Magazine article UNESCO Courier

Coral: Taking the Pulse of the Planet

Magazine article UNESCO Courier

Coral: Taking the Pulse of the Planet

Article excerpt

CORAL reefs are one of the wonders of the world. And one of its most useful. This is how Professor Jean Jaubert, director of the European Oceanological Observatory (l'Observatoire Oceanologique Europeen) at the Monaco Museum, sees them: "Coral reefs are the marine equivalent of primeval forests and, as home to an exceptionally dense and diversified plant and animal life, help to maintain the major balances of the planet." Roughly 400 million years ago they existed in almost every ocean. Today they form the coastlines of 105 (for the most part developing) countries and reefs extending from the surface down to 30 metres cover some 600,000 [km.sup.2].

They are mostly found in the world's warm and temperate waters, in the Indian Ocean, the Caribbean, Polynesia, Australia, usually on the eastern sides of continents which protect them from the prevailing west winds. There are three main types of coral reef: fringing reefs, near coasts; barrier reefs, separated from the coast by a deep lagoon, the best known example being Australia's Great Barrier Reef; and atolls, rings of reefs around lagoons, a typical configuration of many Pacific islands and the kind of thing holidaymakers dream of. As well as being beautiful, coral is also an indicator of marine pollution and variations in global climate. Scientists have noticed that, just as the age of a tree can be read in the concentric circles of a crosscut, coral shows its age in its skeleton and also the traces of any aggression of which it may have been a victim over the years.

ANIMAL, VEGETABLE OR MINERAL?

For many years researchers were stumped as to whether coral was animal, vegetable or mineral. The mystery was solved in the mid-eighteenth century by a French surgeon, Jean-Andre Peysonnel, and an Englishman, John Ellis, who declared coral to be animal! Behind a rock-like appearance conferred by its aragonite skeletons are hidden carnivorous polyps of the coelenterate taxon (in Greek, coelenteron means "hollow tube"). There are from 2,500 to 2,600 species (not counting soft corals without skeletons), 700 of which are found in the Indo-Pacific region alone.

Corals are small animals about a centimetre long, consisting of a cylindrical digestive tube with a mouth at one end surrounded by tentacles armed with stinging cells for capturing plankton. During the day these tentacles are folded inside the digestive sac. Like the big carnivores, they only hunt at night, feeding on plankton, small shellfish and larvae. They evacuate calcium carbonate which enables them to produce the outer skeleton within which they shelter. They live symbiotically with microscopic single-celled algae known as zooxanthellae, that lodge in their tissue (up to 7,000 algae per [mm.sup.2]). The algae process the nitrates, phosphates and carbon dioxide (C[O.sub.2]) produced in the coral polyp. As a result of photosynthesis, which is only possible as far down as sunlight can penetrate, i.e. some 50 metres, they generate oxygen and organic compounds which the polyps can use. They may also help the polyp lay down calcium carbonate. Thanks to its algae, living coral is rainbow-coloured, yellow, blue, purple, orange, brown or even fluorescent (it should not be confused with red coral, used in jewellery, which is not within the scope of this article). When the symbiotic algae leave it, the coral dies and goes white.

More than a century ago Charles Darwin wondered why the Pacific Ocean is almost a desert although its atolls are luxuriant "oases" where coral and fish abound. In 1974 three oceanographers, Yves Magnier, Francois Rougerie and Bruno Wauthy, working on behalf of the French Polynesian Fisheries Service under the aegis of UNESCO'S Man and the Biosphere Programme (MAB), studied the physical-chemical balance of the Takapoto atoll lagoon in the Tuamotu Islands. The food that sustained life in the lagoon clearly came from deep water. But how, since the deep water is cold and does not mix with the warm surface water? …

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