Tuatara: Volume 14, Issue 1, April 1966
The Biological and Economic Importance of Algae, Part 2
The Biological and Economic Importance of Algae, Part 2
In the First Article of this series (Johnston 1965), we dealt with the importance of algae as producers of organic matter—the fuel of the biological world. While this is of fundamental importance to Man, it is not of such direct and personal concern as some of the other algal roles with which we intend to deal. As stated earlier, the range of their influence is rather astonishing and because of this it is difficult to know where to begin — where to make the incision into this corpus of fact and phenomenon.
Algae are photosynthetic, and together with their more highly evolved counterparts on dry land, are the only organisms which can lay aside the vast quantities of food reserves on which the animal world is entirely and irrevocably dependent. It is to be expected therefore that algae will initiate all animal food-chains in the seas and freshwaters, in much the same way as land plants initiate terrestrial animal food-chains. So our next section will deal with algae as articles of food.
Algae as a Source of Food
Since food is the most important requirement of the human body and eating an ever enjoyable pastime, it is perhaps natural enough if we broach this huge topic by considering the algae that Man has used directly as food for himself. Many things that Nature does, Science tries to emulate or do better. Having seen how easily planktonic algae yield to laboratory culture, Science has tried to cultivate algae industrially for food — hoping through advanced technology to be able to improve on Nature's productivity. We must therefore see to what extent Science has been successful in improving on Nature in this sphere. Most important of all we must see how the algae fit into the scheme of things by acting as the biological protyle for aquatic animal foodchains, since these ultimately support the fishing industry — still the second largest industry in the world. It must not be forgotten that fish and not land-animal flesh is the major source of food protein for many millions of people.
In the present article we will deal with naturally-occurring algae as food for man, and the macroscopic marine algae called seaweeds will be our main concern.page 31
For the production of food, people living on continents and large island masses have mostly been accustomed to what we regard as “conventional agriculture” with its cereal crops, pastures and grazing animals. Consequently, the use of seaweeds as food would usually be foreign to such societies except for those folk living on a seacoast — and these would use algae only to allay hunger in times of dire necessity such as crop-failure, to follow a fad, or to perpetuate the practice of an older indigenous population. It so happens that most if not all of the textbooks on algae have been written by people from societies living on land masses pedologically and climatically suited to conventional agriculture. Thus in these books the use of seaweeds as food finds little mention, and one might form the erroneous opinion that they are rather insignificant as articles of diet.
But outside the European, Eurasian, African, Australian and American continents and the larger islands capable of supporting agriculture as we know it, we find many millions of people living on islands where conventional agriculture can never be adopted. For this reason, those people inhabiting myriads of islands in the Pacific and Indian Oceans, the South China Sea and the seas around Borneo, New Guinea and Indonesia have traditionally and of necessity relied on the sea as their major source of food. For this reason, many of these island people have come to rely on seaweeds as an important element in their diet. In certain areas such as Japan this reliance have been so great and the demand so constant that methods of seaweed cultivation have been evolved and put into practice (see later). Acquired knowledge and skill have finally produced specialists in this technique, and given rise throughout time to a thriving industry employing considerable labour. Heavy outside demands have led over the years to the development of an export market.
|Calogossa leprieurii||Catenella impudica||Catemlla nipae||Corallopsis salicornia||Eucheuma edule||Eucheuma gelatinae||Eucheuma korridum||Eucheuma muricatum||Eucheuma serra||Gelidium amansii||Gelidium rigidum||Gelidium latifolium||Gracilaria confervoides||Gracilcria crassa||Gracilaria euckeumoides||Gracilaria lichenoides||Gracilaria taenioides||Grateloupia filicina||Halymenia durvilliae||Hypnea cenomyce||Hypnea cervicornis||Hypnea divaricata||Hypnea musciformis||Laurencia botryoides||Laurencia papillosa||Liagora farinosa||Sarcodia montagneana|
|India, Burma, Ceylon||ø||ø||ø||/||/||/||/||/||ø||ø||/||ø||/||/||/||/||/|
|Thailand and Vietnam||/||ø||ø|
|Borneo and Celebes||/||/||/||/||ø||ø||ø||ø||ø||ø||/||/||/||ø||/||/||/||ø||ø||ø||/||ø|
|Australia and Tasmania||/||/||/||/||/||ø||/||/||/||/||/||/||/||/|
|Fiji, Samoa, Tonga||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/|
|India, Burma, Ceylon||/||/||/||/||/||/||/||/||/||/||ø||/||/||ø||ø|
|Thailand and Vietnam||/||ø|
|Borneo and Celebes||ø||ø||/||ø||/||/||/||/||/||/||/||ø||ø||ø||/||ø||ø||/||ø||/||ø|
|Australia and Tasmania||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/|
|Fiji, Samoa, Tonga||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/||/|
In Zaneveld's article, Japan does not feature as a great consumer of seaweeds; but the algae listed are mainly warm-water ones. Okamura lists more than fifty which are eaten by the Japanese (see Table III). Among these we recognise the cool-water ones familiar to us in temperate waters. The Koreans are just as keen on eating seaweeds as the Japanese and use almost all those quoted in Table III as well as ‘young fronds of Costaria turneri and Pelvetia wrightii’ (Okamura). The earliest reference to the culinary use of seaweed is found in Chinese writings. The Chinese have always regarded seaweeds as a delicacy; yet according to Table I China uses hardly any at all, despite the fact that much of her coastline lies below 32° latitude. This apparent anomaly calls for comment; but this is delayed till near the end of the article.
Before considering the value of seaweed as food, we must answer the question —‘What do we derive from food?’ Lamentably, the human body is neither photosynthetic nor nitrogen-fixing; so among the first things we need are sugars to provide us with energy for our body functions, and proteins whose constituents we can dismantle and remodel into the types of protein the human body requires. As well as the carbon, hydrogen, oxygen and nitrogen contained in sugars and proteins, we also need about a dozen inorganic elements — sodium, potassium, magnesium, calcium, phosphorus, sulphur, iron, copper, zinc, manganese, cobalt, chlorine, and iodine. Since we are unable to manufacture our own vitamins, we must also acquire a ready-made set of these too — which include vitamins A (or its precursor), B1-6, B12, C and D. So, when assessing seaweeds as a source of food, we must evaluate them in terms of what they can provide in the way of sugars, vitamins, fats, proteins and the elements mentioned, apart from any piquancy or flavour which might endear them to our palate.
