Coral reefs are the equivalent of underwater forests. They are diverse underwater ecosystems held together by calcium carbonate structures. Twenty-five percent of all marine life lives in coral reefs. These reefs also undergo coral bleaching in which corals expel algae that turns the coral completely white. The combination of plant life and colorful marine fish make coral reefs vacation destinations among scuba divers. Larger coral reefs, such as the Great Barrier Reef, are actually made up of many smaller reefs that are connected into a single ecosystem.

Great Barrier Reef, Australia

The Great Barrier Reef, off the coast of Queensland, Australia, is the world’s largest coral reef. The reef is made up of 3000 individual reef systems and is the only living organism that’s visible from space. The Great Barrier Reef stretches more than 1,800 miles and tops 40 miles wide in some places. It’s home to manta rays that you can observe while snorkeling or scuba diving. This reef is also a UNESCO world heritage site. Climate change is also a very real problem facing the reef. Since 1995 the Great Barrier Reef has lost half its coral.

Apo Reef, Philippines

The Apo Reef in the Philippines is the largest contiguous reef after the Great Barrier Reef. It covers 67,877 acres off the coast of Mindoro Island and is surrounded by a mangrove forest. The reef was designated a national park in 1996, but environmental problems and overfishing severely taxed the reef. In 2007, the Philippine government enacted a fishing ban in the reef to help restore and preserve it.

Mesoamerican Barrier Reef, Caribbean Basin

The Mesoamerican Reef in the Caribbean Basin is the largest coral reef in the Atlantic Ocean. The reef extends along Mexico, Guatemala, Honduras, and Belize’s water. It’s 585 miles in length and is estimated to be 7,000 years old. More than 500 species of fish species (as well as other invertebrates) and 65 types of coral live within the large reef system. As well as marine animals (such as whale sharks), this reef is home to a variety of ecosystems and biodiversity.

Florida Keys, United States

The Florida Keys Reef system is North America’s only living coral barrier reef. The reef covers 221 miles along Florida’s southeast coast from Key Biscayne to the Dry Tortugas. The Florida reef is protected as an underwater state park known as the John Pennekamp Coral Reef State Park, the first of its kind in North America.

New Caledonia Barrier Reef, New Caledonia

The New Caledonia Barrier Reef in the South Pacific is the second longest reef in the world, covering a length of 930 miles. More than 1000 different species-- some of which are still unclassified -- live within the reef. The New Caledonia encloses a 9,300 square mile lagoon and reaches an average depth of 82 feet.

Red Sea Coral Reef, Red Sea

The Red Sea Coral Reef off the coasts of Egypt, Israel and Saudi Arabia is approximately 5,000 to 7,000 years old. Ten percent of the 1,200 species found in this reef live only in this area. The Red Sea Coral Reef includes the Dahab Blue Hole, one of the most popular and dangerous dive sites in the world.

Maldives-Chagos-Lakshadweep Atolls, Indian Ocean

The Maldives-Chagos-Lakshadweep Atolls are the largest atoll system in the world and the most extensive coral reef system in the Indian Ocean. The islands that make up the atoll were formed by volcanic eruptions and contain 1,300 low coral islands. The Lakshadweep Islands themselves are built on top of coral reefs and covered with coral sand.

Belize Barrier Reef, Belize

The Belize Barrier Reef is a part of the Mesoamerican Reef system. The reef extends from Ambergris Caye in the north to the Sapodilla Cayes in the south. This 185-mile-long reef covers an area of 237,962 acres and is protected by the UNESCO World Heritage program. The reef includes a phenomenon called the Blue Hole that’s visible from space. This reef is famous for sea turtles, manatees, and crocodiles.

Andros Barrier Reef, Bahamas

The Andros Barrier Reef in the Bahamas stretches more than 140 miles. The island sits along the edge of an oceanic trench known as the Tongue of the Ocean. This means the reef extends downwards along the trench to a depth of 6,000 feet instead of lying flat along the ocean floor. It is home to roughly 25% of the world’s marine species (from fish to sponges).

Saya de Malha Banks, Indian Ocean

The Saya de Malha Banks in the Indian Ocean are the largest submerged banks in the world. This ridge connects the Seychelles and Mauritius islands along the Mascarene Plateau. Along with its coral reefs, the marine habitat includes feeding grounds for the green turtle and breeding grounds for blue whales.