Tuatara: Volume 18, Issue 1, July 1970
The Biological and Economic Importance of Algae, Part 3. Edible Algae of Fresh and Brackish Waters
The Biological and Economic Importance of Algae, Part 3. Edible Algae of Fresh and Brackish Waters
The Seaweeds, marine members of the green, brown and red algae, are always larger and structurally more complex than the freshwater members of these groups. Maybe this is a reflection of the better suitability of the sea as an environment for evolution because of its greater stability to climatic change. Through geological time one can imagine the sea to have been a much more stable habitat for organisms — better able than the land to act as a buffer against climatic changes and extremes such as the Ice Ages must have presented.
Life as we know it is inconceivable without water. Not only is it the disperse phase of all cytoplasm but it is the universal biological solvent, the reaction medium and sometimes the catalyst of living processes. There is no evidence that the oceans have ever dried up. But this cannot be said of the land — some areas of which are prone to periodic desiccation and all areas susceptible to this fate. Organisms in such an environment must provide against this hazard or be wiped out of existence. It seems that freshwater algae have organised safeguards against hard times by evolving different types of asexual spores as a means of survival to tide over climatic adversity. Even the zygote of many — if not most — freshwater algae forms a zygospore before germination. But time spent in spore stages induced by desiccation or other unfavourable environmental conditions, although ensuring survival, decreases the turn - over rate of an organism's gene pool; and this must lessen the rate of selection of any genes which might produce a more complex thallus while still preserving features of good survival value in this risky environment. In the seaweeds we find neither aplanospores nor hypnospores — not even zygospores, for here the zygote germinates directly after formation. This is possibly a reflection of the stability of the sea, in that no provision need be made against importunate desiccation. Here, there must be a quicker turn-over of the gene pool and therefore exploitation of the genetical material available.
So maybe the uncertainties of the terrestrial habitat have not allowed freshwater algae to try out all the genetical possibilities open page 20 to them whereby they might have achieved a larger thallus and a greater degree of complexity and differentiation. One might well ask the question — how did Marchantia acquire such a thallus in an environment more hostile than that of a freshwater alga?
On the other hand, were the freshwater algae able to explore their genetical possibilities to the same extent as the seaweeds? It must be remembered that the dominant generation in many freshwater algae is haploid, and any haploid organism is limited in genotypic reaction to its environment. It is an interesting point to ponder that as far as the seaweeds are concerned the dominant generation is diploid, or if it is not dominant, the diploid phase is of a duration equal to the haploid phase. Furthermore, it is to be noted that no land plants — algae or bryophytes — with a dominant haploid generation ever evolved into a complex structure with much differentiation. Only when the sporophytic generation became dominant did evolution towards complexity seem to occur to any great extent. The mechanisms of meiosis are such that they ensure the greatest number of new combinations of characters that is possible for an organism to achieve. Every sporophyte has to undergo meiosis to produce haploid structures which will eventually give rise to gametes. An organism whose sporophyte is one-celled has the minimum possible potential for new combinations of genes which the environment can act upon. But in a multicellular sporophyte, meiosis occurs in many thousands — if not millions — of spore mother cells, as a result of which the number of possible recombinations for selection is beyond easy calculation. So a one-celled sporophyte such as the zygospore of Spirogyra is not endowed with a potential for great variation. This lack of a multicellular sporophyte in many freshwater algae must therefore have been a major rate-limiting factor in their evolution.
Many of these algae also exhibit another curiosity which must have considerably retarded their evolutionary progress. Irrespective of where meiosis occurs between zygote formation and germinating zygospore, the results of this division are four haploid nuclei — of which in many species (e.g. Spirogyra) three die. So the remaining nucleus carries only a quarter of the genetical material, and therefore only a quarter of the genetical possibilities which resulted from the previous gametic union; and the remaining three-quarters is dumped, so to speak. Little wonder their evolution has been slow!
Maybe, then, the uncertainties of an aquatic micro-environment in an otherwise terrestrial habitat coupled with the genetical limitations mentioned have militated against the evolution of the freshwater algae into something comparable in size with their marine counterparts.
It is really not surprising that seaweeds have come to be eaten. They are macroscopic, and their size would bring them to man's notice as something worth trying — particularly as keen observation could have revealed that some marine organisms were able to live on a page 21 diet of seaweed. They are littoral in occurrence and thus generally easy to collect, being there for the taking. In the tropical regions they are present all the year round. Many, if not eaten immediately, can be dried and preserved for later use; in this state they are easy to store and transport. And finally, they are palatable, nutritious12 and of medicinal value in a number of ways — especially as a source of iodine to prevent goitre. Properties such as these have assured the seaweeds greater publicity than any other section of the algae when gastronomic appeal is the criterion — not to mention their potentiality as a food crop.
