The Role of Algae in the Ecological Lifecycle

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The plant or plantlike organisms we call algae are ubiquitous in habitat and vary widely in many characteristics, including in form, structure, and size.  Some algae are microscopic in size and are smaller than some bacteria, while others can become many feet in length, examples of which are the different types of seaweeds (such as kelps). 

Unlike most other microorganisms, algae contain chlorophyll.  This characteristic makes algae a subject of great interest to all biologists; single algal cells are complete organisms capable of photosynthesis as well as the synthesis of many other compounds that make up the cell.

Many thousands of species of algae occur in nature.  While a few of these species may be harmful to humans and other mammals, many others are beneficial.  The beneficial algae come in different forms, and three are cited here:  algae as soil enricher, algae as vitamin synthesist, and algae as food.

Algae as soil enricher stresses the important role that algae play in fertilizing the soil.  Some blue-green algae, like the cyanobacteria, fix atmospheric nitrogen.  Some algae have a gelatinous sheath that safeguards nitrogen-fixing bacteria from drying up and acts as a source of carbohydrate for the bacteria's energy.  Other algae are directly used as fertilizer.  Examples of these are the brown seaweeds (phaeophycophyta) and the red seaweeds (rhodophycophyta) which are plentiful in many countries.

Algae as vitamin synthesist is exemplified in many different species of algae.  For example, the yellow pigment contained in many algae is carotene which is a precursor of vitamin A.  Other algae are known to synthesize vitamin D, a fat-soluble vitamin.  As fish eat the phytoplankton, the vitamins are stored in their organs, from which they can be extracted as a rich source of vitamins for humans.  Appreciable amounts of thiamine (vitamin B1), ascorbic acid (vitamin C), and vitamins K1 and K2 can be found in green algae (chlorophycophyta).

Algae as food showcases the many species of algae that are used as food in many East Asian countries.  In Japan and Korea, for example, porphyra (a red alga) is cultivated and harvested as a food crop - called "nori" in Japan and "gim" or "kim" in Korea.

In some ordinary foods, agar (a gelatinous substance obtained from seaweeds) is added for bulk and stiffening; in juices and beverages, it is used as a clarifying agent.  Carrageenan, an extract from Irish moss (another red alga) is used as a thickening or stabilizing agent, or to hold substances in suspension (example, chocolate in chocolate milk drinks).

The use of chlorella (a unicellular green alga) and other smaller forms of algae as food for humans and domestic animals is becoming increasingly popular.  When these algae are grown under suitable conditions, they provide a rich source of protein comprising all the amino acids necessary for animal growth.  These smaller forms of algae are likewise a good source of fats and carbohydrates.

Of course, general acceptance of the use of algae as food for humans in place of higher plants is not to be expected, unless perhaps there occurs a serious short supply of food from other sources.  But as animal feeds or feed supplements, algae will without doubt find extensive application.

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