Humanities › Geography The Largest Coral Reefs in the World Share Flipboard Email Print Daniel Osterkamp / Getty Images Geography Physical Geography Basics Political Geography Population Country Information Key Figures & Milestones Maps Urban Geography By Amanda Briney Geography Expert M.A., Geography, California State University - East Bay B.A., English and Geography, California State University - Sacramento Amanda Briney, M.A., is a professional geographer. She holds a Certificate of Advanced Study in Geographic Information Systems (GIS) from California State University. our editorial process Amanda Briney Updated December 02, 2019 Covering only about one percent of the ocean floor, reefs are home to an estimated 25 percent of the world's marine species, from fish to sponges. Nearly all of the world’s coral reefs, particularly the largest reefs, are located in the tropics. As you will read, the Great Barrier Reef is the largest in the world by both length and area. What Is a Coral Reef? A coral reef is a submerged oceanic structure made of many different polyps. Polyps are small marine invertebrates that are unable to move. These sessile or immobile creatures cluster with other corals to form colonies and bind themselves together to form a reef by secreting calcium carbonate. This hard substance is also found in many rocks and minerals. Corals and algae have a mutually beneficial or symbiotic relationship. Algae, which live protected in coral polyps, make much of the food consumed by a reef. Each sedentary animal that is part of a reef possesses a hard exoskeleton that contributes to its strength and rock-like appearance, but it is the algae beneath the surface that gives each polyp its color. Coral reefs vary greatly in size and type, but all are highly sensitive to changes in the water. Water properties such as temperature and chemical composition tend to dictate the health of a reef. Bleaching, the whitening and deterioration of a coral reef, occurs when the colorful algae that inhabit polyps leave their coral homes most often due to increasing water temperature and/or acidity. The World's Largest Coral Reefs The following is a list of the world’s nine largest coral reefs in order of size. As many barrier reefs are long ovals, most coral reefs are measured by length. The three last or smallest reefs from this list are measured by area due to their unusual shapes. 01 of 09 Great Barrier Reef Length: 1,553 miles (2,500 km) Location: The Coral Sea near Australia's coast The Great Barrier Reef Marine Park is a protected national park in Australia. The reef itself is large enough to be seen from outer space. This reef features 400 species of coral, 1500 species of fish, and 4000 species of mollusk. The Great Barrier Reef is valuable to the entire world because it harbors several near-extinct species of aquatic animals. 02 of 09 Red Sea Coral Reef Length: 1,180 miles (1,900 km) Location: The Red Sea near Israel, Egypt, and Djibouti The corals in the Red Sea, especially in the northernmost part found in the Gulf of Eilat or Aqaba, are more resilient than most. They are often studied for their ability to withstand high water temperatures. 03 of 09 New Caledonia Barrier Reef Length: 932 miles (1,500 km) Location: The Pacific Ocean near New Caledonia The diversity and beauty of the New Caledonia Barrier Reef earned it a place on the UNESCO World Heritage Sites list. This reef is even more diverse in species count, including threatened species, than the Great Barrier Reef. 04 of 09 The Mesoamerican Barrier Reef Length: 585 miles (943 km) Location: The Atlantic Ocean near Mexico, Belize, Guatemala, and Honduras The largest reef in the Western Hemisphere, the Mesoamerican Barrier Reef is also called the Great Mayan Reef and is part of a UNESCO site also containing the Belize Barrier Reef. This reef is home to 500 species of fish, including whale sharks, and 350 species of mollusk. 05 of 09 Florida Reef Length: 360 miles (579 km) Location: The Atlantic Ocean and Gulf of Mexico near Florida The Florida reef is the United States’ only coral reef. This reef is estimated to be worth $8.5 billion to the state’s economy but is rapidly disintegrating, faster than scientists estimated, due to ocean acidification. It extends into the Gulf of Mexico outside the boundaries of its home in the Florida Keys National Marine Sanctuary. 06 of 09 Andros Island Barrier Reef Length: 124 miles (200 km) Location: The Bahamas between the islands of Andros and Nassau The Andros Barrier Reef, home to 164 marine species, is famous for its deep-water sponges and large populations of red snapper. It sits along a deep trench called the Tongue of the Ocean. 07 of 09 Saya De Malha Bank Area: 15,444 square miles (40,000 square km) Location: Indian Ocean northeast of Madagascar The Saya de Malha Bank is part of the Mascarene Plateau and features the largest continuous beds of seagrass in the world. This seagrass stretches across 80-90% of the area and coral covers another 10-20%. This reef is more round in shape than most long, elliptical reefs, which is why it is most often measured by area rather than length. 08 of 09 Great Chagos Bank Area: 4,633 square miles (12,000 square km) Location: The Maldives In 2010, the Chagos Archipelago was officially named a protected marine area, prohibiting it from being fished commercially. This ring-shaped reef in the Indian Ocean was not studied extensively until more recent years. In 2010, a mangrove forest was discovered. The Great Chagos Bank is the largest atoll or ribbon-like circle of coral reef in the world. 09 of 09 Reed Bank Area: 3,423 square miles (8,866 sq km) Location: The South China Sea (claimed by the Philippines but disputed by China) In the mid-2010s, China started constructing islands upon reefs in the South China Sea in the Reed Bank region to increase its dominion over the Spratley Islands. Oil and natural gas deposits, as well as Chinese military outposts, can be found on this broad tablemount.