Harmful and Useful Activities of Algae | Botany

In this article we will discuss about the harmful and useful activities of algae.

Harmful Activities of Algae:

1. Parasitism:

i. As Parasite on Live Stocks:

The algae of different groups like Volvocales, Chlorococcales, Cyanophyceae and several others occur in such a great abundance which makes the water colour either green or blue green and causes the block­age of gills of fishes. As a result during night time (when photosynthesis stops) the respiration of fishes is hampered causing death.

ii. As Parasite on Higher Plants:

Out of many parasitic algae, Cephaleuros is the impor­tant genus. Different species of Cephaleuros grow on the leaves of different angiosperms like Rhododendron, Magnolia, Camellia sinensis (tea), Coffea arabica (coffee) and Piper nigrun (Pepper). Cephaleuros virescens causes Red rust of tea plants, causing economic losses mainly during slow growth.

2. Reducing the O₂ Level in Water:

Algae like Microcystis, Anabaena, Aphanisomenon form water blooms and can grow well in O₂-deficient water. The continuous respiration by sub­merged plants and animals during night time (when the photosynthesis does not take place) causes the depletion of O₂ to almost zero level. At that condition mortality of both animals and other submerged plants takes place due to suffo­cation.

3. Toxicity to Live Stocks (Domestic Ani­mals like Cow, Pig, Horse etc.):

With the increase in algal population, the water becomes difficult to drink by the live stocks. Toxic substances released by some algae make the water poi­sonous and cause the death of livestock’s after drinking that water.

4. Toxicity to Human Being:

Toxins secre­ted by Gymnodinium affect the muscular and nervous systems of some fishes. Gonyaulax catenella secretes an endotoxin, tetraodontoxin (C₁₆H₃₁O₁₆), which accumulates in the body of shell fish. Consumption of such shell fish by human being causes paralysis or even death within a day.

5. Fouling of Ship:

Some algae become attached and grow on the outer surface of ship called fouling, which retards the speed. To over­come such problem the ships are dried at inter­vals and painted with copper paints.

6. Contamination in Drinking Water:

Algae of different groups mainly blue green, green and some others contaminate the water of reservoirs. They develop a foul odour in water and make it unhygienic for human being. Some mucilagi­nous substances are secreted by algae on which many pathogenic bacteria can grow nicely and cause several human and plant diseases.

Different diseases may appear by drinking that water:

i. Chlorella and Lyngbya cause different skin diseases,

ii. Gymnodinium brevis cause respiratory disease, and

iii. Microcystis, Anabaena cause gastric troubles.

7. Blocking of Photosynthesis:

The epi­phytic algae growing on the leaf surface of other plants hamper photosynthesis, thereby the growth of the mother plant becomes reduced.

8. Destruction of Exposed Fibres:

Some blue green algae grow well on the wet exposed fibres, marks by black spots. The algal growth usually follows bacterial growth and the fibres get damaged severely.

Useful Activities of Algae:

1. Food:

Algae are used by man from ancient times, but due to population boom in the last decades the rate of consumption of edible algae has been increased and it will definitely increase much more in near future. The algal species is becoming a popular food to the man­kind because of its high nutritive value and more yield per unit area than the conventional crops.

In Japan, the food production by marine algae is about eight times more than that of land plants.

Some algae commonly used as food are Chlorella, Chondrus, Codium, Porphyra, Rhodymenia, Ulva etc.

i. Chlorella:

It has become popularly known to human beings after its use in the space research and nuclear submarines for the genera­tion of oxygen.

It is also important for its nutritive value and can be compared with soyabeans. It grows very fast in controlled condition and yields about 13 metric tonnes/year/acre. It contains, carbohydrate 30%, protein 30%, lipid 15% etc. But the diges­tion of its cell wall is a problem to the human being and researches are going on to solve it. According to Witsch (1959) the vitamin B con­tent of young culture is equivalent to the lemon juice.

ii. Chondrus Crispus:

It is commonly known as Irish moss. The alga is cooked with milk and with the addition of vanilla, it makes a highly popular dish, the blancmanges.

