152. The increasing demand for seaweeds, and the supply shortages and rising costs experienced with certain species have underlined the need to establish the nature, extent and location of the world's resources of marine algae. Research to this end has been undertaken by workers in many parts of the world; some areas, for example, Scotland, the Pacific coasts of the U.S.A. and Japan have already been intensively surveyed, other regions much less so.
153. Various International Seaweed Symposia have addressed themselves to this subject, maps being produced at the first such meeting in 1952 of the areas then known to support brown and red seaweeds in concentrations sufficient to justify exploitation. At the Seventh Symposium over 40 papers were presented relating to the distribution, taxonomy or morphology of various algae. A number of other papers have been published elsewhere, for example, that of Kim (1970) presenting a cartographic summary of the distribution and exploitation of Gracilaria throughout the world. The most up-to-date and comprehensive review of worldwide resources of seaweed is that by Michanek (1975), prepared for and recently published by FAO as part of the Organization's continuing programme of appraisal of the fishery resources of the world.1
1 The paper updates and expands a preliminary assessment of the world's seaweed resources, also prepared by Michanek, published by FAO as Fisheries Circular No. 128, July 1971
154. At the practical, field-work level, surveying resources of seaweed is often a difficult task, the results generally being subject to considerable degrees of error. Accessibility to the resource can be a particular problem and, for this reason, surveys of red seaweeds - which for the most part grow in deeper waters than brown species - tend to be especially troublesome operations, with inherently less precise results. The potentials of combining traditional ground survey methods with serial remote sensing techniques are being explored with interest.2
2 See Jamison (1971) and Druehl (1972)
155. An area by area résumé of the present state and development potential of the world's seaweed resources is attached to this paper as Appendix IV. Broad quantitative estimates of possible annual output from these resources are set out in Table XIV.
156. These figures should be treated with considerable reserve. On the one hand, they are believed to provide a reasonable indication of where the greatest potentials lie and the order of magnitude of possible harvests. On the other hand, it is extremely unlikely that these potentials could ever, economically and practically, be realized in full. Many of the known major, untapped resources are located in regions which are exceedingly remote from the main markets for seaweed products or are virtually inaccessible by land - for example, the apparently rich reserves of algae in northwest regions of North America, at the southern extremities of South America, those identified in the Kerguelen Islands and the reportedly vast resources of the Sargasso Sea. The practical difficulties and high costs of exploiting (and bringing to market) such resources effectively probably preclude any attempts at their harvesting under present conditions.
157. In this respect, it is pertinent to note that, notwithstanding the serious shortages in supply and rapidly rising costs of certain species in recent years, there is no indication that the major seaweed processors have so far found it economically and technically feasible to engage in programmes to harvest such untapped resources. Emphasis is rather being placed upon the more efficient harvesting and management of already exploited stocks and upon the establishment of cultural practices in areas near to markets or to existing areas of production.
Seaweed Resources of the World
Recent Harvestsa and Potential Outputb
|'000 metric tons|
|Area||Red Algae||Brown Algae|
|Recent Harvests||Potential Output||Recent Harvests||Potential Output|
|21 Northwest Atlantic||35||100||6||500|
|27 Northeast Atlantic||72||150||223||2 000|
|31 West Central Atlantic||…||10||1||1 000|
|34 East Central Atlantic||10||50||1||150|
|37 Mediterranean and Black Sea||50||1 000||1||50|
|41 Southwest Atlantic||23||100||75||2 000|
|47 Southeast Atlantic||7||100||13||100|
|51 West Indian Ocean||4||120||5||150c|
|57 East Indian Ocean||3||100||10||500|
|61 Northwest Pacific||545||650||825||1 500|
|67 Northeast Pacific||-||10||-||1 500|
|71 West Central Pacific||20||100||1||50|
|77 East Central Pacific||7||50||153||3 500|
|81 Southwest Pacific||1||20||1||100|
|87 Southeast Pacific||30||100||1||1 500|
|Total (approx.)||807||2 660||1 315||14 600|
a Based upon estimates for 1971–1973
b Orders of magnitude of possible annual output
c Say 1 000 if Kerguelen included
Source: FAO Fish.Circ. 138
158. Thus, the still wide margin between recent harvests and (theoretically) potential output apparent from a simplistic comparison of the figures in Table XIV can be misleading, unless considered in the light of the above comments. The estimates, nevertheless, provide useful long-term perspectives. Given the necessary harvesting technology and economic incentives, there are clearly considerable opportunities for an increase in the supply of brown seaweeds. In the case of red algae (which, it should be remembered, are required principally by processors of agar, carrageenan and similar phycocolloids), the possibility of continued problems in supply from traditionally exploited resources is evident from a closer examination of the table. By far the greatest proportion of the “untapped” potential is attributable to one area and one species, the vast resources of Phyllophora in the Black Sea; the majority of the present output of red algae in the Northwest Pacific area arises from cultivated, rather than naturally occurring stocks, whilst in the North Atlantic recent harvests have been equivalent to (approximately) one half of the estimated total potential and harvesting costs have spiralled in recent years.
