Economic Importance of Algae — Uses and Harmful Effects

Many algae are rich in proteins, vitamins and minerals and are eaten by humans and animals:

1. Spirulina and Chlorella — single-celled algae grown as 'single-cell protein' (SCP); rich in protein and used as health-food supplements.
2. Porphyra (Nori), Laminaria (Kombu) and Ulva (sea lettuce) — seaweeds eaten widely in Japan, China and Korea.
3. Sargassum and other seaweeds — used as fodder for cattle and as a feed supplement.

Because they grow fast and need only sunlight, water and minerals, algae are seen as an important future food source.

1. Agar (agar-agar): obtained from red algae such as Gelidium and Gracilaria. It is used to prepare culture media in laboratories (to grow bacteria and fungi), in foods (jellies, ice cream) and in medicines.
2. Algin (alginic acid/alginates): obtained from brown algae such as Laminaria and Sargassum. Used as a thickening and emulsifying agent in foods, paints, cosmetics and textiles.
3. Carrageenan: obtained from red algae such as Chondrus crispus (Irish moss). Used as an emulsifier in chocolates, toothpaste and cosmetics.
4. Iodine: extracted from large brown algae (kelps) such as Laminaria.
5. Diatomaceous earth (diatomite): made from the cell walls of diatoms; used in filters, polishes, toothpastes, insulation and as an abrasive.

1. As fertilisers: blue-green algae (cyanobacteria) such as Nostoc and Anabaena fix atmospheric nitrogen and increase the fertility of paddy (rice) fields. Seaweeds are also used as natural fertilisers.
2. Oxygen production: being photosynthetic, algae release large amounts of oxygen into water and the atmosphere — a major share of the Earth's oxygen comes from algae.
3. In sewage treatment: algae help purify sewage water by using up nutrients and releasing oxygen.
4. Biofuel: some algae are rich in oils and are used to produce biodiesel and other biofuels.
5. In research: Chlorella and Acetabularia have been important in studies of photosynthesis and cell biology.
6. In medicine: certain algae yield antibiotics and other medicinal compounds.

1. Water blooms: rapid growth of algae (especially blue-green algae) in nutrient-rich water forms a thick scum called a water bloom. This makes the water foul-smelling and unfit to drink.
2. Eutrophication: excess nutrients cause heavy algal growth; when the algae die and decompose, oxygen in the water is used up, killing fish and other aquatic life.
3. Toxins: some algae release toxic substances that can poison fish, cattle and even humans who drink the water.
4. Fouling: algae growing on the hulls of ships, on water pipes and on submerged structures cause damage and blockage.
5. Some parasitic algae (e.g., Cephaleuros) cause diseases in tea, coffee and other plants.