英语听力：自然百科 大堡礁：自然奇迹—3（在线收听）

 They respond to touch, temperature, currents, and the cycles of the sun and the moon. And their tiny movements combined to give each colony a rhythm of its own.The polyps can't build the reef alone. For this, they need parterners that are even smaller. Within each polyp's tentacles are millions of tiny brown dots. Each is a microscopic plant, which transform sunlight into food and energy for the corals. It's a miraculous parternship that allows the corals to turn the minerals in the water into limestone, building their stony skeletons. In this way, each colony grows. If we were able to watch a reef over several years, we'd see a continuely growing marine metropolis. Its intricate architecture provides homes for thousands of creatures.