I. Useful Activities:
(i) As food:
Algae being the producers of aquatic environment constitute the primary food sources for aquatic animals.
The algae are considered rich in proteins, carbohydrates, fats and Vitamin A, B, C and E.
The vitamins A and D are commercially extracted from the fish livers, originates through the synthesis of algae. About 70 species of marino algae are used as food.
Prophyra tenera (amanori or nori bread in Japan) has 30-45% protein, 4-45% carbohydrates, vitamins A, B, C and iodine etc. Chlorella, in terms of its nutritional value, is comparable to mixtures of soybeans and spinach; and also grows more quickly than Porphyra. Spirogyra and Oedogonium are dried and sold in Indian marked for preparing soup. UIva (sea lettuce) dried, salted and sold in European market.
Spirulina (Cyanobacterium) is a rich source of proteins vitamins B-Complex and minerals. Biscuits fortified with powdered Spirulina are a very common practice now. Nostoc commune is boiled to be eaten as food in China and Java.
(ii) As Fodder:
Rhodymeria, Sargassum, Laminaria, Pelvetia, Fucus (rock weed), Macrocystis are collected from sea shores to feed the cattle, poultry and pigs.
(iii) Source of minerals:
Bromine extracted from red algae like Rhodomeria and Polysiphonia. Iodine extracted from kelps (brown seaweeds) like Fucus, Lamineria, Ecklonia, Macrocystis etc. Potash extracted from Macrocystis, Nereocystis etc.
(iv) As medicines:
Extracted from green algae (Caulepra and Chlorella), brown algae (Laminaria and Ascophyllum) and red algae (Polysiphonia).
Carrageenin can clot blood.
Sodium Laminarin sulphate extracted from Laminaria is an effective blood anticoagulents.
Agar is used as Laxative.
e) Vermifuges or worm expellents:
Extracts of Corallina and Durvillea are used for expelling worms.
(v) Space travels:
Green algae like Chlorella, Synococcus etc. are used in space flight to get rid of exhaled CO2, generate O2 and food.
(vi) Sewage disposal:
Chlorella Chlamydomonas, Oscillatoria, Scenedesmus etc. are grown in sewage oxidation ponds. They provide surplus oxygen for aerobic decomposition by bacteria and fungi.
(vii) Control of mosquito Larvae:
Anabaena, Nostoc, Chara, Nitella etc. secrete toxins that don’t allow mosquito larvae to grow in ponds, ditches etc.
(i) Nitrogen fixation:
Blue green algae increase the soil fertility by fixing atmospheric nitrogen, e g., Anabaena, Aulosira, Spirulina, Nostoc etc. It is estimated that these BGA can fix 15-40 kg N/ha per season. All nitrogen fixing BGA are filamentous and contain specialized cells called heterocysls for nitrogen fixation. BGA are also used for reclamation of saline usar (alkaline) land.
(ii) CO2 fixation:
About 50% of total CO2 fixation on earth is carried out by algae through photosynthesis.
Large brown and Red algae are used as organic fertilizers. They are richer in K but poorer in N and P than the far manure. In coasted area, sea weeds are directly ploughed as green manure for cultivation. Extracts of sea weeds are sold as liquid fertilizers.
(iv) Plant growth substances like auxins and gibberellins have been isolated forms marine algae by Conard, Saltmann and Joyce A. Mowat.
Algae are useful natural resource of many commercial products. The important algal products of industrial uses are alginates, carrageen and diatomite.
Agar or Agar-agar is a jelly-like complex polysaccharide (phycocolloid) stored in the cell wall of certain red algae Gelidium, Gracilaria, Gigartina etc. Agar extracted from these agarophytes used in various purposes. Agar is used in laboratories to solidify culture media. Agar-agar is also used for preserving cooked fishes, sheep tongues, sizing of silk, making adhesive for plywood, in photographic industry, as a thickening material in the preparation of ice cream, malted milk, jelly candies, pastries, soups and sauces.
Analysis shows that the principal potential food material in agar is galactose and sulphate. Agar is sometimes used in place of pectin for making jams, jellies, marmalades and other preserves. It is also used for making moulds for artificial leg, linoleum, artificial leather, silk and insulating material against heat and sound.
The cell wall of brown algae (sea weeds) contains cellulose like strengthening material called algin. Chemically, algin is the calcium salts of alginic acid (a phycocolloid). Alginates are the salts of alginic acid derived from the cell wall of brown algae like Fucus, Laminaria, Macrocystis, Lessonia etc.
These are gelatinous and substance used as thickener in shampoos, tooth pastes, cosmetics, ice cream, paints etc. Alginates are also used in the production of plastics, flame proof fabrics, security glass, latex, capsules, typewriter rollers, non-inflammable wrapping film etc. Alginates can prevent bleeding, so used in surgical threads and gauzes. Products of alginic acid are used in walking machine belts, sausage skins, tooth brush and dusting powder.
(c) Carragheen (Carrageenin):
It is a sulphated phycocolloid, similar to agar, found in the cell wall of red algae like Chondrus crispus (Irish moss), Gigartina, Eucheuma etc. It has been used as stabilizer or emulsifier in foods such as ice cream, other milk products and relishes. It is used as a binder in tooth paste or in pharmaceutical products, as well as an agent in ulcer therapy.
Carrageen has been found useful in finishing leather textile and paper industries. It is used as a thickening agent in shaving creams and lotions, and in the soap industry. It is also used to thicken sauces and soups, or fresh salads.
(d) Diatomite (Kieselguhr):
It is a rock like deposit of siliceous frustules (cell wall) of fossilized diatoms. Diatomite is used in the preparation of explosives, cement, bleaching powder, cosmetics, chocolates, metal polish, automobile polish and shoe polish. They are also used in insulation of refrigerators, boilers, furnaces and pipes in packing corrosive chemicals, constructing of sound proof-rooms, light bricks, filter for oil, liquors and sugar refining.
II. Harmful Activities:
(a) Water blooms:
In water reservoirs, sufficient nutrient availability results in luxuriant growth of algae that float on water surface in masses and look like foam or soap lather. These algal masses are called water bloom. Some common water blooming algae are Anabaena, Oscillatoria, Microcystis.
Water blooms cause oxygen depletion in the water of reservoirs thus causing death of aquatic animals present in the water. Some of the bloom forming algae also produces toxins which sometimes prove fatal to the aquatic as well as domestic animals consuming that water. Blooms of dinoflagellates like Gymnodinium and Gonyaulax form red tides in sea.
A green alga Cephaleuros virescenese is the cause of red rust of tea. Sometimes it causes extensive damage to tea crop.
(c) Fouling of ships:
Algae corrode the submerged metallic parts of ships and vessels. Sargassum causes hindrance for the smooth movement of ships.
(d) Paralytic shell-fish poisoning (PSP):
Bloom forming dinoflagellates like Gonyaulax secrete powerful toxins called saxitoxin which kill large number of marine fishes and invertebrates. However marine shell-fishes feed on large amount of Gonyaulax remain unharmed. Eating such poisoned shell fishes by human causes a fatal paralysis called PSP.