The less common purple, blue, and mauve colors found in some corals the coral makes itself. It is this relationship that allows shallow water corals to grow fast enough to build the enormous structures we call reefs. The zooxanthellae also provide much of the green, brown, and reddish colors that corals have. These single-celled algae photosynthesize and pass some of the food they make from the sun’s energy to their hosts, and in exchange the coral animal gives nutrients to the algae. Shallow water corals that live in warm water often have another source of food, the zooxanthellae (pronounced zo-o-zan-THELL-ee). Corals differ from sea anemones in their production of a mineral skeleton. Inside the body of the polyp are digestive and reproductive tissues. The tentacles have stinging cells, called nematocysts, that allow the coral polyp to capture small organisms that swim too close. The polyp is like a tin can open at just one end: the open end has a mouth surrounded by a ring of tentacles. ![]() The brownish-green specks are the zooxanthellae that most shallow, warm-water corals depend on for much of their food.Ĭorals are related to sea anemones, and they all share the same simple structure, the polyp. What Are Corals? Animal, Vegetable & Mineral In some places, reefs have been entirely destroyed, and in many places reefs today are a pale shadow of what they once were. Overfishing and destructive fishing, pollution, warming, changing ocean chemistry, and invasive species are all taking a huge toll. Unfortunately, people also pose the greatest threat to coral reefs. dollars each year, providing food, protection of shorelines, jobs based on tourism, and even medicines. dollars and perhaps as much as 172 billion U.S. ![]() The value of coral reefs has been estimated at 30 billion U.S. Because they are so diverse, coral reefs are often called the rainforests of the sea.Ĭoral reefs are also very important to people. This is a remarkable statistic when you consider that reefs cover just a tiny fraction (less than one percent) of the earth’s surface and less than two percent of the ocean bottom. They teem with life, with perhaps one-quarter of all ocean species depending on reefs for food and shelter. Coral reefs are the most diverse of all marine ecosystems.
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