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Acanthaster planci

Linnaeus, 1758

Crown-of-thorns starfish


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Latin name : Acanthaster planci (Linnaeus, 1758)
Synonyms :
Classification : Asteroidea ( Sea stars )
Name : Acanthaster
Coussin de belle mère
Name : Crown-of-thorns starfish
Main identification characters
Acanthaster planci is a spiny star-fish which is often called the "crown of thorns".

Morphology :
- Diameter : 18 to 50 cm in New Caledonia
- Most of these animals have between 11 and 12 arms, sometimes 16 or 17
-The arms of 53 % of the individuals undergo a process of regeneration
- Weight: 200 g to 3 Kg.
Possible confusions
Feel free to update this datasheet and complete this data.
Adult acanthaster are corallivorous (carnivorous), but not strictly so, since they also ingest algae, gorgonians and alcyonaria.

The particularly large size of the stomach when it is bloated with food (it has a much larger relative size than that of the other star-fish) makes for a fast growth rate.

The great flexibility and lightness of acantharia in comparison with the other star-fish inhabiting coral environments make them more mobile and efficient. The adults can move at speeds of up to 10m/h.
Cycle of life / Reproduction
The members of the two sexes always remain apart: since the reproductive substances are ejected into the sea, fertilisation is most likely to occur if a large number of individuals have congregated. It has been observed that the males and females adopt a special position during the process of fertilisation

The reproductive periods: these have been determined on the basis of the data obtained in various countries at diverse latitudes on the mean monthly gonado-somatic ratios (GSR), the volume of the gonads and the animals’ stage of sexual maturity.
Interaction with other species
Acanthaster are to be found throughout the Indo-Pacific region, but they are difficult to quantify because their numbers vary considerably in time and space.

Acanthaster contain sapotoxins which protect them from predators. However, there exist 12 species of fish and coral which feed on acanthaster when they are still at the stage of eggs and larvae.

Charonia tritonis (a gastropod) and Hymenocera picta (a shrimp) prey mainly on juvenile acanthaster.

The damage to the coral :

Just as is it difficult to define a bloom, it is also difficult to assess the resulting damage:

* Sometimes the damage is considerable: 90 % of all the coral on the 38 -Km long coast of Guam were destroyed by blooms, as were 80 % of all the coral on Green Island (Australia) down to depths of 40 m. The acanthaster have luckily caused much lower death rates in Hawai.

* The damage varies from one point to another: the coral in shallow places with turbulent waters has been less severely damaged by acanthaster than the coral in other places.

* The extent of the damage also depends on the coral species: those such as Porites and Pocillopora, which form the most massive blocks, are less highly exposed to acanthaster; in some places where the coral has been scraped bare, there can still be some tiny surviving patches measuring only a few square centimetres, which may suffice for a process of recolonisation to be able to start up.

A single acanthaster can destroy 5 to 6 m2 of coral per year. A whole cluster can destroy several km2 per year.

Coral reef.
Geographical distribution
Acanthaster are to be found throughout the Indo-Pacific region, but they are difficult to quantify because their numbers vary considerably in time and space.
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Data sheet written by Chantal Conand, ECOMAR (univ. Réunion) et Lo?c Charpy, IRD. , 5/03/2003

Updates :
Perrine Mangion - 21/05/2003

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