Algae (seaweeds) are usually aquatic, either marine or fresh water plants. A few algae also occur in terrestrial habitats such as moist soils, wet rocks, tree trunks, etc. These are unicellular or multicellular, autotrophic plants which don’t have vascular tissues {tissues that provide mechanical strengh} and their body are called thallus.

Types of algae

Algae have been divided on the basis of nature of pigments present in them and the mode of storing food. These pigments give them specific color.

Green Algae or Chlorophyceae

Green algae have chloroplast and chlorophyll in their cells. Examples are Chlamydomonas, Volvox, Spirogyra, Ulothrox, Oedogonium and Chara are some example.

Brown algae or Phaeophyceae

Brown algae store food in the form of laminarin and mannitol. Many of brown algae are called Kelps. Ectocarpus, Laminaria, Sargassum are common examples of brown algae.

Red Algae or Rhodophyceae

Red algae are red because of a pigment called Phycoerythrin. Most red algae are found in marine habitats. They store food in Floridean starch. Common examples are Gracilaria, Porphyra etc.

Blue Green Algae or Cyanophyceae

Blue green algae are most primitive algae and are prokaryotic. Modern classification puts them in Kingdom Monera along with bacteria.

Economic Importance of Algae

Nitrogen fixation and Biofertilizers

There are many species of blue-green algae capable of fixing atmospheric nitrogen in the soil and are used as biofertilizers. Common examples are Anabaena and Nostic. Anabaena, in association with water fern Azolla contributes nitrogen and also enriches soils with organic matter.

Other Uses
  • Many green algae such as Chlorella, Ulva, Caulerpa, Enteromorpha, etc. are used as food. Chlorella has about 50% protein and 20% of lipid and carbohydrates. Chlorella also yields an antibiotic chlorellin.
  • Agar is obtained from the Red algae Gracilaria and Agar is used as a culture medium for growing of microbes in labs. Agar is also used in Food and Pharmaceuticals.
  • Carragineen which is used in the Dairy industry is obtained from a red alga called Chondrus crispus. It is also used in cosmetics and Pharma.
  • Alginic acid, which is used as a stabilizer and thickening agent is obtained from Laminaria, the brown algae.
  • Dynamite is prepared with the cell walls of Diatoms.
  • Brown algae Laminaria is a good source of Iodine.
  • Macrocystis algae are source of Potash. It’s a brown algae (phaeophyceae ) and is largest algae among all.
Algal Hazards
Algal toxicity

Some algae are extremely poisonous to fishes. The blue-green alga Microcystis secretes hydroxylamine which kills aquatic life while Lyngbya and Chlorella may cause skin allergies in human beings.

Algal parasitism

The red alga Cephaleuros virescens causes Red Rust of Tea.

Algal blooms

Algae grow abundantly in water reservoirs where excess of nutrients are available to them. This algal growth floats on the water surface and look like foam or soap lather. It is called water bloom. Examples: Microcystis, Anabaena, Oscillatoria, etc.

Color of Red Sea

Red Sea is the part of the Mediterranean sea where a Blue green algae Trichodesmium grows profusely is called Red Sea. It is due to the presence of red Phycoerythrin in the cells of Trichodesmium.

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