Read the text and translate. Be ready to discuss.

    Coral reefs represent some of the oldest and most complex communities of plants and animals on Earth. About 200–400 million years old, they cover about 231,660 600,000 km2 worldwide. (The most popular reefs range from 5,000–10,000 years old.) Reefs are shallow water areas that create abundant habitat for marine organisms. Reefs can be formed by some species of worm, oysters, cyanobacteria, and algae. Engineers also create artificial reefs by sinking large machinery in shallow waters. However, the majority of reefs in the ocean result from the accumulation of calcium carbonate skeletons of tiny invertebrates called corals.

Corals are invertebrates, classified in the phylum Cnidaria. They are related to jellyfish and sea anemones. Reef-building corals are generally colonial, growing in clusters. Each individual has a shape similar to a flower: a cuplike body with tentacles in the place of petals. Within the center of the tentacles is a structure that serves both as a mouth for ingesting small plankton food particles as well as an excretory structure. Coral secrete a hard, cementlike substance called aragonite that makes up a skeleton in which the coral live. As subsequent generations of coral lay layers of aragonite on top of older skeletons, a reef is formed. Corals are found in most of the oceans of the world, in deep as well as shallow seas and temperate as well as tropical waters. But corals are most abundant and diverse in relatively shallow tropical waters, where they have adapted to the constant temperatures provided by these waters. The reef-forming corals, or hermatypic corals, have their highest diversity in the Indian and Pacific Oceans, where over 700 speciesare found. By contrast, the Atlantic Ocean  provides the habitat for less than 40 species. Other physical constraints needed for the success of these invertebrate communities are clear water, a firm substrate, high salinity, and sunlight. Clear water and sunlight are required for the symbiotic unicellular plants that live in the surface tissues of the coral polyps. This intimate plant-animal association benefits both participants. Corals obtain oxygen directly from the plants and avoid having to excrete nitrogenous and phosphate waste products because these are absorbed directly as nutrients by the plants. Respiration by the coral additionally provides carbon dioxide   to these plants to be used in the photosynthetic process.

    The skeletons of hermatypic coral play a major role in the formation of coral reefs, but contributions to reef structure, in the form of calcium carbonate, come from a variety of other oceanic species. Among these are red algae, green algae, foraminifers, mollusk shells, sea urchins, and the exoskeletons of many other reef-dwelling invertebrates. This limestone infrastructure provides the stabilityneeded, not only to support and protect the delicate tissues of the coral polyps themselves, but also to withstand the constant wave action generated in the shallow, near-shore waters of the marine ecosystem.

    There are essentially three types of coral reefs. These categories are fringing reefs, barrier reefs, and atolls. Fringing reefs form borders along the shoreline. Some of the reefs found in the Hawaiian Islands are fringing reefs. Barrier reefs also parallel the shoreline but are found further offshore and are separated from the coast by a lagoon. The best example of this type of reef is the Great Barrier Reefoff the coast of Australia. Because the coral colonies form an interwoven network of organisms from one end of the reef to the other, this is the largest individual biological feature on earth.

    There is the tremendous diversity of marine life found  in, on, and around coral reefs. These highly productive marine ecosystems may contain over 3,000 species of fish, shellfish, and other invertebrates. About 33% of all of the fishes of the world live and depend on coral reefs. This tremendous diversity provides for a huge commercial fishery in countries such as the Philippines and Indonesia.

Even with their calcium carbonate skeleton and exquisite beauty, coral reefs are being degraded and destroyed daily, not only by natural events such as constant wave action and storm surges, but, more importantly, by the actions of man. Of the 109 countries that have coral reef formations within their territorial waters, 90 are losing them because of man-induced environmental degradation. Most is the result of physical abuse or pollutionwhich alters the narrow range of physical and chemical parameters necessary for the coral, or their plant symbionts, to remain viable and thrive. Today, 10% of the world's coral reefs are completely degraded, 30% have reached a critical stage.

Tourism and recreationare inadvertently degrading coral reefs throughout the world as well. Coral is being destroyed by the propellers of recreational boats as well as divers who unintentionally step on coral heads, thus breaking them to pieces, and degrading the very structure of the ecosystem they came to see. Many of the reefs undergoing this degradation are sections that have been set aside for protection.