Essay on Harmful Aspects of Algae. Sometimes the excessive growth of algae in a mass, specially the planktons or floating ones, may cause undesirable effects.
They form the water-bloom which may be harmful to the fish and other animals; or in water-reservoirs may cause pollution and hinder the process of filtration. Some may grow in abundance even in the salt beds and affect the quality of salt, in the crystal formation and in imparting a pink or red colour to it.
Excessive development of phytoplankton is often responsible for the water assuming distinct colours like green, yellow-green, yellowish brown, dark or dirty brown, reddish brown, bluish-green etc. The Red Sea has been named after the Blue-green algae, Oscillatoria erythema, Trichodesmium sp. which gives a red coloration to the sea at the bloom stage.
The green, brown and red tides in the sea are caused mostly by the Dinoflagellates. In fresh water, water blooms fairly common in ponds and lakes and rarely in rivers, are caused by a number of classes of algae (Chlorophyceae, Xanthophyceae, Chrysophyceae, Bacillariophyceae, Dinophyceae, Cryptophyceae, Euglenineae and
Cyanophyceae), each imparting a colour of its own. However, the most common forms belong to Cyanophyceae (Microcystis, Aphanizomenon, Anabaena, Anabaenopsis, Spirulina, Oscillatoria, Noclularia, Nostoc, Coelosphaerium etc.).
Light, temperature, a high pH (7-8-11-0), dissolved organic matter and low redox-potential governs the growth of the bloom. Algal blooms may be ‘mixed’, constituted by several species, or more rarely ‘pure’, constituted by a single species.
The blooms may be temporary or seasonal occurring in November-December and in June or may be permanent.
Besides imparting colour to the water the blooms cause disagreeable smell and taste to the water making it unfit for drinking purposes. In fish ponds, they may cause physical choking of the gills and depletion of oxygen during cloudy weather. Large scale mortality among fishes may also result during their decomposition.
Very strong poisons or toxins have been extracted from algae causing water-blooms (Round, 1966) and reports of death of cattle and birds drinking such water, are also there but so far chemical analysis of Indian water bloom algae or of the water supporting them have not revealed any toxic substance (Singh, 1955) nor the drinking of such water, with moderate blooms, is known to cause any ill effect.
Algal blooms may be used and are used as manure in certain places and light algal blooms are, in fact, induced in fish ponds by adding inorganic fertilizers, to control the submerged weeds.
Large growth of algae in water reservoirs for drinking and other purposes causes two undesirable effects:
(i) By giving a bad taste from their decomposition products
(ii) By interfering with the filtration process.
Various filamentous and unicellular forms belonging to Chlorophyceae Cyanophyceae, Bacillariophyceae etc. cause water pollution. To some degree the presence of certain specific algae indicates the nature of pollution and water condition.
Chemical algicides, specially copper sulphate with intermittent chlorination are usually employed in small doses as a check to the growth of the algae. A beneficial effect of the algal growth, specially the attached forms, in the reservoirs with hard or calcareous ‘water is the precipitation of carbonates and reduction in the hardness of water.’
Disease Producing Algae:
Certain plants of economic importance (Tea, Coffee, Citrus etc.) are sometimes seriously affected by the parasitic alga. Cephaleuros. C. virescens causes the red-rust of tea, one of the most serious diseases of tea-plant (Thea sinesis). The parasite is most destructive as a stem parasite and can cause damage when the host is growing slowly. Another species of Cephaleuros, C. coffea is parasitic on coffee plants.