Crown of Thorns Starfish

Starfish or sea stars are marine invertebrates belonging to the phylum Echinodermata; class Asteroidea. Crown of Thorns Starfish (Acanthaster planci) are found on coral reefs in the tropics ranging from the Red Sea, the Indian and Pacific Oceans, and all the way to the Pacific coast of Panama. It plays a major role in the destruction of fast growing coral species. Scientists believe that this starfish has lived on the reefs for tens of thousands of years and when the populations of this echinoderm increase in number, they can seriously damage the coral reefs.

The Crown of Thorns Starfish has 16 to 18 arms and are covered all over with thousands of long, venomous spines. The spines are extremely sharp and are known to have a toxic reaction in humans. This is also the largest starfish in the world. Their size is usually 10 to 13 inches cm in diameter, but some can grow to 80 cm depending on availability of food and living conditions. It can be dull greyish green with pale tinges of red or a bright blue or purple. Their life expectancy is not certain but Crown of Thorns Starfish have lived up to 8 years in an aquarium.

Crown of Thorns Starfish eat coral. Not the coral skeletons, just the delicate coral polyps. Coral flesh is just a thin film on the outside of the coral skeleton and the polyps can withdraw down into protective little cups, so coral is not very easy to make a meal out of. A hungry starfish climbs up on a coral and pulls its stomach out of its mouth with its tube feet. The starfish has thousands of these flexible tube feet, each ending with a little suction cup. The feet pass the stomach from one to the next until the big yellow stomach is spread out over the coral. Then the stomach expels digestive juices over the live coral to dissolve it. The cells of the stomach scoff up the bits of dissolving coral. When the starfish has cleaned the coral right to the white calcium carbonate skeleton, it sucks in its stomach and moves off, using its tube feet.

If the Crown of Thorns Starfish occur in great numbers they can eat corals faster than corals can grow and reproduce, leading to major reductions in the coral reefs. Populations of the Crown of Thorns Starfish have increased since the 1970s, and this species is at least partly responsible for much loss of coral reefs, particularly on the Great Barrier Reef in Australia.

The term used for reproduction of the Crown of Thorns Starfish is spawning. A single female Crown of Thorns Starfish can produce up to 100 million eggs per year. Under the water, the Crown of Thorns Starfish stand on tiptoes on the tops of rocks. Early summer is the main spawning time, and can happen at any time, day or night, as long as the water temperature is right. From pores on the Crown of Thorns Starfish, sperm and eggs stream out into the surrounding water where they meet and fertilize. The fertilized eggs float away. In this planktonic stage the larva develops a large sack like structure that will grown to 0.2 inches in size and settle onto a reef. After settlement the larva changes into a juvenile starfish. This process takes about 2 days. At first the juvenile starfish has only 5 small arms but additional arms grow rapidly as the starfish begins to feed on algae. At the end of 6 months the starfish is about one half inch in size and begins to feed on corals. It is still vulnerable to predators and it hides, only coming out at night to feed. By the second year it is sexually mature and it has grown to about 8 inches in diameter. By 3 to 4 years they are mature and stop growing.

An electron microscopic picture of the tips of their spines of the Crown of Thorns Starfish shows the sharp crystal point. The spines are so sharp they slide through skin, and most gloves, without any real pressure; just glide in. If Crown of Thorns