However, several instances are known where fresh and brackish water algae are eaten. An account of the location, circumstances of their growth and use forms the topic of this present article.
In his book ‘Our Oriental Heritage’, Durant crystallised for us in a most telling epigram one of the prime causes for the demise of numerous early civilisations — ‘The women were more fertile than the land’. Population pressure and famine have always been and still are forces which cause people to exploit most living things as possible sources of food as well as narcotic.
When the Conquistadores came upon Tenochtitlan, the old site of what is now the present-day Mexico City, they were apparently amazed at its size and population. Conservative estimates place this population at about 250,000 and therefore greater than that of the European towns at the time. Tenochtitlan was located on an island in Lake Texcoco whose water was brackish and undrinkable. Fresh water came to the city from the mainland via an aqueduct to supplement a modest supply from springs on the island. Concerning this city Farrar8 wrote: ‘How was such a large urban population fed, in a country of primitive farming, where all land transport was on the human back? There were fish in the lake, but there were no large edible domestic animals. The staple foodstuff was maize, but the varieties then cultivated were not high-yielding. From the descriptions by the Conquistadores of the wares offered for sale in the great market of Tenochtitlan, it would seem that the people, though by no means starving, were pressing hard on their resources. Nothing edible was neglected, not even snakes, ‘lice’, or the usually despised dog. It was no doubt the pressure of necessity which led to human sacrifice on a vast scale, followed by cannibalism; and to the invention of ‘chinampas’ or ‘floating gardens’, though the latter either fell out of use, or never existed except as an ingenious system of irrigation.’
Fortunately for us some of Cortez's retinue were more interested in chronicling than conquering and left accounts of all aspects of Aztec life. Mention is made by several of a food called Tecuitlatl, the name given to a scum that grew on the water of the lake. This was collected at a certain time of the year, dried in the sun in the form of cakes and then eaten — having a flavour and taste described page 22 as resembling cheese. In his account, a Franciscan friar referred to it as having a clear blue colour; and Hernandez6, who thought it was a mineral, described the colour as purple or green.
Lake Texcoco was one of five that coalesced after the rains of the summer in to one large lake — the Lake of the Moon, situated in the Valley of Mexico. This valley is a natural landlocked drainage basin ‘entirely surrounded by mountains of volcanic origin’4 from which there is no external outlet. So, over geological time soluble salts have been washed down into this lake and concentrated by evaporation to produce ultimately a body of saline water. Humboldt gave a figure for the density of the water which corresponds to about 2.4-3.0% of dissolved salts, which were mainly sodium chloride and carbonate; sulphate was absent’8. Oddly enough, Humboldt does not mention the presence of nitrates among the soluble salts; but maybe he found none, and this would fit in with the fact that the surrounding mountains were volcanic — since nitrates are not usually present in rocks of volcanic origin. The pH of the lake water would be alkaline because of the presence of sodium carbonate.
While in retirement in Spain, Cortez recounted his experiences and observations to Lopez de Gomara, who assembled this information and produced the book ‘Conquest of Mexico’. Apart from giving details on the collection and preparation of Tecuitlatl, Gomara wrote ‘They make it into cakes like bricks, which they sell, not only in the market (of Tenochtitlan) but carry it to others outside the city, and far off. They eat this as we eat cheese, and it has rather a salty taste, which is delicious with chilmolli (a pungent sauce). They say that so many birds come to the lake for this food, that often in winter some parts are covered with them’.
Although we will never know for certain, it is the considered opinion of several who have examined this phenomenon that the scum was in fact a blue-green alga6. It is hardly likely to have been a mineral because few minerals have a specific gravity less than water, and this material was scooped off the surface; and one cannot imagine a mineral that would appear on the water's surface only at a specific time of the year. Neither can one imagine what kind of mineral would be so eagerly sought after as food by water-fowl. Farrar8 wrote ‘The Spaniards were evidently confused about the proper classification of tecuitlatl; they could not (lacking the microscope) identify it as a plant although it ‘bred’, but the breeding of minerals was still a common belief in the sixteenth century’. However the several references are highly suggestive.
