The correct option is C Coral reefs
Species diversity is greatest in the tropics, particularly in tropical forests and coral reefs. Coral reefs are believed to have the greatest biodiversity. Coral reefs are the most productive ecosystem and form the most diverse part of costal region providing a home to fish molluscs, crustaceans sponges, cnidarians, etc.
Mangroves, found in coastal regions usually have plants growing in swampy and saline water. Deserts have mostly xerophytic species and alpine meadows are related to high altitudes and do not show much tree growth.