CORAL COLOR AND REPRODUCTION

How do corals get their color?

Most coral polyps have clear bodies. Their skeletons are white, like human bones. They generally get their color from the zooxanthellae that live inside their tissues. Several million zooxanthellae live in just one square inch of coral and produce pigments. These pigments are visible through the clear body of the polyp and give the coral its beautiful color.

How do corals reproduce?

Coral reproductive methods vary, depending on the species. Some species such as brain and star corals are hermaphrodites, meaning they produce both sperm and eggs at the same time. Other corals, such as Elkhorn and boulder corals, are gonochoric, meaning that they produce single-sex colonies. In these species, all of the polyps in one colony produce only sperm and all of the polyps in another colony produce only eggs.

Coral larvae are formed in two different ways. The larvae are either fertilized within the body of a polyp or outside the polyp's body in the water. Fertilization of an egg within the body of a coral polyp is achieved from sperm that is released through the mouth of another polyp. The sperm and egg merge and form a planula larva, which matures inside the body of its mother. When the larva is ready, it is "spit" into the water through the mouth of its mother. Other species of coral reproduce by ejecting large quantities of eggs and sperm into the surrounding water.When this happens, the eggs and sperm fertilize in the water.

This process is called coral spawning. In some areas, mass coral spawning events occur on one night a year and scientists can predict exactly when this will happen. Trillions of eggs and sperm are simultaneously released into the water in one of the most astounding acts of synchronicity in the natural world!

Once in the sea, larvae are naturally attracted to the light. They swim to the surface of the ocean, where they remain for days or even weeks. If predators do not eat the larvae during this time, they fall back to the ocean floor and attach themselves to a hard surface.

An attached planula metamorphasizes into a coral polyp and begins to grow and divide itself in half, making exact genetic copies of itself. As more and more polyps are added, a coral colony develops. Eventually the coral colony becomes mature, begins reproducing and the cycle of life continues!