Blue-green algae are very unusual in thir pigmentation because they contain one chlorophyll only — chlorophyll ‘a’, as well as one or both of two phycobilin pigments — the red phycoerythrin and the blue phycocyanin. There are two main chlorophylls, each having a distinctive colour; ‘a’ has a blue-green colour while ‘b’ is more yellow-green. So, if a particular species of this class of algae has page 23 very little phycobilin pigments present, it will look blue or blue-green solely because the only chlorophyll it contains is this colour. If, however, it also contains a fair proportion of phycocyanin, the alga is going to appear a more intense blue. Should some phycoerythrin be present, this could account for the purple and brownish colours because quite a number of blue-greens can appear in these shades.
We cannot be certain of the kind of water the alga grew in; but we can piece sufficient information together to give us a very good idea of its possible nature. The famous chinampa gardens of Mexico are found in the southernmost of the five lakes, Xochimilco and Chalco, and of course relied on the availability of fresh water which came from springs on the southern boundaries of these two lakes. In the dry winter, evaporation of water from the Lake of the Moon reduced the level so much that the five independent lakes assumed their own identities. But there was always a constant fear that when the summer rains came and the five lakes coalesced, the salty waters of the eastern part of Lake Texcoco would flood the chinampa gardens and create havoc among them, thereby upsetting the economy of the whole valley. In the Aztec period, this problem of flooding became so acute4 that ‘in the fifteenth century Nezahualcoyotl, the poet-king of Texcoco, supervised for his relative Montezuma I the construction of an enormous dike of stones and earth enclosed by stockades interlaced with branches. The dike extended ten miles across the Lake of the Moon from Atzacoalco on the north to Ixtapalapa on the south. It sealed off the Aztec capital and the other chinampa towns from the rest of Lake Texcoco, leaving them in a freshwater lagoon.’ So the water of Texcoco must have been very saline to cause the people to go to these lengths to exclude it. The figure quoted by Humboldt of 2.5-3.0% dissolved salts gives us a good indication of the salinity particularly when we realise that the figure for open ocean salt-water ranges from 3.3 to 3.75%. A salinity such as that of Texcoco would be a barrier to the majority of algae found growing in bodies of water on land, especially as the pH of the water would be alkaline (conceivably about 10 or 11 due to the sodium carbonate present). No mention of the presence or absence of nitrate was made by Humboldt. Even if one assumes that none was present, this does not mean that algae would be automatically excluded through a lack of nitrogen, since numerous blue-greens are capable of fixing nitrogen. Because of this singular property, a few algae could live in this rather hostile environment providing they could tolerate the soluble salt level and the high pH. In fact, an amazingly similar phenomenon was discovered not many years ago in Central Africa which, when read about, immediately puts one in mind of this unusual food of the Aztecs and possibly gives us a clue to the identity of the organism which constituted tecuitlatl.
And so we move to Central Africa. First mention of an edible page 24 blue-green alga collected and eaten by man in this part of the world was made by Dangeard5. A sample of a foodstuff called ‘die’ was sent back to France by a pharmacist attached to French Colonial Troops situated at Fort Lamy near Lake Chad. This sample was obtained in a local market at Massakori 100 kilometers east of the lake. On investigation it proved to be a mass of spiral filaments of a blue-green alga now known as Spirulina platensis. Dié was used for making soup and formed a jelly-like mass in water. Although this alga had previously been reported from the Rift Valley Lakes in Kenya and known to be eaten by flamingoes to the exclusion at certain times of all other forms of food, there had never been mention of its use as food for man.
Brandily14 wrote a popular article in 1959 highlighting this rather esoteric food of some of the tribes round Lake Chad. Unaware of Dangeard's identification of this alga, Brandily thought this organism to be Chlorella. However, it was not until the reports of a Belgian Expedition began to be published that we really found out the nature and value of this alga14.
There is still new terrestrial ground to cover and new terrestrial adventure to be sought even in these days of the now fashionable space flight and submarine exploration. Take for instance the trip made by the Belgian Trans-Saharan Expedition in 1964-65. Here was an itinerary that would make any potential explorers turgid with envy. While most of the personnel were military, a botanist joined the Expedition about two-thirds along the route. Immediately before his rendezvous at Faya-Largeau he spent several weeks at the Chad Research Station of the Office de la Recherche Scientifique et Technique Outre-mer at Fort Lamy, Chad. And this is where his story becomes of great interest to us.
