Acanthaster planci   (Linnaeus,  1758) (Starfish)
Organism information awaits expert curation
Taxonomy
Kingdom:Animalia
Phylum:Echinodermata
Class: Asteroidea
Order:Valvatida
Family:Acanthasteridae

Image copyrights: David Harasti

Description
Size: 20-30 cm. Specimens of up to 60cm (and even 80cm) in total diameter have been collected (Chesher, 1969; Moran, 1997).

Color: Blue to pale red. Color combinations can vary from purplish-blue with red tipped spines to green with yellow-tipped spines (Moran, 1997).

This sinister looking and rather flattened sea star has a large central disk and 7 to 23 arms (usually 14 to 18) and it displays on the aboral side elongate spines (ca. 5cm) which make it immediately distinctive. The body "appears" to be quite stiff, but can bend and twist into all sorts of shapes to fit the contours of the coral substrate it feeds on. The skin is a sensitive membrane, used for extracting dissolved oxygen from the seawater. A meshwork of small magnesium calcite-ossicles, from which project numerous movable and immovable spines, are embedded in the tissue of the body wall. They should be handled carefully, since the long, sharp spines are mildly venomous and can inflict painful, slowly healing wounds.

A series of closely fitted plates, the ambulacral ossicles form a groove and extend in rows along the underside of each arm to converge on the mouth in the center. The anus and one or more madreporites (through which water is drawn in to fill and control the water vascular system) are in the center of the upper disc surface. This system is essential for locomotion of the sea star. A ring canal connected to the madreporite encircles the mouth and gives off 5 radial canals. Each runs along the underside of each arm and ends at the tip in terminal sensory tentacles. From the radial canals extend thin-walled cylindrical tentacles, called tube-feet or podia. Each podium is connected to a round muscular sac, the ampulla and constitutes a closed unit. When the ampulla contracts, the fluid it contains is forced into the podium, extending it. Small muscles direct the extended podium in one or the other direction (the movements of the body wall and its spines are coordinated by a a skin-receptors themselves connected to a sensory nerve net running just beneath the epidermis; in fact eyespots at the tip of each arm act as light sensors and influence the starfish's movements). The terminal tip of each podium excretes a sticky mucus, which is flared out as a sucker. The batteries of podia in total and their combined efforts move the animal along the substrate. As this system allows Acanthaster planci to move rather slowly over the substrate in search of prey, it becomes more obvious that only sedentary organisms like corals are the main nutritional resource.

Sexes are separate and females release huge amounts of gametes directly into the sea (Benzie, 1999). If conditions are favourable and there is an abundant larval survival, the high reproductive potential of even a few adult Acanthaster planci may allow the production of a massive settlement of juveniles (Birkeland, 1982). Over two-thirds of the population aggregate to participate in this spawning event, which usually occurs in the morning or afternoon and may be driven by pheromones released into currents (Babcock and Mundy, 1992). Acanthaster planci often spawns in a characteristic arched posture, usually on top of elevated rocks or corals at elevations of 30m to reefs flats (Babcock and Mundy, 1992).

After the gametes (eggs and sperms) and hormones (which stimulate other individuals to release gametes) of Acanthaster planci are shed into the seawater, they have a short amount of time to become fertilized before they become unviable (Madl, 1998). After fertilisation, the zygote develops into a larvae. After drifting around for two to three weeks, the 0.5 mm small larvae starts to morph and eventually settles and attaches itself to the sea floor where it completes its metamorphosis (Madl, 1998). Larval life may last longer than three weeks if conditions are unfavourable (Birkeland and Lucus, 1990, in Benzie, 1999). Various substrates, particularly crustose coralline algae with bacterial surface films, induce Acanthaster's planktonic larvae to settle and metamorphose (Johnson and Cartwright, 1996). One group of scientists found that thyroxine accelerates development in Acanthaster through larval stages (Johnson and Cartwright, 1996). After settlement, the larva metamorphoses into a juvenile starfish, a process which takes about two days (Moran, 1997). Initially the juvenile starfish has only five rudimentary arms, but additional arms develop rapidly as the starfish begins to feed on encrusting algae (Moran, 1997). At the end of six months, the starfish is about 1cm in size and begins to feed on corals (Moran, 1997). Individuals are able to reproduce after two years (Lucas, 1973, in Babcock and Mundy, 1992). Being a rapid grazer of coral polyps, it takes only three to four years for the coral-feeding starfish to reach a reasonable size of 30-35cm (Madl, 1998). After three to four years, it is thought to go into a senile phase where growth declines dramatically and reproduction is low (Moran, 1997). It is not known how long starfish live, although they have been kept in aquaria for as long as eight years (Moran, 1997).


Synonym (s)
Acanthaster echinites Ellis & Solander, 1786
Asterias planci Linnaeus, 1758
Asterias echinus Ellis Verrill, 1914
Asterias solaris Schreber, 1793
Stellonia echinites L. Agassiz, 1836
Acanthaster planci James, 1969
Acanthaster echinus Gervais, 1841
Acanthaster ellisi (Gray, 1840)
Acanthaster mauritiensis de Loriol, 1885
Acanthaster pseudoplanci Caso, 1962
Acanthaster solaris Schreber, 1793
Asterias echinites Ellis & Solander, 1786

Common Name (s)
• Coral-eating Starfish (English)
• Crown of Thorns Starfish (English)
• Giant Thorny Starfish (English)
Economic Importance and Threats
Importance:  Commercial, Ecosystem balance, Dangers
(The carcasses of starfish were used as fertiliser.
Acanthaster planci is a significant coral predator and is known as a keystone species. It has the potential to alter coral ecosystems in significant and important ways. This makes it a useful indicator species and one which should be monitored when assessing the health of coral reef ecosystems.
Predation results in reduction of abundance and surface cover of living corals, species composition, species diversity, and colony size distribution.)

