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The crown-of-thorns starfish (frequently abbreviated to COTS), [1] Acanthaster planci, is a large starfish that preys upon hard, or stony, coral polyps (Scleractinia). The crown-of-thorns starfish receives its name from venomous thornlike spines that cover its upper surface, resembling the biblical crown of thorns .
Acanthaster is a bitypic genus of large and venomous starfish placed in its own family, Acanthasteridae. Its two members are known as crown-of-thorns starfish. Acanthaster are native to coral reefs in Indo-Pacific region. [2]
The crown-of-thorns starfish has few other natural predators, and are capable of destroying large sections of coral reef. The struggle between a starfish and an Atlantic triton can last up to an hour before the seastar is subdued by the snail's paralyzing saliva. Tritons can be observed to turn and give chase when the scent of prey is detected.
The population of crown-of-thorns sea star, a natural predator of corals, is closely monitored and controlled to prevent outbreaks. [14] The sea stars are injected with ox bile that painlessly kills them and does not harm the rest of the ecosystem. [14] A coral nursery project was also piloted in 2020. [14]
Much debate has occurred on whether plagues of crown-of-thorns starfish are natural or are caused by overfishing of the few organisms that can eat this starfish, including C. tritonis. In 1994, Australia proposed that C. tritonis should be put on the CITES list, thereby attempting to protect the species. [5]
Starfish sometimes have negative effects on ecosystems. Outbreaks of crown-of-thorns starfish have caused damage to coral reefs in Northeast Australia and French Polynesia. [59] [70] A study in Polynesia found that coral cover declined drastically with the arrival of migratory starfish in 2006, dropping from 50% to under 5% in three years.
The body form of A. brevispinus is fundamentally the same as that of a typical starfish or seastar. Like A. planci, however, its distinctive traits include being disc-shaped, multiple-armed with multiple madreporites, flexible, prehensile, and densely spined, and having a large ratio of stomach surface to body mass.
It often feeds by turning over rocks, stirring up sand and biting off pieces of branching coral. This is why other smaller fish species are often seen around it, as they feed on the detritus and smaller organisms that are stirred up. Titan triggerfish are one of a number of species of fish which can hunt and eat the crown-of-thorns starfish. [4]