Branching Coral and Soldier Fish on the Great Barrier Reef (© Pniesen | Dreamstime.com)
Just before 11 pm on June 11th, 1770, the HMS Endeavour, captained by Lieutenant James Cook, ran aground. Cook had been exploring the northeast coast of Australia when the accident occurred. The ship was stuck fast on a reef and the crew made desperate attempts to refloat her by lightening the ship. This meant throwing anything not immediately useful overboard, including the ship’s ballast and most of its cannon. Long boats were then used to carry the ship’s anchors away from the reef and secure them to the bottom. By winching in chains attached to the anchors, the ship gradually pulled itself off the bank. The reef had torn a hole in the bottom of the ship, however, and the Endeavour was quickly taking on water. Working feverishly the crew managed to temporary plug the leaks. They then sailed for the safety of the shore where the ship was breached and repaired.
Though Cook hadn’t realized it at the time, the coral reef he had run onto was part of a vast system of 3,800 coral banks and islands that ran along the coast of Australia. Known as the Great Barrier Reef, it has a length of 1,600 miles (2,600 km) and covers 133,000 square miles (344,400 sq. km). It is the largest structure in the world created by living organisms and supports a wide diversity of life, including fish, whales, dolphins and sea turtles. For this reason coral reefs are often referred to as the “rainforests of the ocean.”
Seven Quick Facts
|Length: 1,600 miles (2,600 km).|
|Area: 133,000 square miles (344,400 sq. km).|
|Depth: Surface to between 150 feet and 400 feet depending on how far light can reach below the surface in a particular location.|
|Discovered: The Australian Aboriginals have been aware of the reef for 40,000 years. The first European to notice it was French explorer Louis de Bougainville in 1768.|
|Location: Off the Northeastern coast of Australia.|
|Age: 20,000 years.|
|Other: Often referred to as the largest structure in the world created by living organisms.|
A coral reef forms underwater when thousands of tiny animals, only a few centimeters in length, establish a colony. These coral polyps build themselves hard, carbonate, exoskeletons to protect their bodies. When the polyps die they leave these exoskeletons behind and this becomes the surface on which a new generation of coral polyps can grow. Because one generation of coral builds on the last, the coral can “grow” vertically from 1/3 of an inch to almost one inch a year under good conditions. Their habitat is limited, however, from the surface of the sea to the maximum depth that light can penetrate the water, which, depending on conditions, is between 150 feet to 400 feet in the open ocean. Most corals can only thrive in warm tropic waters near the equator. If the water temperature gets too cold, or too hot, they will die.
The coral polyps are animals that feed on a variety of small organisms, like microscopic plankton or even small fish, using tiny tentacles with poisonous stinging tips. After capturing the prey, the tentacles contract and bring it to the polyps’ stomach where it is digested.
The reef as seen from space. (NASA)
Many of the corals also have a symbiotic relationship with a type of algae. The algae live inside the polyp and use photosynthesis to give the coral energy and help it build its exoskeleton (The sunlight needed for the algae’s photosynthesis is what limits how deep the coral can live). In return the algae get a safe place to live and they consume the polyps’ waste products. The algae also give the coral its color. Under certain conditions the algae can put stress on the polyp and it will eject the algae and turn white (an effect known as “bleaching”). If stress continues on the coral it will die, so bleaching is considered a sign that the coral is sick. If conditions return to normal, however, the coral can regain algae and its color will return.
The most recent incarnation of the Great Barrier Reef got its start 20,000 years ago when sea levels around the coast of Australia began to rise after the peak of the last ice age. As glaciers began to melt and flow into the sea the coastal plain near the northeast Australia became flooded making hills on the plain into islands. This area was shallow and warm enough for the coral to start growing around the edge of these islands. As the water continued to get deeper the coral grew upward keeping the living part of the reef within range of the sunlight. These smaller coral reefs grew larger but never completely merged so the system is actually made up of thousands of separate reefs and coral islands. There is also evidence that there are older versions of the reef that grew in the gaps in between the earlier ice ages. These may date back as far as 600,000 years.
There are over 400 different species of coral that inhabit the reef. Not all of them, however, create the hard exoskeletons necessary to build a reef. Those that do can take a number of different forms. Brain coral grows in a rounded lump up to six feet (1.8 m) in diameter. It gets its name from the convoluted grooves that cover their surface that resemble the folds on a brain. Table coral, elkhorn coral and staghorn coral grow in various shapes with antler-like branches. Pillar corals grow as a number of columns, or fingers, stretching up from the sea floor.
Coral reefs are a haven for sea life. They occupy less than one-tenth of one percent of the oceans, but provide a habitat for a quarter of all marine species. Over 1,500 types of fish live in the Great Barrier Reef alone. These include the colorful clownfish, angelfish and butterflyfish. Also, a large number of highly poisonous animals live on the reef including the box jellyfish, sea snakes, cone-shells and blue-ringed octopi. The top predator on the reef is the Great White Shark.
The first humans to become aware of the reef were Australian Aboriginal groups. For the past 40,000 years the reef has provided them food in the form of sea turtles and dugongs (Large marine mammals related to the manatee). About 10,000 years ago the Torres Strait Islanders also moved into the area. Like the aboriginals they used wooden outrigger canoes to hunt and move from coral island to island. The activities surrounding the hunting of these creatures was of great cultural significance to these peoples and the animals were an important resource. For example, traditionally the shell of the sea turtle would be fashioned into items such as combs and fishhooks.
Rare bush of branching black coral. – (© Caan2gobelow | Dreamstime.com )
The first European to become aware of the reef was the French explorer Louis de Bougainville who came through the area in 1768 on a trip to circumnavigate the globe. He was searching for Australia when he was forced to change course after seeing waves breaking on the reef.
Protection of the Reef
In recent years efforts have been focused on protecting the Great Barrier Reef from damage. In 1975 the government of Australia created the Great Barrier Reef Marine Park which gives protection to a large part of the reef system. Fishing and the removal of coral or artifacts is highly regulated. Commercial shipping traffic is restricted to certain lanes that avoid the most sensitive parts of the park.
The park is a popular tourist destination and much of the management effort is directed at making sure these activities are ecologically sustainable. Tourists can visit the reef on special glass bottomed boats or see it from the air by helicopter. The most popular way to visit the reef, however, is by snorkelling or scuba diving. Approximately two million people travel to the Great Barrier Reef each year which generates billions of dollars of economic activity for the region.
The Great Barrier Reef, along with many other coral reefs, is under threat from a number of environmental problems. Global warming may increase the water temperature to the point where the coral becomes stressed enough to bleach. Coral bleaching events were recorded on the reef in 1998, 2002 and 2006. Pollution can also damage the reef. Fertilizers and pesticides used in farm production can be carried out to sea and damage the fragile ecosystem.
The corals also have a natural predator in the crown-of-thorns starfish. When overfishing reduces the number of fish eating the starfish, their numbers can skyrocket, allowing them to do great damage to the reef.
Hopefully, careful management by the Great Barrier Reef Marine Park Authority will protect the reef from extensive damage. If so, it will remain a natural wonder of the world for many generations to come.