used to crop the weed. Ealier cropping vessels were able to carry about 300 tons of fresh seaweed and had the mower mounted in the bow, but later models have the mower at the stern and greater carrying capacity (Booth, E., In Firth, 1969). In California where, in common with a number of other kelp harvesting areas, cropping is controlled by licensing and/or royalty arrangements, regulations require that the kelp be cut no more than 4 ft (i.e., about 1.25 m) below the water's surface; the plant grows at such a rapid rate that this permits about three harvests yearly. With a crew of four men, up to 125 tons of kelp can be harvested in four to five hours (Druehl, 1972). Similar mechanical cropping vessels are in use, or being considered, in harvesting the other giant kelp, Nereocystis, which is also present in considerable quantities in the colder waters off the west coast of Canada, Alaska, South America, New Zealand and Tasmania.

20.     The smaller brown seaweed, Ascophyllum nodosum, which grows in shallow intertidal waters off Canada, the British Isles, Norway and France, is normally harvested, when uncovered at low tide, by hand from small boats or on shore, although it was reported (Booth, E., In Firth, 1969) that a small barge similar to the Macrocystis cropping vessels has been used in Nova Scotia to harvest Ascophyllum as it floats at high tide.

21.     Another group of brown seaweeds of considerable commercial importance are the Laminaria or bottom kelp. Present in vast quantities in many parts of the world, but notably in the northern hemisphere, Laminaria grow only on hard, rocky ocean bottoms down to depths of 25 m. As the plant rarely exceeds 4.5 m in length, mechanical harvesting is extremely difficult, although two mechanized methods have been tried, one using reciprocating cutters mounted on dredges, the other a system of continuous grapnels. Those species, such as L. digitata, which grow in somewhat shallower waters can be harvested by hand-cutting at low tide or with grappling hooks and long-handled rakes operated from small boats.

Fig. 5 Macrocystis pyrifera (Br.)	Fig. 6 Ascophyllum nodosum (Br.)
“Giant kelp”	“Knobbed-wrack”
Fig. 7 Laminaria digitata (Br.)	Fig. 8 Nereocystis leutkeana (Br.)
“Horsetail kelp”	“Bladder or Ribbon kelp”

22.     However, the greater part of the harvest of Laminaria is taken in the form of cast weed, particularly in the case of L. cloustoni in the northern Atlantic coasts. At the beginning of the vegetative period, the winter, a new frond-like blade grows out of the stipe of Laminaria, the old blade dying off gradually until it is shed from the plant. This sloughing-off process results, in association with spring storms, in regular casts of weed upon neighbouring shores, from where the drift weed can be easily collected, providing access to the beaches is possible.

23.     There is general agreement that one of the greatest problems facing the seaweed industry is the need for improved efficiency in harvesting. In the production of phycocolloids roughly half of the total expenses are raw material costs. Hand collection still accounts for the great majority of weed gathered and, certainly in the case of many of the major producers of the northern hemisphere, these labour-intensive methods are becoming increasingly expensive and slow. With the principal exception of the Californian Macrocystis beds, few mechanized methods of harvesting have been successfully developed. At the same time, this situation presents interesting socio-economic opportunities for developing countries with underexploited seaweed resources and a surplus of labour. Under these circumstances, the hand collection and natural drying of seaweed can provide supplementary employment and income for all members of littoral families and a potential source of foreign exchange to the country itself.

Drying

24.     After harvesting the enormous wet bulk of the weeds must be reduced by drying before processing. Wet weed deteriorates fairly quickly; it is thus particularly important to deal with cast weed before it decays, or is swept out to sea. Moreover, when agar is to be produced, drying is essential because extracts of the wet weed do not gel. Once properly dried, the weed can be stored for a number of years without appreciable loss of gel content.

25.     Irish moss (Chondrus) and Gigartina spp. are washed in seawater after collection to remove sand and other impurities. As the salts which control the gelling process for which the weed is used are readily washed out by freshwater, only seawater can be used for this cleansing process. Whilst the majority of weed is dried naturally through exposure to sun and air, artificial mechanical drying methods are now being used increasingly.

