Question

Read the following statements (A-D) and select the correct statement(s) related to algal bloom.

A. It is an excessive growth of the planktonic algae in water bodies.
B. It imparts a distinct colour to the water bodies.
C. Bloom-forming algae are not toxic to humans.
D. It results in deterioration of water quality and fish mortality.

• A. A, B and C
• B. A, C and D
• C. B, C and D
• D. A, B and D

Answer 1

The correct option is D A, B and D

An algal bloom is a rapid increase or excessive growth of the planktonic (free-floating) algae in water bodies. One of the major reasons for the occurrence of algal blooms is the presence of excess of nutrients like phosphorus and nitrogen in the waters. These nutrients reach the water bodies through the sewers and surface runoff.

Hence statement A is correct.

Algae possess distinct pigments, so based on the type of algae present in the water bodies, there are three kinds of algal blooms: red, brown and green. Hence algal bloom imparts a distinct colour to the water bodies.

So, statement B is correct.

The algal blooms caused by protists (dinoflagellates and diatoms) and cyanobacteria (blue-green algae) can produce toxins (poisons) that are harmful to humans, animals and other aquatic organisms. It badly affects the food chain in the aquatic ecosystem.

Hence statement C is incorrect

Algal blooms can reduce the ability of fish and other aquatic life to find food, as the algae block the free movement of organisms and can cause entire populations to leave an area or even die.

Harmful algal blooms cause thick, green muck that impacts clear water and affects recreation and irrigation.

The accelerated growth of algae depletes the oxygen in the water bodies which affects aquatic life. It also leads to fish mortality.

Thus, statement D is correct.

Figure: Algal bloom