Crown Of Thorns (Acanthaster Planci) Sea Star

Crown of Thorns starfish are one of the most beautiful and intriguing creatures in the ocean. The Crown of Thorns Sea Star often called the COTS for short, is a venomous starfish that is considered a pest. While they are considered pests, there is no need to fear them as they are not dangerous to humans at all. While their spiky appearance may suggest otherwise, they are harmless to people.

The scientific name of the Crown of Thorns sea star is Acanthaster Planci. It is commonly known by several names, like Unnamed Animal, Japanese Labeling, Plague Starfish, and Crown-of-Thorns. The crown of thorns sea star (COTS), Acanthaster planci, is a large, multiple-armed sea star that usually preys upon hard, or stony, coral polyps (Scleractinia). The crown-of-thorns starfish receives its name from the venomous thorn-like spines that cover its upper surface, resembling the biblical crown of thorns. It is one of the largest starfish in the world.

How to Identify Crown Of Thorns Starfish?

The Crown of Thorns starfish is among the most beautiful starfish in the world, with its long and spiny arms. The Crown of Thorns Sea Star is easily recognized by its appearance as its entire body is covered in long venomous spines that give it a crown-like appearance. The spikes grow up to an inch long with some being longer than others. They have been known to grow spines up to three inches long!

These sea stars are one of the more unique-looking species because it has a round body with 21-23 arms. The spines that cover its body are flexible and not rigid like the ones you see on a hedgehog. These starfish, like other starfishes, have a central disc and move with their tube feet. They are characterized by their red color and the presence of sharp spines along their back. These spines cover their body except for the underside.

They are called ‘Acanthaster planci’ because of their horn-like spines. These covered spines are used for protection against predators. Their size varies based on species, but they usually grow between 12 to 30 inches in diameter.

Diet of Acanthaster planci

Crown of Thorns starfish is carnivorous. Their diet includes other starfish, mollusks, sea urchins, soft corals, and crustaceans. They are also known to feed on algae and tunicates.

These creatures have a very slow digestion time and can consume up to six times their own body weight in a single day.

They possess a special sensory system called ‘Ampulla,’ which helps them locate their prey and then kill them using the tiny poisonous spines present on their bodies.

The crown of thorns starfish is a destructive predator and most of its prey includes reef-building corals like staghorn, which are already endangered species. This is one of the reasons why these creatures are considered pests in most regions.

They feed on a variety of different animals, including corals and fish. They also sometimes eat other echinoderms, like sand dollars, brittle stars, and sea urchins.

They typically hunt at night. During the day they will hide under ledges or among rock crevices. When they find a potential food source, they will use their arms to push their body over the object and then bring their mouth down to the food source.

These starfish contain two stomachs. One is sac-like, while the other is branched and tubular. The sac stomach is located in its disc and is responsible for digesting prey and absorbing nutrients. The tubular stomach can be everted through the mouth to catch prey. The eversible stomach can also be used to absorb dissolved organic matter directly from the water column.

Natural Habitat

Crown Of Thorns Sea Stars is commonly found in the South Pacific and the Indian Ocean. They live on shallow reefs and feed exclusively on corals. Crown of Thorns Starfish are found in the Indo-Pacific region — from the east coast of Africa to the west coast of Central America, Hawaii, and French Polynesia. They are most abundant in the lagoons and reefs of Micronesia, Melanesia, and Polynesia.

The crown of thorns starfish is normally found in coral reefs and can be spotted on the surface of the water. Its numbers are greatest in the Indo-Pacific region, where it is considered a serious coral reef pest due to its feeding habits.

It is one of the largest starfish in the world. It has a very wide geographic range and inhabits tropical reef areas throughout the Indo-Pacific region, from South Africa to Hawaii and down to Australia. Large populations of Crown-of-thorns starfish can be found on reefs in northern Queensland, Micronesia, and Papua New Guinea. The species also occurs on a few Pacific islands where there are no reefs, including Chagos and Palmyra Atoll. It was recently reported near Rio De Janeiro in Brazil, where it had not been seen before.

So Crown of thorns sea stars is found throughout the Indo-Pacific, including the east and west coasts of Africa, the Red Sea, Australia, Japan, and the Indian Ocean. They prefer living on coral reefs but can be found in other areas that have plenty of food.

Reproduction & Growth

The crown of thorns starfish reproduces sexually, like most other animals. It has both male and female reproductive organs (they are called hermaphrodites) and can reproduce all year round.

The Crown-Of-Thorns Starfish is viviparous, which means that the females bear living young. The female releases a swarm of fertilized eggs from her body and a male fertilizes them outside of her body. Unlike many other sea stars, the larvae have no radial symmetry, nor do they have eyes or tube feet (features that would aid in movement). Instead, they are shaped like fish eggs with cilia to move them through the water. Because of this, there is little chance for a larva to find its way back to coral after being released by the mother.

