Coral reefs are underwater structures made from calcium carbonate secreted by corals. Corals are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster the groups. Coral reefs flourish even though they are surrounded by ocean waters that provide nutrients. They are most commonly found at shallow depths in tropical waters, but deep water and cold water corals also exist on smaller scales in other areas.
Mangroves are tropical trees and shrubs that grow in inter tidal areas. They can also refer to the forest communities with their associated microorganisms(bacteria, fungi, algae) and fauna(crabs, shrimps and fish).Because they are exposed to extreme environmental factors of high salinity, alternating water saturation and desiccation, and anaerobic substrates. Mangroves is the only species of tree which flourishes in sea water. Coral reef and mangrove is very important to us so we need to nourish and take care of it. Because if this two will destroy we are the one who will suffer.
Hope this will help ;)