26.     In the case of natural drying, the washed weed is thinly spread on portable racks, wooden platforms or, when available, extensive areas of clean flat rock; drying on grass or sand is to be avoided. In favourable (i.e., dry, sunny, windy) conditions one or two days are sufficient to reduce the moisture content to the 18 to 20 percent level required by the carrageenan processors. The danger of spoilage to partly dried weed through moist, foggy weather is a problem, particularly in the northern hemisphere; it has been reported¹, for example, that some 10 000 kg of dulse (Rhodymenia palmata) annually go to waste in Canada, when the late summer and autumn weather is mild enough for harvesting but is too uncertain to allow spreading and drying.

¹ Proc. Mtg. Canadian Atlantic Seaweeds Industry, Charlottetown, October 1971

27.     These uncertainties have given impetus to the development of artificial drying methods, notably flame-heated rotary driers particularly on the eastern seaboard of the U.S.A. and Canada and in France. They are expensive to install but, in addition to permitting drying irrespective of weather conditions, it has been demonstrated that a much more uniform extract can be obtained from controlled, artificially-dried raw material. In general, artificial driers have been provided by the carrageenan manufacturers and it has been suggested² that it might be in the interests of the seaweed gatherers if they were to install and operate driers themselves on an independent, cooperative basis.

² Aberdein (1968)

28.     Traditionally, Irish moss is generally bleached during the drying process, the weed being sprinkled with salt water and turned frequently. In recent years, however, there has been a distinct trend toward the sale of unbleached material (“black weed”), which yields a stronger jelly as no gelose has been washed out. The dried weed is usually marketed in 100 to 200 lb burlap-covered bales, although transport economies can be obtained by grinding the dried moss and packaging it in heavy paper bags or cartons.

29.     The drying of the agar-yielding group of seaweeds, principally Gelidium and Gracilaria, follows very similar procedures to those described above. In Japan and several other Asian countries the fresh weed, after a preliminary cleaning and washing, is spread on bamboo racks or mats to dry in the open air, a process that normally takes several days; in other countries wire nets are widely used. Artificial drying with the aid of flue-heated air is advantageous in wet climates.¹

¹ Selby, H.H., In Firth (1969)

30.     Chapman (1970) gives a description of drying and bleaching treatments used in Japan, the world's major producer of agar. The traditional method involves cleaning the wet weed by beating and pounding and picking out the larger pieces of foreign matter by hand, followed by a washing in running water; the weed is then laid upon mats to bleach, a process requiring warm weather and much aided by overnight dew. A more modern technique is to wash and stir the weed in vats, keeping the water temperature below 10°C. For normal commercial purposes bleaching is not really necessary but it is desirable in the case of weed destined for bacteriological uses.

31.     In the production of algin both cast and cut brown seaweeds are used in either the fresh or dried state, depending upon the processing techniques to be used. Maximum extraction is considered to be achieved if the weed is dry rather than wet; on the other hand the costs of drying may outweigh the benefits of using dried weed. Most Laminaria digitata is air-dried by spreading on land or hanging on racks or walls; the rod-like stipes of L. cloustoni generally are piled in ricks for an initial drying before transport to central drying plants for artificial drying and milling into small pieces.² When wet weed has to be stored, the dangers of deterioration can be reduced by the use of sulphur dioxide or spraying with a formaldehyde solution.

² Aberdein (1968)

Trends in exploitation

32.     The data available regarding world seaweed production are extremely variable in coverage and reliability. Production statistics for some countries are provided by national authorities for publication in the FAO Yearbook of Fishery Statistics - Catches and Landings series. Such data, however, have not been made available for a number of important seaweed-producing countries; moreover, in a number of cases, even where data are provided, information from other sources clearly indicates that the statistics are often incomplete or biologically incorrectly classified.

33.     An attempt is made in Appendix I to tabulate both “official” data and “best estimates” regarding world seaweed production over the period 1960–1974. A resumé of these estimates, by major producing countries, is presented in Table II.