The gelatinous carbohydrate obtained from this algae is used in pudding. It is used as stabi­lizer and cleaning agent in beer industry.

iii. Codium and Ulva:

These are used as salad in Japan.

iv. Porphyra:

It is a seaweed, belongs to Rhodophyceae. It contains carbohydrate 40- 45%, protein 30-35% and vitamin B and C. The common name of food item is laver or nori in Japan, tsats’ai in China, sloke in Britain. It is very popular in different countries including Japan.

v. Laminaria:

L. saccharina is rich in carbohydrate (57%) and the commonly used food is called ‘kombu’.

vi. Rhodymenia:

R. palmata is used to pre­pare a salty confection, commonly known as ‘dulse’.

vii. Monostroma:

In Japan, it is used in the preparation of common food, known as ‘aonori’.

viii. Spirulina:

It is a blue green alga, rich in protein (60%), vitamin and unsaturated fatty acids. In India it is available as tablet prepared by CFTRI (Central Food Technological Research Institute), Mysore.

ix. Scenedesmus:

It is rich in protein and threonine and is equivalent to the skimmed milk.

x. Nostoc:

N. commune is boiled and used as soup in China.

xi. Spirogyra and Oedogonium:

In South India, Green Laver, a kind of food is prepared from Spirogyra and Oedogonium.

2. Fodder:

Many algae become popular as fodder due to their vitamin and micronutrient, in addition to their protein and carbohydrate content. The algae commonly used as fodder in different countries are Fucus, Laminaria, Sargassum, Alaria, Rhodymenia, Ascophyllum, Macrocystis etc.

The fat content of milk becomes increased with the addition of seaweed. The seaweeds like Rhodymenia palmata and Ascophyllum esculenta are used to feed the cattle in Scotland, Ireland etc. Macrocystis, the Pacific-coast kelp is used directly or indirectly in the form of powder to feed cattle, hogs and poultry birds in USA because of high mineral and vitamin content.

The algae also become popular as fodder in other countries like France, Norway, Germany, Denmark etc. Macrocystis sp. is rich in vitamins A and E — used as fodder in France. Dried Pelvetia, a seaweed used as cow feed increase the milk yielding capacity of catties.

The iodine and carotene content in egg-yolk increases by feeding the processed sea weeds used as food. The egg lying capacity of the poultry birds also increases by feeding the processed sea weeds like Fucus, Laminaria etc. Sargassum is used as fodder in China.

3. Industry:

Algae have been used to develop many products of commercial and phar­maceutical importance. These are Agar-agar, Carrageenan, Diatomite, Alginate, Funori, Medicine etc.

i. Agar-Agar:

Commercially it is obtained from Gelidium nuditifons, G. pusillum, G. robustrum, Gracilaria verrucosa and also from diffe­rent species of Ahnteltia, Chondrus, Gigartina, Acanthopeltis and Pterocladia.

It is composed of two polysaccharides, agarose and agaropectin. The agar-agar is readi­ly soluble in hot water but not in cold water. At 1.5% concentration it forms a clear, solid and elastic gel on cooling the melted agar to 32-39°C and does not melt again below 85°C.

Southeast Asia and Japan are the main cen­tres of agar-agar production.

For the commercial production of agar-agar following procedure is followed:

Collection of plants from sea → bleached in the sun → boiled the material for few hours → the extract is acidified → material is then frozen and thawed → it is then dried. It is available in the market in the form of cakes, flakes or powder.

Use:

The agar-agar is used in food, pharma­ceutical, cosmetic industries and scientific labo­ratories.

a. Food:

It is used in processed cheese, jam, jellies, cream and pudding etc. It is also used as gelling and thickening agent in the preservation and canning of meat and fish.

b. Pharmaceutical:

It is used as laxa­tive, pills, different ointments and also used in drug for slow release when requires.

c. Cosmetics:

It is used in cosmetics like lotions etc.

d. Scientific Laboratories:

In scientific laboratories it is used for stiffening the culture medium used at 1.5-2.0% concentration.

ii. Carrageenan:

It is obtained from the cell wall of Cigartina stellata, Chondrus crispus, the Irish moss and Eucheuma.

It is a phycocolloid, almost similar to agar- agar, but the ash content is higher and requires higher concentration to form solid gels. The phycocolloid consists of K-carrageenan and X-carrageenan.

The carrageenan acts as a blood coagulant. It is also used to stabilise emulsions and to cure cough. It is used as a component of deodorants, cosmetics, toothpastes, paints etc.

iii. Alginic Acid:

It is extracted from the cell wall of some brown algae like Ascophyllum, Fucus, Ecklonia, Macrocystis, Laminaria, Durvillea and Lessonia. The content of alginic acid varies in different genera and ranges from 10-40%. The salts of alginic acid found in the cell wall are the alginates.

It is non-toxic, insoluble in water, viscous, but becomes hard when dry.

