- A-Z Animals
Crown-of-thorns starfish, also called COTS, is a heavily spined species of marine invertebrates that eat coral. It is the second-largest starfish in the world that gets its name from the poisonous thorn-like spines covering its body, which resemble the crown of thorns worn by Jesus Christ. Like other starfish species, the COTS has a disk-shaped, flexible, and prehensile body with multiple radiating arms. It is mostly found in the regions where stony or hard corals occur in the Indo-Pacific.
Size: Adult crown-of-thorns starfish vary in size, ranging from 9.8-13.8 in (25-35 cm). The larger specimens can grow over 100 cm in diameter.
Weight: This spiny sea star species can weigh anywhere between 200 g and 3 kg.
Color: It typically has soft and light colors, including gray-green, pale brown, purplish-blue, and reddish-gray. Some specimens can have a bright red, yellow, and bluish appearance.
Arms: Adult COTS can have 12-23 arms that extend from the central disk. Underneath each of the arms, there are a series of closely fitted plates that create a groove.
Spines: The spines are stiff, long, and very sharp, occurring on the sides of its arms and upper surface; these spines form a crown-like shape.
Body: Its body may appear stiff, but the COTS can easily bend and twist its body to fit around the curves and outlines of the coral that it eats.
The crown-of-thorns starfish is widely distributed across the Indo-Pacific region. Although they are commonly found in Australia, large populations can exist in tropical and subtropical environments, extending from the Red Sea through the Indian Ocean off the east African coast, across the Pacific to the coastal waters off western parts of Central America.
They prefer living in relatively undisturbed waters, such as lagoons, deep seawater, and protected, shallow parts of the backreef where they feed on coral colonies.
Although the actual life expectancy of crown-of-thorns starfish in the wild is not known, they grow old, reaching the senile phase after 3-4 years. Most specimens that have been studied died between 5 and 7.5 years. In captivity, they can survive for about 8-15 years.
The crown-of-thorns starfish is a corallivore, which means it preys on coral. As a voracious predator, it is estimated that this starfish species can eat up to 65 sq. ft (6 sq. m) of living reef coral per year.
Crown-of-thorns starfish, like most echinoderms, reproduce by spawning. The male and female starfish release or deposit their gametes into the water so that fertilization can occur. This starfish species release chemicals, which trigger spawning in other individuals. Not all individual starfish in a specific population, however, spawn simultaneously.
They seasonally spawn during the summer months, depending on the location of each population. In the northern hemisphere, spawning occurs between May and August, but in the southern hemisphere, it takes place between November and February.
The spawning process involves a crown-of-thorns starfish to climb high up on a coral reef and arch its body. It vigorously moves its arms and tube feet so that it can release the gametes through the five holes located on the aboral surface of its body. Female starfish may produce around 60 million eggs all through a breeding season.
Eggs that have been fertilized turn into planktonic larvae, passing through different developmental stages. The embryo that hatches from the egg is known as a gastrula, after which the gut forms, and the larva develops into a bipinnaria. By day 5, it turns into a brachiolaria larva. When the brachiolaria stage ends, the larva sits on a hard surface and undergoes metamorphosis into a juvenile COTS. The juvenile starts with five arms, which gradually increases to around 23 by adulthood.
Crown-of-thorns starfish have not been listed under IUCN Red List, US Federal List, or any other conservation programs.