|(a)||The monosaccharides — which have only one sugar unit making up their molecules, e.g. glucose:|
|(b)||the oligosaccharides — whose molecules consist of any number of units from two to nine, e.g. sucrose, with two units;|
|(c)||the polysaccharides—whose molecules consist of any number of units from 10 to 1,000 or more, e.g. starch and cellulose.|
|Western Europe||England & Wales||Scotland||Ireland||Mediterranean||Iceland||Eastern Canada||Eastern U.S.A.||Alaska||Western U.S.A.||Chile|
References: Brook, Chapman, Kirby(1950), Newton (1951, 1963), Tiffany.page 36
The monosaccharides can be directly assimilated by the human body and hence are of immediate food value without further modification; the oligosaccharides must be dismantled to their constituent monosaccharide building-units before they are of use; the polysaccharides, likewise, have to be broken down into their monosaccharide units. Being insoluble, the latter group in any case could not be digested before being broken down. If we examine higher plant carbohydrates we find that most occur as polysaccharides, and in not very many plants do we find mono- or oligosaccharides in plenty. The two major exceptions are sugarcane and sugar-beet. We must therefore focus our attention on polysaccharides in greater detail. In assessing polysaccharides in terms of food value, we must consider whether they can be hydrolysed to their monosaccharide units and thus be useful as a source of food, and therefore energy. The human body can hydrolyse the polysaccharide starch to its structural monomer very easily; but the body cannot attack cellulose. To see why this is so, we must look at the structures of cellulose and starch — remembering that both substances are built entirely of glucose units. Why, then, the difference in digestibility?
|Caulerpa Okamurai||Monostroma sp.|
|Codium fragile||Prasiola japonica|
|Enteromorpha, several spp.||Ulva lactuca|
|Alaria crassifolia||Laminaria angustata|
|Arthrothamnus bifidus||Laminaria cichorioides|
|Arthrothamnus kurilensis||Laminaria coriacea|
|Chorda filum||Laminaria japonica|
|Chordaria firma||Laminaria longipedalis|
|Cladosiphon decipiens||Laminaria ochotensis|
|Eckionia bicyclis||Laminaria religiosa|
|Ecklonia kurome||Mesogloea crassa|
|Ecklonia stolonifera||Myriocladia kuromo|
|Eckloniopsis radicosa||Sargassum enerve|
|Endarachne Binghamiae||Turbinaria fusiformis|
|Eudesme virescens||Undaria Peterseniana|
|Heterochordaria abietina||Undaria pinnatifida|
|Kjellmannielia crassifolia||Undaria undarioides|
|Acanthopeltis japonica||Gracilaria compressa|
|Ahnfeltia plicata||Gracilaria contervoides|
|Bangia fuscopurpurea||Gracilaria textorii|
|Ceramium boydenii||Grateloupia flabellata|
|Ceramium (Campylaephora) hypnaeoides||Meristotheca papulosa|
|Ceramium rubrum||Nemalion pulvinatum|
|Eucheuma amakusaensis||Nemalion vermiculare|
|Gelidium, several sp.||Porphyra tenera and other species Pterocladia capillacea|
Table III: Seaweeds eaten by the Japanese.
cellulose— by cellulolytic enzymes called cellulases which are quite rare and not possessed by many organisms be they plant or animal.
Despite the hundreds of different kinds of herbivorous animals, we at present know of very few possessing cellulase in their kit-bag of enzymes. These biochemical elite include the silverfish, the snail (Helix pomatia), the limpet (Patella patella) and the chiton. There may be others; but these seem to be the only ones whose oddity has up to the present been recorded in the literature. And yet most of the world's agriculture relies (as does almost the whole of New Zealand's export income) on the digestion of cellulose in the gut of cows, beef cattle and sheep, and other hoofed animals. However, all these are ruminant animals and maintain in their rumen intestinal bacteria and protozoa which excrete a cellulase capable page 38 of hydrolysing the cellulose in pasture plants to glucose. When viewed in this light, almost our entire economy is based on one biochemical capacity of rumen micro-organisms. An exceedingly slender thread!
It appears that the stability of cellulose may be due to its being composed of beta-glucose units, which seem to have a much more stable structure electronically than those of the alpha-glucose form. Maybe this is why cellulose was the carbohydrate selected during evolution as the structural material of plant-life after the latter had appeared on dry land. The difference in stability between the alphatype linkage and beta-type linkage is even reflected in their ease of hydrolysis in acid conditions: alpha-linkage is broken by dilute hydrochloric, but the fracture of beta-linkage requires the use of concentrated sulphuric acid and prolonged boiling. The structural stability of cellulose is not a feature of starch — with its polymerised array of alpha-glucose units whose unions are so easily severed.
Funnily enough, if we cross the border into the zoological world, we see a similar demonstration of the choice on biochemical grounds of the right material for the right job. Glycogen, the main metabolic polysaccharide of animals, is a polymer of glucose units joined by alpha-1:4 and 1:6 linkages. Chitin, the structural material of the insects and crustacea, is a polymer of a nitrogen-containing glucose derivative called N-acetylglucosamine. This polymer consists of N-acetylglucosamine units joined together in beta-1:4 linkage — just as we see in cellulose. This similarity is perhaps more easily appreciated after comparing the formulae of these two structural substances.
In both plant and animal worlds, the metabolic polysaccharides which must be broken down very quickly for immediate release of energy are built on the alpha-linkage pattern — i.e. starch and glycogen. But the structural polysaccharides which must ‘stand four-square against all the winds that blow,’ even to the extent page 39 of resisting the subtle biochemical weapons of parasite attack, are built on the beta-linkage system — i.e. cellulose and chitin. What is the explanation of this coincidence — trial and error, teleological or theopneustic?
In our digestive interiors we produce the following polysaccharide-splitting enzymes: salivary amylase (ptyalin) which acts to a limited extent on starch and glycogen and breaks them down to dextrin and maltose by hydrolysing alpha-1:4 linkages; pancreatic amylase (diastase or amylopsin) which attacks the alpha-1:4 links of starch and glycogen: and finally the intestinal enzymes for splitting carbohydrates. The latter include maltase for hydrolysing maltose (alpha-1:4 linkage); a specific sucrase or invertase for splitting sucrose; a specific enzyme for hydrolysing lactose: and an oligo-1:6 glucosidase for hydrolysing the alpha-1:6 linkages of the dextrins formed as a result of salivary amylase working on starch and glycogen (Cantarow and Schepartz). Not being ruminants, we cannot break down cellulose; but we can handle starch quite readily and reduce it to its constituent glucose molecules: i.e., we cannot hydrolyse the 1:4 links between beta-glucose units, but we can rupture the 1:4 and 1:6 links between alpha-glucose units. Armed with this information, let us now look at seaweeds as a source of food in terms of hydrolysable polysaccharides, since this class of substance is the main supplier of energy for our metabolic reticulation system.
When assessing the major carbohydrates of seaweeds as energy sources, we should use the same classification for these carbohydrates as we used above.
There appear to be no free monosaccharides in seaweeds, but we do find some polyhydric alcohols related to monosaccharides e.g. dulcitol, sorbitol, mannitol and one or two derivatives. Also found are mannoglyceric acid and floridoside, the former being a compound between mannose and glyceric acid, and the latter a compound between galactose and glycerol (Meeuse). These two chemicals have alpha-glycoside links and are not difficult for humans to hydrolyse.
Sucrose has been found in Chlorophyta and Rhodophyta but not in Phaeophyta. This sugar we can handle very easily. Trehalose, also a disaccharide, is found in a few algae but has not yet been reported from the usual edible seaweeds.
