Coral reefs are, in short, underwater structures made of calcium carbonate secreted by corals. Coral reefs begin to form when free-swimming coral larvae attach to submerged rocks or other hard surfaces along islands or continents. These larvae are polyps that produce calcium carbonate, which turns into a hard exoskeleton that provides protection and support to the polyp's body. As a polyp grows, it continues to secrete calcium carbonate, leading to continued growth of the reef. Each polyp bonds with other polyps to form the reef. Most of a coral reef is actually made up of dead skeletons. The top layer is usually the only part of the structure that is living. The upper layer is mainly made up of soft corals. The polyps work in symbiosis with the coralline algae which also constitute an important part of the reef. Algae deposits limestone in layers on the reef. Limestone strengthens it and protects it from sea waves. As corals expand and form reefs, they can take on three different forms: Fringing reefs, the most common, project seaward directly from the shore , forming borders along the shore and around the islands. Barrier reefs also line the shores, but at a greater distance. They are separated from land by a deep, open water lagoon. If a fringing reef forms around a volcanic island that subsides completely below sea level while the coral continues to grow upward and an atoll has formed. Atolls are generally circular with a central lagoon as a coral reef. Parts of the reef may appear as islands and openings in the reef provide access to the central lagoon. Most coral reefs are between 5,000 and 10,000 years old and grow very slowly. On average, they grow about an inch... middle of paper ...... dumped into the oceans, many off those coral reefs damaged in one way or another. We must keep in mind that most of the waste we produce will sooner or later reach the oceans. Many of these wastes, such as agrochemicals, sewage and oil pollution, poison the reefs. Sewage and runoff from agriculture increase nitrogen levels in seawater, causing algae blooms that cover corals and cut them off from sunlight. Mining, agriculture, logging, and construction cause erosion, which leads to increased sediment in rivers. This will also cover or “choke” the corals, with the destruction of mangrove forests exacerbating this problem. Global warming has already led to increased levels of coral bleaching, as corlas cannot survive if water temperatures are too high. Is this the end of an already stressed ecosystem?