Coral reefs are built up by limestone skeletons of coral, and are found only in tropical saltwater where bright sunlight can penetrate, because corals cannot exist without the symbiotic algae that live in coral tissues and require sunlight for photosynthesis.
- coral [ˈkɔrəl] n.珊瑚
- reef [ri:f] n.礁, 暗礁
- build up [bild - ʌp] v. 堆积
- limestone [ˈlaimˌstəun] n.石灰岩
- skeleton [ˈskelitn] n.骨骼
- tropical [ˈtrɔpikəl] adj.热带的
- saltwater [ˈsɔ:ltˌwɔ:tə] n. 盐水
- penetrate [ˈpenitreit] v.穿透
- symbiotic [ˌsimbaiˈɔtik] adj.共生的
- algae [ˈældʒi:] n.藻类， 海藻(singular: alga [ˈælɡə])
- tissue [ˈtisju:] n. 组织
- photosynthesis [ˌfəutəuˈsinθəsis] n.光合作用