As in land plants, we find that glucose is a major building unit; but we also find polymers of galactose and a few of xylose and page 40 mannose. These polysaccharides can be classified according to the type of linkage between units — keeping in mind the fact that humans can handle the alpha-1:4 and alpha-1:6 but not the beta-1:4 type. This classification will immediately give a clue to what humans can handle metabolically and what defeats their digestion.
alpha-1:4 and alpha-1:6 linkage between glucose units: here, as in higher plants, we find storage products, e.g. starch and floridean starch.
beta-1:3 linkage between glucose units — again the compound is a storage product, e.g. laminarin.
beta-1:4 linkage between
beta-1:3 alternating with beta-1:4 linkage between galactose and 3:6-anhydrogalactose and sulphated derivatives, e.g. agar, carrageenin and iridophycin.
beta-1:3 occurring with beta-1:4 linkage between xylose units, e.g. dulsin.
beta 1:2 alternating with beta-1:3 linkage between fucose units, e.g. fucoidin.
The first point to emerge from this classification is the exotic nature of some of the linkage types which the seaweeds seem to specialise in. These are quite unlike any types found in land plants and therefore quite foreign to the human digestive system's enzyme complement. Let's take each of these linkages and see what the chances are of digesting such polysaccharides.
The first group contains alpha-1:4 and alpha-1:6 linkages. This is well known to our gastronomy because starch and glycogen molecules are based on this pattern. True starches identical with those of higher plants are found in the green seaweeds. This group includes floridean starch, the usual product of photosynthesis in a number of red seaweeds such as Rhodymenia pertusa. It appears to be very closely related to the higher-plant amylopectins. Apparently there are a few 1:3 linkages as well. Myxophycean starch also belongs within this group; but very few blue-greens are used as food and they therefore hardly warrant further consideration.
In the second group we find those polysaccharides with a beta-1:3 linkage. It is now thought that these are probably the most abundant polysaccharides on earth — even usurping the exalted position of cellulose. ‘the greatest’ of the organic carbon compounds. They are also found in highe ‘plants — as callose in grapevine phloem, as a deposit in the cell walls of other plant tissues, and as yeast glucan from yeast cell walls. In algae they are found in the cell walls of some greens such as Caulerpa—but more particularly page 41 in laminarin in brown algae, as paramylon in Euglena, as chrysolaminarin in certain diatoms and possibly all Chrysophyta (Meeuse). The compound of interest to us is laminarin — not that it is widespread in the browns, since it has so far been found in quantity only in Laminaria and Fucus, though it has also been isolated from Eisenia bicyclis (Nisizawa 1938).
The enzyme laminarase which degrades laminarin is rather infrequently encountered. It has been identified in wheat, barley, oats, potato, malt, and in hyacinth bulbs — to match, no doubt, the distribution in these plants of a glucan of this nature. It has also been found in snail juice (Helix potmatia or H. aspersa) (Barry 1941) and in the sea-hare, Tethys punctata (Nisizawa 1939); and laminarin can also be degraded by enzymes in the fore-and midgut of the herbivorous marine snail, Tegula funebralis (Galli and Giese). The question arises — can laminarin be broken down easily in the human body or is it like cellulose in being difficult to degrade because of these beta-linkages? Remembering that the polysaccharide-attacking enzymes produced by humans can operate only on alpha-1:4 and alpha-1:6 linkages, we are forced to admit that a feast of laminarin seems synonymous with a famine of monosaccharide — particularly since it is impregnable to diastase (i.e. amylase) and ptyalin (Barry 1938).
The next group for review contains carbohydrates with beta-1:4 linkage. Here we are amongst old friends — cellulose, xylan and mannan: the newcomer is alginic acid which is a mixture of a polymer of mannuronic acid units and a polymer of guluronic acid units. Cellulose is not common in seaweeds. It has been found in Chondrus crispus (2.2% D.W.), Rhodymenia palmata (2.1% D.W.), Laminaria saccharina (5.7% D.W.), and Laminaria digitata (3.7% D.W.), Mannan occurs in Porphyra umbilicalis — the only record so far in the reds. It has also been found in some of the greens e.g. Codium fragile. This compound consists of beta-1:4 linked mannose units. Xylan (of beta-1:4 xylose units) as we know it in higher plants occurs in red seaweeds too. We are already aware of our inability to do anything with cellulose; and it appears that xylans and mannans along with galactans are also immune to our digestive attack (Tiffany).
As far as alginic acid is concerned, it seems we are unable to handle this any better than we can cellulose because although alginic acid has a -COOH group where cellulose has a -CH2OH, it is the nature of the connecting bond between the monomer units which seems to determine ultimate digestibility. This link is the same for cellulose and alginic acid.
We come now to groups which are hybrid as regards type of linkage; in which beta-1:3 alternates with beta-1:4 (as in agar and its allies) or where there is a different ratio of beta-1:3 to beta-1:4 (as in the particular type of xylan called ‘dulsin ’ found page 42 in dulse, Rhodymenia palmata). Since human enzymes will not attack either of these linkages, we are unable to claim any of the photosynthetic prizes locked away in these polysaccharides. And the same would apply to fucoidin — found in some of the laminarians, Fucus, Chordaria and others. Bacteria from a sheep's rumen have been found capable of hydrolysing dulsin — but one would expect this since some of these bacterial types can split the beta-1:4 link in cellulose.
Thus it seems that seaweeds cannot be relied upon to provide a large proportion of usable carbohydrates. Tiffany has this to say — ‘About 65% of the dry weight of most edible algae is composed of complex carbohydrates with rather low digestibility. In fact Oshima places the digestibility of edible seaweeds of Japan at 67.7% which is lower than that of any carbohydrate of common foodstuffs.’ In 1906 Saiki wrote —‘Experiments with a variety of alga preparations (Irish moss, kombu, wakame, asakusanori, kanten (agar-agar)—H.W.J.) containing a large proportion of polysaccharide carbohydrates indicated that the latter were not readily transformed to sugar by carbohydrate-digesting enzymes of animal origin and scarcely more readily by vegetable enzymes or bacteria. Corresponding with this, the digestibility and availability of such products in the alimentary tract were found to be very imperfect in both man and animals.’ Anybody who has grown fungi and bacteria will know that not many organisms of these two classes will attack agar, although most would excrete carbohydrate-splitting enzymes of some kind into the growing medium. It looks then as if we can dismiss seaweeds as a high-class source of carbohydrates.
