Some corals eat zooplankton (tiny drifting animals) or small fishes. Others consume organic debris. Many reef- building corals derive their nutrition from zooxanthellae.
Method of Eating
Coral polyps are generally nocturnal feeders. At night, they extend their tentacles to capture food with the aid of nematocysts. Some corals secret films or strands of mucus to collect fine organic particles. In reef-building corals, mobile filaments originating from the stomach cavity can capture larger food particles. These filaments are also capable of digestion.
The stomach cavities of colonial corals are interconnected. Food obtained by one polyp can be passed to other polyps in the colony.
A polyp excretes solid wastes through its mouth.