After about 10 days of living off their yolk sacs and consuming plankton, the young starfish develop into bipinnaria larvae. They will develop an eyespot on one end and three bands around their bodies that run the length of their bodies. It takes approximately 2 months for a bipinnaria to develop into brachiolaria larvae. With another month or two, they settle on coral reefs and begin feeding on soft coral polyps.

The average size of an adult crown of thorns seastar is between 20 and 30 cm across. There are some species, however, that can reach up to 40 cm in diameter. Their growth rate is fairly slow in the beginning, as a young seastar will only grow about 2-4 mm per month for the first year of its life. Once it reaches sexual maturity – which usually happens after two years – it grows a lot faster, at a rate of about 14mm per year.

The Crown of Thorns Sea Star is a unique and magnificent creature that is known for its large size and thorny appearance. The Crown of Thorns Sea Star is one of the largest sea stars in the world, reaching diameters of up to 24 inches. This species also has a long lifespan, living an average of 10 years.


Predators of the crown-of-thorns sea star include large fish, such as the giant Maori wrasse, and some species of coral trout, which are known to prey on juvenile crown-of-thorns sea stars. The most significant predators, however, are humans, who find them a nuisance and have been known to kill them.

The crown of thorns starfish has a number of predators, including the giant triton snail, humpback whale and some species of nudibranch. The main predator of the crown of thorns starfish is the Triton’s trumpet snail (Charonia tritonis), which can be found in the Indo-Pacific region.

This snail preys on the crown of thorns starfish by using its hard shell to attack and crush it. This snails’ shell can grow up to two feet in length, but it only uses an inch of this for protection. The rest is used to attack other animals and prey. Crown of thorns is a large sea star and it has its own defense mechanism, as well as the ability to eat fast. The fact that this sea star is venomous does make it a bit more dangerous for predators.

The Crown of Thorns Sea Star will often use camouflage to hide from predators. This is where it will change colors to blend in with the environment. The colors allow it to hide in the coral or on the ocean floor.

Other predators include sharks, turtles and dolphins. Those animals that do eat these sea stars will often eat them when they are very young or if the sea star is sick or injured. They will also eat them when they are not fully grown into an adult.

Aquarium Guide- How to maintain tank for Crown of Thorns starfish

The crown of thorns starfish has been popular in aquariums for many years and is extremely easy to care for. They are a great choice for beginners who are looking for an interesting, unique addition to their tank. The crown of thorns starfish can be a bit difficult to maintain. However, with proper care, you can successfully keep it in your tank. Here is how you should care for this aquatic animal:

Tank Size

The crown of thorns starfish do not have any specific requirements when it comes to tank size but should be kept in at least a 55-gallon tank since they can grow quite large. They are relatively slow-moving creatures and will not outgrow their tank very quickly, so don’t worry about finding a large tank if you don’t have one available now. However, the larger your tank is, the easier it is to provide stable water conditions and maintain a healthy aquarium.

Tank Mates

The main thing you have to keep in mind with tank mates is that they do not eat sessile invertebrates or corals. If you are keeping them in a reef aquarium with corals, it is very important that they do not eat this coral because they can destroy your entire setup in a very short time period. You should also avoid keeping them with other large or aggressive predatory sea stars such as linckia sea stars or chocolate chip stars which may try to eat them.


The crown of thorns starfish has no real temperature requirements and will thrive in most tropical aquariums ranging from around 72°F to around 82°F. The pH-value should be 8,2-8,4 and the specific gravity 1.023-1.025. In the wild, this starfish feeds on living hard and soft coral polyps, so it may not be suitable for reef aquariums unless it is fed live corals or other meaty foods on a regular basis.

Waterflow & Lighting

Crown Of Thorns starfish are marine animals that can be found in tropical waters throughout the world. They do well with medium water currents in the aquarium but prefer moderate lighting, as they are more apt to come out at night when the lights are off. If there is too much light they will hide in dark areas during the day which means less feeding opportunities for them because they rely heavily on photosynthesis from algae growths on their skin.


When it comes to filtration, the crown of thorns starfish has no real requirements. Some aquarists choose to keep their starfish in a tank with no filtration; others use traditional canister or hang-on-back filters.


The crown of thorns sea star needs a lot of open space to move around in its aquarium. Because it moves in a crawling manner, it does not need an extensive substrate that might otherwise slow down faster-moving fish species. A bare-bottom or very thin sand bed is fine. In addition, the crown of thorns should be provided with plenty of live rock or strong PVC pipes to which it can attach itself when not feeding. This will help keep it from falling over and potentially injuring itself on aquarium equipment or decorations.


Because the crown of thorns sea star is such an aggressive feeder and can quickly devour corals and other invertebrates, it must be housed in a tank by itself. Some aquarists have successfully kept their crown of thorns stars alongside other species of sea stars, but this is always risky. If you do use live rock or coral skeletons, be sure that they are large enough to support the heavyweight of the sea star; if not, the rock will collapse under it and injure the animal.

