Consider the Coral Reefs of Ras Mohamed: they grow only on the beach or shallow bottoms and nowhere else (corals don't float in the middle of the Sea and won't grow on beach sand out of water). So many species of fish and crustaceans (pronounced crust-a-shans and is a single name for all types for lobsters, shrimps, and their marine look-alikes) live on the corals and call it their habitat. They just cannot leave it because there is where all the fun and life and food for them. This place (Habitat) together with all its creatures are called the Ecosystem of Coral Reefs.