Corals are the architects and builders of the massive structures that form the bulk of the coral reef. Each reef began from a single coral polyp (an animal!) that settled down on the seafloor of shallow waters, and began to grow.

The basic unit of a coral is a polyp. It is a tubular animal with a ring of tentacles surrounding its mouth, which is located right smack in the center. It grows by budding off neighbours, which settles down and does the same, until there is an entire colony. These polyps build a cup shape skeleton around themselves for protection, and the colony grows with the skeleton into branches, coulders, shelves or pillars amongst others.



After a long enough time, the colony dies off. New colonies take over the dead skeletons as a base to grow on, and when they die another colony will. Eventually there is a build up of large mounts of calcarous matter, and you will obtain a thin mantle of living polyps covering an enormous stony mass, which are the corals you see



Corals under ideal situations will grow and grow and grow everywhere and every size imaginable. However, nature is rather harsh, and only the fittest will survive. Waves pound against the corals, tidal ebb and flow reduce coral skeletons to sand, predators feed on the polyps and large amounts of freshwater from storms kill off corals on shallow waters. Furthermore, zooxanthallae living in the tissues of corals require sunlight and certain temperatures, limiting corals to depth of less than 30++ metres and geographic distributions of between latitudes 25N and 25S.(the warmer areas. there are reefs in Japan too, actually, even though it's rather cold over there)

The growing of corals can lead to different kinds of reefs, as shown below:



Reefs around Singapore, Malaysia and the philipines are fringing reefs

Corals and their reefs also support a HUGE ecosystem, and are one of the most beautiful places on Earth. While reefs are damaged from natural events, the most serious threat comes from humans. Coral reefs are exploited for food, trophies, building materials and so on. Healthy coral reefs are exotic and beautiful, supporting unbelievable amounts of yummy seafood and other resources, and shields us mortals from the terrors of tsunamis.

Read our other articles (click on the links on the right side) to learn more about the reefs and how people enjoy, threaten and save them (:

References:
1) Henrey, L.. Reefs and Builders, In: Coral Reefs of Malaysia and Singapore. 1982, The Print House Pte Ltd. pp 3 - 10
2) Wood, E. M.. Introduction, In: Corals of the World. 1983, T.F.H Publications, Inc., Ltd. pp 11 - 25
All pictures were sponsored by Ms Karenne Tun and Ms Angie Seow
(Except the last one. That one is from www.geology.uprm.edu)