The formation of coral reefs is the result of long-term accumulation and deposition of calcium on reefs by reef-building corals and other reef-building organisms. For a long time, people have always thought that corals live by catching animal food. They decompose and absorb food and produce reef-forming calcium. It is found that there is a unicellular algae called Chrysophyta in coral. Insect yellow algae can not only provide nutrition for corals, but also produce oxygen necessary for corals to survive. Insect yellow algae can also promote the formation of coral bones and accelerate the formation process of coral reefs. Carbon dioxide is released during the metabolism of zooxanthellae. Carbon dioxide dissolves in water to produce carbonate ions, and calcium carbonate synthesized by carbonate ions and calcium ions in corals is the main component of coral bones. In the long geological era, coral reefs have formed many different shapes of islands and coral reefs. Coral reefs can be divided into shore reefs, barrier reefs, atolls (lagoons), platform reefs and point reefs according to their position in the ocean and the shape of reefs.

Coral is distributed in warm ocean currents, at the bottom of shallow water, which is the masterpiece of a coelenterate called coral. They have bones in their bodies and many corals live together. The coral we see is actually the skeleton of coral. Because most ectodermal cells of coral secrete bones, which are formed by keratin or calcium secreted by ectoderm, there are monomers and groups in common six-release corals, and each insect is similar to an anemone. Calcareous substances secreted by ectodermal cells at the bottom of its basal plate and body wall accumulate in the bottom, side and diaphragm of insect body, as if every insect body is sitting on a lime seat, which is called coral seat. The ectoderm of the same part of colony coral can secrete calcium because the colony shape of coral is different. So their bones are stacked together in different shapes. For example, the bones of antler coral are dendritic, while the bones of brain coral are massive. They are delicious in color and can be used as high-grade decorations. Coral is very easy to reproduce. They can reproduce and grow on dead coral bones, just like corals grow taller in a year.