In the markets of Fort Lamy, it is possible to buy a foodstuff called ‘Diné’ or ‘Douhé’ in the form of a flat greenish cake. These were subsequently found to consist almost exclusively of a blue-green alga Spirulina platensis. Dihé has a slight odour of dried fish and is slightly salty to the taste. The cakes are broken into small pieces and soaked in water, mixed with pimento, a little salt, and made into a nourishing sort of soup — sometimes with the addition of small pieces of meat. Or the dihé can be made into a thick gravy which is used as a seasoning on balls of millet. This food is eaten mainly by the Kanem tribe, north-east of Lake Chad.
The alga grows in the water of shallow ponds in wadis. When the water level drops, the algal mass concentrates and is collected in big baskets. The water is got rid of by decantation, and the remaining thick slush is spread out on the warm sand to dry in the sun in the form of large cakes about 1 cm thick. (Although collected in areas where bilharzia is prevalent, there seems little danger from this protozoan parasite since the dihé is dried and subsequently cooked).
The botanist of this Belgian Expedition also found a similar algal page 25 bloom in abundance in a couple of lakes near the Oasis of Ounianga Kebir, right in the middle of the Sahara about 750 miles to the northeast of Fort Lamy. Suspecting this to be similar to what he had seen near Lake Chad, he prepared cakes from it after the fashion of the folk at Lake Chad, keeping these for later identification. His suspicions were well-founded for this material turned out to be Spirulina platensis. The inhabitants of the Ounianga Kebir area seem ignorant of the use and nutritive value of this alga. Ducks, however, feed extensively on this algal scum and were seen frequently on Lakes Yoan and Katam but were not seen on Lake Djobo which contains very little of this alga. It was assumed that the ducks ate the alga although no stomach content analyses were done to verify this observation.
Spirulina is rare or not abundant in the soft, iron or salty waters of Chad. But it seems to proliferate and become exceedingly abundant in soda waters rich in sodium sulphate or carbonate, whose pH varies from 9.5 to 11. In this apparently very particular but nevertheless ideal environment, Spirulina platensis is the dominant planktonic alga — often occurring in practically pure culture14.
Lake Yoan has a pH of 11, is highly charged with sodium salts and astonishingly green14. The shore of the lake is bordered by a white collar of crystallised salts to a width of 15-18 feet. The lake water itself has the following content:
|sodium carbonate||—||23.3 gms/litre|
|sodium sulphate||—||22.3 gms/litre|
|sodium chloride||—||16.0 gms/litre|
|sodium bicarbonate||—||3.7 gms/litre|
According to people living in the near vicinity of the lake, the water has this green colour right throughout the year. The Spirulina can be found in small windrows on the shores of the lake. Lake Katam has a pH of 9.5.
Reports of the presence of Spirulina platensis in Africa are not new. Miss Jenkin, member of the Percy Sladen Expedition to East Africa in 1929, collected plankton from the Rift Valley Lakes in Kenya — Lakes Baringo, Naivasha, Nakuru, Elmenteita, and a small crater lake about 2° south of the Equator. An analysis of the last four lakes (which were examined more fully than Lake Baringo) is very interesting11.
She remarked that ‘in increasing concentrations alkalinity appeared to effect a marked reduction in quantity of fauna and flora’; and that the sodium ‘was derived from the surrounding alkaline lavas’. The increase in alkalinity raised the pH of the water from 9.0 to about 11.2. Analysis was made of the stomach contents of some of the flamingoes, when it was found that they had been feeding almost solely on Spirulina. Miss Rich18, who examined Miss Jenkin's plankton samples quoted Miss Jenkin as saying that the water of the last three lakes had the appearance of ‘green soup’.page 26
|Lake||Nature of Water Life||Water||Reserve Alkali||pH|
|Planktonic Entomostraca and Rotifera, with diurnal vertical migration patterns;||hardness due to sodium||0.004N|
|Naivasha||Microcystis and diatoms; Myriophyllum; Fish and rich bird life.|
|Baringo||Crustacea, rotifera, insect larvae; Fish Microcystis No higher plants seen.||0.01N||9.0|
|Crater (near Naivasha)||Mainly rotifera and insect larvae; Spirulina||0.11N|
|Elmenteita||Flamingoes No shore vegetation||soda waters||0.22N|
|Nakuru||Only 1 species of Brachionus||0.27N||11.2|
Miss Rich also stated that Spirulina platensis had been described from specimens found in standing water in Uruguay; and that it had subsequently been recorded by W. and G. S. West24 in a collection taken from Lake Losuguta in Kenya. The Wests apparently commented on the remarkable habitat — ‘water with sulphides’ — but unfortunately gave no analysis of the water.
