Energy flow
Most species of coral have a mutualistic relationship with the algae zooxanthellae. Zooxanthellae process polyp waste before they are excreted so that no nutrients go to waste. The zooxanthellae uses the nutrients to perform photosynthesis and create oxygen and organic compounds that are used by the coral as well. In return the coral provides the zooxanthellae with shelter inside its own cells. Also, zooxanthellae produce pigments, which give coral its color.
Coral reefs are also important in the energy flow in other ecosystems. One of the ecosystems in which coral reefs play a major part are mangroves, which are forests in swampy areas near the coastline. Mangroves protect the coastline from severe storms, floods, and erosion. They are feeding grounds for many commercial fish, shellfish, turtles, and dugong; and they help to purify water. During storms, many of the organisms that live in the mangroves will flee to the coral reefs for safety. Organisms that live in the coral reef often spawn and grow up in the mangroves before living in the reefs because of the favorable conditions in the mangroves. Coral reefs protect the mangroves from high wave action and create lagoons favorable for mangrove growth.
Seagrass beds play a huge role in reef development. Coral reefs may often grow in the seagrass beds. Seagrass absorbs the excess nutrients and mixes fresh water with salt water in order to improve water quality for the coral. They also act as buffers for sediment runoff from the land. Coral reef organisms often lay there eggs here as well.