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The Crown-of-Thorns starfish (Acanthaster planci) feeds on coral. Low numbers of this starfish increase reef diversity, but large numbers can destroy reefs. Avoiding human activities that increase starfish numbers is more effective than trying to control Crown-of-Thorns outbreaks once they happen.
The Crown-of-Thorns starfish is a predator of coral. In low densities, this starfish promotes diversity in coral reef ecosystems, because it prefers to feed on fast growing Acropoid coral. This gives slower growing coral space to establish and grow.
Populations of the Crown-of-Thorns starfish periodically boom and when this happens thousands of starfishes swarm a reef devouring up to 90% of the coral there. This alters the coral reef ecosystem in 3 ways by:
Crown-of-Thorns starfish outbreaks reduce diversity because many of the species that rely on coral to provide food and shelter are lost when coral is removed. Diversity loss decreases reef productivity and resilience against further disturbance.
We can make Crown-of-Thorns outbreaks worse by:
Increasing nutrient levels on the reef
Removing starfish predators
Predators of the Crown-of-Thorns starfish change throughout its lifecycle because its defense of venomous spines becomes more formidable as it gets older. Effective biological control of the Crown-of-thorns relies on coral reef diversity because these predators change throughout the starfish’s life cycle.
Predators of Crown-of-thorns starfish larvae
Predators of juvenile Crown-of-thorns starfish
Predators of adult Crown-of-thorns starfish
Some species of crab and shrimp species defend their coral colony homes from Crown-of-Thorns attacks. These animals drive the starfish away from the coral, but do not kill them.
Our attempts to control Crown-of-Thorns outbreaks are usually unsuccessful because they are labor-intensive, ineffective over wide areas, expensive, and/or potentially dangerous. Outbreaks typically continue until disease or starvation causes starfish populations to crash.
Attempts to control the Crown-of-Thorns have included:
Like many types of disturbance, the Crown- of-Thorns starfish can be good or bad for the coral reef ecosystem. Low numbers of this starfish increases diversity, but large numbers lower it. Our activities can add to the disturbance rate by increasing Crown-of-Thorns numbers. This erodes the sustainability of coral reefs.
AIMS. (2007, November 7). Crown- of-Thorns starfish. Australian Institute of Marine Science. Retrieved 18 August 2008 from http://www.aims.gov.au/docs/research/biodiversity-ecology/threats/cots.html
CRC Reef Research Centre. (2003, November). Crown- of-Thorns starfish on the Great Barrier Reef. CRC Reef Research Centre. PDF retrieved 18 August 2008 from http://www.reef.crc.org.au/publications/brochures/COTS_web_Nov2003.pdf
Great Barrier Reef Marine Park Authority. (1995, April). Controlling Crown- of-Thorns starfish. CRC Reef Research Centre. Crown- of-Thorns starfish. Retrieved 18 August 2008 from http://www.reef.crc.org.au/publications/explore/feat45.html
Kosarek, N. (2000). Acanthaster planci. Animal Diversity Web. Retrieved 18 August 2008 from http://animaldiversity.ummz.umich.edu/site/accounts/information/Acanthaster_planci.html
Madl, P. (2002, December). Acanthaster planci (An overview of the Crown- of-Thorns starfish). University of Salzburg. Retrieved 18 August 2008 from http://www.sbg.ac.at/ipk/avstudio/pierofun/planci/planci.htm
Sweatman, H. (2008, 22 July). No-take reserves protect coral reefs from predatory starfish. Current Biology 18(14): 598-599. PDF retrieved 28 August 2008 from http://www.aims.gov.au/source/media/news2008/pdf/sweatman-2008-cots-mpas-biology-paper.pdf
Wikipedia. (2008, August 8). Crown- of-Thorns starfish. Wikipedia. Retrieved 18 August 2008 from http://en.wikipedia.org/wiki/Crown-of-thorns_starfish
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