The correct answer is Option 1: Both A and R are true, and R is the correct explanation of A.

Explanation:

Assertion (A) states that mangroves are very specialized forest ecosystems of tropical and subtropical regions bordering certain sea coasts. This statement is true. Mangroves are unique ecosystems found in coastal areas and estuaries, primarily in tropical and subtropical regions. They are characterized by the presence of salt-tolerant trees and other plant species that are adapted to survive in brackish water environments. Mangrove forests provide critical habitats for numerous plant and animal species, and they play a vital role in coastal ecology.

Reason (R) states that mangroves stabilize the shoreline and act as a bulwark against encroachments by the sea. This statement is also true and provides the correct explanation for Assertion (A). Mangrove forests have extensive root systems that help trap sediments and prevent erosion along the shoreline. The complex network of roots acts as a natural barrier, reducing the impact of waves and tidal forces. This function of mangroves helps to stabilize the coastline and protect against erosion and land loss caused by the sea. Mangroves also act as a buffer zone during storms, absorbing and dissipating wave energy, which helps protect inland areas from damage.

Additionally, mangrove ecosystems provide several other important ecological services. They serve as nurseries and breeding grounds for many fish and marine species, contributing to coastal fisheries and supporting local livelihoods. Mangroves also help to filter pollutants and improve water quality by absorbing excess nutrients and trapping sediments. Furthermore, they play a significant role in carbon sequestration, storing large amounts of carbon in their above-ground and below-ground biomass, which helps mitigate climate change impacts.

In conclusion, both Assertion (A) and Reason (R) are true, and Reason (R) provides a correct explanation for Assertion (A). Mangroves are specialized forest ecosystems found in tropical and subtropical regions bordering sea coasts. They stabilize the shoreline and act as a natural barrier against sea encroachments, among many other ecological functions and services they provide.