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Acanthaster plancicrown-of-thorns starfish

By Larissa Ault; Juliet McCardle; Caitlin Sussman

Geographic Range

Acanthaster planci is found throughout the Indo-Pacific region, ranging from the Indian ocean (Red Sea and East Africa) to the Pacific (from mainland Japan south to Lord Howe Island, and from the west coast of Panama to the Gulf of California). This species is particularly common on the Great Barrier Reef of Australia. (Moran, 1988a; Moran, 1988b)

Habitat

Acanthaster planci is commonly found on coral reefs, foraging over coral colonies in shallow, protected areas of the backreef. (Moran, 1988b)

  • Average depth
    10 m
    32.81 ft

Physical Description

Acanthaster planci bears between 8 and 21 arms that radiate from a central disc. Adults normally range from 250 to 350 mm in diameter, with some individuals over 700 mm in diameter. The mouth is located on the underside of the central disc (the aboral surface), and light-sensitive eyespots are present 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. Acanthaster planci 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 A. planci injects toxins through the spines. (Moran, 1988a; Moran, 1988b)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    700 (high) mm
    27.56 (high) in

Development

Like most echinoderms, A. planci reproduces sexually through broadcast spawning. The female releases millions of eggs into the water column that are fertilized by a male's sperm. 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 5 arms, which will increase to as many as 21 arms by adulthood.

Researchers note three age classes for A. planci: juvenile, sub-adult, and adult. Growth rates are age-specific: growth is rapid for juveniles (up to 16.7 mm per month) while the rate slows as they transition from sub-adult to adult (4.5 mm per month). (Engelhardt, et al., 1999; Moran, 1988b; Stump, 1996)

Reproduction

Crown-of-thorns starfish reproduce by spawning, in which males and females release their gametes into the seawater, where fertilization occurs. Unlike some other starfish, which can reproduce through somatic fission or arm autonomy, A. planci is not known to reproduce asexually. There is evidence that A. planci releases chemicals that induces spawning in nearby individuals. However, not all individuals in a given population spawn at the same time.

When spawning, A. planci will climb to a high place on a coral outcrop, then arch its body. Gametes are released through five pores on the aboral surface of the body, as the animal waves its arms and moves its tubefeet vigorously. (Birkelanci and Lucas, 1990; Moran, 1988a; Moran, 1988b)

Acanthaster planci spawns seasonally during summer months, according to each population’s location. Populations in the northern hemisphere generally spawn between May and August, while populations in the southern hemisphere spawn between November and February. These seasons have been roughly correlated with periods of warmer water temperature in the respective habitats. Gravid females may contain anywhere from 12 to 24 million eggs, and may produce as many as 60 million eggs throughout a season. (Birkelanci and Lucas, 1990; Moran, 1988a; Moran, 1988b)

  • Breeding interval
    Acanthaster planci breeds once a year.
  • Breeding season
    This species breeds in the summer months in the northern and southern hemispheres.

As this asteroid is a broadcast spawner with a planktonic larval stage, there is no parental investment in offspring. (Birkelanci and Lucas, 1990)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

Acanthaster planci is expected to live to about 15-17 years barring predators or limiting resources; however, the actual lifespan of this organism in the wild is unknown. (Engelhardt, et al., 1999; Stump, 1996)

  • Average lifespan
    Status: wild
    16 years

Behavior

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 A. planci are typical of predatory starfish. Individuals crawl at the rate of up to 35 cm 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. (Engelhardt, et al., 1999; Engelhardt, et al., 2001; Stump, 1996)

Home Range

This species does not maintain a home range or territory.