Later, in 1933, Miss Rich19 published an account of the phytoplankton collected by the Cambridge Expedition to the Lakes of Kenya and Uganda. The recordings of the occurrence of Spirulina are of interest. They were all found in association with Lake Rudolph, and only in the following places:
in crater lakes B and C on Central Island, in Lake Rudolph; in an enclosed alkaline pool on Ferguson sand spit — a part of Ferguson Gulf.
‘The alkalinity of these pieces of water was greater than that of Lake Rudolph itself, though less than that of Lake Elmenteita and Nakuru and Crater Lake’19.
Ross20 later gave the following pH values for some of the lakes mentioned above:
He described the water in the Ferguson Gulf of Lake Rudolph as having the appearance of green soup, due to a very thick phytoplankton of Spirulina and Anabaenopsis. The pH of the water of this Gulf was about 9.8 whereas the value for the Lake water was about 9.5. His remarks about Lakes Nakuru and Elmenteita are that they ‘are almost identical both in their physical and their chemical conditions. They are both very shallow, mostly less than 1 m deep, and very alkaline with pH c.11. When visited their water level was low and there were wide areas of dry soda flats around their margins. The water of both was a thick green soup of Spirulina and Anabaenopsis, on which large flocks of flamingoes were feeding’. These three lakes — Rudolph, Elmenteita and Nakuru — are in the Eastern Rift Valley and have no outlet.
Duvigneard and Symoens14 found this alga in a collection taken from Lake Mugunga, near Nzulu, in the Congo. This lake is south of the laval plain and immediately north of Lake Kivu. The water is alkaline with a pH of 8.5. Spirulina has been reported from Zambia, in a lagoon in the swamps of Lake Bangweulu; and its growth has also been studied in the open lakes of Ethiopia.
A condensation of information about Spirulina in Africa allows one to make the following statements.
Spirulina, a planktonic blue-green alga, is eaten by man as well as water fowl.
It is found in waters with a high pH caused by the presence of sodium carbonate, high salinity and high sodium content — a more specialised environment than the sea.
Places where standing water of alkaline pH seems to be found are those areas collecting drainage from rocks of volcanic origin high in sodium salts which include sodium carbonate or react with the atmosphere to produce this chemical.
How reminiscent this picture is of the conditions reported to occur in the old Aztec capital. Maybe tecuitlatl was Spirulina platensis! Evidence certainly points that way.
We will now shift scenes from the tropics to the cold temperate and sub-arctic areas of the globe — to the Far East and Asiatic Far North, and continue with an account of two more blue-green algae. The first is Nostoc. Despairing of being able to base a good classification on cell details, the Russian algologist Elenkin7 resorted to using morphological features of the Nostoc colony as the basis of a workable system of classification. We will follow suit and apply his system to help us correlate various accounts about this genus.
Elenkin divided edible Nostoc mainly into two groups; one where the colonies are often encountered in great quantities, the other where they are rather rare. The latter group is not significant and will not concern us further. The former group he divides into three main page 28 types which he calls —
Sphaeronostoc — characterised by its colonies being invariably spherical; it occurs submerged but not attached to a substratum.
Stratonostoc — whose colonies are laminate; it is mainly terrestrial in habitat.
Nematonostoc — those occurring in thread-like colonies.
Let us consider the first — Sphaeronostoc pruniforme, which he reckons to be synonymous with Nostoc edule. It does not occur free-floating on the surface but can be found in large masses at the bottom of rivers, lakes and swamps. It is very common in the Northern parts of U.S.S.R. where it is found sometimes in enormous quantities. Elenkin quotes from the accounts of Middendorf who in 1860 wrote of his travels through Siberia. At one stage the food supply of his party must have been getting perilously short. Discussing this predicament later, he lamented not knowing at the time that Nostoc was edible because he recalled that in one stream his party could have collected about 1000 cubic feet of colonies, which would have been most useful in alleviating their problem of food shortage. Meyer, in a review article ‘The Algae of the Lake Baikal’, reported that Sphaeronostoc has been found in unbelievable quantity in various bays around this lake, where it has been known to occur as a solid layer 10-20 metres thick over the bottom of the bay. It has also been found from Leningrad to Kamchatka.
