Question

Given are some of the stages of the hydrarch.
A. Marsh-meadow stage
B. Reed-swamp stage
C. Submerged plant stage
D. Phytoplankton stage
E. Free floating plant stage
Select the option that represents the correct sequence of these stages.

• A. D $\to$ C $\to$ E $\to$ B $\to$ A
• B. C $\to$ E $\to$ A $\to$ B $\to$ D
• C. B $\to$ D $\to$ C $\to$ A $\to$ E
• D. D $\to$ E $\to$ C $\to$ B $\to$ A

Answer 1

Answer: (A)

D $\to$ C $\to$ E $\to$ B $\to$ A

Phytoplankton stage: In the initial stage of succession algal spores are brought in the body of water. The simple forms of life like bacteria, algae and many other aquatic plants (phytoplankton) and animals (zooplankton) floating in water are the pioneer colonizers. All these organisms add large amount of organic matter and nutrients due to their various life activities and after their death, they settle at the bottom of pond to form a layer of muck.

Submerged plant stage: The phytoplankton stage is followed by submerged plant stage. When a loose layer of mud is formed on the bottom of the pond, some rooted submerged hydrophytes begin to appear on the new substratum. These plants form tangled mass and have marked effects upon the habitat. When these plants die their remains are deposited at the bottom of the ponds or lakes. The eroded soil particles and other transported materials are also deposited at the bottom. This gradually raises the ho t the ponds and lakes up.

Free floating plant stage: When the depth of water reaches about 4 to 8 feet, the submerged vegetation starts disappearing from its original place and then the floating plants make their appearance gradually in that area. In the beginning the submerged and floating plants grow intermingled but in the course of time the submerged plants are replaced completely. Due to continuous interaction between plant communities and aquatic environment, the habitat becomes changed chemically as well as physically. More water and air borne soil and dead remains of plants are deposited at the bottom. Thus, the substratum rises up in vertical direction.

Reed-swamp stage: When the ponds and lakes become too shallow (water depth one to three feet) and the habitat is changed so much that it becomes less suited to the floating plants some other plants which are well adapted to new environment will then come in .Under these conditions, the floating plants start disappearing gradually and their places are occupied by amphibious plants which can live successfully in aquatic as well as aerial environment. Deposition of soil and plant debris at the bottom reduces the depth of water and makes the habitat less suitable for the pre-existing plants. They bring about reactions by which the habitat becomes less suitable for most of the existing species, and consequently new successional step follows.

Marsh-meadow stage: The filling process finally results in a marshy soil which may be too dry for the plants of pre-existing community. Now the plants well adapted to new habitat begin to appear in the pre-existing community in mixed state. As these plants grow most luxuriantly in the marshes, they modify the habitats in several ways. They absorb and transpire a large quantity of water and also catch and accumulate plant debris and wind and water borne soil particles. Consequently a dry habitat results which may be totally unfit for the growth of normal hydrophytes. Gradually the mesophytes start appearing and after some time the sedge vegetation is totally replaced by them.

So the correct option is 'D $\to$ C $\to$ E $\to$ B $\to$ A'.