Kirby (1950) made a pertinent observation about the digestibility of seaweeds — ‘It is interesting to note that in Japan the weeds are often left until they have been attacked by fungi. These may help to break down the weeds so that they are more easily digested when eaten.’ Fungi are well-known for their ability to break down most things, and few of the algal polysaccharides are likely to withstand the onset of fungal attack. Some are even equipped with cellulases to break this intractible beta-1:4 linkage. One encounters more bacteria capable of breaking down agar than fungi; and because of this fact, maybe bacteria are just as important as fungi in this softening-up process. In many cases this predigestion would be necessary because some seaweeds appear to be rather indigestible. Ulva, for instance, has been described by one writer as something which would tax the digestive system of the mighty. There is a certain amount of conflicting evidence about the digestibility of seaweeds. If, in the experiments, the seaweeds were eaten fresh, the digestibility could quite easily be low; but if the seaweeds had been kept for sometime and thus were partially predigested by fungi and bacteria, the results would understandably page 43 be different. This may explain the discrepancy. Several writers have implied that people used to eating seaweed may have brought about the selection of intestinal micro-organisms capable of processing this type of food. Because of this, they may be able to digest seaweed to a greater extent than their less fortunate friends who have not eaten this type of food frequently enough to bring about about an ecological change in the types of the intestinal bacteria.
|protein||29.19% D.W.||10.7% D.W.|
|Codium sp.||2.34% D.W.|
|Enteromorpha compressa||32.3% protein D.W.|
|Gelidium latifolium||15.3page 44|
If we compare the protein content of algae with that of the garden pea (Pisum sativum), we find that certain seaweeds contain more protein than do green peas — whose content is about 27% D.W. (Spector). While the seaweeds are not rich in protein when compared with animal sources, what is present in some would make a useful supplement to the diet. (Additional protein figures are quoted below).
|Porphyra laciniata||—0.22% D.W.||(Kirby 1950)|
Green peas are quoted as having 1.58% D.W. (Spector). Other edible seaweeds which have fat figures similar to these can be dismissed as unimportant sources of this high-energy form of food.
The fatty acids are of the same type as those found in higher plants. Of the saturated-acid series, palmitic (C16) is found in highest concentration — followed by myristic (C14) and stearic (C18) in that order. Among the unsaturated acids, oleic (C18) is present to the greatest extent followed by palmitoleic (C16) and then gadoleic (C20) (Fogg). Humans are used to handling these molecules and what little fat is present could be easily assimilated.
|(Kirby 1951)||(Kirby 1951)||(Lombard)|
|(iron — in p.p.m.)||435||–||254|
|Laminaria digitata stems||8.0||8.49||3.95||1.12% D.W.|
|Laminaria stenophylla stems||6.1||9.44||3.69||0.7|
|Laminaria digitata fronds||7.4||4.13||3.01||1.2|
|Laminaria stenophylla fronds||6.6||3.62||3.78||0.94|
|Laminaria saccharina||8.8||4.45||0.22% D.W.|
These figures reveal the high potassium content of most of these seaweeds as well as high amounts of sulphur, sodium and chloride. In those cases given, calcium is quite high; but the phosphorus figure seems low when compared with that for garden peas (0.44% D.W.).
There is not a great deal of information available on the minor-element content of seaweeds. Black and Mitchell report some analyses for several brown algae gathered off the Scottish coast in early summer 1949. Except for ash, the other figures are expressed as parts per million (p.p.m.) on a dry-weight basis.
|Laminaria digitata frond||31.84||138||9||3||64||–||0.29|
|Laminaria digitata stipe||–||293||10||5||62||–||0.92|
|Laminaria cloustoni frond||32.16||159||10||14||76||–||0.25|
They also give a figure called the ‘concentration factor’: this is the ratio of minor-element content in the fresh seaweed to the content of the same minor-element in the sea-water.page 46
|Laminaria digitata frond||-||1||negative||400||2||133|
|Laminaria digitata stip||-||1||negative||600||3||200|
(No Fe figure was given by them for the sea-water analyses).
Seaweeds vary in their contents of these elements. For instance, it seems that minor-elements, which may have some role in reproduction, are lower in quantity in sterile fronds than in sporulating ones. Then there is seasonal variation, as well as variation due to location, proximity to land drainage, type of shoreline rock. There is also the variation within the plant itself, for we see that the minor-element content is higher in Laminaria digitata stipe than in the frond.
|Laminaria sp.||4 p.p.m. Cu (D.W.)|
|Ascophyllum nodosum||1.1 to 1.4|
|Fucus serratus||5.8 to 17.4|
|Fucus vesiculosus||3.4 to 8.4|
The presence of iodine has been known for a long time — seaweed was the first commercial source of this element. Arsenic has also been known to be present. Many other elements are found — such as nickel, lead, tin, vanadium, titanium, chromium, silver, strontium. The presence of the latter calls for some comment. The strontium figures given below are also taken from Black and Mitchell and represent analyses done on seaweeds collected in winter time.
|Laminaria digitata frond||4,000 p.p.m. Sr D.W.|
|Laminaria digitata stipe||4,000 p.p.m.|
|Pelvetia canaliculata||>2,400 p.p.m.|
|Ascophyllum nodosum||2,600 p.p.m.|
|Fucus serratus||>2,800 p.p.m.|
|brown;||Fucus serratus||833 p.p.m. Sr. D.W.|
|Laminaria digitata||1045page 47|
This differential concentration of strontium between groups may occur because brown algae contain alginic acid which can act like a cation exchange resin whereas the greens and reds do not contain this chemical.
The absorption of strontium by certain algae is highlighted in the following analysis of Macrocystis pyrifera — expressed in p.p.m. on a D.W. basis (Wilson and Fieldes).
|Arsenic||60 p.p.m.||Iron||500 p.p.m.|
|Aluminium||100 p.p.m.||Manganese||5 p.p.m.|
|Barium||7 p.p.m.||Molybdenum||1 p.p.m.|
|Boron||15 p.p.m.||Strontium||1,000 p.p.m.|
|Cobalt||0.5 p.p.m.||Zinc||30 p.p.m.|
In relation to metabolically required minor-elements it is interesting to see that iron is again high, with zinc next in order, followed by copper, manganese, molybdenum and cobalt.
We will now examine seaweeds as a source of vitamins — the last group of essential requirements for human nutrition to be considered. Beta-carotene is present in all seaweeds, and since it is the precursor of vitamin A, there should be no shortage of this vitamin in people who include seaweed in their diet. The beta-carotene of several algae investigated is not much affected after harvest: but in one, Rhodymenia palmata, there is a very quick enzymatic breakdown unless the enzymes are killed (Haug and Larsen).
|Vitamin A||— 3,000 international units/|
|Vitamin B||— thiamin — 45 international units/page 48|
|— riboflavin — 3,500 microgram/|
|— pantothenic acid — 300 Univ. of California units/|
Apparently green seaweeds contain more than red, and both are higher than brown. It has been shown that some algae can accumulate cobalt to the remarkable extent of producing a concentration factor of 10,000 (Ericson). The origin of the B12 is bacterial — due either to the presence on the algae of epiphytic bacteria which synthesize this vitamin or to the occurrence of these bacteria in the surrounding sea-water. In either case the vitamin is taken up by the seaweed and accumulation occurs. ‘Bacteria from algae which were poor in vitamin B12, generally produce small amounts of B12, while bacteria from vitamin B12-rich algae formed larger quantities of the vitamin’ (Lundin and Ericson). These authors also suggested that red and green seaweeds may have higher B12 contents than brown because the former ‘often have greater surface areas per gram dry weight than the brown algae.’