Dr. Hooker, in a paper read before the Linnean Society of London, January 20, 1852, mentioned that N. edule was found abundantly in streams in Tartary. It was highly esteemed as an ingredient in soups. This form of Nostoc was well known and eaten in Mongolia and China in which countries it was used extensively as an article of commerce, generally sold in dried form. Although common in northern China, its use as food has been recorded by the Frenchman, Ivan, in such southern places as Canton and Macao. Apparently it was highly esteemed as a dish to be eaten on feast days and other occasions for celebration.
Sphaeronostoc pruniforme appears to be wholly aquatic, Undoubtedly this type of habitat permits the colonies to develop their spherical shape. Another characteristic seems to be that it is submerged but not attached to a substratum. These properties clearly delineate this species from the next one we will talk about — Stratonostoc, which is described by Elenkin as occurring in laminate colonies, found mainly on the soils of steppes and semi-desert areas.
Stratonostoc commune (the Nostoc commune of other folk) is found free-lying on the soil as convoluted small plates which can grow to many centimetres both in length and width. These very dark-coloured plates are brittle when dry but become leathery when wet. It occurs all over U.S.S.R., Tibet, Mongolia, and from Pamir down to central China: also in numerous west European and non-European page 29 countries. Elenkin considers this alga also synonymous with Nostoc esculentum. He subdivides the species into four forms, and reports this about the form ‘crispum’. This is found in enormous quantities in Mongolia where it is eaten after boiling with meat and other additives. Harvey 9 quotes from the journal of Dr. Sutherland describing travels in the Arctic regions of Canada. ‘It grows,’ says Dr. Sutherland, ‘upon the soft and almost boggy slopes around Assistance Bay; and where these slopes become frozen at the close of the season, the plant lying upon the surface in irregularly plicated masses becomes loosened, and if it is not at once covered with snow, which is not always the case, the wind carries it about in all directions. Sometimes it is blown out to sea, where one can pick it up on the surface of the ice, over a depth of probably one hundred fathoms. It has been found at a distance of two miles from land, where the wind had carried it. At this distance from the land it was infested with Podurae, and I accounted for this fact by presuming that the insects of the previous year had deposited their ova in the plant upon the land, where also the same species could be seen in myriads upon the little purling rivulets, at the side of which Nostoc was very abundant.’ Sutherland later mentions having tried it as an article of food, and found it more nutritious than the ‘Tripe de Roche’ of the arctic hunters and perhaps not inferior to Iceland Moss. Harvey also mentions that Dr. Thomson noticed a very similar plant growing in Tibet up to a height of 17,000 feet, floating in large masses on the surface of pools and lakes in soils impregnated with carbonate of soda, and drifted in heaps by the winds along their banks.
Large amounts of Stratonostoc are found in saltpans where the temperature is high in summer and low in winter. In a wet spring or autumn the alga may grow on the soil to such an extent that the soil is seen only through an algal film. In summer, the layer dries out and becomes brittle and black in colour. It was reported9 that ‘a similar species has been seen in Australia, after a shower of rain, to cover what had seemed previously to be a bare hillside, with such a thick coating of jelly as to render it impossible to walk over it without sliding’.
Elenkin also mentions another species of Stratonostoc, S. verrucosum. This is an aquatic underwater form found attached to stones and growing up to about 10 cms. diameter. It is very soft, often crenulated but sometimes spherical and smooth. Here is a report by Smith21 taken from the Journal of the Siam Society which seems to refer to this species.
‘Under the names of dok hin (rock flower) and kai hin (rock egg) the people of the Chiengmai region in North Siam designate small dark green spheroidal plants which grow in abundance in clear, cool streams attached to the top, sides, and under-surfaces of stones and boulders. The plants when apparently full-grown are 10 to 15 mm. in diameter, and have a bladder-like form, a gelatinous consistency, and page 30 rather thick walls that are complete except at the place of attachment to the stones.’
‘These plants are rather extensively eaten by the local people. On the Mekhan, a mountain stream southwest of Chiengmai, on February 8, 1932, four men from the nearest village were observed scraping or pulling the plants from the rocks with their fingers and holding them in baskets and loose-mesh bags attached to their waists, their combined product at the time of observation being over two liters. The plants are prepared for use by boiling, and are eaten with sugar, salt, or dried prawns.’
