Crown-of-Thorns Starfish
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Crown-of-Thorns Starfish
Acanthaster planci
Venonous Marine Organism
Temp image from Coral Reef CD
The crown-of-thorns starfish is a large, many-armed invertebrate covered with long and sharp venomous spines. It is named after the crown-of-thorns placed on the head of Jesus during the Crucifixion. This infamous predator feeds exclusively on living corals by everting its stomach over the coral and digesting the soft tissue. It is normally uncommon, but periodically, large concentrations appear on certain reefs. When in such numbers they may form a moving front that advances along the reef, wiping out nearly all the living coral in their path. Evidence of recent predation by the crown-of-thorns starfish is easily seen in the form of numerous bleached coral skeletons. These bleached corals soon get covered with green filamentous algae and eventually crumble into rubble that may form the foundation for new coral colonies to settle and grow. Until the corals return, the variety of fishes and aesthetic value of the reef is greatly diminished, but populations of herbivorous fishes that feed on filamentous algae may actually increase. Needless to say, the crown-of-thorns starfish is considered an unwelcome pest.
The cause of crown-of-thorns infestations has been the subject of intensive research for many years. The weight of the evidence indicates human activity is the culprit. Although infestations occur naturally, they are rare events, occurring at an average of once every 400 years. But in areas where there are increased nutrient levels in the water as a result of agriculture or other land use practices that enhance soil erosion, infestations occur frequently and the reefs may never completely recover. It seems that the increased level of nutrients favors the development and survival of the planktonic larvae or juvenile starfish when they settle on the reef.
There are very few natural predators of the crown-of-thorns starfish. These include large humphead wrasse (tangison) and two rare invertebrates, the trito
trumpet (a large shell) called kulo' in Chamoru, and the tiny colorful harlequin shrimp.
Guam Comprehensive Wildlife Conservation Strategy, 9/27/2005