Communication and Perception

Like other asteroids, A. planci uses a combination of chemical detection and tactile senses via its tube feet to locate mates, detect its prey, and perceive its environment. (Clark and Downey, 1992)

Food Habits

While developing as larvae in the water column, individuals of this species consume smaller planktonic organisms. As an adult, this asteroid is an opportunistic carnivore, consuming sclerectinian corals, encrusting sessile invertebrates, and dead animals. It feeds by everting its stomach through its mouth onto its prey and digesting the tissues, absorbing the nutrients through the stomach wall. Acanthaster planci consumes most types of Indo-Pacific stony corals, such as Pocillopora, Acropora, Pavona, and Porites. (Keesing and Lucas, 1992; Moran, 1988a; Pratchett, 2007)

  • Animal Foods
  • cnidarians
  • other marine invertebrates
  • Plant Foods
  • algae

Predation

The crown-of-thorns starfish is protected from many types of predators by its long, venomous spines, though many adults (up to 60% within a population) may have missing arms, indicating that predation does occur. Juveniles assume more cryptic behaviors, inhabiting crevices and the undersides of ledges. Predators of A. planci include the giant triton shell Charonia tritonis and various fishes in the families Balistidae and Tetraodontidae, which have horny plate-like scales and strong sharp teeth that allow them to remove chunks of tissue from A. planci. (Moran, 1988b)

Ecosystem Roles

This asteroid is a corallivore, almost exclusively consuming live sclerectinian corals. An average sized adult (40 cm) can kill up to 478 square cm of live coral per day through its grazing activities. The crown-of-thorns starfish can be seen as an ongoing disturbance factor on the reef, removing swaths of clonal corals in its path, and opening up bare areas of coral rock for settlement and recruitment of other species of sessile invertebrates. Thus, A. planci can be seen to have a role in diversifying the habitat. However, if coral cover is drastically reduced, populations of coral reef specialists (animals that depend exclusively on coral cover for shelter and food) may decrease. Thus the impact of A. planci in their environment depends on how abundant they become. (Glynn, 1976; Keesing and Lucas, 1992; Wilson, et al., 2008)

Acanthaster planci harbors several genera of ectoparasitic copepod crustaceans on its dermal surface. (Mah, 2010)

Commensal/Parasitic Species
  • Onychopygus impavidus, a copepod
  • Molucomes ovatus, a copepod
  • Anthessius alatus, a copepod
  • Stellicola acanthasteris, a copepod
  • Stellicomes bisphaerulifer, a copepod
  • Synstellicola acanthasteris, a copepod

Economic Importance for Humans: Positive

There are no known economic benefits for humans.

Economic Importance for Humans: Negative

Much research has been conducted on the grazing effects of A. planci on coral reef cover and survival. Large populations of these starfish can devastate a reef, which has occurred on the Great Barrier Reef. Furthermore, after live coral cover has been reduced, both juvenile and sub-adult starfish preferentially choose to feed on newly-formed hard coral, which significantly impacts the coral recovery process. Surveys conducted since the early 1990’s have illustrated the decline in live hard coral cover coincident with crown-of-thorns outbreaks along the reef systems between Lizard Island and Townsville (coastal Queensland, Australia). Researchers have emphasized the importance of raising public awareness of these continually increasing outbreaks, since starfish predation on coral can seriously damage the reefs to the point where sustainability of the lucrative reef tourism industry could be impacted. To protect these reefs as well as the people who depend on them for their economic livelihood, researchers need to determine how human activities affect the cycle of starfish outbreaks. Specifically, more research needs to be conducted on the effects of overfishing known predators of A. planci, and on how increased nutrient runoff from land affects survival, recruitment, and growth of larval A. planci. (Engelhardt, et al., 1999; Engelhardt, et al., 2001; Stump, 1996)

  • Negative Impacts
  • injures humans

Conservation Status

This species is not listed under any conservation program.

Contributors

Larissa Ault (author), San Diego Mesa College, Juliet McCardle (author), San Diego Mesa College, Caitlin Sussman (author), San Diego Mesa College, Paul Detwiler (editor), San Diego Mesa College, Renee Mulcrone (editor), Special Projects.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

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benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

detritivore

an animal that mainly eats decomposed plants and/or animals

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

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oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

radial symmetry

a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

scavenger

an animal that mainly eats dead animals

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

References

Benzie, J., P. Dixon. 1994. The effects of sperm concentration, sperm:egg ratio, and gamete age on fertilization success in crown-of-thorns starfish (Acanthaster planci) in the laboratory. Biological Bulletin, 186 (2): 139.