34.     The accuracy of the estimates of total world output depends largely on the validity of the assumptions made regarding output by China; the few shreds of evidence available indicate that Chinese production of seaweeds is most likely as great as (and probably even more than) that of the other leading producer, Japan; together, their harvests of algae appear to account for well over a half of present total world production and a similar proportion of the increase of approximately 100 percent experienced in the world harvest of seaweed over the last decade and a half.

Fig. 9 Porphyra tenera (R) “Laver”, “Nori”	Fig. 10 Eucheuma muricatum (R)
Fig. 11 Undaria pinnatifida (Br.) “Wakame”	Fig. 12 Rhodymenia palmata (R) “Dulse”

Table II

World Production of Seaweeds (1960 and 1973) and Estimated Value (1973)

( ) broad estimates of production

^a Some figures, e.g., Japan, U.K., Argentina, Morocco, are officially published data, converted into U.S. dollars at average exchange rates for 1973; others, e.g., Korea, Spain, are estimates based upon relative data for 1972; for a number of countries, notably China, U.S.S.R., U.S.A., Brazil, the estimates are broad indications calculated on the basis of the species composition of the harvest, uses of the weeds and unit production values elsewhere

35.     The Japanese data, fortunately, are among the most reliable and comprehensive available. A considerable part of the rapid growth in Japanese output arises from the remarkable expansion experienced in the production of cultivated Porphyra, the red seaweed used in the preparation of “nori”, an edible product widely demanded on the Japanese domestic market. An even more rapid rate of growth has recently occurred in the output of the Republic of Korea, especially of cultivated brown algae.

36.     Another particularly notable feature has been the marked expansion in seaweed harvests by a number of South American countries; output of algae on the subcontinent now probably exceeds 150 000 tons (fresh weight) per annum, a fourfold increase since 1965.

37.     Over the last decade, cultivation, compared with the harvesting of naturally occurring resources, has become of increasing importance, particularly in areas where the culture of seaweed has a long tradition (for example, Japan and the Republic of Korea) but also elsewhere. This intensifying interest in seaweed farming is to some extent a reflection of the growing concern on the part of the major phycocolloid manufacturers about the need to secure greater stability in the supply and price of their raw materials, but also has had valuable socio-economic repercussions in the localities where these practices have been developed; the successful establishment of Eucheuma cultivation in The Philippines is a notable case which is discussed more fully in a later section of this paper.

38.     An attempt is also made in Table II to estimate the total value to producers, at firsthand sale, of the seaweed harvests of 1973. This is an exercise even more fraught with difficulties and inherent inaccuracies than that of estimating the weight of production. Not only is reliable information conspicuously lacking in a large number of cases, but unit values clearly vary enormously not only between countries but also depending upon the species involved and, particularly, the form (wet, dried or semi-processed) in which the weed is first sold, which in turn depends upon the end-use envisaged. Converting values in national currencies to the common denominator of U.S. dollars also creates further distortions between countries, particularly over a period of time.

Table III

Japan - Production Value of Seaweeds 1970–1973

Source: Ministry of Agriculture and Forestry, Annual Statistical Report on Fishery and Aquaculture Production, 1973, Tokyo

39.     For example, the tremendous value (U.S.$ 563 million) in 1973 of Japanese seaweed production reflects the fact that most seaweed operators in Japan not only cultivate and harvest the algae, but also dry them and semi-process them into very high-value edible products which are then marketed through a strong producers' association. Moreover, not only did unit prices for edible seaweeds in Japan rise by about 25 percent in 1973 compared with 1972, but changes in the yen/dollar parity also resulted in a proportionately much higher dollar value. On the basis of the then prevailing exchange rates, the values of Japanese seaweed production in earlier years were: U.S.$ 363 million in 1972, U.S.$ 308 million in 1971 and U.S.$ 277 million in 1970 (see Table III).

40.     Over 95 percent of the estimated first-hand value of total world seaweed output in 1973 was in fact attributable to the sale of semi-processed edible products in Japan, the Republic of Korea and China. Seaweeds harvested for use by the phycocolloid extractive industries, and generally first sold in a simple dried and unprocessed state, account for the greater part of the balance (U.S.$ 25 million); average unit values are a mere fraction, especially in the case of brown seaweeds, of prices obtained for edible seaweeds.