The coral reef builds upwards, growing towards the light much like trees in a rainforest, competing for space and light. Once the coral reef reaches sea level it cannot survive the harsh surface conditions so begins to grow outwards. Creating spectacular formations of coral that spawn further growth and spreading of the reef ecosystem. Through time, animals grow and the sand, rubble and debris of life is broken down by waves and eroding animals, such as worms and sponges. A complex reef ecosystem is built over time. Today’s underwater gullies and caves were formed because of that erosion. These are the same formations scuba divers enjoy exploring today because they are shelters for an abundance of marine life. Coral reefs tend to grow where there is a lot of water movement, bringing nutrients, oxygen and new species. Most reef-building corals cannot grow in waters shallow enough to expose them at high tide or deeper than 50 metres, making them highly sensitive to changing sea levels. The Reef is continually evolving and changing as climate and sea levels change. Healthy, diverse reef ecosystems are more resilient, that is, they are able to adapt to change. The Great Barrier Reef Marine Park Authority is concentrating on maximising reef resilience through research and management.

Corals are actually tiny, soft-bodied animals that belong to the same group as jellyfish and sea anemones, the Cnidarians. An individual coral animal is called a polyp. Coral polyps can live alone, but typically polyps live in colonies that may consist of hundreds to hundreds of thousands of individuals. Corals are split into two main groups: soft corals and hard corals. Hard corals, also known as reef building corals, are the best-known type of coral, forming the large, colourful reefs found in clear, tropical seas. There are over 800 known species of reef-building coral.

Two-thirds of the coral loss has occurred since 1998 and the rate of decline has increased in recent years, averaging around 1.45% a year since 2006. "If the trend continued, coral cover could halve again by 2022," said Peter Doherty, a research fellow at the institute.Tropical cyclones, predation by Cots, and bleaching accounted for 48%, 42%,and 10% of the respective estimated losses. In the past seven years the reef has been affected by six major cyclones. Cyclone Hamish, for example, ran along the reef, parallel to the coast for almost 930 miles (1,500km), leaving a trail of destruction much greater than the average cyclone, which usually crosses the reef on a path perpendicular to the coast.The starfish problem was first recorded in 1962 at Green Island off Cairns. "When we say outbreaks, we mean explosions of Cots populations to a level where the numbers are so large that they end up eating upwards of 90% of a reef's coral," Gunn said. "Since 1962 there have been major outbreaks every 13-14 years."

Known for their distinctive shape and often strikingly colourful markings, Angelfish are one of the more numerous species of fish in the Great Barrier Reef, with over 80 different species in the family in total. Typical characteristics of the Angelfish include their beauty, inquisitive nature, and tendency to be found in all levels of the upper reef, from the surface to the base of the area’s coral formations. Patterns which can be found on Angelfish range from thin, vivid stripes to multi-coloured speckled patterns that make no two fish of the families look exactly alike, and they form

There are 23 species of marine reptiles that inhabit the Great Barrier Reef including 6 species of sea turtles and 17 species of sea snakes. Occasionally, the saltwater crocodile also ventures out to forage on the reef, although such visits are quite rare. The sea turtles that inhabit the Great Barrier Reef include the green turtle, loggerhead turtle, hawksbill turtle, flatback turtle, leatherback turtle and the Pacific ridley turtle. Some sea turtle species, such as the green turtle, loggerhead turtle and hawksbill turtle, nest on coral cays. The flatback turtle nests on continental islands and the green and leatherback turtles nest on mainland Australia. When not nesting, these sea turtle species use the waters of the Great Barrier Reef as foraging grounds. Among the sea snakes of the Great Barrier Reef are the olive sea snake, the turtle-headed sea snake and the sea krait. All sea snakes are venomous.

Corals are colonies of made up of tiny animals called polyps. Hard corals have polyps with 6 tentacles, or multiples of 6 tentacles. Soft coral polyps have 8 tentacles. The oldest coral on the Great Barrier Reef would be a Porites sp. and is probably about 1,000 years old. Old colonies of this species are the size of a small room. These corals grow at about 1 cm in height per year and their skeleton reflects the weather conditions at the time of the growth. Hence large corals which are hundreds of years old can provide information about water temperature and rainfall patterns that pre-date European settlement. Tiny algae called zooxanthellae live in the flesh of most corals. The algae photosynthesise and transfer energy to the coral. Therefore, coral reefs (which are built mostly by these corals) are generally confined to shallow waters because like other plants, the algae require light to survive.

Forms of life include at least 300 species of hard coral as well as anemones, sponges, worms, gastropods, lobsters, crayfish, prawns, crabs, and a great variety of fishes and birds. The most destructive reef animal is the crown-of-thorns starfish (Acanthaster planci), which has reduced the colour and attraction of many of the central reefs by eating much of the living coral. Encrusting red algae Lithothamnion and Porolithon form the fortifying purplish red algal rim that is one of the Great Barrier Reef’s most characteristic features, while the green alga Halimeda flourishes almost everywhere. Above the surface, the plant life of the cays is very restricted, consisting of only some 30 to 40 species. Some varieties of mangrove occur in the northern cays.

Coral reefs are fragile ecosystems. Because corals need warm, sunlit water to live, they often grow close to the top of the water. Sadly, being so close to land makes them often be damaged by poisons and dirt that can come from boats and the land nearby. Dirt makes the water more cloudy, which makes the sunlight less. Poisons can bleach and kill corals. Also, they are hard for ships to see, but easy to hit, which makes ships often run into the coral, damaging both the boats and coral. Because of this, many countries are trying to lessen the kinds of building that usually happen near beaches that have coral reefs nearby, and be more careful about the boats that go around reefs.[4]

It is difficult to work out the age of the Great Barrier Reef. This is because of the way a reef can grow and shrink as the sea level changes. A coral reef can grow in diameter, that is how wide they are, from 1 to 2 cm per year. They can also grow upwards from 1 to 15 cm per year. Coral can not grow if the water is too deep (150 metres or more) because it needs light from the sun. They cannot grow out of the water (above sea level).[5]

n not grow if the water is too deep (150 metres or more) because it needs light from the sun. They cannot grow out of the water (above sea leve

Global warming is a threat to coral reefs. When the ocean temperature increases coral bleaching occurs; that is the symbiotic alga inside the polyps die, which causes the polyps to turn white and eventually die. In 1998, coral bleaching affected approximately 90% of the Great Barrier Reef. The coral reefs are endangered by the unprecedented climatic change. The coral ecosystem is bound to get physically damaged if there is an increase in the sea levels and also in the frequency of the tropical storms. Only curbing global warming can prevent the destruction of the coral reef. Australian government and the concerned organizations around the world are trying to reduce the emission of greenhouse gases.

Four hundred species of coral have been found there, as well as 4,000 species of mollusk and 2,000 different kinds of fish.The Great Barrier Reef acts as a buffer between the strong waves of the Pacific and the shores of Australia.Many parts of the Great Barrier Reef have islands made of piled up coral sand.

Coral Bleaching - Coral reefs are fragile ecosystems and are extremely sensitive to water temperature; so, any changes can have an effect. When the ocean water temperature rises, it causes coral bleaching. That means that the symbiotic alga inside the coral polyps dies, which causes the polyps to turn white and eventually die. The reefs can recover from only a limited amount of bleaching before they are no longer able to recover.Shelter - Barrier reefs play an important role of sheltering the coastline from the full effect of the ocean’s waves. If the reef crumbles, the coastlines are exposed to damaging waves and the people there would have to deal with erosion and wave action, and low-lying structures could be at risk.