Vitamin C is well represented. Ascorbic acid content of Fucus vesiculosus may reach 77mgs./100gms. wet weight — which is considerably higher than lemon juice at 31-57mgs./100gms. Vitamin C content also varies with season and depth (Mautner). Several browns compare favourably with many fruits and vegetables as sources of B1 and C (Mautner). Lundin and Ericson stated ‘it can be concluded that many marine algae are good sources of vitamins;’ and this would seem to be the case.
From a dietetic point of view, we lack a great deal of analytical information on the constituents of seaweeds. The little page 49 that is available and quoted here does not permit us to make any well-founded generalizations. But what there is points to the fact that the seaweeds, like many of our home-grown vegetables, seem to emerge mainly as suppliers of minerals and vitamins with a possible contribution of proteins in some cases. Thus, many islands edaphically unsuited for the culture of land vegetables may be encircled instead by a ring of seaweeds — the marine equivalent of terrestrial vegetables. The fringing sea, therefore, can be regarded as a marine vegetable garden — one which requires no cultivation and harbours neither weeds nor pests apart from a few fungi. It is really a colossal hydroponics system which is maintained in uniform condition without the supervision of Man. What a fabulous garden! On land the soil serves as a medium for anchoring the plant as well as a source of nutrients; but water has always to be supplied. Similarly, a rocky or coral shore-line provides a medium for anchoring the plant, with the added advantages that the plant is always bathed in a never-ending supply of its nutrients and a shortage of water is inconceivable. In many ways, the sea makes a better vegetable garden than the land-based one on which we usually spend so much time and effort, and is ideal for those situated along a coast-line.
The absence of insect pests to ravage this marine vegetable garden is rather interesting to ponder. Many land plants are poisonous, and their poisonous nature is thought by some to have been evolved through selection as a survival mechanism against predation by insects and other forms of animal life. But one never sees reference to poisonous seaweeds. Some algae are toxic — but these are planktonic and microscopic. Maybe it is too soon to state categorically ‘There are no poisonous seaweeds!,’ because future research may reveal examples. There are certain seaweeds, for example Desmarestia, which would not be toxic in the normally-accepted meaning of the word but might have to be considered hazardous because of the relatively high sulphuric acid content. At the moment no truly poisonous seaweeds appear to have been reported. Alkaloids are the toxic chemicals present in many terrestrial plants: for example nicotine, colchicine, coniine (from hemlock), ricinine (from castor oil seeds), atropine and hyoscyamine (from the Solanaceae), strychnine and brucine, curine and curarine (from Strychnos); and all the opium poppy alkaloids such as narcotine, morphine and codeine. It seems that alkaloidal compounds have not been found in seaweeds so far. Another often-found plant poison, oxalic acid, has not yet been reported although two of its non-poisonous cohorts — citric and malic — are known to occur.
This apparent lack of poisonous seaweeds is of some consequence since any seaweed — apart from those with a violently acid taste — could therefore be used as food by starving castaways. Looking page 50 through one or two books on survival, one finds no mention of the use or value of seaweeds under such circumstances; yet they would provide vitamins and trace elements not otherwise readily obtainable, as well as small amounts of proteins. Knowing how people of the Pacific and other areas have used seaweeds as food for centuries, one finds it difficult to understand why the recommendation of this practice should have been omitted from manuals on survival when precedent is centuries old and hoary with age.
In what form are the seaweeds eaten? How are they prepared for the table? In Western European countries such as Scotland and Wales, Porphyra laciniata (popularly called ‘laver bread’) has been collected and eaten for centuries. It was harvested and washed free of extraneous materials and slime, shredded very finely and kneaded like dough into balls or rolls. These were eaten raw or fried with oatmeal and butter (Newton 1957). Or it was pickled and stored in stone jars. ‘It was then served cold with oil, vinegar, pepper and a dash of sugar —’ (Newton). One of the earlier delicacies was moor mutton with laver sauce. The sauce was made by boiling the cleaned weed ‘to a stiff green mush; two cupfuls of this were added to a knob of butter and the juice of half a lemon or Seville orange (not a sweet orange)’. This mixture was beaten and served hot (Hartley).
|Caulerpa peltata var. racemosa — Phillipines|
|Chaetomorpha crassa — Phillipines|
|Enteromorpha intestinalis — Phillipines|
|Chnoospora pacifica — Vietnam|
|Hydroclathrus clathratus — Phillipines|
|Corallopsis salicornia — Bali|
|Gracilaria confervoides — Phillipines|
Some are eaten as dessert: Caulerpa racemosa var. clavifera is quite often eaten as a dessert after a rice meal. Padina australis is made into a gelatine-like sweetmeat in Indonesia; and in the Phillipines, Agardhiella is made into a sweetmeat by boiling with sugar and spices. Ulva lactuca is made into a soup or is used in a garnish for other dishes. Others are prepared in various ways, such as — page 51 dried, boiled and eaten with bacon — Chaetomorpha javanica with coconut milk or vinegar — Sargassum granuliferum—Moluccas as a vegetable — Sargassum siliquosum — Phillipines with coconut milk — Turbinaria ornata — Moluccas as a vegetable — Gracilaria eucheumoides — Phillipines.
And if some of these accounts have not activated your salivary glands, you might like to tantalise them with either of these two recipes. In Burma Catenilla nipae is eaten raw (or boiled) mixed with oil of Sesamum indicum, salt, powdered fruit of Capsicum annuum, fried rhizome of ginger (Zingiber officinale), onion and garlic. On the island of Bali, Hypnea cervicornis is collected, dried and bleached on the beach for 3 or 4 days. It is then boiled, filtered and cooled; the resulting jelly is eaten with palm sugar and grated coconut.
Because of their agar content, a number are used for making jellies. Notable amongst these are Corallopsis salicornia; Eucheuma edule, E. gelatinae, E. horridum, E. muricatum; Gelidium amansii, G. rigidum, G. latifolium; Gigartina spp; Gracilaria confervoides, G. lichenoides, G. taeniodes; Hypnea divaricata, H. museiformis.
Japan ranks very high as a user of seaweeds; and for this reason we will now consider in some detail how the Japanese prepare and use some of their seaweeds. Most are eaten raw after having been thoroughly washed. These include Porphyra, Nemalion vermiculare, Undaria pinnatifida, Cladosiphon decipiens, Mesogloea crassa, Grateloupia flabella — and many more. Others are blanched by boiling just enough to change their colour: this treatment is accorded to Gracelaria confervoides, G. compressa, young shoots of Codium, and Meristotheca papulosa. All of these may be eaten as side dishes to the regular meal or may be taken with saké. Others such as Laminaria, Undaria, Cladosiphon, Porphyra, Gloiopeltis, are used in soups. Many are eaten with boiled rice — for instance Laminaria, Eisenia, Ecklonia spp., Undaria spp., Porphyra (mainly tenera), Enteromorpha; but they require some form of pre-treatment. Laminaria, Undaria, Porphyra and Enteromorpha are sun-dried before use, while Eisenia and Ecklonia are boiled first to remove an astringency before being sun-dried.
Okamura states that of all the seaweeds eaten in Japan the most important are Porphyra, Laminaria and Gelidium. Some Porphyra is eaten fresh but most is sun-dried and preserved in thin sheets. The following passages referring to Porphyra and Laminaria are taken from his article.
