Why are coral reefs biologically valuable? how are they being degraded by human impact? what is causing the disappearance of mangrove forests and salt marshes

The coral reefs, mangrove forest, and salt marshes are disappearing due to pollution, over exploitation by humans, and climate change.

Explanation:

Corals are aquatic animals. They form calcium carbonate deposits in the shallow seawater which becomes coral reefs. The corals feed on bacteria, algae. The coral reef provides a microenvironment for many aquatic fishes, plants, and animals. The coral reef acts as the keystone species of the aquatic habitat. That's why they are important for the survival of different aquatic life. The human activities like overfishing, marine pollution causes the degradation of coral reefs. The pollution kills many algae, bacteria, which are the foods of corals. Therefore, they die.  

The mangrove and salt marshes are present near the coast. They live in saline waters. Mangrove provides a protective environment by preventing sea tides, home for many organisms.  

The salt marshes are formed due to the accumulation of sea salts, and soils in the coastlines. They are seen also at river banks. The salt marshes are provided with grasses. It helps in soil fertility and provides habitat to different organisms.  

Both the salt marshes and mangroves forest destroys by over-cultivation, aquaculture, and industrialization near the coast. The construction of dams also damages the mangrove and salt marshes. Mangroves are cut down for timber, fodder purposes. Pollution and climate change also the major cause of the disappearance of this ecosystem.

it has one origin of replication, but it proceeds in two directions - d)

who knows

explanation: