Coral is one of the ocean's most beautiful and mysterious inhabitants. Coral reefs are entirely self-supporting ecosystems and are the largest living structures on our entire planet. All kinds of exciting species of fish find shelter in the reefs coral build; without it, many of these species would not be able to survive. Coral itself is actually a living organism that eats, breathes, and even reproduces.
Coral, like all other living things, gets old and dies. In order for it to be replaced by new coral, it must reproduce during it's lifetime. There are two ways that it can reproduce: sexually and asexually.
Sexual reproduction requires a male's sperm to fertilize the eggs of a female. The eggs can be fertilized either in the water (external) or while they are still in the female (internal). During external fertilization, the sperm and egg are released into the water by both parents; when they meet, they sink down to the surface of the coral and begin to grow. Internal fertilization means that the female will hold the eggs inside for a period of days or weeks until they are developed enough to be out on their own.
Once the sperm and the egg have met, they form into a small larva. The little larvae can swim, but not very well. When they're ready to settle down, they sink to the surface of the existing coral and find their own piece of real estate. They attach themselves and begin forming the base of their skeleton, and they continue to grow in that spot for the rest of their lives.
Some types of coral are hermaphroditic, which means that they have both male and female cells. Hermaphroditic creatures can reproduce asexually because they already have the sperm and egg recipe that they need. Another way that coral can asexually reproduce is by budding, which is the formation of polyps on an adult body. These polyps are like small clones of the adult, and the process is similar to what we know as cell division (except it's a lot more complicated).
By the time coral has matured, it's fully equipped with either male or female reproductive cells or is hermaphroditic (has both male and female cells). Each coral polyp can reproduce throughout it's entire adult life cycle, which can last up to three years; however, the chain of life is constantly in motion on a coral reef - some reefs, like the Great Barrier Reef in Australia, have been around for over 500,000 years.