In this article we will discuss about the economic importance of algae.
Algae like other plants are intimately connected to human beings from times immemorial. Algae can be both beneficial and harmful to mankind. Algae are primarily producers of food in a very large ways and are used as food, fodder and manures. Many industrial products e.g., agar-agar carrageenin, iodine are obtained from algae.
Algae can sometimes be harmful to man causing damage to ships, buildings and by causing diseases in plants and animals.
The beneficial and harmful aspects of algae to some extent are as follows:
A. Beneficial Aspects of Algae:
(i) Food:
Algae have been in use as human food for centuries in various parts of the world, including Scotland, Ireland, Norway, Sweden, France, Germany, North and South America, China, and Japan. Algae are taken in several ways according to the choice and taste of the people. They may be taken as a salad, cooked with meat or eaten as vegetable, sprinkled with oatmeal or fried with meat.
Some are added for flavour to various dishes, while extract from others is taken as a beverage. Their nutritional value is quite high, as they contain a good amount of proteins, carbohydrates, fats and vitamins, specially A, B, C and E.
Commonly used species, are mostly marine, and they belong to Chlorophyceae [Ulva lactuca (Sea lettuce), Enteromorpha compressa, Caulerpa racimosa], Phaeophyceae (Laminaria saccharina, Alaria esculenta, A. fistulosa, Sargassum sp., Durvillea sp.), Rhodophyceae [Porphyra tenera, P. umbilicalis, P. laciniata, Rhodymenia palmata, (Dulse), Chondrus crispus (Irish moss), Gigartina stellata, Gracilaria sp.] and Cyanophyceae (Nostoc sp.).
In Japan, about 20 different kinds of algae are being harvested and eaten. ‘Aonori’ is a preparation of Monostroma, ‘Kombu’ of Laminaria and ‘Asakusa-Nori’ of Porphyra tenera.
The total area used for the cultivation of Porphyra throughout Japan is estimated to be 155,000 acres. Every year 4000-5000 metric ton of dry weight of the algae is produced and it fetches more money than any other marine products including whales, fish etc.
Similarly, Laminaria is widely cultivated in Japan and China. It is cultivated more like a crop plant which has resulted in the development of a more stable economic crop. With the development of the techniques of mass culturing of algae, specially with Chlorella and Scenedesmus, there are probabilities of solving the problem of food deficiency.
The salient feature of Chlorella is that the cell is rich in protein and vitamin contents (Single cell protein, SCP). It contains all the amino acids known to be essential for the nutrition of human being as well as animals.
It contains vitamins C, pro-vitamin A, thiamine, riboflavin, pyridoxine, niacine, pantothenic acid, folic acid, inositol and p-amino benzoic acid. The minerals present, in order of contents, are phosphorous. potassium, magnesium, sulphur, iron, calcium, manganese, copper, zinc and cobalt. These algae are also being used for the production of low cost protein.
(ii) Fodder:
The sea weeds as fodder have been widely used in Norway, Sweden, Denmark, Scotland, America, China and New-Zealand. In Norway, Rhodymenia palmate has come to be known as ‘Sheep’s weed’ since sheep are very fond of this particular alga. Laminaria saccharine, Ascophyllum sp., Sargassum sp. and Fucus sp., are equally liked by the catties.
In many countries factories have been established to process the seaweed into suitable cattle-feed. Eggs, from hens fed on sea weed meal, have an increased iodine content while increased butter-fat content of milk is reported from cattle whose diet is supplemented with sea-weed meal.
(iii) Pisciculture:
Algae, both floating and attached forms, marine as well as fresh water, provide the primary food for fish and other aquatic animals. The great fishing grounds of the seas are found where these are present in large numbers. In many countries pond culture for fishes has been taken up and they are fed with various forms of algae.
Judged by the works carried out by various investigators in India, on the food and feeding habits of fishes, it appears that the Green algae, the Diatoms and some Blue-greens are most widely eaten up by the fishes. Fish food is mainly the planktons (the floating forms), phytoplankton’s and zooplanktons. Zooplanktons develop by feeding upon the phytoplankton’s.
It is now known that several vitamins found in fish can ultimately be traced to the phytoplankton’s on which they feed. So, directly or indirectly, the algae form the source of food for fishes. At the same time, these algae keep the water habitable for fishes by absorbing the carbon dioxide and enriching water with oxygen by the photosynthetic activity.
(iv) Fertilizers:
The large Brown and Red algae are used as organic fertilizers, especially on land close to the sea. The weed is used either directly or as a seaweed meal. A concentrated extract of seaweed is also sold as a liquid fertilizer. Coralline algae Lithothamnion calcareum and Lithophyllum sp. are used profusely for liming the soil. Similar is the use of Chara which becomes encrusted with calcium carbonate.
