Answer :
well u need 2 remember coral is a plant and still needs sun and other organisms 2 live, and shallow water has both sun light and many other organisms.
Corals are the important part of marine ecosystems. They are found in both deep water and shallow water. However, coral reef are found in shallow water. The environment factor on which coral reef is depends is the presence of sunlight. In shallow water where sunlight can reach because corals depend on algae zooxanthellae. These algae grow inside them and provide oxygen for them through photosynthesis. Besides coral need clear warm water to grow which is present in the shallow region of an ocean.