Crown-of-Thorns Starfish: Characteristics, Feeding, Coral Reef Damage

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crown-of-thorns starfish in Thailand

The crown-of-thorns starfish (Scientific name:Acanthaster planci) is a coral eating starfish with 12 to 19 arms. that can destroy up to 400 square centimeters (62 square inches) of coral a day. Growing up to one meter (three feet) in diameter, they eat coral polyps and are protected from predators by toxic spines. Their average lifespan in the wild is 16 years.[Source: Larissa Ault; Juliet McCardle; Caitlin Sussman, Animal Diversity Web (ADW) /=]

Crown-of-thorns starfish are found throughout the Indo-Pacific region, ranging from the western Indian ocean, the Red Sea and East Africa in the west to Japan in the north, Lord Howe Island of Australia to the south and Panama to the Gulf of California in the east. The species is particularly common on the Great Barrier Reef of Australia.

Crown-of-thorns starfish are commonly found on coral reefs, foraging over coral colonies in shallow, protected areas of the backreef at an average depth of 10 meters (33 feet). Much research has been carried out conducted on the grazing effects of crown-of-thorns starfish on coral reef cover. Large populations of these starfish can devastate a reef, which has occurred on the Great Barrier Reef (See Below). In addition, after live coral cover has been reduced, both juvenile and sub-adult starfish like to feed on newly-formed hard coral, which significantly impacts the ability of coral in a reef to come back

Crown-of-thorns starfish have not been evaluated for the International Union for Conservation of Nature (IUCN) Red List. They have no special status according to the Convention on the International Trade in Endangered Species (CITES).

Websites and Resources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase; Encyclopedia of Life; Smithsonian Oceans Portal ; Monterey Bay Aquarium ; MarineBio; Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) ; International Coral Reef Initiative ; Coral Reef Alliance ; Global Coral reef Alliance ; Global Coral Reef Monitoring Network

Crown-of-Thorns Starfish Ravage the Great Barrier Reef

crown-of-thorns starfish (Acanthaster Planci)

Million of these of creatures ravaged the Great Barrier Reef in early 1960s, late 1970s, early 1980s and late 1990s, leaving behind thousands of hectacres of bleached, dead coral. The attack in the 1960s was particularly devastating. It lasted for 10 years and killed one fifth of the 2,600 reefs that comprise the Great Barrier Reef. On the Great Barrier Reef near Townsville crown-of-thorns starfish starfish turned once vibrant reefs into bleached skeletons. Around Cairns people were hired to remove the starfish from popular diving and snorkeling spots on a daily basis. Divers attempted to get ride of the starfish by injecting them with copper sulfate but environmentalists worried the toxin could damage the reef more than starfish and enter the food chain.

In the early 1990s, the crown-of-thorns starfish mysteriously disappeared. But in 1994, scientist began noticing a build up of starfish in the north of the reef and predicted another outbreak would occur when these starfish matured. Females lay up to 100 million eggs at one time and these eggs can float for hundred of miles before settling on a reef and developing into starfish. It was first thought the starfishes were flourishing because the natural predator the giant triton mollusk was being taken by shell hunters, but most scientists now insist the infestation is part of a natural cycle.

Surveys conducted since the early 1990s have illustrated that declines in live hard coral cover have occured at the same time as crown-of-thorns outbreaks along the reef systems between Lizard Island and Townsville in the Great Barrier Reef off of Queensland, Australia. The decline of the coral reef is bad in itself but also seriously and negatively affects the tourism industry in the region. Researchers are trying to determine if and how human activities affect the cycle of starfish outbreaks, particularly how increased nutrient runoff from land affects survival, recruitment, and growth of larval crown-of-thorns starfish.

Crown-of-Thorns Starfish Characteristics and Toxins

Crown-of-thorns starfish have between eight and 21 arms that radiate from a central disc. Adults normally range from 25 to 35 centimeters (10 to 14 inches) in diameter, with some individuals reaching over 70 centimeters (28 inches) in diameter. [Source: Larissa Ault; Juliet McCardle; Caitlin Sussman, Animal Diversity Web (ADW) /=]

Crown-of-thorns starfish are venomous, ectothermic (use heat from the environment and adapt their behavior to regulate body temperature), heterothermic (have a body temperature that fluctuates with the surrounding environment) and have radial symmetry (symmetry around a central axis), Sexual Dimorphism (differences between males and females) is minimal. Both sexes are roughly equal in size and look similar.

crown-of-thorns starfish spines regenerating

The crown-of-thorns starfish mouth is located on the underside of the central disc. There are light-sensitive eyespots at the tips of the arms. Individual coloration varies from red and orange to purple, and is thought to be the result of differences in diet. The interior of the body contains the internal organs (stomach, digestive gland, and gonads). The skeletal structure is composed of tiny structures called ossicles, made of magnesium calcite.

