At least half the carbon fixation of the earth is carried out by algae in the surface layers of oceans. This primary production is at the base of all aquatic food chains. These algae are also responsible for half the oxygen released by plants into the atmosphere. Algae can be used in some parts of the world as a direct food source for humans and they may be used as fertilizers on coastal farms. Unicellular green algae such as Chlorella are easy to cultivate and can be used as a source of a single cell protein (SCP) for human and animal consumption.
Green algae provide oxygen for the aerobic bacteria which break down sewage. Derivatives of alginic acid found in the cell walls of many brown algae are non-toxic and readily form gels. These alginates are used as thickeners in many products including ice cream, hand cream, polish, medicine, paint, ceramic glazes and confectionery.
Excessive numbers of algae may develop in bodies of water following pollution by fertilizers or other chemicals. These ‘blooms’ cause the water to smell and taste unpleasant and may lead to oxygen depletion and the death of fish.