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Cruising the Waters: All About Coral Reefs

Written by: John Maguire

Some people call coral reefs the "rainforests of the oceans" because they are actually a very large and diverse aquatic ecosystem. The coral that makes up coral reefs is actually made from living creatures that belong to the same family as sea anemones and jellyfish. Coral reefs occur in tropical waters close to the equator or in other areas where currents bring in warm waters. Coral reefs are home to many different organisms. These organisms count on the presence of coral reefs to give them both food and shelter. Some scientists guess that up to 8 million undiscovered organisms make their homes in coral reefs. Not only are coral reefs important for maintaining aquatic ecosystems, but they are also directly involved with providing services and goods worth billions of dollars every year. This contribution helps sustain many local economies around the world. For instance, the Virgin Islands Coral Reef National Monument sits off the island of St. John, and it covers a three-mile area under the waters that attracts scores of visitors every year.

How Are Coral Reefs Formed?

Coral reefs form slowly over thousands of years. They begin with coral larvae attaching themselves to rocks underneath the ocean near continents and islands. Different reefs grow at different rates. Some corals grow very slowly, adding 2 or fewer centimeters of growth each year. Other types of coral, such as branching coral, can grow as much as 10 centimeters each year.

Different Types of Coral Reefs

Slowly, the corals grow to become one of three different types of structures. Fringing reefs are the most common type of coral reefs. These reefs form borders along shorelines, and they project seaward. Barrier reefs also sit along shorelines; however, they are further away from the shorelines. An area of open water separates barrier reefs from the land. Atolls generally have a circular shape with a lagoon in the middle. Sometimes, these reefs actually protrude out of the water as islands.

Notable Coral Reefs Throughout the World

A number of notable coral reefs exist throughout the world. These reefs draw visitors who wish to explore their beauty. The Great Barrier Reef is the largest coral reef in the world. This reef is located off the shore of Australia. It includes more than 900 separate islands and more than 2,900 individual reefs. The Great Barrier Reef covers about 133,000 square miles of ocean. The Belize Barrier Reef is the next-largest coral reef in the world, covering nearly 200 miles. This reef borders Mexico between Belize and Honduras. The New Caledonia Barrier Reef receives notable mention as the second-longest double-barrier reef. This reef sits in the south Pacific Ocean in New Caledonia. The New Caledonia Barrier Reef encircles a lagoon with an area of about 9,300 square miles.

Coral Reefs of St. John

The U.S. Virgin Islands include three islands, one of which is St. John. Coral reef areas sit off the shore of St. John. These coral reefs are the fringing variety, and they form a three-mile-long stretch off of the island. The St. John reefs are unique because they display impressive mangrove forests and beautiful marine gardens. Hurricane Hole is an area inside the mangrove forests that contains shallow bays and a narrow stretch of red mangrove trees.

Coral Reef Zones

Coral reefs contain various zones that make up the entire structures. These zones vary for different types of reefs. The back reef generally lies closest to the shoreline. This area features shallow water and higher amounts of light and heat. The reef crest sits farther from the shore between the fore-reef and the back reef. The reef crest generally receives the most wave action. The fore-reef sits farthest from the shoreline, usually on the oceanic face of the reef crest. The fore-reef displays slopes with steep angles. Because of the reduced amount of wave action, corals in the fore-reef tend to grow larger.

Coral Reef Biodiversity

Coral reefs represent expansive ecosystems, providing homes to many different organisms. Many sea creatures, such as sea turtles and sharks, live in and around coral reefs. As many as 4,000 different fish species and 800 species of hard coral live in and near reefs. Some scientists think that coral reefs have the highest biodiversity on earth.

Environmental Issues With Coral Reefs

Coral reefs have evolved and survived throughout thousands of years. However, many reefs either are experiencing damage or are threatened due to a number of issues. Overfishing and fishing practices that are destructive to the environment are wreaking havoc on many coral reefs. Tourists can also have a negative impact on coral reefs with destructive snorkeling and boating practices. Pollution and climate change are two other threats that are disrupting the natural algae growth in these areas. The damage to coral reefs can be extensive. Many reefs are actually dying with no hope for rehabilitating them. However, with better management, it may be possible to reverse some of the damage.