Coral reefs are one of the most biodiverse ecosystems in the world, are also the marine environments characterized by the greatest number of species which present a high diversity of shapes and colors. They are distributed in inter-tropical, because, in order to exist, they require temperatures "high" water should never be less than 20 ° C or so. They are living structures, they are in fact better or "constructed" by some particular types of corals ( Madrepores ) said just reef-building, corals or manufacturers can consolidate and secrete a limestone skeleton strong and able to withstand the waves, sometimes very strong. The existence of these corals, which are almost all colonial polyps, is due to the symbiosis between them and some unicellular algae, the zooxanthellae , in a very close association called symbiosis. The reef-building corals, in fact, in the absence of such unicellular algae would not be able to grow, reproduce and secrete their calcareous skeleton, could not even survive on their own algae secrete some sugars are crucial for growth of the colony. Given their close dependence on symbiotic algae, corals can not survive beyond certain depth, as the light would fail to reach the algae, preventing the photosynthetic process and making them die, thus blocking the formation of limestone skeleton. This depth depends on the transparency (or vice versa turbidity) of water, but generally a limit of few tens of meters in conditions of perfect transparency (water corals need to grow as transparent as possible). The Great Barrier Reef Australian (the north-eastern Australia, off the coast of Queensland) , with its 2,300 km, is the structure largest living land. Despite the poverty of nutrients present in its waters, it has a high number of species of marine organisms belonging to very different groups with each other and about a third of the entire fish fauna of the oceans is concentrated right here (including a large number of species shark). In recent years, increasing temperatures is happening on a global scale, together with other secondary factors, are helping to destroy the delicate balance between symbiotic corals and their small algae, thus requiring the expulsion of the coral seaweed . The coral die and he will remain only its skeleton of limestone, a phenomenon known as coral bleaching. And 'good remember that corals living in areas of the planet where the temperature is already high for her, and then a slight rise in temperature can be fatal to a sensitive ecosystem such as coral reefs. The problem of raising global temperatures, although the principal does not seem to be the only one. Another problem that may prevent the normal development of coral reefs could be caused by dirty water of nutrients from rivers that receive water "fertilizer" from the farmlands of intensive agriculture. The excess of these nutrients favors the formation of a "carpet" algae that covers the coral, leading to death and preventing the recolonization by new larvae from not contaminated by neighboring sites. Another problem that occurs on these two is increasing acidification of seawater by the increase of carbon dioxide in the air that you are having in recent decades. The acidification makes it difficult, if not impossible, the construction of the limestone skeleton by the coral polyps. According to some researchers who have conducted extensive studies on these cases, in about 40 years it will inevitably lead to total collapse of this beautiful marine environment and return to the initial state will be very difficult, perhaps impossible.
In a beautiful photo aerial image of the Great Barrier Reef in Australia.
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