The next species of Nostoc to be considered is the one Elenkin calls Nematonostoc flagelliforme. This appears to be what the Chinese refer to as earth-hairs’ or Fah Tsai: and in the Eurasian Continental mass. Northern China seems to be the centre of distribution although it is found in all semi-arid zones of the U.S.S.R. as far west as Astrakan. It is also reported from Texas, Mexico and Montana in America, and Morocco in Africa. It is a highly prized food in China and was traded widely. Like Sphaeronostoc, it finds special use at times of celebration. Skvortzow22 has this to say: ‘In China the forms living on the surface of the ground are used as food …’
‘Nostoc in the Shantung province appears in summer rainy time on the clayey ground and on humid soil, but when the ground dries the alga contracts and begins to be imperceptible. The local population eat the Nostoc not for lack of food, but simply for the same reason as mushrooms, and wild vegetables are used.’
‘Nostoc has no particular flavour. They eat it roasted with different seasonings, which give it taste. Indubitably Nostoc is used in other places in China, seeing that here on account of a damp climate, this alga is very common. In masses it is found in June and in July near Shanghai and in South China.’
According to Prescott17, at one time Nostoc commune was eaten in Ecuador where it was called Yuyucho; and Tiffany23 comments that it was boiled with garden vegetables to add flavour. Wood25 also reported that a form of Nostoc has been eaten in Fiji: and the same alga has been eaten in Okinawa.
We move to Japan to consider the next blue-green alga which is still eaten by man. This is Phylloderma sacrum or suizenji-nori. It was collected mainly in the mountainous regions of the provinces of Higo and Chikugen in the southern-most island of Japan — Kyushu. It was gathered with nets all the year round but mainly in the summer months, and cleaned of other adhering algae. The mass of colonies were cut into small pieces, spread on bricks and dried in the sun — forming thin sheets15. In present times it can still be bought but is regarded as a somewhat expensive delicacy.
The last group of edible freshwater algae we will deal with all belong to the Chlorophyceae, and include the filamentous Spirogyra page 31 and Oedogonium collected and eaten in some sub-tropical areas and the laminate Prasiola from high altitude cold water streams. Biswas1 mentions that a thick coarse species of Spirogyra is widely eaten in the Northern Shan States of Burma. The algal filaments are dried in bundles, packed in boxes and sold in this form in the markets. Spirogyra is also mentioned by Bourrelly14 as being eaten in Vietnam where it is sold fresh. Tiffany23 says that both dried Spirogyra and Oedogonium could be bought in packets in Indian markets.
Prasiola is the remaining alga to discuss. Jao10 reported that Prasiola yunnanica was collected and sold in dried form in the local markets of Yunnan in West China. Unlike the blue-greens and the green algae Spirogyra and Oedogonium already described, Prasiola is macroscopic and quite large — growing up to 8 inches long and 1½ inches wide. Apparently it is very abundant in mountain streams at altitudes of about 8000 feet. Reference is also made by Bourrelly14 to the edibility of this genus, who mentions that it was eaten in the Himalayan region by various of the local population. Prasiola japonica is eaten in Japan; and again comes from reasonably high altitudes — about 6,000 feet or more. (Prescott17 mentioned that some species are confined to swiftly flowing cold water such as is found in the Andes and the Rocky Mountains.) Namikawa15 reported that it was collected mainly at Nikko, in central Japan — hence one of its names, Nikko-nori. It was also known as Daiyagawa-nori; in recent times, Kawa-nori or Fuji-nori. It is made into sheets like asakusa-nori — but is much more expensive.
Now that we have reviewed the edible fresh and brackish water algae, let us see what published chemical analyses reveal about the nutritive value of these forms of food. All figures are expressed on a dry weight basis.
|Spirulina14 platensis||Nostoc16 flagelliforme||Phylloderma15 sacrum||Prasiola26 japonica|
|Crude Protein||gms %||44.4||23.41||26.85||42.03|
|Carbohydrate (excluding cellulose)||gms %||20.7||43.7||64.3||45.9|
Unfortunately, analytical figures for fresh and brackish water algae are sparse and incomplete. The main point to notice is the high crude protein levels of Spirulina and Prasiola. It is also surprising that Nostoc, a known nitrogen-fixer, has such a low crude protein content compared with Spirulina. A figure of 20.6% quoted for Nostoc commune13 is of the same order as the one quoted in the above table for N. flagelliforme. Since protein is much more important than carbohydrate, discussion will be confined to a few aspects concerning the protein contents. If Spirulina fixes nitrogen, then its high protein figure can be accounted for; but one is at a loss to explain why Prasiola should be so high. However, Spirulina is the only alga of this group to be eaten in large quantities and is thus the one which merits much comment. Considerable work has been done on its chemical and nutritional analysis and several points should be brought to focus more sharply.
