The Great Barrier Reef's Coral Threats

The Great Barrier Reef's Coral Threats

Think of the Great Barrier Reef, and thoughts of bright beautiful fish and a kaleidoscopic of corals come to mind. The Great Barrier Reef is one of seven natural world wonders and was listed as a World Heritage Area for protection. It is the largest collection of coral reefs in the world spanning over 1,250 miles; it extends along the north-eastern coast of Australia, along the eastern shore of Queensland. It stretches from the Torres Strait near the coast of Papua New Guinea to the Tropic of Capricorn between Gladstone and Bundaberg. The Great Barrier Reef contains 600 continental islands, 305 coral cays, and approximately 3,400 individual reefs (An Introduction, n.d.). "It is one of the most complex ecosystems on Earth, rivaled only by tropical rain forests in the richness of its species" (Landscapes, n.d., para. 4). The Great Barrier Reef has more than 2,800 species of fish, 400 different types of coral, and many other species of various animals depending on it to survive. The three greatest stresses on the Great Barrier Reef are coral bleaching, water quality, and the crown-of-thorns starfish.

Coral bleaching strips the beautiful colors from the coral of the Great Barrier Reef, and leaves a white skeleton. By definition, coral bleaching is "a process in which corals expel the algal cells (zooxanthellae) that normally live within their tissue" (Threats Ð'- Bleaching, n.d., para. 1). High water temperature from global warming is thought to be a major contributor to coral bleaching. If the temperature of the sea goes above the long-term monthly average by as little as one degree Celsius, coral bleaching can occur. Two major bleaching events have occurred in the summers of 1998 and 2002. During these two mass bleaching events, up to five percent of the reefs were critically damaged, however, 60 to 90% of the reefs were affected during the mass bleaching event of 2002. The time that it will take for the Great Barrier Reef to recover fully from these mass coral bleaching will be anywhere from many years to decades (Coral bleaching and mass bleaching events., n.d.). However, high water temperatures are not the only stress that causes coral bleaching, water quality can contribute as well.

There are many contributors that influence the Great Barrier Reef's water quality; however, the major influencers are nutrients, sediments, and salinity. Nutrients that run off into the rivers of Australia from monsoon floods, then wash into the Great Barrier Reef causing an excessive increase in organisms that compete with coral for space, such as tubeworms and sponges. Land sediments or debris affect coral in two ways by suffocating the coral once the debris or sediment settles and decreasing light availability while the sediment or debris is floating in the water, which could hinder the growth and photosynthesis of coral. Salinity is essential to coral, 25 to 42% salinity is the range that coral live in, when it is lowered by the fresh water from floods or storms coral bleaching can occur (Principal water quality influences on Great Barrier Reef ecosystems., n.d.). With all of these challenges floating in the water, there is also another attacker of the coral and that is the crown-of-thorns starfish.

The crown-of-thorns starfish is "devastating to the coral reef itself, as it is a natural predator of the coral itself" (Monk, 2006, para. 2): The crown-of-thorns starfish is an abnormally large starfish that has up to 21 arms and can grow up to 1 meter in diameter, with long venomous spines covering the complete top surface of its body. Crown-of-thorns starfish begin eating coral about six months of age. In small numbers, a healthy coral reef can support 20-30 crown-of-thorns starfish per 10,000 square meters, however, in large numbers, during a major outbreak, they will compete for food and leave less than one percent of hard coral cover before moving on. This kind of infestation could cause the reef to take more than 10 years to recover (Crown-of-thorns Starfish, n.d.). Only the giant triton snail,