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30. Crown-of-Thorns (Acanthaster planci)


The Crown-of-Thorns starfish (Acanthaster planci) is the world's third-largest starfish, with the Sunflower Starfish (Pycnopodia helianthoides) being larger and the deep water Midgardia xandaros being the largest. The Crown-of-Thorns starfish can have up to 21 arms and is known for its distinctive spines. It can reach a diameter of 40cm/16inch. While visually striking, this corallivorous predator has a taste for hard coral polyps, making it a controversial creature among divers, with many considering it to be a pest.

The Crown-of-Thorns starfish receives its name from venomous thorn-like spines that cover its upper surface, resembling the biblical crown of thorns, a woven crown made out of thorny twigs that was placed on Jesus’ head during the events leading up to his crucifixion. These spines, containing saponins which have haemolytic properties (destroying red blood cells), can easily penetrate the skin of a potential predator and cause severe harm. Besides being toxic, they also have an unpleasant taste for those who would like to take a bite out of the starfish.

The Crown-of-Thorns starfish inhabits the coral reefs of the Indian and Pacific Oceans, from Africa’s East coast to Central America’s West Coast.

Large populations of these efficient predators of stony and hard corals have the ability to destroy large parts of the reef. The reefs that suffer the heaviest impact of these so-called break-outs are those that are already in a bad shape and where most predators of the Crown-of-Thorns starfish have vanished, or reefs that are impacted by an increased terrestrial runoff. Often, fertilizers increase the growth of phytoplankton, which in turn leads to a better survival rate of the Crown-of-Thorns starfish’s larvae.

The best-known predator of this starfish is the Triton’s Trumpet (Charonia tritonis), a big sea snail that grows to a length of 50cm/20inch. Certain Triggerfish and Pufferfish are also known to prey on the Crown-of-Thorns starfish. A few crustaceans, like the beautiful Harlequin Shrimp (Hymenocera pictus) and some hermit crabs, have also been observed preying on the starfish. Some coral polyps feed on the planktonic eggs and larvae of this starfish and, by doing so, they reduce the number of starfish that will reach adulthood.

Despite their reputation for destroying reefs, the Crown-of-Thorns starfish plays an active role in maintaining the biodiversity of the marine ecosystem. By feeding on the fast-growing hard coral polyps, they can clear the way for other, less fast-growing sessile animal species such as sponges, tunicates, bryozoans, and anemones to settle on the remaining white skeleton of the dead coral. By doing so, the Crown-of-Thorns starfish helps in creating more diversity on the reef.


To expose the often-overlooked beauty of the Crown-of-Thorns’ anatomy, with a forest-like scene of sharp elongated spines covering nearly its entire upper surface, I created a series of detailed close-up shots. It is only at the end that the entire animal is revealed. The subtle anticipation thus created intrigues the viewers.

The Crown-of-Thorns starfish is a fascinating creature that provides a unique opportunity for underwater videographers. By showcasing the beauty of all the denizens of the coral reefs, including animals with a bad reputation, underwater video images and photographs can help raise awareness of the importance of preserving our world’s coral reefs.

Filming location:

This short underwater videoclip has been filmed in Mauritius 🇲🇺

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