Dear student,
Coral comes under the phylum Cnidaria, these have the skeleton composed of calcium carbonate which deposits in huge amount with time and forms coral reefs. These coral reefs are very beneficial for mantaining the marine ecosystem and providing the habitat for certain fishes. These are also fed up by certain fishes like parrotfish. So, being one of the very useful structures for providing the habitat and acting as food, these are of quite significance in the sea.
Regards