Species of the week

Meet the Acanthaster planci, the biggest natural coral polyps predator.

Common name: Crown-of-Thorns

Scientific name: Acanthaster planci

Kingdom: Animalia

Phylum: Echinodermata

Class: Asteroid

Order: Valvatida

Family: Acanthasteridae

Genus: Acanthaster


Size: Can reach 70 cm in diameter when adult.

Diet: Varies with the animal’s developmental stage. In the larval stage, the Acanthaster planci feeds on phytoplankton and dissolved organic matter. In the juvenile stage, it feeds on encrusted coralline algae. Already in the adult stage it feeds mainly on scleractinous coral polyps.

Longevity: Can live up to eight years.


Description

Acanthaster planci is the largest starfish of the phylum echinodermata. Different to the other species, the crown-of-thorns can present up to 20 long arms, about 18 cm long, and venomous spines that varies from 4 to 5 cm in length. Its coloration varies according to its distribution, being greenish gray to red in the Pacific Ocean, pale blue to pale red in the Indian Ocean and present a combination of colors that can range from purplish blue with red-tipped spines to green with yellow-tipped spines.

Acanthaster planci is a predator of corals, then, due its feeding method it is considered one of the greatest threats to the coral reefs of the Indo-Pacific. The crown-of-thorn expels its gastric folds with digestive enzymes to digest prey during its feeding, which causes it to destroy a vast area of coral reefs in a short time. The area of coral reefs devastated takes normally 5 years to recover, but in a severe state can take up to three times more. In some cases, these areas do not regenerate and are change by algae species.

Habitat

Acanthaster planci is generally found in lagoons and deep water. This starfish prefers habitats with substrate that provide shelter against waves. The depth at which the crown-of-thorns can be found, varies with its development. The larvae are pelagic and shelter in shallow reefs. Pre-juveniles, can be found up to 80 meters deep where they remains for 3 years with up to 5 cm in diameter. When it reaches the juvenile stage, it rises to 20 meters deep, where it completes its life cycle.

Ecology

Acanthaster planci is a voracious predator of corals and can alter the coral reef ecosystem by reducing the its biodiversity and richness, stimulating the colonization of algae on the. This species is predated by some large molluscs such as the Giant Triton (Charonia tritonis), the Helmet shell (Cassis sp) and some fish species, such as Napoleon fish (Cheilinus undulatus) and Balloon fish.

Distribution

The geographical distribution of Acanthaster planci ranges from Mauritius in the western Indian Ocean, including the Red Sea and across the Pacific to the west coast of America.

Reproduction

They are dioecious and reproduce during the summer, when the temperature and intensity of light increases. In this period, the females release eggs and the males the sperm in the water column. The number of eggs released depends on the size of the female, and can reach up to 60 million eggs per breeding season, when the female is an adult. One day after fertilization, the eggs pass several changes becoming larvae that spend two to four weeks drifting in the ocean currents. After one month, the larvae settle in the benthos and begin the final metamorphosis to reach adult stage.

Curiosities

  • Acanthaster planci has spines with toxic venom to humans.
  • Acanthaster planci is the natural predator of corals along the Indo-Pacific.
  • A single crown-of-thorns can devastate an area of about 6 m2 per year.

Sources

Laxton, J. H. (1974). Aspects of the ecology of the coral-eating starfish Acanthaster planci. Biological Journal of the Linnean society6(1), 19-45.

Longhurst, K, Foley, L & Ferguson, A, (2014). Crown of thorns seastar (Acanthaster planci) Assessment Report. Napantao. San Francisco

Clark, C., & Weitzman, B. (2006). Population study survey of Acanthaster planci, the Crown-of-Thorns Starfish on the northwest coast Moorea, French Polynesia. Rapport de l’Université de Californie Santa Cruz.

Vantier, L. M., & Deacon, G. (1990). Distribution of Acanthaster planci at Lord Howe Island, the southern-most Indo-Pacific reef. Coral Reefs9(3), 145-148.

Zann, L., Brodie, J., Berryman, C., & Naqasima, M. (1987). Recruitment, ecology, growth and behavior of juvenile Acanthaster planci (L.)(Echinodermata: Asteroidea). Bulletin of Marine Science41(2), 561-575.

Reichelt, R. E., Bradbury, R. H., & Moran, P. J. (1990). The crown-of-thorns starfish, Acanthaster planci, on the Great Barrier Reef. Mathematical and Computer Modelling13(6), 45-60.

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