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Coral reefs are immense calcium carbonate structures, built layer over layer on the tropical sea bottoms by great colonies of tiny micro-organisms. They are roughly parallel to the coasts of continents or surrounding the minor islands and able to form coral islands in their turn, when their upper parts frequently emerges from the seas. These flat islands, with their typical ring shape and a lagoon in their inside (where once there was a volcanic island, today disappeared) are well known as atolls.

Coral reefs are built up by the limestone exoskeleton of tiny polyps living in symbiosis with unicellular algae (Zooxanthellae) within their body.
The algae provide the polyps with the carbohydrates produced by their photosynthesis and receive in exchange from them minerals like P, Ca, Mg and others, necessary for their metabolism.

Every colony is formed by billions and billions of these polyps, gathered in branched, pillow-shaped or leaf-like structures. When they die, the skeletons of many species of corals form sediments and remain as a basis for the new polyps coming from the open sea, where their larvae have passed the first period of their life.

Together with corals, an impressive number of fish, molluscs, crustaceans and algae of all the possible colours and shapes live in a delicate relation of reciprocal dependence between predators and preys. This is surely the richest marine environment of the world or, better, it has been so far because the environmental damage made by human activities worldwide is really endangering coral reefs survival and their regeneration ability in many ways.

The researches made by many teams of marine biologists, zoologists, ecologists are more and more frequently recording the progressive damage and death of many coral reefs in all the world. Many are the causes, surely, not natural; in fact, excluding what directly and indirectly caused by man, no other present natural phenomenon or trend can explain the progressive death many coral reefs are suffering in the last 20-30 years. Once again, those who deny or consider not worrying the destructive impact of human activities on the environment who gives us life, simply don't know what they say.

1) Global warming

Corals can live within a narrow range of water temperature, not < 18-20 C and not > 27 C. Above this temperature, corals begin to have problems and this is just what is happening with the global warming caused by the greenhouse effect, no doubt caused by CO2 and CH4 released

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