The crown of thorns looks like a starfish with a lot of spines protruding from its body. Coming in contact with one of these is will cause painful swelling that could last 5-7 days. These are commonly found around Okinawa.
They do not swim (except very weakly at the Laval stage) juvenile and adult crown of thorns starfish do not walk on their arms but rather on a large number of tiny tube feet which occur along grooves extending underneath each arm The tube feet are operated hydraulically using fluid within the cavity of the starfish.
The crown of thorns starfish is somewhat sinister in appearance as it is covered by a large number of long, very sharp spines (4-5 cm in length) which can inflict a painful wound. The crown of thorns starfish ranges in color from purplish-blue with red tipped spines to green with yellow-tipped spines. Those on the Great Barrier Reef are normally brown or reddish grey with red-tipped spines while those in Thailand are a brilliant purple. Their color may change somewhat depending on diet and the degree to which hair-like projections (papulae) extend from the skin.
Although crown of thorns starfish normally range in size from 25-35 cm in diameter, individuals as large as 80 cm have been found. We don't know how old these large individuals are since it is not possible to determine the age of crown of thorns starfish from their size. Like most echinoderms size is determined by what they eat, availability of food and number of starfish in the population. Starfish grown in aquaria for 2 years on a diet of encrusting algae may be up to 20 times smaller than those fed on corals.
The crown of thorns is a serious problem here on Okinawa since they eat our reefs. The Okinawans have tried several ways to stop these things from eating the reef.
One of the most well-known of predators, the giant triton (Charonia tritonis) pictured below, is most adept at feeding on both large and small crown of thorns starfish. The triton uses its rather primitive foot to restrain the starfish and then inserts its proboscis (trunk-like feeding organ) inside the animal to feed on its soft tissues (eg. gonads, caeca). Often the starfish will escape from the triton by leaving behind that part of its body which is being held. Small starfish are normally ingested whole by the triton. After the meal has been concluded the spines and other skeletal material normally are regurgitated. Please don't remove the giant triton (Charonia tritonis) from the areas around Okinawa.
The crown of thorns starfish contains toxic compounds called saponins which are a group of chemicals that are related to steroids. These chemicals have been isolated from all stages of the life history of the starfish and are thought to prevent predation by certain animals. Apart from being toxic to certain marine organisms the crown of thorns starfish also is known to be toxic to humans.
Most injuries to humans occur on the hands and feet. Symptoms range from intense pain (which may last several hours) to nausea and vomiting. Frequently, the area around the puncture turns a dark blue (erythema) and begins to swell (oedema). The swelling may persist for a number of days. Where the victim has suffered multiple wounds the whole limb may stiffen and swell. In such cases the patient may experience a numbness around the wound(s) and the swollen area may become extremely itchy.
Notice in the image above the many spines and arms. The white patch on the left has been recently eaten by the starfish. It is termed a feeding scar.
This last symptom indicates that some victims also may respond in an allergic manner to injuries from the crown of thorns starfish.
The crown of thorns starfish prefers to live in more sheltered areas such as lagoons, and in deeper water along reef fronts. They generally avoid shallow water on the tops of reefs where the water conditions are likely to be more turbulent. Occasionally they may feed in these areas, particularly when the weather is calm. Consequently care should be taken when walking around these areas as they can produce a toxic and inflammatory reaction if trodden upon.
