page_title: Environmental threats to the Great Barrier Reef
section_title: Crown of Thorns Starfish
hierarchical_section_title: Environmental threats to the Great Barrier Reef / Crown of Thorns Starfish
caption_attribution_description: Español: Acanthaster planci devorando corales en el arrecife Boulder, Gran Barrera de Arrecifes australiana. Los corales blancos de la imagen son los esqueletos de los corales, una vez que sus pólipos han sido comidos por la estrella de mar depredadora.
context_page_description: The Great Barrier Reef is the world's largest reef systems, stretching along the East coast of Australia from the northern tip down to the town of Bundaberg, is composed of roughly 2,900 individual reefs and 940 islands and cays that stretch for 2,300 kilometres and cover an area of approximately 344,400 square kilometres. The reef is located in the Coral Sea, off the coast of Queensland in northeast Australia. A large part of the reef is protected by the Great Barrier Reef Marine Park.
  According to the 2014 report of the Australian Government's Great Barrier Reef Marine Park Authority, says that climate change is the most significant environmental threat to the Great Barrier Reef, while the other major environmental pressures are listed as decreased water quality from land-based runoff, impacts from coastal development and some persistent impacts from fishing activities. The reef is also threatened by storms, coral bleaching and ocean acidification. The 2014 report also shows that, while numerous marine life species have recovered after previous declines, the strength of the dugong population is continuing to decline.
context_section_description: The Crown-of-Thorns Starfish is a coral reef predator which preys on coral polyps by climbing onto them, extruding its stomach over them, and releasing digestive enzymes to absorb the liquefied tissue. An individual adult of this species can eat up to six square meters of living reef in a single year. Geological evidence suggests that the Crown-of-Thorns Starfish has been part of the Great Barrier Reef's ecology for "at least several thousand years", but there is no geological evidence for Crown of Thorns outbreaks. The first known outbreak occurred during the 1960s. Large outbreaks of these starfish can devastate reefs. In 2000, an outbreak contributed to a loss of 66% of live coral cover on sampled reefs in a study by the CRC Reefs Research Centre. Although large outbreaks of these starfish are believed to occur in natural cycles, human activity in and around the Great Barrier Reef can worsen the effects. Reduction of water quality associated with agriculture can cause the crown-of-thorns starfish larvae to thrive. Fertilizer runoff from farming increases the amount of phytoplankton available for the Crown of Thorns Starfish larvae to consume. A study by the Australian Institute of Marine Science showed that a doubling of the chlorophyll in the water leads to a tenfold increase in the crown-of-thorns starfish larvae's survival rate. Overfishing of its natural predators, such as the Giant Triton, is also considered to contribute to an increase in the number of Crown of Thorns Starfish. The CRC Reef Research Centre defines an outbreak as when there are more than 30 adult starfish in an area of one hectare. There have been three large outbreaks of COTS on the reef since observation began, between 1962 and 1976; 1978 and 1991; 1993 and 2005, and a fourth began in 2009. Investigation is being undertaken into mimicking a chemical scent released by the COTS' natural predator, the giant triton snail.
caption: Crown-of-thorns starfish and eaten coral off the coast of Cooktown, Queensland.
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