The Red Sea is the continuation of the huge fault that first split the continent of Africa, and in so doing created the African Rift Valley before extending northwards to produce the Red Sea and the Gulfs of Aqaba and Suez.
The Red Sea reefs are among the most beautifully developed in the world and contain a wide range of coral species. Corals have been amazingly successful in transforming sterile environments below the water into a thriving ecosystem.
The word coral is applied to a range of different animals in a group known as the coelenterata.
The coral animals, or polyps, actually create the reef. Each polyp is like a short hollow tube with the base sitting on, or in, its limestone skeleton, and with a mouth at the top surrounded by tentacles. They range in size from less than a millimetre to several centimetres in diameter. The tentacles are armed with small stinging cells which fire out barbed darts to paralyse and capture plankton drifting by in the currents.
However, the polyp needs more food to sustain itself, which must come from another source. Within their tissues they contain millions of single-cell plants known as zooxanthellae. These plants, safely protected inside the tissues of the polyp, are able to photosynthesise using the energy of the sun to convert carbon dioxide and water into carbohydrates and oxygen. It is the partnership between the polyp and these tiny single celled plants that is the key to the building of these great structures that are known as coral reefs. This symbiotic relationship explains why reefs grow where they do – in shallow, clear seas – and rarely below a depth of 40m, for without sunlight, the zooanthellae can not perform.
The coral polyps supply the zooanthellae with carbon dioxide and this single cell plant then uses the sunlight to convert this, together with carbon dioxide from seawater and their own waste products into oxygen and carbohydrates.
The excess carbohydrates are taken up by the coral polyp and used to its advantage. Carbon is used to make limestone or calcium carbonate, a process known as calcification, so building the stony skeleton in which the polyp lives.
Coral reefs have existed for 450 million years making them probably the oldest ecosystems on the planet. The reefs are also some of the largest structures – made by life on earth.