Correct Option (A):
Assertion (A) states that mangroves are very specialised forest ecosystems of tropical and sub-tropical regions bordering certain sea coasts. This statement is true. Mangroves are halophytic plants uniquely adapted to thrive in harsh intertidal zones, characterized by brackish water, tidal fluctuations, and anoxic (low-oxygen) soils. Their adaptations include specialized root systems (e.g., pneumatophores for respiration, prop roots for support) and mechanisms for salt exclusion or excretion, making them distinct and highly specialized ecosystems.
Reason (R) states that they stabilise the shoreline and act as bulwark against encroachments by the sea. This statement is also true. The dense, intricate root systems of mangroves trap sediments, which helps in land accretion and prevents coastal erosion. They also dissipate wave energy, acting as natural barriers that protect coastlines from storm surges, tsunamis, and the erosive forces of the sea, thereby preventing coastal encroachment.
Reason (R) is the correct explanation of Assertion (A). The protective and stabilising functions described in Reason (R) are a direct consequence and a defining characteristic of the specialised adaptations of mangroves mentioned in Assertion (A). Their unique ability to survive and flourish in dynamic coastal environments, coupled with their ecological role in coastal protection, underscores their specialised nature as an ecosystem.
Incorrect Options:
Option 2 is incorrect because Reason (R) directly explains a key aspect of why mangroves are considered specialised ecosystems. Their unique adaptations enable them to perform the crucial functions of shoreline stabilization and protection against sea encroachment, which are integral to their ecological distinctiveness.
Options 3 and 4 are incorrect because both Assertion (A) and Reason (R) are factually correct statements regarding mangrove ecosystems.