159. At the same time valuable opportunities appear to exist in a number of areas for the harvesting of resources so far neglected or only partially exploited. One example is Hypnea, a phycocolloid raw material of potential importance, resources of which are fairly widespread and generally only lightly exploited. Such opportunities may be of particular importance to developing countries where the ready availability of relatively cheap labour indicates the possibilities of low-cost harvesting and the acquisition of socio-economic benefits locally and foreign exchange nationally.
160. Two other factors affecting the long-term potential of particular seaweed resources also have to be considered. One is the problem of disease and pests, which may may well increase as monoculture grows in importance. For example, beds of Macrocystis can be eliminated by black-rot disease (Chapman 1970); this and other species are also very susceptible to attacks by sea urchins which graze on rocky banks of seaweed. The other relates to the deleterious effects upon the algae of changes in the nature and quality of the water regime; for example, the cultivation of Porphyra in Japan dates from the gradual loss of traditional supplies as a result of the siltation and increasing encroachment of freshwater influences in the bay where the main natural resources occurred. In the case of industrial pollution the effect upon seaweed growth is not yet clearly understood. Its direct consequences may be small, although Kim (1970), citing the inner part of Conception Bay as an example, has reported that considerable damage can be caused to Gracilaria beds by sewage, whilst pollution from chemical plants has been identified as a cause of a disease observed in Porphyra.1 Pollutants such as petroleum products would almost certainly adversely affect the quality of edible seaweeds and the extraction of phycocolloids, whilst high colon bacteria might produce a health hazard in seaweeds used for food and fodder.2
1 Ishio, Yano and Nakagawa (1972)
2 Druehl (1972)
161. In the case of already heavily exploited resources, future potential has also to be considered in the light of the growing need, in some important cases, for management and protection. Some commentators (including Stanford, the discoverer of algin acid, as long ago as 1884) have claimed that the world's supplies of seaweed are virtually inexhaustible. Chapman (1970) suggested that, at least in the case of kelp, even complete harvesting of particular beds may not prove to be as disastrous as might be imagined, arguing that because of the astronomic number of reproductive spores produced by a single plant, so long as some adult sporing plants are spared by the harvest, future supplies probably will not be greatly decreased.
162. However, there are undoubtedly serious risks in uncontrolled exploitation without knowledge of the size of the resource and its capacity for regeneration. Lund and Christensen (1969) cite the mid 1960s decline in the harvest of Furcellaria on traditional grounds in the Kattegat as an example of such dangers. More recently, unrestricted harvesting has denuded beds of seaweed in parts of southern India (Raju and Thomas, 1971). In other areas the need for regulation of harvesting methods, seasons, etc., has already been felt and a variety of conservation measures have been introduced, for example, in Japan, Denmark, California, France and Chile.
163. Optimum harvesting and effective conservation of seaweed resources require knowledge of the species' capacity for regrowth after harvesting, the seasonal variations in the alga's chemical and other properties and the reproductive characteristics of the area being studied In the case of Gelidium robustrum, for example, Barliotti and Silverthorne (1971) have demonstrated that the best period to harvest is August to November as at this time the agar content of the weed is at its highest, reproduction has already occurred and regeneration is at its maximum value; harvesting should be undertaken only once every two years. The optimal harvesting period appears to vary to some extent among different geographic areas and between subtidal and intertidal populations.