‘These dried Porphyra sheets are extensively used in Japanese cooking, and are the special delight of children. The sheets, almost black, are gently heated over the fire until the colour changes to green, when they also become quite crisp. Used with soy the taste is much improved. Porphyra sheets are an essential article in the page 52 preparation of ‘sushi,’ which may best be described as rice sandwiches. To the boiled, hot rice which has been mixed with a little vinegar, certain foods and condiments are added, and the whole is then spread over the Porphyra sheet. It is then rolled up and cut transversely into smaller cylinders. The Porphyra being fairly tough, holds the rice and the ingredients together, acting the part of a sausage skin. Porphyra is also cooked with soy and made into a paste called ‘norino - tsukudani.’ This condiment, which is greatly relished, is an expensive luxury, with the result that cheaper substitutes are made from Monostroma, Enteromorpha and Ulva.'
‘‘Kombu’ is a general term for several species of Laminaria, chiefly L. japonica and L. ochotensis, both widely consumed for food in Japan. ‘Kombu’ is prepared in a dozen or more ways. The most important form in which it is manufactured is shredded, greendyed ‘kombu.’ This is prepared by dyeing the dried Laminaria green in a large kettle containing a boiling solution of malachite green. The dyed kelp is drained and partially dried. After partially drying, the fronds are flattened out and arranged in wooden frames in piles. Each pile is then tightly compressed and held by four transverse cords. When the frame is completely filled with the evenly-arranged pieces, the whole mass is compressed by means of ropes, wedges, and levers. One of the sides of the frame is then removed and the ‘kombu’ is shredded by means of a hand plane The shredded ‘kombu’ is spread out on boards or on mats and dried in the open air. When the surface of the shreds has become dry, it is packed for shipment.’
‘Other forms are manufactured by scraping the epidermis, the remaining green covering, and the thick white cores of the fronds, etc. These scrapings take the form of exceedingly thin and delicate filmy sheets and strips.’
‘Dried ‘kombu’ is used by itself as confectionery and also in the candied state. It is also ground into fine powder to be used in sauces and soups and to be sprinkled on boiled rice like curry powder or to be mixed with other ingredients for making cakes, etc. When boiling water is poured on a quantity of the finely chopped ‘kombu’ a sort of substitute for tea is obtained.’
‘‘Kombu’ is used directly in various ways, not only by itself, but with other ingredients in the preparation of stocks. Bean-curd prepared with this stock is much appreciated by ‘saké’ drinkers. ‘Kombu’ is also cooked in soy and salt and used as a pickle. It is also used as a pickle for putting into ‘miso’ (salted bean-paste, ‘saké,’ or ‘mirin’-lees, and rice-bran mash (‘nukamiso’). ‘Kanten’ made from Chondrus elatus, is also used in this way in Chiba Prefecture.’
Gelidium, Ceramium (Campylaephora) hypnaeoides, C. boydenii and various species of Gracelaria are used in the manufacture of agar page 53 — or what the Japanese call ‘kanten.’ The process will be dealt with in a later article, but the end-product has for centuries been one of the favourite sea-foods of the Japanese and Chinese. ‘Kanten’ is used for making jellies and as a thickener of soups, sauces and gravies — in much the same way as we use flour and cornflour. It has found its way into many forms of food now — even into puddings and desserts.
Because of our ready access to good soil and our ability to use this to cultivate vegetables, we never think of the possibility of using a stretch of rocky coastline as a site for cultivating plants. However, this idea has become a reality and has been practised for centuries especially by the Japanese, and also by the Filopinos in the North of the Phillipines, by the Chinese at Lienyunkang and possibly by the Koreans. (This reference to seaweed culture by the Chinese is the only one known to the writer, and no further detail can be given. Knowledge of this comes solely from a photograph in a book entitled ‘People's Communes,’ edited by the Ministry of Agriculture, People's Republic of China). Porphyra tenera (amanori) is a favourite seafood in Japan and demand has always exceeded supply. For this reason a technique has been developed for the cultivation and harvesting of this red seaweed. To understand the mechanics of the process, it is necessary to be familiar with certain features of the life-cycle — which is as follows.
There are two different generations in this life-cycle — a leafy thalloid plant which is the main macroscopic plant called Porphyra; and a filamentous microscopic phase referred to generally as Conchocelis (for reasons which need not concern us in this article). In tracing this life-cycle let us start with the leafy thallus. In the early spring with the approach of long days, this phase begins to senesce and the plant body forms carpospores; with increasing senescence the tissues begin to disintegrate and finally the carpospores are released into the open water. These germinate in the late-spring to early-summer to form the filamentous Conchocelis phase which needs the long days of summer to mature. With the shortening days of the late-summer, this phase forms monospores which when released germinate to form the leafy Porphyra. This grows throughout the short days of autumn and winter and with the onset of the lengthening days of spring begins to form carpospores and degenerate. And so the cycle carries on. The edible phase is the leafy Porphyra which grows over the autumn and winter.
Now let's see how the practice fits the theory. In late summer fishermen plant out bundles of twigs and bamboo shoots by embedding them very securely in holes which they make in the mud. This is done at low tide. These close rows of brush intercept and form a place of attachment for the monospores released from the Conchocelis page 54 phase at the end of summer. It has been found that the monospores germinate better under high saline conditions, and thus the brush is planted in areas where the salinity is high. The monospores germinate; and while the plants are still young the brush is transferred to areas of low salinity near a river mouth, since experience has taught these folk that the highest quality of amanori is grown in areas of low salinity and higher nitrogen. The fresh water carries fair quantities of nitrogenous fertiliser which produces amanori of suitable succulence. The young plants grow throughout the autumn and early winter and are harvested in mid-winter (December-January) when mature and before degeneration starts. The plants are merely pulled off the brush. Some plants escape harvest and under the environmental stimulus of lengthening days form carpospores from about the end of January to mid-February. These germinate to form the Conchocelis phase — which grows during the summer on stones, gravel and other bottom detritus. During the summer the fishermen remove the old brush and set out new material — in time to intercept during late-summer the released monospores from the Conchocelis phase which has received its reproductive cue from the shortening days. Fig 1 sets out the cycle in a diagrammatic form — which shows more clearly the coincidence of practice and theory. The only point to remember about the coincidence is that the practice was worked out centuries before the theory was known!
The harvesting of amanori is carried out in mid-winter by women and girls. It appears that Japanese women, like their European counterparts, can tolerate more cold than the men: conceivably, this is why the harvesting is a female occupation. One other interesting point is that in mild winters trouble is experienced with a marine fungus attacking the amanori thallus — a marine example this time of the troubles which beset those who engage in intensive and close cultivation of one particular plant. It seems axiomatic that no matter where one indulges in a monoculture — either on land or in the sea — the ogre of parasitism will surely appear.
