In the sea, simple plants, known as algae, are the most important organisms at the bottom of the food chain. More complex algal plants include seaweeds, which are an important diet for many fish. There are several kinds of algae including, coralline algae are a type of red algae that lay down skeletons of calcium carbonate and work with corals in building reefs and cementing the rubble together.
In addition to algae plants there are also mangroves, trees and shrubs that grow in the intertial zone between the land and the sea. The only plants that are actually submerged in the water are seagrasses.
Both seagrasses and mangroves are abundant and diverse in tropical waters. These plants are vital because they filter and hold the sediments in the water and thus keep the water in the coral reef clean and clear.
Link:
http://encarta.msn.com/encyclopedia_761572186_2/Coral_Reef.html
