The growth rate of Corals varies depending on the type and the environment in which it lives, but they generally grow from a few centimeters to over 10cm per year.
There are several ways for Corals to grow .

• A "division" in which an individual creates clones and forms a colony
• This is a form of "sexual reproduction" in which eggs are fertilized by sperm through spawning, and the eggs attach to a new location to form a colony.

exists.
The spawning of sexually reproducing Corals, type 2, can be further divided into two types: ``spawning type'', which releases capsules containing sperm and eggs called bundles, and ``larval rearing type'', which fertilizes the eggs inside the Corals and releases the larvae that have developed into larvae.

Fertilized Corals are oval in shape and about 1mm in size, and in this state they are called "planula larvae." Planula larvae have cilia and can swim on their own.
The swimming period varies depending on the species, but it takes about 1 to 2 weeks for the coral to attach to rocks and other objects, and then after a few days it becomes what is called a "polyp." Once it becomes a polyp, it continues to make copies of itself, and then forms a skeleton made of calcium carbonate. Over a long period of time, it becomes a Corals like its parent.

In addition to the above-mentioned "sexual reproduction,"Corals also reproduce asexually, without using sperm or eggs. When a mature Corals breaks off due to waves or other creatures hitting it, the pieces attach to rocks and other objects and continue to grow until they reach their original size.
Our aquarium takes advantage of this growth pattern to cultivate and transplant Corals such as Bushy whipcoral and Acropora gracilis.

Spawning season varies by species, but most "broadcast-type"Corals spawn only once a year. They mature their eggs in preparation for spawning in accordance with seasonal changes in water temperature, and many species wait until the night around the full moon to spawn.
On the other hand, there are observations of "larval rearing" corals, which, although they are in the minority, release larvae every month throughout the year. The spawning methods and timing of Corals spawning vary in pattern depending on the type of Corals.

The planula larvae attach to a certain location and become polyps. After they grow into Corals, the Corals continue to divide and grow. Corals choose locations with the best conditions for them to grow, but they cannot generally move.
As each coral grows and gets bigger, it becomes a big obstacle for the corals to hide in the shadow of nearby Corals or bump into each other. Corals with stronger toxicity have an advantage in terms of survival in order to compete with the Corals next to them, while Corals with weaker toxicity may succumb to the toxicity of other Corals and become weaker.

Many species of Corals also have means of attack. For example, there are species of coral that have long, specialized tentacles called "sweeper tentacles." These "sweeper tentacles" extend out and swing back and forth, attacking nearby Corals with poison, which can be seen as a kind of weapon to create a better environment for the coral to live in.

Bleaching refers to the phenomenon in which the algae (zooxanthellae) with which Corals live symbiotically die due to various factors, causing the coral's skeleton to become visible and the entire body, which was previously colored, to turn white. The Corals is still alive immediately after bleaching, but since the symbiotic algae can no longer photosynthesize, the Corals itself cannot obtain energy and dies.
The main causes of bleaching include extreme differences in water temperature, light intensity, UV rays, salt content of seawater, etc. Furthermore, the current situation is one of crisis, with corals all over the world declining in numbers due to human activities (marine pollution, coastal development, overfishing, sand inflow due to deforestation and farmland development, drug inflow), mass outbreaks of crown-of-thorns Corals , which are said to eat Corals , and bleaching caused by high water temperatures due to global warming.

Furthermore, while the many typhoons that hit Okinawa Prefecture every year cause disasters and affect crops, they also work to lower the temperature of the ocean by stirring up the sea. Conversely, if there were no typhoons, the seawater temperature would remain high and the Corals would bleach, so typhoons can also be said to be a beneficial meteorological phenomenon for Corals.

Corals have a calcareous skeleton underneath their soft body. When Corals die, only the pure white calcareous skeleton remains, and this bone becomes brittle and weak. Over a long period of time, the remaining skeleton is broken down into pieces by the force of waves, forming the white sandy beach.

The broken Corals reefs are home to a variety of bacteria.
Bacteria have the ability to neutralize harmful substances, and the ocean water is purified as it passes through dead Corals with the force of the tides.