The Great Barrier Reef is the world’s longest and largest reef complex. It is located in the Pacific Ocean off the northeastern coast of Australia. The Destination Great Barrier Reef, spans more than 1,250 miles (2,000 km) in a generally northwest-southeast direction, with an offshore distance of 10 to 100 miles (16 to 160 km) and a breadth of 37 to 155 miles (60 to 250 km).
Approximately 135,000 square miles (350,000 square kilometres) in size, the Great Barrier Reef has been referred to, albeit incorrectly, as the greatest structure ever created by living things.
Actually, there are 800 fringing reefs and 2,100 distinct reefs that make up the reef (formed around islands or bordering coastlines). Many are dry or only just submerged at low tide; some feature cays or islands made of coral sand; still others encircle high islands or the shore of the main land.
Despite their differences, all reefs were produced over millions of years from the bones and skeletal remains of a range of living sea animals. The calcareous remnants of coral polyps and hydrocorals serve as the “bricks” in the structure of the reef, and coralline algae and bryozoans serve as the “cement” that holds these remains together.
Large amounts of skeletal detritus generated by the pounding of the waves and the predation of burrowing organisms have filled the gaps in this framework.
The reef was first explored by Europeans in 1770 after British explorer Capt. James Cook drove his ship aground there. Cook began mapping the waterways and tunnels through the labyrinth of reefs, and this work was continued throughout the 19th century.
The 1928–1929 Great Barrier Reef Expedition made significant contributions to our understanding of coral physiology and coral reef ecology. On Heron Island, a cutting-edge lab continues scientific research, and numerous more studies have been done.
Since corals cannot survive in waters with an average temperature below 70 °F (21 °C), the reef has grown on the shallow shelf around the Australian continent. Reefs were forming on the continental shelf as early as the Miocene epoch, according to borings (23.0 million to 5.3 million years ago).
Since the early Miocene, the continental shelf has continued to sink, with occasional reversals.
The surface water layer of the south-west Pacific Ocean contributes to the formation of the Great Barrier Reef’s aquatic habitat. The surface-water temperature in the reef’s waters is high, ranging from 70 to 100 °F (21 to 38 °C), and there is no seasonal change.
Generally speaking, the waters are clean, making submarine objects apparent at 100-foot depths (30 metres).
At least 450 different kinds of hard coral are among the living things, along with anemones, sponges, worms, gastropods, lobsters, crayfish, prawns, and crabs. The reef is home to more than 1,500 different species of fish and other creatures.
Wrasses, damselfish, triggerfish, and angelfish are a few of the most prevalent fish species. Rays and sharks are larger species (e.g., tiger sharks and whale sharks, the largest living fish). Additionally, the reef is home to nearly two dozen different bird species, more than a dozen sea snake species, and six of the seven known species of sea turtles.
The crown-of-thorns starfish (Acanthaster planci), which has greatly reduced the colour and appeal of many of the central reefs by consuming most of the remaining coral, is the most damaging species of reef animal.
One of the most recognisable elements of the Great Barrier Reef is the strengthening purple red algal rim formed by the encrusting red algae Lithothamnion and Porolithon, while the green alga Halimeda grows practically everywhere.
Only about 30 to 40 species of plants make up the cays’ restricted above-ground plant life. The northern cays are home to certain mangrove species.
Destination Great Barrier Reef
The reef has grown in significance as a tourist destination in addition to its scientific interest. Increased limitations on potentially dangerous operations like drilling for petroleum resources are the result of growing concern about the preservation of its natural heritage.
In the late 20th and early 21st centuries, there was debate regarding the widespread usage of tourist boats and the viability of commercial fishing.
However, additional variables also pose a threat to the health of the reef. It is vulnerable to recurring instances of coral bleaching, which is the “whitening” of the coral skeleton brought on by the breakdown of the coral’s symbiotic relationship with zooxanthellae algae.
Since 1998, there have been at least six mass bleaching events brought on by climate change, which have caused a significant decrease in coral cover. According to some marine biologists, coral bleaching, invasive species like the crown-of-thorns starfish (Acanthaster planci), and tropical storm damage caused a roughly 50% decrease in coral coverage on the reef between 1985 and 2012.
In the northern half of the reef, coral covering decreased by up to one-third as a result of bleaching in 2016 and 2017. The southern portions of the reef saw a second major bleaching episode in 2020.
The Great Barrier Reef Marine Park, which includes the great bulk of the region and was established in 1975, is mostly responsible for reef supervision. Additionally, there are smaller national and state parks. The Great Barrier Reef was included on the Unesco World Heritage List in 1981.