Coral reefs have a high species diversity with recent estimates indicating over 100,000 species. They are very beautiful places with a wide variety of corals such as coral domes, like the huge brain coral,(picture of brain coral) branches, fans, antlers and organ pipes all coming in a huge array of colours. Living in and around the corals are millions of fish and other animals, all dependent on the coral reef and each other for their existence.
Coral reefs are the largest structures built by an animal on the planet, humans included. They are thousands of miles long and weigh billions of tons.
The earliest reefs developed two billion years ago in the mid- to late Precambrian era. These reefs were built by colonies of calcareous algae, not corals. Corals, sponges, bryozoans, and calcareous algae enhanced the growing reef community in the Paleozoic era, 245 to 570 million years ago. During this era, natural environmental changes led to periodic reef demise. Hard corals developed into the prominent reef builders during the Mesozoic era, 65 to 245 million years ago. Coral reefs flourished until a devastating demise at the end of the era, when many coral families disappeared. The species of corals that made up the reefs of the Tertiary period, 2 to 65 million years ago, were similar to today's species.