When harvested, the amanori fronds are washed in tubs of fresh water to remove sand and other adhering matter. The plants are sorted for quality, chopped finely and spread out uniformly on bamboo-mats to dry in the air. These sheets are then baled and sold. In this form they are sold under the name of ‘asakusanori.’ Before being eaten, the asakusanori is crisped over a fire in which process it changes colour from dark brown to green. It is rubbed between the hand and dropped into soups or sauces to which it imparts a pleasant flavour.
A diagram showing how the life-cycle of Porphyra is related to the seasons of the year and the practice of the fishermen.
‘The field work of nori-culture begins in the autumn when nets are hung on racks at ground level just as the spores emerge into the water. Since the harvest of the season depends greatly upon the abundance of the spore attachment, the relationship between the occurrence of the spores and hydrographical as well as meteorological conditions has been studied over a period of many years. Attempts have also recently been made to make quantitative determinations of the spores in sea-water. To give growers the maximum benefit from those various researches, the local experimental stations often announce over the radio the best time for collection.’
‘Artificial seeding of the nori spores is carried out to obtain spores for the season from the carpospores cultured since the preceding winter. The result of this research, however, still remains to be seen. Another method of artificial seeding recently found is connected with a species of laver, Porphyra yezoensis, whose distribution is limited to the northern part of Japan. The monospore formed on the summer plantlet of this laver is made to attach and grow on the collecting net.’
‘The height of the spore collector on the racks is adjusted in accordance with the growing stages of the laver and the seasonal fluctuation of the current and water temperatures so that the growth of the laver may be promoted, avoiding as much as possible any damage by disease. Fertilisers are also used in the growing areas alongside the spore collector.’
Earlier, it was mentioned that Porphyra can be attacked by a fungus in warm winters. The only treatment known so far for combating this disease is to move the racks to higher ground so that the seaweed will remain out of the water for about three hours each day. This is so simple but so ingenious, since the seaweed can stand a limited amount of exposure to air because of its mucilaginous covering, but the fungus (presumably, like most of its class) lacks this covering and its cells are desiccated and therefore killed.
In what other way could this fungus be controlled? Ordinary methods of using fungicides as practiced on land are just not applicable in the sea because of the physical nature of the page 57 environment. One cannot imagine applying a fungicide in wettable powder form, or as an emulsion to an area of seaweed under water. How would the fungicide stick to the alga in a liquid medium? And what would happen when the tide goes out? The constant surge of the water would prevent the chemicals from settling on the diseased plants to any great extent. If the tidal rise and fall was such that the beds of Porphyra were exposed at low tide, presumably a spray could be applied then before the tide came in; but would the chemical adhere to the algal surface when the tide did come in? Would sea-water inactivate our present fungicidal compounds? Under the circumstances, the locals have evolved by far the best form of control and possibly the only one for a problem such as this.
|Enteromorpha||green||Japan||(Marshall & Orr)|
|Gracelaria||red||Japan||(Marshall & Orr)|
A rougher type of cultivation was practised by the Irish for cultivating Fucus vesiculosus, which they collected and used as a fertiliser (Newton 1951).
One further curious point that emerges from this study of seaweeds as food is that people in different parts of the world have picked on one particular genus of seaweed to eat — namely Porphyra. Maoris in New Zealand gather and relish it. The Chinese in New Zealand collect it and send it home to China as do the Chinese in California. The Chinese in southeastern Alaska collected and ate Porphyra laciniata. The Japanese, as we have seen, farm several species of Porphyra. The Koreans eat it, and it is farmed in North Luzon in the Phillipines. It was eaten by people around the western European coasts, in England and Wales, and also in Chile. Apart from any appeal to the palate, all the members of this genus may be like Porphyra laciniata which, as we have seen earlier, has such a high total nitrogen figure. It is an interesting thought that these different peoples, without the aid of analytical chemists to tell them what is good for them to eat, should have selected in each case the local species of a genus that possibly is the most nutritious seaweed available, because of its high nitrogen content and its stock of major and minor elements. Funny how empirically-determined practice is so often substantiated by research! And yet we are all too often inclined to denigrate it because it was evolved by a non-academic society.page 58
Earlier, we saw that China scarcely figures at all in Table I either as a user of seaweeds for food or as a substrate for their occurrence. This situation contrasts strongly with that of her near neighbours, Japan and Korea; and the disparity merits closer investigation.
The earliest extant writings reveal the importance and esteem with which seaweeds were regarded by the ancients of China, who have eaten these plants since time immemorial. It has been said that the Japanese acquired the habit of using seaweed as food from the Chinese — in much the same way as they learnt the techniques of flower-arranging, development of ming trees, and other things cultural as well as horticultural. In those early days ‘the term for algae was also used in a complimentary sense, as in praise of the thinking of a learned man, to signify that his thoughts were ordered as systematically as the parts of an alga’ (Kirby 1950). In a book by Sze Ten in about 600 B.C. it is written that ‘some algae are a delicacy fit for the most honourable guest, even for the king himself.’ The Chinese attitude to seaweeds differs completely from that of the ancients of Rome who regarded these plants as the most loathsome and useless of the biological world. In fact the Romans used the term ‘seaweed’ as a synonym for the nadir on their scale of what was useful and useless or obnoxious. Hence the reference by Vergil in his Eclogues VII, line 42: ‘horridior rusco, proiecta vilior alga’ — prickly as butcher's broom and useless as seaweed which has been cast up. Horace in his Fifth Satire reckons that family and virtue, without wealth, are as worthless as seaweed; and in his Ode to Aelius he speaks of ‘inutilis alga’ — worthless seaweed (Brook).
In view of the esteem bestowed by the Chinese on seaweeds, it is surprising that an industry centred around the latter's cultivation and harvesting was never developed to the extent of achieving mention in the history books. One imagines that the early knowledge of seaweeds’ delectability and their use as effective herbal medicines would surely have led the inhabitants to ensure a good supply to meet this type of luxury demand; and yet no indications of this are found. This enigma becomes more complex when we come to look for present-day references to the marine algal flora of China. There are very few. In Table IV those seaweeds that are eaten and sold in the markets are listed (Kirby 1950). But when we come to look for a source of these seaweeds in China, we find an unbelievable paucity of indigenous marine algae along her coast. This is all the more intriguing when we realise that the country possesses about 5,000 miles of coastline. Of course we are not entitled to believe that the last word has been written on the incidence of seaweeds around the China coast.
|Seaweed||Locality Where Found|
|Enteromorpha spp.||Amcy, Pei-tai-ho. Wei-hai-wei|
|Ulva lactuca||Amoy, Pei-tai-ho, Swatow|
|Sargassum spp.||Hong Kong, Macao, Wei-hai-wei|
|Undaria pinnatifida||Chushan Is. (Chekiang)|
|Gelidium divaricatum||Amoy, Macao|
|Gloiopeltis coliformis||North China|
|Gloiopeltis tenax||North China|
|Gracelaria confervoides||Amoy, Pei-tai-ho. Wei-hai-wei|
|Grateloupia filicina||Swatow, Wei-hai-wei|
References: Cotton, Gepp, Grubb, Kirby (1950), Tseng and Tang.
before considering the oddities of distribution, we must become acquainted with certain physical features of the coastal land-form and sea-water characteristics because these two things seem to explain much that is puzzling.
