31.

Explain how does:

(a) a primary succession start on a bare rock and reach a climax community?

(b) the algal bloom eventually choke the water body in an industrial area?

(a) Pioneer species is the species of organism that invades the bare area. Lichens usually are the pioneer species on a bare rock. They secrete acids which dissolve rocks, thereby leading to weathering of rocks and soil formation. This paves the way for small plants like bryophytes which are able to take hold in the small amount of soil. They are succeeded by bigger plants, several more stages, and ultimately by a stable climax forest community which remains stable as long as the environment remains unchanged.

(b) Algal bloom is the excessive growth of the free-floating (planktonic ) in the water bodies , due to the presence of large amount of nutrients in the water. Water bodies in the industrial area have excess of nutrients which in turn promotes algal bloom. The algal bloom imparts a distinct colour to the water bodies and also robs the water of dissolved oxygen that is vital to aquatic organisms. They cause deterioration of the water quality and also produce toxins which are harmful to other organisms. The other pollutants flowing into the lake further decrease the oxygen levels in the water and poison the lake. Thus algal bloom can literally choke the lake to death.