Acanthaster planci
crown-of-thorns starfish

Ancanthaster planci are found in Red Sea and Indo-Pacific coral reefs. These starfish are especially abundant in Australia's Great Barrier Reef (Johnson and Cartwright, 1996; Shmid, 1998).

Acanthaster planci are sedentary dwellers in seabeds and reefs. Their tube feet enable them to slowly roam the waters in search of food (Perrins and Middleton, 1985).

Acanthaster planci are red colored echinoderms protected by thorn-like spines. They grow to a diameter up to 40 cm across. They have 12-19 arms extending from their center. These animals do not have a head, and are pentamerically symmetrical about the axis of the mouth. Acanthaster planci have tubed feet, or branched tentacles arranged along each arm that function in gas exchange and food gathering (Schmid, 1998; Perrins and Middleton, 1985; Encyclopedia Britannica, 2000).

Once an egg is fertilized in the water column and develops into a larva, they settle to the sea floor and continue development there, transforming to an adult form and continuing to grow.

Well-equipped with muscular tube feet, they can efficiently move across the floor of the ocean. These starfish are capable of moving in reverse, turning around, or moving one arm independently from the rest. Their motility is well adapted to their needs (Perrins and Middleton, 1985).

Acanthaster planci are insensitive to touch and gravity, as they lack statocysts. They are able to sense predators as well as prey through waterborn chemicals.

Acanthaster planci prey on coral polyps. It digests its food by climbing onto its prey and extruding its stomach over the coral colony, releasing digestive enzymes to then absorb the liquified tissue. They feed solitarily at night and maintain a constant distance between themselves and other A. planci. Individual starfish feed on up to 13 square miles of coral per year. During times of food shortage, these animals can live on energy reserves for over six months at a time. However, a proliferation of this species can be detrimental to the survival of coral reefs. In recent years Acanthaster planci have reduced the colorful attraction of the Great Barrier Reef with its ravenous appetite (Johnson, 1996; "Cnidarians", 2000; Perrins and Middleton, 1985; Schmid, 1998; "Great Barrier Reef", 2000)

These starfish are armored with impressive spines, making attack difficult. However, a number of animals are known to prey on crown-of-thorns starfish, including molluscs, fish, crustaceans, and a worm.

These are voracious predators of corals and can wipe out large areas of coral, thus potentially upsetting the basis of one of the world's most diverse ecosystems. It is possible that crown-of-thorns starfish eggs and larvae are preyed upon by economically important reef fish. The decline of these reef fish populations may contribute to population increases in crown-of-thorns starfish.

The long spines of Acanthaster planci are capable of pricking and stinging humans, inflicting great pain that can last up to hours. Glandular cells located on the epithelium covering each spine release toxic chemicals into the skin when it stings. There is temporary paralyzation at the sight of stinging accompanied by nausea (Grzimek, 1972).

Although Acanthaster planci are considered one of the most damaging creatures among coral reefs, their outbreaks have inspired extensive research. More information involving thyroxine-accelerated larval development and temperature effects upon the larval ecology of larval development has been obtained, also giving insight into other species of the Phylum Echinodermata (Johnson & Leland 1996).

This species has greatly increased in population size since the 70's, causing great damage to the coral reefs of the Indo-Pacific ocean, as well as the Red Sea and Australia's Great Barrier Reef. Core sampling and radiocarbon dating of sediments from different reefs suggest that this has been occuring for thousands of years, but is increasing in frequency. Control methods for this environmental disaster are currently being researched (Birkeland, 1989).

Ancanthaster planci has been described as one of the most influential species in the diverse biotic communities that make up tropical reefs (Birkeland, 1985).