It is used as:

a. Thickeners:

In food industries, it is used in the preparation of sauce, soup, cream etc.; in textile industry as printing pastes and cosmetics.

b. Emulsifiers:

It is used in polish, emul­sion paints etc.

c. Gelling Agent:

It is used in confec­tionary, powders, paints, ice-cream etc.

d. Other Uses:

It is used in the produc­tion of artificial fibres, plastics, rubbers etc.

iv. Diatomite:

After the death of diatom cells the outer covering i.e., the silicified wall becomes accumulated at the bottom of water. The accumulation may be thicker during favourable condition. These deposits are called diatomaceous earth or diatomite.

It is very sui­table for use in different industries:

a. As Filter:

It is used as filter in different industries like sugar (to filter microorganism), oil and chemical industry. Diatomite is also used as filter for battery boxes.

b. As Insulator:

It is used as insulator in boilers and blast furnaces for its heat resistant ability.

c. As Absorbent:

It is used as absorbent of liquid nitroglycerine.

d. Other Uses:

Diatomite is used as abrasive (i.e., capable of rubbing or grinding down) substance for manufacture of metal paints, polish, varnish and toothpaste etc. It is also used with bake-lite for fuse and switch boxes.

v. Funori:

It is a type of glue, obtained from Gloiopeltis furcata, used as sizing agent in paper and textile industry. In cosmetic industry it is used for curling of hairs and preparation of dyeing.

vi. Medicine:

Chlorellin, an antibiotic is extracted from Chlorella. It is used to control microorganisms like Gram -ve bacteria.

In addition to above, other algae such as Cladophora, Laminaria, Lyngbya and Halidrys are able to synthesize antibiotics.

Both Gram +ve and Gram -ve bacteria can be controlled by the extract of Ascophyllum nodosum. Extracts of Cordium, Corallina and Durvillea etc., are used as vermifuge. In China, an antithelmintic drug ‘Tse-ko-Tsoi’, is prepared from Digenia simplex, a red alga.

Different sea weeds are used as good sources of vitamins:

a. Riboflavin from Porphyra tenera, Gelidium amansii,

b. Thiamine from Rhodomela subfusca,

c. Vitamin C from Porphyra lacinata and

d. Vitamin A from Nitzschia, a diatom.

Various brown algae like Ecklonia, Eisenia, Fucus and Laminaria are the richest source of iodine, used to control goiter. About 100 tonnes of iodine are produced per year in Japan from brown sea weeds.

The Gelidium is used to control stomach disorders.

The cultivation of Nitella in the pond greatly reduces the population of Mosquito, indi­rectly controls malaria.

4. Biofertiliser:

Members of Cyano- phyceae like Nostoc, Anabaena etc. can fix atmospheric nitrogen and form nitrogenous compounds. These compounds are further absorbed by the plant for their metabolic activity and increase yield.

5. Minerals:

Minerals like Copper, Cobalt, Chromium, Boron, Iron, Zinc, Vanadium and Manganese are present in high amount in sea weeds. Hence the seaweeds are used as stock feed as well as natural fertiliser.

The Polysiphonia and Rhodomela, the mem­bers of Rhodophyceae are richest source of bromine.

Various brown algae like Ecklonia, Eisenia, Fucus and Laminaria are the richest source of iodine.

Soda and Potash are present at high percen­tage in brown algae, thus the ash of those algae are used in the manufacture of alum, glass wares and soap.

6. Disposal of Sewage:

Water-borne wastes of industry and domestic house are called ‘sewage’. It is rich in sulphur, nitrogen, phospho­rus and potassium. The anaerobic breakdown of sewage, gives out bad odour. So the aerobic breakdown is preferred, which does not give out bad odour and the products can also serve as fertiliser.

Bacteria are carried out in a container and the required oxygen is collected from algae. Unicellular algae like Chlamydomonas, Chlorella, Scenedesmus, Euglena etc. are used in this pro­cess. In turn, ammonia and nitrogen compounds become available to the algae as nutrient.

7. Use in Biological Experiments:

Algae are used as experimental material for different research works. Chlorella has been used to study the path of carbon in photosynthesis and Acetabularia in genetical researches. Halicystis is used to study membrane permeability.

8. Use in the Production of H₂ Fuel:

Production of H₂ is an important area of biotechnology for the production of non- conventional energy. Different algae like Chlamydomonas, Dunaliella, Porphyridium, Oscillatoria etc. are used in this process. Normally photosynthesis takes place in the above plants and the photosynthetic principal is utilized to gain the goal.

In the first part of photosynthesis, photolysis of water takes place by which water splits into, hydrogen ion (H⁺), O₂ and electrons. The hydrogenase enzyme of the above algae generates hydrogen gas (H₂) from hydrogen ion (H⁺). Some Cyanophycean members such as Anabaena etc. are used in this process, but here nitrogenase is utilised as the main hydrogen producing enzyme.