164. The cultivation of seaweed, principally for human consumption, is a traditional and still expanding industry in the east, especially in Japan, and increasing interest is being taken in the extension of these practices to other parts of the world for industrial as well as edible purposes. With supplies from certain naturally occurring resources failing to match rising demands and many of the world's major untapped resources of seaweeds being remotely located, difficult of access or costly to harvest, cultivated raw materials almost certainly will become of increasing significance to processors of both edible and industrial products.
165. A succinct overview of the practices and potentials of seaweed cultivation is given by Mathieson (1973). Most seaweeds produce an enormous number of spores and they can be multiplied extensively if culture conditions are perfected. Such conditions depend upon attention to a number of factors.1 Care needs to be taken with the selection of protected habitats, free from pollution, and of suitable hydrographic environments; the algae need to be protected from predatory fish, sea urchins and other pests and parasites; transplanting of the germlings has to be undertaken with extreme care and harvesting carried out in such a way as to maintain peak productivity. In effect, a full knowledge of the plant's biology and reproduction is a fundamental prerequisite to successful seaweed cultivation.
1 See inter alis, Krishnamurthy (1965)
166. The most extensively cultured seaweed is Porphyra, the Japanese “nori”. Some 60 000 to 70 000 Japanese fisherman are now cultivating “nori” and producing the dried edible products which are very profitably marketed through a cooperative selling system. Porphyra culture in Japan dates back to the seventeenth century and the earliest cultural practices relied upon the positioning of tree (and later bamboo) twigs to capture the spores. Subsequently, nets became widely used as collecting agents instead of twigs, but the major advance in cultural technology resulted from the work of a British phycologist, K.M. Drew, who discovered in 1949 the Conchooelis-phase of the Porphyra life-history. This is a minutely filamentous, shell-boring stage which grows throughout the summer and which can be collected on oyster shells. In the autumn, when the temperature and light levels drop, the conchospores are liberated from the shells and attach themselves to a suitable medium (i.e., the collecting net) to grow into leafy thalli. The nets can thus be artificially “seeded” in tanks and then transported to the growing areas where they are attached to bamboo poles; about two months after budding the plants grow to between 15 and 20 cm in length and are then harvested.1 These and improved techniques (including freeze-drying of the thalli buds for storage) have resulted in marked increases in yields, in total output of “nori” and in profitability. Bardach et al. (1972) reported that in some areas up to 750 kg of “nori” can be obtained per hectare during the six to eight months' growing season; the average production value of “nori” has risen from approximately U.S.$ 870 per ton in 1970 and 1971 to over U.S.$ 1 400 per ton in 1973, suggesting the possibility of gross earnings exceeding U.S.$ 1 000 per hectare. According to Suto (1974) “nori” farmers earn a “net income rate” of 60 to 70 percent, making Porphyra cultivation “the most profitable of all fisheries in Japan”.
1 For a fuller description of “nori” cultivation techniques see, inter alia, Ryther et al. (1968), Imada, Saito and Teremoto (1971), Wildman (1974) and Suto (1974)
167. The brown alga Undaria or “wakame”, is also extensively cultured in Japan. Two main systems are used - rope cultivation and stone “planting”. In the former method, strings of synthetic fibre are immersed in seaweed tanks with fertile Undaria weeds in the spring; enormous numbers of spores are released which adhere to the fibre. The fibres are lashed to frames and stored in tanks until late autumn when the young plants, having reached about 1 mm in length, are transferred to rafts in the sea. The “wakame” grows quickly in the cold winter waters and is harvested when it has reached about 1 m in length. The amount of labour in “wakame” cultivation is much less than in “nori” farming; yields of about 10 kg of wet weed per 1 m of cultivating rope can be obtained in northern areas, about a half that yield in warmer districts.2 Where large quantities of Undaria are already growing “wild”, the planting of large stones or concrete blocks on the sea bottom has been found to help the attachment of the spores and the subsequent growth of the young plants.
2 Suto (1974)
168. Increasing amounts of Laminaria, or “kombu”, are also being cultivated in Japan, using similar stone planting and rope-culture techniques.3 Laminaria culture, however, differs from the other two by the use of dynamite to improve the substrata and control harmful weeds.4 Propagation of Laminaria has also been long practised in China. Druehl (1972) notes a unique Chinese method of fertilizing Laminaria through the use of porous, elongated earthenware bottles filled with nutrients and seawater which are placed, with young vegetative Laminaria plants, inside a basket-like structure made of bamboo poles and the whole suspended about 1 m below the sea surface.