Crown-of-thorns starfish possesses large, venomous spines in contrast to the short, blunt spines usually present on starfish. The venomous quality of these spines is not fully understood; saponin has been discovered in the spines’ underlying tissue, though the quantity is not sufficient to trigger the painful reactions seen in humans who have come into contact with the spines. There is no evidence that Crown-of-thorns starfish injects toxins through the spines./=\

Crown-of-Thorns Starfish Behavior, Senses

Crown-of-thorns starfish are diurnal (active during the daytime), nocturnal (active at night), crepuscular (active at dawn and dusk), motile (move around as opposed to being stationary) and solitary. They do not maintain a home range or territory. /[Source: Larissa Ault; Juliet McCardle; Caitlin Sussman, Animal Diversity Web (ADW) /=]

According to Animal Diversity Web (ADW): Juveniles and sub-adults are the most geographically widespread asteroids recorded within the Great Barrier Reef region. One year after settlement onto the reef, newly formed adults migrate great distances over reef habitats. Locomotory behaviors observed in Crown-of-thorns starfish are typical of predatory starfish. Individuals crawl at the rate of up to 35 centimeters per minute over coral reefs and rubble, encountering and consuming stony corals by everting the stomach onto the coral substratum and digesting the polyps. Juveniles feed at night on exposed front reef zones, where apparently they are less likely to be noticed by predators, while adults are more commonly seen in protected back reef zones. /=\

Crown-of-thorns starfish sense using touch and chemicals usually detected with smell and communicate with touch and chemicals usually detected by smelling. They also employ pheromones (chemicals released into air or water that are detected by and responded to by other animals of the same species). Like other sea stars, crown-of-thorns starfish uses a combination of chemical detection and tactile senses via its tube feet to locate mates, detect its prey, and perceive its environment.

Crown-of-Thorns Starfish Feeding and Predators

a Triton's trumpet — a predator of crown-of-thorns starfish

Crown-of-thorns starfish consumes most types of Indo-Pacific stony corals, such as Pocillopora, Acropora, Pavona, and Porites. Adults are opportunistic carnivores, consuming sclerectinian corals, encrusting sessile (fixed in one place) invertebrates, and dead animals. They feeds by everting their stomach through their mouth onto their prey and digesting the tissues, absorbing the nutrients through the stomach wall. During their development, larvae floating in the water column, consume smaller planktonic organisms. [Source: Larissa Ault; Juliet McCardle; Caitlin Sussman, Animal Diversity Web (ADW) /=]

Crown-of-thorns starfish feed mostly on live stiny corals. A 40-centimeter (1.4-foot), average- sized adult can kill up to 478 square centimeters of live coral per day while grazing. Large numbers of sea stars can remove swaths of corals and open up bare areas of coral rock for settlement by other species of sessile (fixed in one place) invertebrates. In this way crown-of-thorns starfish can be viewed as having a role in diversifying the bluefin tuna habitat. On the other hand, coral cover is drastically reduced, populations of coral reef specialists (animals that depend exclusively on coral cover for shelter and food) may decrease.

The main known predators of crown-of-thorns starfish are giant tritons, white-lined pufferfish, harlequin shrimp, triggerfish and lined fireworm. The crown-of-thorns starfish are protected from many types of predators their long, venomous spines. However, many adults — up to 60 percent in some populations — are missing arms, indicating that predation does occur. Juveniles seek cover more than adults, hiding in crevices and the undersides of ledges. Fishes in the triggerfish and pufferfish families — which have horny plate-like scales and strong sharp teeth that allow them to remove chunks of sea star tissue — are the fish most likely to feed on crown-of-thorns starfish.

Crown-of-Thorns Starfish Mating and Reproduction

Crown-of-thorns starfish are oviparous (young are hatched from eggs) and iteroparous (offspring are produced in groups). They engage in external reproduction in which sperm from the male fertilizes the female’s egg outside her body and employ broadcast (group) spawning, the main mode of reproduction in the sea. It involves the release of both eggs and sperm into the water and contact between sperm and egg and fertilization occur externally. [Source: Larissa Ault; Juliet McCardle; Caitlin Sussman, Animal Diversity Web (ADW) /=]

Crown-of-thorns starfish breed once a year. The breeding season is in the summer months in the northern and southern hemispheres when water temperature are warmer. Those in the northern hemisphere generally spawn between May and August, while those in the southern hemisphere spawn between November and February. Gravid females may contain anywhere from 12 to 24 million eggs, and may produce as many as 60 million eggs throughout a season. As these sea stars are broadcast spawners with a planktonic larval stage, there is no parental involvement in the raising of offspring. /=\

Crown-of-thorns starfish are polygynandrous (promiscuous), with both males and females having multiple partners. Males and females release their sperm and eggs into the seawater, where fertilization occurs. Unlike some other starfish, which can reproduce through somatic fission or arm autonomy, crown-of-thorns starfish are not known to reproduce asexually using thise method of any other..When spawning, crown-of-thorns starfish climb to a high place on a coral outcrop, then arch their body. As the sea star actively moves its tube feet and waves its arms, eggs and sperm are released through five pores on the aboral surface of the body. There is evidence that crown-of-thorns starfish release chemicals that induce spawning in nearby individuals. However, not all individuals in a certain area spawn at the same time.

Crown-of-Thorns Starfish Development

Crown-of-thorns starfish development is characterized by metamorphosis and indeterminate growth (they continue growing throughout their lives). Fertilized eggs develop into planktonic larvae, which depend on phytoplankton for nutrition while they pass through several developmental stages, from gastrula to bipinnaria to brachiolaria. Near the end of the brachiolaria stage, the larva settles onto a suitable hard surface and metamorphoses into a juvenile starfish. Its arms will begin to develop as it matures. The juvenile starfish begins with five arms, which will increase to as many as 21 arms by adulthood. [Source: Larissa Ault; Juliet McCardle; Caitlin Sussman, Animal Diversity Web (ADW) /=]

Scientists recognize three age classes for Crown-of-thorns starfish: 1) juvenile, 2) sub-adult, and 3) adult. Growth rates are age-specific — rapid for juveniles (up to 16.7 millimeters per month) and then slowing down as they transition from sub-adult to adult (4.5 millimeters per month).

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated May 2023

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