People are mainly aware about the algae as seaweeds or algal blooms. They are the organisms with ability of photosynthesis and very much diverse community as well. But algae are important to man and their economic importance is manyfold. They are used as food, fodder and manure. They are also important in industrial field as well as agriculture.

there are 7 major types in algae

• Chrysophytes
• Euglenophytes
• Pyrrophytes
• Chlorophytes
• Rhodophytes
• Phaeophytes
• Xanthophytes

these are the benificial roles of algae

1. Algae is a food source: In different parts of the world algae have been utilized as direct source of food. They are rich in proteins, carbohydrates, oils, vitamins and minerals hence used as a diet food. They possess minerals like Cu, Fe, Zn, Co, V, Mn and Cr. About 20 different seaweeds are used as food source. Nostoc,
2. Algae as fodder: Many seaweeds are as food for cattle, poultry and aquatic organisms. Sargassum is used as cattle feed in China. Laminaria and Fucus are also used for the same purpose. Seaweed meal increases the egg laying capacity of fowls. These eggs contain high amount of iodine and carotene.
3. Algae in agriculture: Algae are used as green manures in agriculture. Sargassum, Laminaria, Macrocystis and Gracilaria are the most commonly used ones. Seaweed manure increases the yield of barley, potato, coconut palms, citrus etc. Many blue green algae have the ability to fix the atmospheric nitrogen into the soil. So they can be used as biofertilizers. Saline and alkaline soils can be converted into productive ones by growing some blue-green algae on soil. Anabaena, Rivularia, Spirulina are used for this purpose.
4. Algae in Industries: In Industries many algae have been used as sources for the extraction of commercial products like agar-agar, diatomite, carrageenin and algin. Agar-agar is used as culture media for bacteria. It is also used as emulsifier in ice-cream, fruit jellies and dairy product preparation. Algin is used as painting pastes in textile industry and thickeners in cosmetics, pharmaceutical products etc. Carrageenin which is extracted from Chondrus crispus and Gigartina are used in food industry, textiles and leather industry. It is a remedy for cough.
5. Algae in sewage disposal: Sewage water contains organic and inorganic substances which makes it low in oxygen content. But sewage finds use in agricultural practice as they are rich in salts. To decrease the foul smell algae are used. Algae are used to decompose the organic and inorganic substances.
6. Algae and Research: Algae are used in the study of effects of pesticides, herbicides and UV light. They are used in the research for preparing biofuels.
7. Algae as pollution indicator: Some algae grow well in polluted water as they are more tolerant towards pollution. Growth of these algae indicates the pollution and its intensity. Scenedesmus indicates copper wastes and Ulothrix zonata indicates indicates paper mill wastes.

Though many algae are useful, there are harmful algae are also there. The development of water blooms is considered to be a bad effect of algae. There are some parasitic algae cause diseases in plants. Attachment of algae tp ship retards the speed of the ship. growth of algae on cloths are also seen and they ruin the cloth.