Saturday, 1 October 2011

Crown of thorns starfish

Kingdom: Animalia
Phylum: Echinodermata
Class: Asteroidea
Order: Valvatida
Family: Acanthasteridae
Genus: Acanthaster
Species: Acanthaster planci
Common Names: Crown of thorns starfish

The crown of thorns starfish (Acanthaster planci) is a large starfish with its name deriving from the venomous thorn-like spines that cover its body. It can be found in tropical coral reefs of the Red Sea, the Indian Ocean, and the Pacific Ocean. It is one of the largest starfishes in existence, only coming second to the sunflower starfish

Crown of thorns starfish Description
It has a varying size, ranging size from 25 to 35 cm (10-14 inches). Adults have thirteen to sixteen arms, which extend out radially from a central body. They come in a variety of colors like purple, blue and brow with their spines usually being in a different color than the rest of their body.
Their average lifespan is not known, however they are known to surpass the 8 years of age.

Crown of thorns starfish Venom
The Crown of thorns starfish is best known for the spines it bears in the limbs. These spines are thorn-like giving the animal a crown-like shape. These spines are sharp, venomous and can easily penetrate normal wetsuits and clothes.
They can also transfer a neurotoxin that the crown of thorns starfish produces. If a human is penetrated by these spines, he will surely experience some (if not all) of the symptoms below:
  • Great and sharp stinging pain, lasting up to many hours
  • Nausea
  • Vomiting
  • Wound that swell and turn into dark blue. The edema may last for many weeks.
  • It is common for the spines to break and stay inside the skin, sometime resulting into infection.
Crown of thorns starfish Predators
Most of the reef predators instinctively find this type of star fish highly unattractive due to it being covered by sharp spines. Nevertheless the crown of thorns starfish does have some natural predators that will prey and feed on it:
  • The Giant Triton, a type of mollusk)
  • In some occasions some large reef also pray on it (for instance the humphead wrassem and the Green triggerfish)
The starfish's larvae are planktonic (organisms very small in size), and during this phase they are eaten by a large variety of planktonic eating organisms

Crown of thorns starfish Diet
They are corallivorous animals, which mean that they eat coral polyps. In order to feed they will first climb onto reef structures, and then extrude their stomach onto them. After doing so, they begin to release various digestive enzymes that liquefy the coral tissue. Then they simply absorb these liquids which are full of nutrients. They also prey on brittle stars in a similar way.
They are considered to be voracious (with a big appetite) predators consuming up to 6 square meters of living corals in a single year. However they can survive for more than 6 months without food using only their stored energy reserves!

Crown of thorns starfish breeding
Typically, before breeding occurs, many individuals will gather together to increase the chances of egg-fertilization, with their fertilization rates being the highest among all starfishes. Spawning takes place from December to April when temperatures are about 28 C. Females release their eggs (up to 60 million) into the water, and so do the males with their sperm. Sperm and eggs are released from pores on the top of the central disc. The fertilized eggs then develop into plactonic larvae that spend 2 to 4 weeks drifting in the ocean currents. After this period of drifting they go through a process known as metamorphosis during which they transform into small juvenile sea stars that have five arms. These younglings have a size of 1-2 mm across, and they settle on the reef, hiding among rubble and rocks from potential predators. They are very small and for the first 6 months are practically invisible to the naked eye. They will continue growing more and more arms for the next couple of months, and two years after their birth, they will be able to mate and reproduce.

Video featuring the Crown of thorns starfish

Crown of thorns starfish - A threat for coral reefs
The total population of the crown of thorn starfish has been continuously increasing for the past four decades. Their overpopulation has caused widespread coral reef damages, with many reefs under serious threat of extinction. Unfortunately controlling their population is a very difficult task. This is because killing these animals is very tough since they can even regenerate from just one severed limb!
The best strategy as of now is to inject them with sodium bisulphate which is toxic to them and kills them without harming the surround organisms.

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