By Avinash Darsimbe Assistant Professor Department of Botany Shri Shivaji Science College, Amravati B.Sc. I (Sem- I) BOTANY Diversity & Applications of Microbes and Cryptogams Unit-VI Application of Microbes and Cryptogams 6.1. Harmful aspects of Algae

1. B.Sc. I (Sem- I)
BOTANY
Diversity & Applications of Microbes and Cryptogams
Unit-VI
Application of Microbes and Cryptogams
6.1. Harmful aspects of Algae
By
Avinash Darsimbe
Assistant Professor
Department of Botany
Shri Shivaji Science College, Amravati

2. What are harmful algae?
Phytoplankton blooms, micro-algal blooms, toxic algae, red
tides, or harmful algae, are all terms for naturally occurring
phenomena. About 300 hundred species of micro algae are
reported at times to form mass occurrence, so called blooms.
Nearly one fourth of these species are know to produce toxins.
The scientific community refers to these events with a generic
term, ‘Harmful Algal Bloom’ (HAB), recognising that, because a
wide range of organisms is involved and some species have toxic
effects at low cell densities, not all HABs are ‘algal’ and not all
occur as ‘blooms’.

3. Why are Algae harmful?
Proliferations of microalgae in marine or brackish
waters can cause massive fish kills, contaminate seafood with
toxins, and alter ecosystems in ways that humans perceive as
harmful. A broad classification of HABs distinguishes two groups
of organisms: the toxin producers, which can contaminate
seafood or kill fish, and the high-biomass producers, which can
cause anoxia and indiscriminate kills of marine life after
reaching dense concentrations. Some HABs have characteristics
of both.

4. 1. Harmful to living stock:
The algae are harmful to humans in several ways. Volvocales, Chlorococcales,
Myxophyceae and several others occur in such a great abundance in water, that they colour
the whole water either green or blue green and cause the death of fishes.
The algae block the gills of the fishes and they respire during night and make
the respiration of fishes difficult by complete depletion of oxygen.
Sometimes the algae are found in water so abundantly that they make difficult
to drink water of livestock. Some blue green algae have been reported poisonous and they
directly cause the death of living stock who drink this contaminated water.

5. 2. Blocking of photosynthesis:
The epiphytic algae which are found upon other plants
and trees block photosynthesis and indirectly harm the trees and
plants.

6. 3. Parasitic algae:
The well known disease ‘red rust of tea’ is not caused by any parasitic fungus
but an algal form Cephaleuros virescens. This causes havoc to tea plants in
Assam tea gardens. Besides, this parasitic form attacks several other plants,
e.g., Mangifera, Rhododendron. Coffea, etc. The heavy losses are caused to
tea and coffee by this parasitic algal form.

7. 4. Mechanical injury:
Sometimes the filamentous forms of algae are found in such a great
abundance and net-like behaviour, that many fishes and other aquatic
animals may get perish in these tangles, and direct death is inflicted upon
them.

8. 5. Contamination of water supply:
Many blue-green, green and other algae contaminate the water of city reservoirs. This
contamination develops a foul odour in the water and makes the water unhygienic. The
algae also form some mucilaginous secretions which are the seats of harmful bacteria and
other pathogens causing several human and animal diseases.

9. 6. Fouling of ships:
Some algae are attached to the ships, and this is called fouling of ship. The
fouling retards the speed of the ship. To avoid this nuisance the ships are
periodically dried up and painted with copper paint.

10. 7. Deterioration of exposed fabrics:
Commonly in rainy season, if the wet fabrics are exposed, within a few days
a blue green alga appears on it and makes the cloth black spotted and weak.
This was a serious problem during the Second World War. This algal growth
is usually followed by bacterial infection and the fibers of cloth are
completely destroyed.

11. AnyQuestions?