Crown Of Thorn Starfish: A Venomous Beauty of the Ocean

Starfish are beautiful, but not all of them. Some have the destructive power to impact an entire ecosystem. Meet the crown of thorn starfish: armed with venomous spines, it can devastate entire coral reefs. Despite its importance in the marine ecosystem, this prickly predator is often seen as a nuisance. Let’s have a look at some interesting facts about COTS to know more about it, from its adaption to its impact on the whole ecosystem!

Crown Of Thorn Starfish
Scientific name: Acanthaster planci
Phylum: Echinodermata
Class: Asteroidea
Order: Valvatida
Family: Acanthasteridae
Genus: Acanthaster

They have 21 arms

Among many sea stars, the Crown of Thron Starfish (COTS) is a special species with its size and appearance. It is one of the biggest starfish with a size of about 50 cm in diameter, with some even growing to 80 cm. Their size depends on how old they are and how much food is around them. When they’re young, they’re smaller, but as they get older, they can become really big. It has spines around its body, these spines are usually purple, but they can also be green or brown.

Crown Of Thorn Starfish has poisonous sting

Out of the 2,000 species of starfish in the ocean, most starfish have 5 arms. However, some species, like the crown-of-thorns starfish, are quite extraordinary. It stands out with up to 21 arms, covered in a thorny texture that helps them grip onto surfaces.


These species come from the coral reef ecosystems in the Indo-Pacific region. These starfish are typically found in tropical and subtropical waters, ranging from the Red Sea and the Indian Ocean to the Pacific Ocean, including the Great Barrier Reef in Australia. They prefer shallow, warm waters with abundant coral reef formations.

They are found within coral reef ecosystems, including reef flats, reef slopes, and coral gardens. Additionally, they are known to inhabit both healthy and degraded coral reefs, although their populations can increase rapidly in areas with declining coral health due to factors such as pollution, overfishing, and climate change.


Crown of thorns starfish (COTS) are sea creatures that eat coral. Their sharp spikes help them climb onto coral colonies. Once they’re there, they spread out their stomachs over the coral and release special enzymes to break down the coral. This lets them get nutrients from the coral that other animals can’t. The young of this species eat small coral polyps when they’re little, but as they grow, they start eating larger coral polyps.

Crown Of Thorn Starfish location
The species is eating coral

These starfish can eat a lot of coral – up to 6 square meters per year. This can cause big problems for coral reefs and the animals that depend on them in the ocean.

They are toxic

The crown of thorn starfish gets its name from the many sharp spines covering its upper body, which can be up to 4cm long. These spines serve as a strong defense against predators. If predators dare to attack, the starfish has another defense mechanism: a toxic slime.

The spines of these creatures have plancitoxins, which can hurt the liver. Additionally, when these sea stars feel threatened, they release saponins, which can damage red blood cells. Both of these toxins can cause a lot of pain to any animal, including humans, that touches them.

Despite the starfish’s defenses, there are still predators that manage to get through. These predators have developed ways to deal with the starfish’s spines and toxic slime. For instance, the giant triton snail can slowly hunt down and eat the crown of thorn starfish in a rather gruesome manner. Other creatures like the humphead maori wrasse, titan triggerfish, and starry pufferfish also prey on adult starfish. Their young are targeted by shrimp, crabs, worms, filter feeders, and various types of fish.


The Great Barrier Reef crown of thorn starfish (Acanthaster planci) has a sexual reproduction. During the breeding season, they release their eggs and sperm into the water. This process, called spawning, happens outside of their bodies. The female of this species is capable of releasing an impressive number of eggs each year, with some laying over 200 million eggs!

After hatching, the larvae float in the ocean currents for about 10 to 30 days before finding a spot to settle on the ocean floor. During this time, they mainly eat crustose coralline algae. Once they find a place to stay, they change into juvenile starfish, which quickly grow and start eating coral polyps. In just two years, they can become mature and start reproducing. The lifespan of the crown of thorn starfish is about 9 – 12 years.

Crown of thorn starfish Outbreaks

Crown of thorns starfish outbreaks are a big problem for coral reefs. When these outbreaks happen, there can be thousands of these starfish in just one hectare of reef. This invasive species eats a lot of coral, especially the branching kind. This can wipe out whole colonies of coral and make other problems like coral bleaching even worse.

Scientists, reef managers, and divers are collaborating to protect coral reefs from COTS outbreaks. They’re using different methods to control and reduce the impact of these outbreaks.

One successful approach involves creating marine protected areas (MPAs) and conservation zones within parks. Studies show that areas with stronger protection have fewer COTS, emphasizing the need for careful, long-term planning when managing reefs.



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We are passionate animal enthusiasts with over a decade of experience studying animals. With a degree in zoology and conservation biology, we've contributed to various research and conservation projects. We're excited to bring you engaging content that highlights the wonders of the animal kingdom. We aim to inspire others to appreciate and protect wildlife through informative content grounded in expertise and passion. Join us as we delve into the captivating world of animals and discover the incredible stories they have to tell.

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