However, the greatest utility of the algae, as a friend to the farmers, is seen in some common forms belonging to Cyanophyceae for their capacity to fix atmospheric nitrogen and thus enriching the soil. In the paddy fields they have been seen to produce an effect almost similar to that of manuring with 30 kg. of ammonium sulphate per acre.
Aulosira fertilissima, the common Blue-green algae of the Indian rice fields is found to add 47-6 lb. of nitrogen fixed /acre/crop. At the same time there is a considerable increase in the total organic matter content of the soil. In India, the nitrogen-fixing blue-green algae play a part of tremendous importance in maintaining the fertility of the rice fields.
(v) Reclamation of Alkaline, ‘Usar’ Land:
In India, vast tracts of land cannot be cultivated for crops because of high alkalinity of the soil, commonly known as ‘usar’ soil. The ‘usar’ lands would be cultivable, if their pH could be lowered, and organic contents and the water holding capacity of the soil increased. Exactly all these functions are carried out by the blue-green algae.
During the rainy season the blue-green algae, notably species of Nostoc, Scytonema, Anabaena and Aulosira, grow in plenty. According to R. N. Singh (1950), these algae can be of use in the reclamation of the ‘usar’ lands. The process involves a series of successive growth of the algal crop in a water-logged condition.
After a year of such reclamation, the pH fell from 9-5 to 7-6, organic contents increased from 36-5% to 59-7%, nitrogen contents from 30% to 38-4%; exchangeable calcium from 20% to 33% and water holding capacity of the soil is also increased by 40%. In such a ‘reclaimed’ land, the transplanted paddy crop grew with a yield of 1576-2000 lbs/acre. This method of reclamation is now being practiced widely.
(vi) Binding of Soil Particles:
Algae act as an important binding agent on the surface of the soil. Disturbed or burnt soils are soon covered with a growth of green and blue-green algae thus reducing the danger of erosion. The role of Cyanophycean members as a pioneer in colony formation and thus in soil formation is well known.
(vii) Commercial Products:
Many forms of marine algae, Phaeophyceae and Rhodophyceae, are highly valuable for certain commercial products, chiefly agar-agar, algin or alginic acid and carrageenin.
(viii) Agar-Agar (Agar):
Agar-agar is obtained from various species of red algae for e.g., Gelidium corneum, G. cartilageneum, Gracilaria lichenoides, and species of Chondrus, Gigartina, Furcellaria, Phyllophora, Pterocladia, Ahnfeldtia and Gampylaephora. It is a non-nitrogenous extract obtained almost in a pure mucilaginous form. The chief constituent of agar is a carbohydrate galactan.
The algae are collected, bleached and the mucilaginous matter is extracted with water under pressure. The purified agar is sold in the form of flakes, granules or strips which are brittle when dry but become tough and resistant when moist.
The important use of agar is in microbiology and tissue culture (in the preparation of culture media for growing algae, fungi and bacteria in the laboratories).
Other uses are in the cosmetics, paper and silk industries, in dentistry for making impressions, in canning fish, to prevent the soft fish from being shaken to pieces during transit, in sizing material, in clarifying liquors etc. It is also used as food and in the preparations of ice-cream, jellies, sweets and baking.
(ix) Carrageenin:
This is a metabolic product similar to agar, obtained from Chondrus crispus, Gigartina stellata and Iridaea laminaroides.
The mucilage has several important industrial applications for e.g., in textile industry, in paper making to give body to the paper, in the manufacture of straw and felt hats as a stiffening agent; as an ingredient in cosmetics, shoe-polishes, hand lotions, tooth paste etc., as an emulsifying and suspending agent, in the baking, dairy industries and in clarifying liquors.
(x) Algin and Alginates:
Algin is a calcium magnesium salt of alginic acid present in the intercellular substance of the Phaeophyceae. Because of its special colloidal properties alginic acid and its derivatives find considerable use in industry. Its salts are used in the manufacture of variety of goods ranging from ice-cream, salad cream, custard and jams to cosmetics, films, fabrics, ceramics and textiles.
They are also used as a suspending agent in compounding drugs, lotions and emulsions; in the rubber industry in latex production; as an insulating material and as dental impression powder, as a gel in the freezing of fish and in the medicinal antibiotic capsules.
The production of algin by the Phaeophycean members varies from species to species and genus to genus besides the seasonal variations in the contents, the values being highest in the winter and lowest in the summer.
