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Adaptations of the Crown of Thorns Starfish

In recent years, the crown-of-thorns starfish has been derided as a major destructive force in coral reef ecology. However, this starfish has its role in nature and it is only when the overall health of a reef and the availability of the starfish's predators is disturbed do starfish populations rise and reefs suffer. The foremost predator of the starfish is the giant triton snail, which has a large and beautiful shell that is badly over-fished due to its appeal to collectors. That the crown-of-thorns starfish has so few major predators and is so efficient in its mode of living and reproduction is largely due to its extraordinary adaptations.

The Ability to Sense Coral Reef Stress
- Coral reefs must be healthy to keep the crown-of-thorns at bay.
  
  Research indicates that the crown-of-thorns starfish usually does not destroy reefs that are healthy and which have sufficient numbers of the triton shell and its few other predators to keep their numbers in check. But when a reef is stressed or damaged, it releases a metabolite to which the starfish and its larvae are sensitive. This causes the starfishes to gather for the feast.
The Ability to Eat Live Coral
- The crown-of-thorns starfish is hardly alone in its ability to eat live coral. The parrot fish is also a live coral eater and is responsible for the deposition of white sand beaches in tropical waters. But the crown-of-thorns has two special adaptations that make this easier and more efficient. Coral produces a waxy layer that protects each live coral polyp in its cup. To counteract this, the starfish produces a wax-digesting enzyme that strips away the waxy protectorant so that the starfish can easily digest the polyp.
  
  The second adaptation is the starfish's remarkable stomach. The crown-of-thorns can exteriorize its large stomach, passing it down with its feet to the tasty coral. When there, it covers the coral and drenches it with digestive juices. It then siphons up the polyp slush. The stomach is then passed by the feet back to its original location.
The Ability to Protect Itself and Move
- The crown-of-thorns starfish is one of the largest members of the starfish family. Some of them can be a meter across and have from eight to 20 arms, allowing them to move relatively quickly across a reef. Each arm is lined with sucker feet on the bottom and very sharp spines on the top which can easily penetrate a diver's glove or wet suit. The spines are also armed with a potent neurotoxin to complete the animal's defensive weaponry. Few predators are equipped to take on such defenses.
The Ability to Reproduce in Large Numbers
- The starfish is capable of producing millions of larvae from a single mating. Without predators to keep the population in check, the crown-of-thorns starfish is capable of overpopulating and destroying a reef in short order.

Animals & Science