The seas in the immediate vicinity of the Chinese coastline are dominated by the huge outflow of fresh water from the major rivers — especially the Yangtze Kiang and the Hwang Ho whose anglicised name (Yellow River) has been applied to the sea surrounding its mouth (the Yellow Sea). The southern end of the Yellow Sea also receives silt and fresh water in even greater quantity from the Yangtze, which emerges close to Shanghai. Immediate effects of all this fresh water are that the salinity of the sea is altered, as well as its transparency and the nature of its floor. Thus, much of the coast of Northern China is unfavourable for a good seaweed flora due to decreased salinity and transparency of the water, and also to the lack of a suitable substratum. Cotton remarked that the Gulf of Chihli (the upper part of the Yellow Sea) is for the most part muddy. The coastline of this Gulf round to the Shantung Peninsula and south of this peninsula down to the mouth of the Yangtze is deltaic in origin, having been built up from silt brought down by these rivers. Shantung however is a rocky promontory. Little wonder that not many algae grow page 60 when they lack a firm substratum for attachment: what substratum is there is being covered over by new layers of silt, since the coastline rapidly encroaches on the continental shelf. It has been estimated ‘that the Yangtze-Kiang alone deposits annually sufficient sediment to create in the Pacific each year a new island, 1 mile square and 15 fathoms deep, while the floor of the Gulf of Pei-chi-li (i.e. Chihli — H.W.J.), on the shores of which Pei-tai ho is situated, is silt from the Hwang Ho’ (Grubb). Coming further south and then west from Shanghai — that is from Chekiang to the large island of Hainan, the coastline is again rocky without being interrupted by any more large rivers — except the Siang Ho which meets the sea near Hong Kong.
The second feature to consider is the geological nature of this shoreline. Most of the coast bordering the Yellow Sea is composed of alluvium — except for the Shantung peninsula. Grubb, describing the substrate near the Pei-tai-ho, said that the ‘coast is alluvial, with a few jutting out reefs of rocks. The strata in this district appear to be of quaternary or tertiary origin, and the rocks are a hard coarsely-grained granite. They do not offer any very satisfactory foothold for algae, and the flora, even in rock-pools, is confined almost wholly to species of Corallina, Hypnea, and Gelidium.’ Gepp quoted a letter from a surgeon of the Royal Navy who collected some seaweeds on an island close to Wei-hai-wei: ‘the rocks are metamorphic, consisting of beds of quartzite, gneiss, crystallite, and limestone cut across by dykes of volcanic rock and granite. Mica abounds everywhere. Where the seaweeds were found, the rocks were mainly granite and gneiss.’
The third feature contributing to this paucity of seaweeds is water temperature. At its western extremity the Pacific North Equatorial current turns north along the eastern side of the Phillipines and becomes the Kuro Siwo, the ‘Black Current’ or Japan stream. This forks, and one part comes up on the eastern side of Formosa and Japan as far as the heel of Honshu, then turns east across the North Pacific (Grubb). The other arm of the Kuro Siwo flows on the western side of Formosa and bathes the coast of China. As one would expect, this is a warm current having a mean temperature of 80° F.— which is about 5°-15° warmer than the surrounding water (Grubb). This temperature therefore effectively excludes the cool-water seaweeds of the Fucales and Laminariales.
It will now be appeciated how the interplay of these ecological factors helps to reduce the size of the Chinese seaweed flora. When we refer again to Table IV we find a number of algae sold in the markets which are not found anywhere on the China coast as far as the present records show us. These include Ecklonia cava, Laminaria spp., Chondrus elatus, Eucheuma papulosa and E. spinosum. It is obvious these must have been imported — more than likely from page 61 Japan, since this country would probably be the nearest source of the cool-water weeds. Actually, Japan has for some time enjoyed a large export business in seaweed products to China. Imports by China of all kinds of seaweeds during 1935-37 averaged about 326,000 tons, most of which came from Japan (Kirby 1950). Let's assume the imported material averaged about 15% of moisture and the fresh wet weed about 45%. This means that the import figure quoted above could be equivalent to more than a million tons wet weight of seaweed! The processing of a million tons of seaweed per year amounts to a sizeable industry — especially when it is remembered that there is little mechanization used in the early preparative stages and that all handling must therefore be manual.
Embassy exchanges between China and Japan have been recorded for almost two thousand years (Reischauer), and it is known that the establishment of trade relations has always been one of the aims of the Japanese embassies since the first mission went to China in 57 A.D.. Over the period 838-847 A.D. a diary was kept by a Japanese Buddhist monk who accompanied one of these embassies. In this he mentioned that Kombu was taken to China as one of the articles for which the Japanese hoped to develop a market. It could be that trade in seaweeds between these two countries has been occurring for well over a thousand years. When we couple production for Japan's home market with that needed to provide such a large export quantity (assuming present day exports to be about the same as previously!. we are forced to realise how large the seaweed industry in Japan must be. However, this is getting more into economics; and although it is intended to look at the economic aspect of seaweeds, this must be delayed a while.
So we will close this section now, leaving you with the thought that people should not be like the Romans and regard seaweeds as utterly useless: on the contrary, these plants can supply all the minerals and most if not all the vitamins needed by the human body. Spinach cannot do any more than this! Having the population explosion in mind, one need not romance too wildly to envisage the use of small factory-ships to collect the cold-water seaweeds and process them as food additives.
And here is a special thought for those to whom the use of artificial fertilisers, hormone weedkillers and pest-control chemicals is an anathema. The eating of seaweeds would provide a never-ending supply of ‘pure and wholesome food’ — unsullied by pesticidal members of the Periodic Table, uncontaminated by chlorinated hydrocarbons and unpolluted by organo-phosphorus compounds. Being plants, the seaweeds do not ingest food that has already been elaborated; they start from the ground floor up, so to speak, and build their own complex molecules from simple chemicals obtained from the surrounding sea. They therefore do not come into contact with such compounds as DDT through being a link in a food page 62 chain in the same way as do members of the zoological world. Thus one would not expect to find a build-up of pesticidal chemicals in this type of plant. Since chlorinated hydrocarbons such as DDT are fat-soluble, they will concentrate in fatty or oily tissues. We saw earlier that seaweeds seem to have low fat contents. In view of these two facts, it is inconceivable that seaweeds could be contaminated to the degree found in certain marine fish. For this reason, the seaweeds may constitute the last major section of the botanical world to still retain a pristine chemical purity and because of this they should be regarded as highly suitable fare for those worried about Man's latest weapons against the insect legion.
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Bersamin, S. V. and others, 1961. Some Seaweeds Consumed Fresh in the Phillipines. Proc. Indo-Pacific Fisheries Council 9th Session, Section 2: 115-119.
Black, W. A. P., and Mitchell, R. L., 1952. Trace Elements in the Common Brown Algae and in Sea Water. J. Mar. Biol. Assoc. 30: 575-584.
Bowen, H. J. M., 1956. Strontium and Barium in Sea Water and Marine Organisms. J. Mar. Biol. Assoc. 35: 451-460.
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