As far as man is concerned, not only is it necessary to ingest protein, but it must be of the right kind. He has inherited a number of physiological inabilities, not the least being his incapacity to synthesize certain amino acids. These are — threonine, valine, methionine, leucine, isoleucine, lysine, phenylalanine, tryptophane, histidine. It is critical therefore to analyse for these amino acids. No matter how rich a foodstuff is in protein, it is of little use if any one of these is missing, particularly in places where protein intake is low. Spirulina comes out well in terms of these acids with the exception of methionine which is 62% of the value defined in the provisional pattern of necessary amino acids laid down by Food and Agriculture Organisation of the United Nations. For all the other required acids, Spirulina is a good source. Methionine is one of the sulphur-containing amino acids. FAO also set a minimum level on sulphur-containing acids in their provisional pattern; and here Spirulina does not fair well, reaching about 43%. But this is its only limitation in terms of essential metabolites for man. This comes as a surprise in a way when one considers the sodium sulphate figure quoted earlier for Lake Yoan at Ounianga Kebir in the Sahara — 22.3gms/litre. One would have expected Spirulina to be well stocked with these sulphur amino acids. Tryptophane and lysine which are deficient in many foods, are present in sufficient quantity (Clément and others3). They also go on to say: ‘A relatively good correlation was found between the chemical score calculated from standard amino acid analyses and the net protein utilisation determined on rats. The limiting amino acid assessed analytically is methionine; however, another essential amino acid, present but not in an available form, might contribute to reducing the protein value.’
Referring to the use of Spirulina in Chad, Clément and his co-authors wrote3: ‘According to local opinion, ‘dié’ advantageously replaces meat sauce and largely contributes to maintaining the nutritional value of the diet when meat is scarce. At one time, ‘dié’ page 33 was the main source of protein of the tribes’. It is tragic to think that 750 miles from Chad Spirulina grows luxuriously and the local tribes appear to be ignorant of its use as a wonderful source of protein. Who in Africa can afford to neglect a foodstuff which can partially if not completely prevent the pall of kwashiorkor from enshrouding them?
At the beginning of this article we mentioned the fact that freshwater members of the green, brown and red algae are always smaller and much less complex than the marine members of these groups. In terms of a large and well-developed thallus, which algae among the freshwater greens can compare with Ulva, Enteromorpha, Monostroma or even the coenocytic Codium or Caulerpa? An immediate answer to this is Prasiola, having a thallus 8 or so inches long and 1½ inches wide.10. One is then required to seek a reason to explain this apparent exception.
Prasiola is a genus whose species range over the whole gamut of algal habitats, except thermal hot-pools. It is found in salt-water as well as fresh, and it is known to live in the spray-zone above high-tide level as well as in pools which can vary from full salinity, through brackish to freshwater. Prescott reports it as being even subaerial. Because Prasiola shows such tolerance it is easy to believe that the freshwater species could be readily derived from their saline counterparts merely by shifting from one habitat to another. A similar migration can be envisaged for Enteromorpha and Cladophora, both of which show a somewhat similar range of tolerance except that they are not reported from subaerial situations. But Prasiola and Enteromorpha are of more interest because they have an expanse of thallus and are not filamentous like Cladophora; they are thus more complex in structure than the latter.
Altogether Prasiola is a most unusual alga. Boney2 reports that the cells of the thallus are double-walled; the inner-most being cellulose impregnated with pectin, and the outer-most layers forming a continuous ‘coating lamella’. However, the really unusual feature is to be found in its reproduction and the cytological character of its thallus. In at least two species investigated so far (Prasiola stipitata and P. meridionalis), it appears that the lower half of the thallus is always sporophytic, whereas the upper half may be sporophytic or gametophytic. Therefore the basal vegetative half is always diploid. The species mentioned are both marine. Thus this structurally complex, sporophytic vegetative state must have evolved in the sea, and not on the land.
So, the opening statement of this article still stands — that the marine members of the green, brown and red algae are always larger and structurally more complex than the freshwater members of these groups. Although freshwater species of Prasiola appear to be exceptional, they are in all likelihood marine ones transposed — with a diploid thallus already dominant before they moved from the sea. page 34 One cannot really compare Prasiola with other freshwater algae since those with a haploid-dominant generation must have migrated from the sea into their terrestrial aquatic habitats in the haploid condition, or evolved from earlier haploid ancestors. We must therefore regard Prasiola as something quite different from all other algae which share a freshwater environment.
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