Humanities › Geography The Great Barrier Reef Share Flipboard Email Print Jeff Hunter Creative #: 183173840 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 February 05, 2020 Australia's Great Barrier Reef is considered to be the world's largest reef system. It is made up of over 2,900 individual reefs, 900 islands and covers an area of 133,000 square miles (344,400 sq km). It is also one of the Seven Natural Wonders of the World, a UNESCO World Heritage Site and it is the world's biggest structure made out of living species. The Great Barrier Reef is also unique in that it is the only living organism that can be seen from space. Geography of the Great Barrier Reef The Great Barrier Reef is located in the Coral Sea. It is off the northeast coast of Australia's state of Queensland. The reef itself stretches over 1,600 miles (2,600 km) and most of it is between 9 and 93 miles (15 and 150 km) from shore. In places, the reef is up to 40 miles (65 km) wide. The reef also includes Murray Island. Geographically, the Great Barrier Reef stretches from Torres Strait in the north to the area between Lady Elliot and Fraser Islands in the south. Much of the Great Barrier Reef is protected by the Great Barrier Reef Marine Park. It covers over 1,800 miles (3,000 km) of the reef and runs along Queensland's coast near the town of Bundaberg. Geology of the Great Barrier Reef The geologic formation of the Great Barrier Reef is long and complex. Coral reefs began forming in the region about between 58 and 48 million years ago when the Coral Sea Basin formed. However, once the Australian continent moved to its present location, sea levels began to change and coral reefs started to grow quickly but changing climate and sea levels after that caused them to grow and decline in cycles. This is because coral reefs need certain sea temperatures and levels of sunlight to grow. Today, scientists believe that complete coral reef structures where today's Great Barrier Reef are were formed 600,000 years ago. This reef died off however due to climate change and changing sea levels. Today's reef began to form about 20,000 years ago when it started growing on the remains of the older reef. This due to the fact that the Last Glacial Maximum ended around this time and during glaciation sea level was much lower than it is today. Following the end of the last glaciation about 20,000 years ago, sea level continued to rise and as it got higher, the coral reefs grew on the hills being flooded on the coastal plain. 13,000 years ago the sea level was almost where it is today and the reefs began to grow around off the coast of Australia islands. As these islands became further submerged with rising sea levels, the coral reefs grew over them to form the reef system present today. The current Great Barrier Reef structure is about 6,000 to 8,000 years old. Biodiversity of the Great Barrier Reef Today the Great Barrier Reef is considered a World Heritage Site due to its unique size, structure and high levels of biodiversity. Many of the species living in the reef are endangered and some are endemic only to that reef system. The Great Barrier Reef has 30 species of whales, dolphins, and porpoises. In addition, six species of endangered sea turtles breed in the reef and two green sea turtle species have genetically distinct populations in the north and south of the reef. The turtles are attracted to the area due to the 15 species of seagrass that grow in the reef. Within the Great Barrier Reef itself, there are also a number of microscopic organisms, different mollusks, and fish that inhabit spaces inside the coral. 5,000 species of the mollusk are on the reef as are nine species of seahorses and 1,500 species of fish, including the clownfish. The reef is composed of 400 species of coral. The areas closer to land and on the islands of the Great Barrier Reef are biodiverse as well. These places are home to 215 bird species (some of which are seabirds and some of which are shorebirds). The islands within the Great Barrier Reef are also home to over 2,000 types of plants. Although the Great Barrier Reef is home to many charismatic species like those previously mentioned, it should also be noted that a variety of very dangerous species inhabit the reef or areas near it as well. For example, saltwater crocodiles live in the mangrove swamps and salt marshes near the reef and a variety of sharks and stingrays live within the reef. In addition, 17 species of sea snake (most of which are venomous) live on the reef and jellyfish, including the deadly box jellyfish, also inhabit nearby waters. Human Uses and Environmental Threats of the Great Barrier Reef Due to its extreme biodiversity, the Great Barrier Reef is a popular tourist destination and around two million people visit it per year. Scuba diving and tours via small boats and aircraft are the most popular activities on the reef. Since it is a fragile habitat, tourism of the Great Barrier Reef is highly managed and sometimes operated as ecotourism. All ships, aircraft, and others that want to access the Great Barrier Reef Marine Park need to have a permit. Despite these protective measures, however, the Great Barrier Reef's health is still threatened due to climate change, pollution, fishing, and invasive species. Climate change and rising sea temperatures are considered the greatest threats to the reef because coral is a fragile species that needs water to be about 77 F to 84 F (25 C to 29 C) to survive. Recently there have been episodes of coral bleaching due to higher temperatures.