Great Barrier Reef

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The Great Barrier Reef, located near Queensland, Australia, is the world's largest coral reef. It stretches for 2.300 kilometres in length. James Cook discovered it on 11 June 1770, because of damage under his ship. When the ship approached the reef the captain realised that his vessel could not travel over it and he then ran aground and finally sank.the great barrier reef will be black in the future.

[change] Geology

Ben Dover, of The Reef Research Centre, a Cooperative Research Centre, has found coral 'skeleton' deposits that date back half a million years.^[1] Corals have been growing in the region for as long as 25 million years, but have not always formed coral reefs.^[2]

Disagreements about the age of the Great Barrier Reef stem from how reefs grow and shrink as the sea level changes. They can increase in diameter from 1 to 2 centimetres per year, and grow upwards anywhere from 1 to 15 centimetres per year; however, they are limited to growing above a depth of 150 metres due to their need for sunlight, and cannot grow above sea level.^[3]

According to the Great Barrier Reef Marine Park Authority, the current, living reef is believed to have begun growing on an older platform about 20,000 years ago.^[2] The Australian Institute of Marine Science agrees, which places the beginning of the growth of the current reef at the time of the Last Glacial Maximum. At around that time, the sea level was 120 metres lower than it is today. The land that formed the base of the Great Barrier Reef was a coastal plain with some larger hills (some of which were themselves remainders of older reefs).^[4]

From 20,000 years ago until 6,000 years the sea level rose steadily. As it rose, the corals could grow higher on the hills of the coastal plain. By around 13,000 years ago the sea level was 60 metres lower than the present day, and corals began to grow around the hills of the coastal plain, which were, by then, continental islands. As the sea level rose further still, most of the continental islands were covered by water. The corals could then overgrow the hills, to form the present cays and reefs. Sea level on the Great Barrier Reef has not risen significantly in the last 6,000 years.^[4]The CRC Reef Research Centre estimates the age of the present, living reef structure at 6,000 to 8,000 years old.^[1]

The remains of an ancient barrier reef similar to the Great Barrier Reef can be found in The Kimberley, a northern region of Western Australia.^[5]

The Great Barrier Reef World Heritage Area has been divided into 70 bioregions,^[6] of which 30 are reef bioregions,^[7] and 40 are non-reef bioregions.^[8] In the northern part of the Great Barrier Reef, ribbon reefs and deltaic reefs have formed; these structures are not found in the rest of the Great Barrier Reef system.^[1]

The dugong (Dugong dugon) is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's Sea Cow (Hydrodamalis gigas) was hunted to extinction in the 18th century. It is also the only sirenian in its range, which spans the waters of at least 37 countries throughout the Indo-Pacific,[3] though the majority of dugongs live in the northern waters of Australia between Shark Bay and Moreton Bay.[4] In addition, the dugong is the only strictly-marine herbivorous mammal, as all species of manatee utilize fresh water to some degree.[3] Like all modern sirenians, the dugong has a fusiform body with no dorsal fin or hindlimbs, instead possessing paddle-like forelimbs used to maneuver itself. It is easily distinguished from the manatees by its fluked, dolphin-like tail, but also possesses a unique skull and teeth.[5] The dugong is heavily dependent on seagrasses for subsistence and is thus restricted to the coastal habitats where they grow, with the largest dugong concentrations typically occurring in wide, shallow, protected areas such as bays, mangrove channels and the lee sides of large inshore islands.[3] Its snout is sharply downturned, an adaptation for grazing and uprooting benthic seagrasses. The dugong has been hunted for thousands of years, often for its meat and oil,[6] although dugong hunting also has great cultural significance throughout its range.[7] The dugong's current distribution is reduced and disjunct, and many populations are close to extinction.[3] The IUCN lists the dugong as a species vulnerable to extinction, while the Convention on International Trade in Endangered Species limits or bans the trade of derived products based on the population involved. Despite being legally protected in many countries throughout their range, the main causes of population decline remain anthropogenic, and include hunting, habitat degradation, and fishing-related fatalities.[8] With its long lifespan and slow rate of reproduction, the dugong is especially vulnerable to these types of exploitation.[3] In addition, dugongs are threatened by storms, parasites, and their natural predators, sharks, killer whales, and crocodiles

[change] References