Ecology
Habitat:  Reef Associated, Coastal
Trophic Level:  Secondary Consumer
Prey:  Larvae feed on phytoplankton (Birkeland, 1982) and dissolved organic matter; juvenile starfish feed on encrusting algae; adult Acanthaster planci feed primarily on coral (mainly hermatypic, i.e. reef building, scleractinian corals and shows a marked preference for acroporids -Acropora spp. and Montipora spp.)
Predator:  Annelids (Pherecardia striata), crustaceans (Hymenocera picta, Phyllognathia ceratophthalma), mollusks (Charonia tritonis), fishes (Lethrinus nebulosus, Lutjanus sebae, Cheilinus undulatus, Balistapus undulatus, Balistoides viridescens, Arothron stellatus, Arothron hispidus)

Biogeography


• Lakshadweep, Bangaram INDIA (Record: 23/12/1979)
• Lakshadweep, Kavaratti INDIA (Record: 05/02/1986)
• Lakshadweep, Minicoy Lagoon INDIA (Record: 01/1990-12/1991)
• Goa INDIA
• INDIA
• Lakshadweep, Kadamatt INDIA (Depth: 1-2 mts)
• Andaman and Nicobar Islands, Nancowry INDIA
• Andaman and Nicobar Islands, Port Blair INDIA
• Andaman and Nicobar Islands, Nicobar Islands INDIA
• Lakshadweep, Agatti INDIA (Depth: 1-2 mts)
• Lakshadweep, Kavaratti INDIA (Depth: 1-2 mts)
• Lakshadweep, Minicoy INDIA (Depth: 1-2 mts)
• Lakshadweep, Kalpeni INDIA (Depth: 1-2 mts)
• Andaman and Nicobar Islands INDIA

Literature Source(s)
  • Species belonging to porifera in Indian Ocean
  • Society for the Management of European Biodiversity Data (2009) World Register of Marine Species (WoRMS) Available at - http://www.marinespecies.org
  • Sastry, DRK (1991) Echinodermata: Asteroidea, Ophiuroidea and Echinoidea State fauna series 2: Fauna of Lakshadweep ZSI, Calcutta 363-397 Available at - NIO, Goa
  • Global invasive species database Available at - http://www.issg.org/database
  • Madl, P (2002) Acanthaster planci Colloquial meeting of Marine Biology I Available at - http://www.sbg.ac.at/ipk/avstudio/pierofun/planci/planci.htm
  • Scuba equipment USA - Marine species gallery Available at - http://www.scuba-equipment-usa.com/marine/index.html
  • Navas, KA and Mathew, KJ (1995) Present status of coral erosion in Lakshadweep with special reference to Minicoy Mariculture research under the postgraduate programme in mariculture part 6 CMFRI Special Publication cmfri 61 1-5 Available at - http://eprints.cmfri.org.in/3467/
  • James, DB (1983) Research on Indian echinoderms-A review Journal of Marine Biological association of India The Marine Biological Association of India. 25(1&2) 91-108 Available at - http://eprints.cmfri.org.in/1294/1/James_91-108.pdf
  • James, PSBR ; Thomas, PA ; Pillai, CSG and Achari Kumaraswamy, GP (1969) ´╗┐Catalogue of types and of sponges, corals, polychaetes, crabs and echinoderms in the reference collections of the Central Marine Fisheries Research Institute Bulletin of Central Marine Research Institute CMFRI, Cochin 7 1-66 Available at - http://eprints.cmfri.org.in/567/1/Bulletin_7.pdf
  • James, DB. (1983) Sea cucumber and sea urchin resources and Beche-de-mer industry Mariculture potential of Andaman and Nicobar Islands-An indicative survey Bulletin of Central Marine Fisheries Institute CMFRI, Cochin 34 85-93 Available at - http://eprints.cmfri.org.in/809/1/Bulletin_No_34.pdf
  • Sastry, DRK (2007) Echinodermata of India : An annotated list Records of Zoological Survey of India Occassional paper No. 271 ZSI, Kolkata 1-387 Available at - http://zsi.gov.in/checklist/Echinodermata_India_Checklist.pdf
  • Sealifebase Available at - http://www.sealifebase.org/
  • James, DB (1989) Echinoderms of Lakshadweep and their zoogeography Marine living resources of the union territory of Lakshadweep: An indicative survey with suggestions for development Bulletin of Central Marine Research Institute CMFRI 43 97-144 Available at - http://eprints.cmfri.org.in/8213/1/Bulletin_No_43.pdf
  • Rao, GC (1991) Distribution of plants and animals on the rocky sea shores of Andaman and Nicobar Islands Journal of the Andaman Science Association Andaman Science Association, Port Blair 7(2) 30-42 Available at - NIO, Goa

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