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close this bookBiodiversity in the Western Ghats: An Information Kit (IIRR, 1994, 224 p.)
close this folder4. Fresh- and brackishwater
View the document4.1 Estuarine ecosystems
View the document4.2 Mangroves
View the document4.3 Mangrove communities
View the document4.4 Wetlands
View the document4.5 Freshwater wetlands: Carambolim Lake
View the document4.6 Freshwater algae

4.6 Freshwater algae

Like all plants, algae contain chlorophyll. Unlike plants, however, they have no roots, stems or leaves. They range in size from 0.5 microns to huge seaweeds. Algae can be found in many conditions worldwide. As many as 450 species have been recorded.

Algae as food

Algae are efficient photosynthetic "machines" which convert solar energy into biomass. In fact, it has been suggested that some algae be used as a new weapon to fight worldwide protein shortages. Algae can produce 55-110 tonnes of dry matter/hectare/year, of which up to 50% is protein. The blue-green algae Spirulina has received much attention from nutrition researchers. Chlorotea, a green algae, has been proposed as an organism that could absorb CO2 and regenerate oxygen in space stations.

Treating sewage

Algae are important in treating sewage. They help in oxygenating waste water and reduce the number of fecal coliform bacteria in the water by 99%. The algal biomass produced from treating sewage contains toxic substances but can be used to make biogas.

Blue-green algae

Blue-green algae, or cyanophyceae, are highly adaptive and can colonize even polluted water. This means they can be used as an "indicator species": large numbers of blue-green algae show that water is polluted. Some rivers in Goa contain large quantities of iron because of mining. This encourages the growth of blue-green algae.

Monitoring water quality

Nature clubs, schools and non-government organizations can help monitor rivers and lakes for dangerous levels of pollution. They can do this by regularly measuring the water pH, CO2 content, oxygen content and hardness. They should also watch for algal blooms. Any unusual changes should be reported to the local pollution control board. These groups can also mobilize public support ro prevent pollution.

Toxic algae

Many algae are toxic to animals and humans.


Species affected


Anabaena, Microcystis,
Coelosphaerium, Rivularia

Sheep, cattle, dogs, gulls

Weakness, jaundice, diarrhoea, convulsion

Oscillatoria intestini





Gastro-intestinal disorders



Crampy stomach pains, nausea, vomiting



Abdominal pain, nausea, vomiting, diarrhoea

Monitoring water quality