Types of Algae

Algae are simple, autotrophic organisms that can synthesize their own food by means of photosynthesis. The taxonomy of algae is very confusing. Previously, algae were classified under the kingdom Plantae, as they possess chlorophyll for photosynthesis. However, algae are mostly aquatic and lack true roots, stem and leaves, which are not so in plants. Hence, in the modern classification, they are excluded from Plantae and categorized under Protists. The size of algae may range from few micrometers to several meters. For example, the freshwater alga Micromonas is about 1 micrometer, whereas the giant marine kelp can grow to about 60 meters in length. The branch of science that deals with the study of algae is called phycology. Those who specialize in the study of algae are known as phycologists.

Types of Algae

Algae are classified based on the type of pigments and food reserves present in the particular species. The difference in the pigments play a major role in determining the habitat distribution of the particular algal species. Regarding the distribution of algae, they can adapt in diverse environmental conditions. Majority of algae are found in aquatic habitats, either in freshwater or marine water. Some of the species are found in extreme environments like snow and ice, whereas some are adapted in hot springs.

Blue Green Algae (BGA)
Blue green algae (BGA), also referred to as cyanobacteria, are the simplest forms of algae. Examples of BGA are Nostoc and Calothrix. As the name suggests, they are blue green in color, ranging from single-celled organization to colonial forms. BGA contain chlorophyll a, b and phycobilins. They are prokaryotic in cellular organization, that resemble bacteria. BGA are considered to be an intermediate between bacteria and plants. Hence, the name cyanobacteria is assigned to these algal species. Since BGA lack specialized organelles, they photosynthesize directly through the cytoplasm.

Green Algae
Green algae, belonging to the phylum Chlorophyta, contain chlorophyll a, b, carotenoids and xanthophylls. The main food reserve of green algae is starch. Some examples of green algae are Ulva, Codium and Caulerpa. As of now, about 7000 species of green algae are identified. They may be either unicellular or multicellular. Most of them are freshwater algae, while a few species are found in the marine water.

Red Algae
Red algae, belonging to Rhodophyta, contain chlorophyll a, d, carotenoids, xanthophylls and phycobilins. The food reserve of red algae is floridean starch. The examples of red algae are Chondrus and Gelidiella species. Majority of red algae are marine species. More than 6500 species of red algae have been identified, out of which about 200 are freshwater species. The red pigment, phycobilin helps in harvesting light at a greater depth, hence some members of red algae are found in such a depth in the ocean floor, where no other photosynthetic organisms can adapt.

Brown Algae
Brown algae, belonging to the class Paeophyceae, contain chlorophyll a, c and fucoxanthin pigment. Due to the green color, chlorophyll and brown pigment, fucoxanthin, the members belonging to phaeophyta exhibit a typical greenish-brown coloration. The food reserve of brown algae are complex carbohydrate polymers, called laminarin. Laminaria and Macrocystis are the examples of brown algae. Similar to red algae, majority of these algal group are adapted in marine water. Brown algae are the most complex algae, in which some species are adapted at certain depths in the seas and oceans. The giant kelps, found in the ocean floor are brown algae belonging to the order Laminarales. Kelps are the only algae with tissue differentiation.

Algal species are very sensitive to the changes in the environmental conditions. Hence, they are used as biological indicators to determine any modification in the environment. For example, simple freshwater algae like Euglena and Chlorella are used to indicate the extent of water pollution.