The harvesting of the weed depends upon the genera used and their habitat. Species of Laminaria, Ascophyllum, Macrocystis, Nereocystis, Ecklonia, Durvillea and Sargassum are the chief sources of commercial algin.
(xi) Medicinal use:
Alaria was once used for strengthening the stomach and restoring the appetite after sickness. Alginates are used for their haemostatic nature; fucoidin and sodium lamanarin sulphate are used as ‘blood anticoagulant’. Digenia simplex, a Rhodophycean alga, provides an antihelmnitic drug. Agar-agar, for its absorptive and lubricating action, is used medicinally in the prevention of constipation.
(xii) Antibiotics:
The antibacterial product chlorellin, obtained from Chlorella is well known. The antibacterial effects are more pronounced against coliforms and other related intestinal bacteria.
Extracts from Rhodomela larix and Ascophyllum nodosum are effective against both gram positive and gram negative bacteria. Several algae, e.g., Halidrys, Pelvetia, Laminaria, Polysiphonia, Nitzschia and Hapalosiphon, have been reported to possess antibiotic or antibacterial properties which, however, need further confirmation.
(xiii) Sewage Disposal:
Sewage disposal is one of our main defences against those diseases which are spread by the agency of human waste. There is only one way of sewage disposal and that is into water, streams, rivers, lakes or the sea. Sea side towns can dispose the sewage directly into the sea but in other cases the sewage should be treated before disposal.
Essentially, there are two phases of sewage treatment—the physical and biological. The most important and common physical processes are straining and tedious. The biological process i.e., sewage disposal is simple and less expensive.
Sewage disposal treatment is essentially a process of biochemical oxidation and its basic requirement is oxygen. The parts or amount of oxygen needed for the purification of 100,000 parts of sewage by weight is called the Biochemical Oxygen Demand (B. O. D.).
In other words, we may say that the ever present bacteria break down the sewage into its components complex organic compounds into such simple inorganic compounds as ammonia, carbon dioxide etc. and water with the needed amount of oxygen.
This oxygen demand may be supplied artificially which is quite expensive or through the agency of the photosynthetic algae which grow in sewage disposal ponds The purification of sewage is designed to render the organic wastes present in the sewage harmless and inoffensive.
Only after extensive research has the relationship that exists between these sewage algae and bacteria become apparent. The most common algal species present in the sewage oxidation ponds are Chlamydomonas, Scenedesmus, Chlorella, Euglena, Eudorina and Pandorina.
Aerobic bacteria breakdown products of sewage, from complex organic substrates into simple inorganic products, fulfill the primary-requirements of these photosynthetic algae and in return the bacteria receive the necessary oxygen for their activity.
Moreover, ammonical wastes have a high oxygen demand and these algae which are the effective photosynthetic oxidizers use ammonia to build up their protein. The relationship existing between algae and bacteria in a stabilization oxidation pond is summarized in the following figure (Fig. 1).
Raw sewage which enters the pond is immediately acted upon by bacteria and the sewage breakdown starts.
As the algae utilize the minerals and carbon dioxide, made available by bacterial activity, the sewage becomes more and more alkaline. The discharged treated sewage show a very small percentage of bacteria due to the higher alkalinity and due to the antibacterial substances or extracellular substances produced by the algae (especially Chlorella).
Now-a-days, sewage is regarded as a raw material carrying some basic requirements for fertility—nitrogen, phosphorous, potassium and water. The yield of algae, with the nutrients tied up in the protoplasts, may also be very high; annual yield from a population of 1,000 may be as much as 4 tons in dry weight.
Tests have shown that the algae recovered can be used as animal food and in certain regions it may be a valuable source of fodder.
Partially purified sewage from such ponds is led into fish pond where it stimulates a larger growth of algae beneficial to fish. Algal cells along with the effluents are also used to enrich the soil, in the cultivable lands as manure. Higher crop yields by such treatment have been observed.
(xiv) Funori:
A product similar to agar obtained from Gloiopeltis furcata and from species of Chondrus, Ahnfeldtia, Iridaea and Grateloupia, is chiefly used as a glue and as a sizing agent.
(xv) Diatomite (Kieselguhr):
Fossil forms of diatoms in some regions are found in large deposits which are called ‘Diatomaceous earth’ or ‘kieselguhr’. Silica, the basic constituent of glass and granite rock, is deposited on the cell walls of the diatoms. Because the silica walls are hard and chemically inert, the sediments accumulate in marine and fresh water basins.
Deposits of fossil marine diatoms over 1,200 feet thick are known. Once kieselguhr was used as an absorbent of nitro-glycerine in the manufacture of dynamite.