Birkelanci, C., J. Lucas. 1990. Acanthaster planci: Major Management Problem of Coral Reefs. Boca Raton, Florida: CRC Press.

Clark, A., M. Downey. 1992. Starfishes of the Atlantic. London: Chapman & Hall.

Engelhardt, U., M. Hartcher, J. Cruise, D. Engelhardt, M. Russell, N. Taylor, G. Thomas, D. Wiseman. 1999. Fine scale surveys of crown-of-thorns starfish (Acanthaster planci) in the central Great Barrier Reef Region. CRC Reef Research Centre Technical Report, 30: 1-97.

Engelhardt, U., M. Hartcher, N. Taylor, J. Cruise, D. Engelhardt, M. Russell, I. Stevens, G. Thomas, D. Williamson, D. Wiseman. 2001. Crown-of-thorns starfish (Acanthaster planci) in the central Great Barrier reef region. Results of fine-scale surveys conducted in 1999-2000. CRC Reef Research Centre Technical Report, 32: 1-100.

Fabricius, K., G. De'ath. 2004. Identifying ecological change and its causes: A case study on coral reefs. Ecological Applications, 14 (5): 1448-1465.

Fong, P., P. Glynn. 2000. A regional model to predict coral population dynamics in response to El Nino-Southern Oscillation. Ecological Applications, 10 (3): 842-854.

Glynn, P. 1976. Some physical and biological determinants of coral community structure in the Eastern Pacific. Ecological Monographs, 46 (4): 431-456.

Hay, M., J. Parker, D. Burkepile, C. Caudill, A. Wilson, Z. Hallinan, A. Chequer. 2004. Mutualisms and aquatic community structure: The enemy of my enemy is my friend. Annual Review of Ecology, Evolution, and Systematics, 35: 175-197.

Johnson, L., R. Babcock. 1994. Temperature and the larval ecology of the crown-of-thorns starfish, Acanthaster planci. Biological Bulletin, 187 (3): 304.

Keesing, J., J. Lucas. 1992. Field measurement of feeding and movement rates of the crown-of-thorns starfish Acanthaster planci (L.). J. Exp. Mar. Biol. Ecol., 156: 89–104.

Mah, C. 2010. "WoRMS Taxon Details: Acanthaster planci" (On-line). World Asteroidea database. Accessed through: World Register of Marine Species. Accessed May 24, 2011 at http://www.marinespecies.org/aphia.php?p=taxdetails&id=213289.

Moran, P. 1988. Crown-of-Thorns Starfish: Questions and Answers. Queensland: Australian Institute of Marine Science.

Moran, P. 1988. The Acanthaster phenomenon. Australian Institute of Marine Science Monograph Series, 7: 379-480.

Pratchett, M. 2007. Feeding preferences of Acanthaster planci (Echinodermata: Asteroidea) under controlled conditions of food availability. Pacific Science, 61 (1): 113-119.

Stump, R. 1996. An investigation to describe the population dynamics of Acanthaster planci (L.) around Lizard Island, Cairns Section, Great Barrier Reef Marine Park. CRC Reef Research Technical Report, 10: 1-56.

Walbran, P., R. Henderson, A. Jull, M. Head. 1989. Evidence from sediments of long-term Acanthaster planci predation on corals of the Great Barrier Reef. Science, 245 (4920): 847-850.

Wilson, S., S. Burgess, A. Cheal, M. Emslie, R. Fisher, I. Miller, N. Polunin, H. Sweatman. 2008. Habitat utilization by coral reef fish: Implications for specialists vs. generalists in a changing environment. Journal of Animal Ecology, 77 (2): 220-228.

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