How was the beautiful coral reef coast formed?

Produced by: Science Popularization China

Author: Blue Ocean Team

Producer: China Science Expo

Under the azure sea, colorful "stone flowers" are in full bloom. Colorful tropical fish happily shuttle back and forth among the stone flowers, swimming up and down. Clusters of red, green and white "stone flowers" complement the bright red and purple fish.

(Photo source: Veer Gallery)

This is not only a beautiful picture, but also a tribute to marine life. People are not unfamiliar with tropical fish. Although they may not have been to tropical oceans, they can appreciate the gorgeous beauty of tropical fish in their home fish tanks.

However, not many people have seen the beauty of the "stone flowers" on the seabed. The origin of the "stone flowers" is also unfamiliar to many people. Where do these beautiful "stone flowers" come from?

What? The beautiful "stone flowers" are actually made of "insects"?

It turns out that the scientific name of what we call "stone flowers" is coral. The blue, blue-green, and red seaweed in modern oceans play an important role in the formation of corals. But the dominant role is played by coral polyps.

Coral polyps are a type of coelenterate in the ocean (no internal organs, only one cavity in the body), which can prey on tiny plankton in the ocean. During their growth, they can absorb calcium and carbon dioxide from seawater, and then secrete limestone to form their own shells. Each individual coral polyp is only the size of a grain of rice. They live together, metabolize from generation to generation, grow and reproduce, and constantly secrete limestone to stick together.

Soft coral

(Photo source: Veer Gallery)

These limestones were compacted and petrified to form many islands and reefs in the tropical oceans of the world today. Even the entire territory of some island countries in the oceans was built by tiny coral polyps (including some algae that can secrete limestone) over millions of years. Therefore, people call coral polyps the greatest architects in the ocean.

Although corals look common, they are actually quite delicate!

Corals have strict requirements for their growing environment. The most suitable seawater temperature for their growth must be above 20℃. They are very clean and cannot stand unclean seawater. They neither like salt nor fresh seawater, and require the salinity of seawater to be kept at around 35‰. They like fresh and sufficient oxygen in seawater. The depth of their growth does not exceed 40-60 meters. If the above conditions are not met, they will not be able to live. If the originally comfortable living environment deteriorates, they will fight to the death, with a spirit of "rather die in glory than live in disgrace".

(Photo source: Veer Gallery)

At the mouth of a river, there is no coral reef colony due to the intrusion of fresh water and silt. In a bay where the sea water is too calm, the coral colony grows very slowly and is dying due to insufficient oxygen. Since corals have strict requirements for growth conditions, they can only grow in tropical and subtropical seas that have the conditions they need, as well as in temperate areas affected by warm currents. Therefore, the coral growth boundary is mainly in the sea area between 28 degrees south latitude and 28 degrees north latitude on both sides of the equator.

There are different types of coral reefs

There are three types of coral reefs in modern oceans: reefs, barrier reefs and atolls.

Shore reefs grow along the coast of the continent and in the marginal areas around the islands. Their distribution width ranges from ten to one hundred meters. Their distribution range and shape are closely related to the underwater topography and water depth of the coast. In the early stages of their growth and development, shore reef corals are generally small in size, but they are distributed over a wide range. There are scattered coral shore reefs around Hainan Island in my country.

(Photo source: Veer Gallery)

Barrier reefs grow in the sea far from the shore. They surround the land like a castle, so they are called barrier reefs. There is a water area with a width of several kilometers to tens of kilometers between the barrier reef and the land. This water area is basically surrounded by coral reefs, so it is called a lagoon (lagoon originally refers to a shallow bay, which is closed into a lake by silt accumulation, but can be connected to the ocean at high tide). The water depth of the lagoon is generally tens of meters, and can reach hundreds of meters at most. The width of the barrier reef itself ranges from hundreds of meters to several kilometers. But it is completely continuous, and there are gaps in some places that connect the lagoon to the open sea. There are sometimes reefs in the lagoon. Ships sailing in the lagoon must be particularly careful, otherwise they will hit the reefs and sink.

(Photo source: Veer Gallery)

Atolls are similar to barrier reefs in distribution, but they do not grow around land or in the ocean close to land. They are generally a system of coral islands and reefs in the ocean. A fully developed atoll consists of reef rings around it, a diving lagoon in the middle, and several coral islands in the lagoon. The diameter of the reefs distributed like a ring ranges from a few kilometers to dozens of kilometers.

If you look down from a high-altitude airplane, the atoll is like a garland thrown into the blue sea, or a string of white jade pearl necklaces scattered on the sea surface, colorful and gorgeous. When the tide is high, the reefs are submerged under the water. Through the clear sea water, people can see the outline of the coral reefs hidden under the water. Because the water is shallow where the reefs grow, the waves will produce broken waves when they spread here. Looking from the sky, it forms a silvery-white ring.

Conclusion

Corals are not only beautiful scenery, but also protect the coastline. Not only that, their existence is also conducive to maintaining the diversity of marine life. You know, a coral reef can support up to 400 species of fish. There are tens of thousands of species living in the coral reef area, which can be said to be a veritable "undersea rainforest"!

Editor: Sun Chenyu