3 For an account of Laminaria cultivation in Japan see MacFarlane (1968)
4 Wildman (1974)
169. Some artificial propagation of Gelidium and other agarophytes is practised in Japan but it has not yet been possible to control the release of spores from these species as has been done with many other algae; moreover, the spores take two years to grow and reach harvestable size.
170. Other than in Japan, China and the Republic of Korea, the most successful instance of seaweed culture is perhaps that established in recent years with Eucheuma in The Philippines, largely through the initiatives of one of the world's largest phycocolloid manufacturers. Doty (1973) and, with Alvarez (1975), Parker (1974), and Caces-Borja (1974) give descriptions of methods used, productivities obtained, costs and returns and the socio-economic impact of the development upon the local fishing communities. Following a series of feasibility studies, a family-farm system of cultivation was introduced in the early 1970s wherein the farmer-fisherman and his family provide the labour, seedlings and mangrove stakes while the company loans nylon nets, offers technical assistance and market outlet. By mid-1974 more than 1 000 families were involved in Eucheuma cultivation in the Mindanao-Tawitawi area alone and production of the weed exceeded 5 500 tons in the first eight months of 1974, about eight times that of the whole of the previous year. Parker reported that cultivated Eucheuma productivity is of the order of 13 m tone per hectare (dry weight basis). About half a hectare can be effectively harvested by one family, which, at an average purchase price of about U.S.$ 0.22 per dry kg, can earn an annual gross income of approximately U.S.$ 1 500. The operations are low in overhead costs (roughly 10 percent of gross earnings) and the net income possible represents about five to six times the current minimum annual wage for an agricultural worker in The Philippines. These rapid developments and the socio-economic returns are an example, suggests Caces-Borja, of what might be done elsewhere in the shallow water areas which abound in southeast Asian countries.
171. The practical and economic feasibilities of culturing Eucheuma isiforme species in Florida have been illustrated by Dawes (1974) who considered two proposals, cultivation in natural sites (as in the Central Pacific) and in outdoor tanks. Dawes' investigations indicated that tank culture would yield a much higher crop per unit area than mariculture in natural embayments. In the case of field culture, yields in the Florida Keys might average about 20 tons (4 tons dried, clean) Eucheuma per hectare but problems could arise from herbivores, storm damage and admixtures of other weeds; conversely, operating costs should be low. With controlled harvesting in culture tanks, Dawes postulated a potential yield of the equivalent of 243 tons dried, washed material per hectare; net profits, of course, must be considered in the light of tank construction, water movement costs, temperature control expenses, etc.
172. The potential, through cultural activities, for the development of a major red seaweed industry in Puget Sound and the Strait of Juan de Fuca, in the State of Washington, U.S.A., has been described by Jamison and Beswick (1972) and the possibilities of seaweed culture have also been considered in other parts of the world. Raju and Thomas (1971), for example, have reviewed the results of experimental cultivation of Gracilaria edulis in India; fragments of healthy vigorously growing plants were threaded to coir ropes fixed in the sea and successive harvests at five, eight and ten and a half months produced an annual yield of some 3.5 kg of Gracilaria (fresh weight) per 1 m length of rope. In France, consideration is being given to the growing of the giant kelp Macrocystis pyrifera in order to provide additional raw material urgently needed for French alginate production1; initial doubts about the effect upon the regional ecosystem of introducing this exotic species to the northern hemisphere, in particular, fears of uncontrolled proliferation, now appear to have been resolved, and permission for a trial cultivation scheme is believed to be imminent.
1 Pérès (1973)
173. Reference has already been made in an earlier part of this paper to the interest being taken in the mass culture of microalgae, generally freshwater species such as Chlorella and Scenedesmus, or brackishwater algae such as the blue-green Spirulina. A number of serious technical, toxicological and cost problems remain to be solved before microalgal products are likely to find other than specialized applications in human nutrition.2 Economic production may, however, be possible from simple lagoon culture, perhaps in conjunction with sewage to assist in water purification3 and Soeder (1974) has drawn attention to further potential for the cultivation of microalgae in association with the aquaculture in marine or brackishwaters of shrimps, oysters, and mussels; cultured microalgae are, for example, already used in Japan as a feeding stuff in penaeid shrimp rearing.
2 Gordon (1969)
3 See Ryther et al. (1968)