Coral reefs need time, special habitat and climate to develop

BANDA, Maluku (JP): A coral reef takes thousands, even millions, of years to develop.

Coral reefs are found only in oceanic waters having the right natural conditions: an average temperature between 20 and 30 degrees Celsius, a salinity between 30 and 36 parts per thousand, a depth of not more than 50 meters, abundant sunlight, just the right amount of wave action, good water circulation and no freshwater runoff or sedimentation.

Reef-producing coral "animals" have a distinct and indispensable symbiotic relationship with a type of algae "plant" known as zooxanthellae.

The algae provides oxygen and nutrients and at the same time receives carbon dioxide from the coral. It is also responsible for the coral's calcium depositions.

Reefs are actually the skeletons of millions of individual, calcium carbonate-producing corals. The calcium carbonate is secreted by the coral as a waste product.

Although corals make up most of the reef, in many cases other calcium-secreting marine organisms, such as calcareous algae, also help to build it up.

Only after thousands or millions of years of complicated processes, where layer after layer of limestone builds up, can a fully-fledged reef finally form.

There are three major types of reefs: fringing reefs, barrier reefs and atolls. Each of them, to a certain extent, reflect part of a natural evolution.

A fringing reef, for instance, is located close to the shore. As it grows seaward and farther away from shore, a widening channel develops between the shore and the reef.

As the channel becomes wider and finally forms into a lagoon or a strait, the once-fringing reef becomes a barrier reef.

If the fringing reef began around an island, and in the process of becoming a barrier reef it was followed by the sinking of the island, then an atoll, or "reef island" would form.

As the reef continues to grow upwards, towards the sea surface and the island to sink downwards, in the end what would be left would be the perfect ring of an atoll with a shallow lagoon -- the former island -- in the middle.

English naturalist Charles Darwin was the first to come up with the theory, which he established in 1842, on the formation of an atoll. To this day it is still the dominating theory followed by most scientists.(pwn)