Now-a-days, for its hard and chemically inert nature, kieselguhr is mainly used in insulation, as a filtering agent and as an abrasive, in the industrial filtration processes of sugar refining, brewing and wine making, in the recovery of chemicals and for removing waste mycelium in the production of antibiotics.
It is used as an industrial catalyst, as filler in paints and varnishes, in paper industry; and in insulation materials for use at extremes of temperatures. It is also used widely to absorb coloured substances from oils and other liquids; as a cleaning powder in soaps and in metal polishes.
(xvi) Other Products:
From members of Phaeophyceae, two important products mannitol and fucoidin are obtained. Mannitol is used in food and medicinal products, inks and plastics etc. and fucoidin is used as a mucilage and in medicines.
The burnt ‘ash’ of larger Brown algae, specially the Kelps belonging to Laminariales, has been used for the extraction of minerals (sodium sulphate, potassium chloride and potassium sulphate), iodine and bromine. It is also used as a source of soda in the manufacture of soaps, glassware and alum.
B. Harmful Aspects of Algae:
Sometimes the excessive growth of algae in a mass, specially the planktons or floating ones, may cause undesirable effects.
They form the water-bloom which may be harmful to the fish and other animals; or in water-reservoirs may cause pollution and hinder the process of filtration. Some may grow in abundance even in the salt beds and affect the quality of salt, in the crystal formation and in imparting a pink or red colour to it.
(i) Water-Blooms (Algal-Blooms):
Excessive development of phytoplankton is often responsible for the water assuming distinct colours like green, yellow-green, yellowish brown, dark or dirty brown, reddish brown, bluish-green etc. The Red Sea has been named after the Blue-green algae, Oscillatoria erythema, Trichodesmium sp. which gives a red coloration to the sea at the bloom stage.
The green, brown and red tides in the sea are caused mostly by the Dinoflagellates. In fresh water, water blooms fairly common in ponds and lakes and rarely in rivers, are caused by a number of classes of algae (Chlorophyceae, Xanthophyceae, Chrysophyceae, Bacillariophyceae, Dinophyceae, Cryptophyceae, Euglenineae and
Cyanophyceae), each imparting a colour of its own. However, the most common forms belong to Cyanophyceae (Microcystis, Aphanizomenon, Anabaena, Anabaenopsis, Spirulina, Oscillatoria, Noclularia, Nostoc, Coelosphaerium etc.).
Light, temperature, a high pH (7-8-11-0), dissolved organic matter and low redox-potential governs the growth of the bloom. Algal blooms may be ‘mixed’, constituted by several species, or more rarely ‘pure’, constituted by a single species.
The blooms may be temporary or seasonal occurring in November-December and in June or may be permanent.
Besides imparting colour to the water the blooms cause disagreeable smell and taste to the water making it unfit for drinking purposes. In fish ponds, they may cause physical choking of the gills and depletion of oxygen during cloudy weather. Large scale mortality among fishes may also result during their decomposition.
Very strong poisons or toxins have been extracted from algae causing water-blooms and reports of death of cattle and birds drinking such water, are also there but so far chemical analysis of Indian water bloom algae or of the water supporting them have not revealed any toxic substance nor the drinking of such water, with moderate blooms, is known to cause any ill effect.
Algal blooms may be used and are used as manure in certain places and light algal blooms are, in fact, induced in fish ponds by adding inorganic fertilizers, to control the submerged weeds.
(ii) Water Pollution:
Large growth of algae in water reservoirs for drinking and other purposes causes two undesirable effects:
(i) By giving a bad taste from their decomposition products
(ii) By interfering with the filtration process.
Various filamentous and unicellular forms belonging to Chlorophyceae Cyanophyceae, Bacillariophyceae etc. cause water pollution. To some degree the presence of certain specific algae indicates the nature of pollution and water condition.
Chemical algicides, specially copper sulphate with intermittent chlorination are usually employed in small doses as a check to the growth of the algae. A beneficial effect of the algal growth, specially the attached forms, in the reservoirs with hard or calcareous ‘water is the precipitation of carbonates and reduction in the hardness of water.’
(iii) Disease Producing Algae:
Certain plants of economic importance (Tea, Coffee, Citrus etc.) are sometimes seriously affected by the parasitic alga. Cephaleuros. C. virescens causes the red-rust of tea, one of the most serious diseases of tea-plant (Thea sinesis). The parasite is most destructive as a stem parasite and can cause damage when the host is growing slowly. Another species of Cephaleuros, C. coffea is parasitic on coffee plants.