Fun Facts related to the Pest Sea Stars – Crown Of Thorns

  • The world’s oceans are filled with exotic sea creatures. Among the most unique of these is the crown of thorns starfish, a large, hardy sea star that can live in a wide range of climates and feed on an even wider range of coral species.
  • The Crown of Thorns Sea Star is an interesting and cutest species of sea star. It’s one of the most popular animals for many aquarium hobbyists around the world.
  • These beautiful sea stars are not only great pets because they look gorgeous but they will also help keep your tank clean by eating algae and different types of waste that accumulate in your tank.
  • Crown Of Thorns’ venom contains several toxins: tetrodotoxin, veratridine, saxitoxin and batrachotoxin. These toxins paralyze prey by blocking nerve transmission; they can even kill humans if ingested in large amounts!
  • They have been known to eat entire colonies of coral over time, so they are considered pests by many people who live near coral reefs or work in marine biology fields.
  • Crown of thorns sea stars have about 18 to 21 arms. But some may have as many as 23 arms. The sea star’s color is normally black or dark purple. But it can also be brown, green, or yellowish in color.
  • Crown-of-thorns sea stars have eyespots at the end of each arm that allow them to detect light and movement.
  • The outer covering of crown-of-thorns is called a test. The test is quite rigid and has small spines on it. There are also two rows of larger spines running down the length of each arm. The spines are hollow and filled with venom. This venom protects the sea star from predators.
  • The crown of thorns starfish receives its name from venomous thorn-like spines that cover its upper surface, resembling the biblical crown of thorns. It is one of the largest starfish in the world.
  • The underside of the crown-of-thorns has two stomachs, a mouth and a nerve ring connected to an anal pore by a canal. Arms can be regrown if they are lost or damaged. A new arm will grow back in 3 to 4 months if conditions are right.

Crown Of Thorns Starfish- Related FAQs

Q1. What does the crown-of-thorns starfish need to survive?

The crown-of-thorns starfish feeds primarily on hard and soft corals, but will also feed on other invertebrates such as sand dollars and sea urchins. The crown-of-thorns starfish is a large, multiple-armed starfish (Acanthaster planci) that usually preys upon hard, or stony, coral polyps (Scleractinia). The crown-of-thorns starfish is a species of sea star that eats coral polyps. A small group of them can destroy large areas of coral reefs.

Q2. What does a Crown-of-thorns Starfish look like?

The body of crown of thorns sea stars is round to oval in shape with long, spiny arms that resemble a crown. The color ranges from dark red to brown, sometimes even purple or green. Their underbelly has soft fleshy skin and they have tube feet on their underside that help them move around and find food.

Q3. How are Crown of Thorn sea stars helpful?

Crown-of-Thorn starfish are very helpful! The Crown-of-Thorn starfish is a predator that feeds on certain species of coral polyps. As it moves across a reef, it devours the coral, leaving only their skeletons behind. Naturally, this has devastating effects on the coral reef community.

On the other hand, by removing these corals from the reef for food, Crown-of-Thorns starfish are actually helping to keep the ecosystem in balance. They play an important role in preventing the overgrowth of specific corals and keeping an ideal balance between different coral species.

Q4. How long do crown-of-thorns starfish live?

These marine animals can survive as long as 40 years, if they escape the perils of their existence. The average life span is about 3 years. The oldest known individual is a captive specimen that lived for more than 40 years.

Generally, Crown-of-thorns starfish live between 5 and 35 years, depending on the size of the animal. The larger the individual, the longer its lifespan is.

Q5. Are crown-of-thorns starfish nocturnal?

Crown-of-thorns starfish are nocturnal, which means that they come out to hunt at night. However, some species are also active during the day and prefer to feed in broad daylight.

These animals tend to rest during the day, usually on the sea floor or on top of corals. At nightfall, they start moving around in search of prey.They are most active in the evening, after dusk and before dawn. While these animals are active hunters, they are also adept at scavenging for food.

They will typically spend their days hiding in crevices or under coral ledges. Because of their nocturnal habits, divers sometimes find them hidden under rocks or coral rubble to get protection from sunlight during the day.

Q6. How poisonous is the crown-of-thorns starfish?

Crown-of-thorns starfish are not poisonous to humans. It is very unlikely that you would be injured by one, and if you were it would probably be because of a sharp spine in its body rather than any venom.

The crown-of-thorns starfish does have a venomous bite, but this only affects other sea creatures. The main use of its venom is to help it digest its prey.

Q7. How does the crown-of-thorns starfish interact with the environment?

The crown-of-thorns starfish interacts with the environment in a few ways. The crown-of-thorns starfish has an important role in nature’s way of keeping the coral and algae populations down, so that it does not take over an area. This starfish is considered a keystone species, because of this role. The crown-of-thorns also helps to keep other sea life in balance by consuming them when there is too many of one species.

Q8. What are some adaptations for the crown-of-thorns starfish?

The crown-of-thorns starfish has many adaptations. The crown-of-thorns starfish has sharp spines on its body that help protect it from predators. It also has a water vascular system, where water is pumped in and out of its body through the tube feet to help move it around. Along with these two adaptations, the crown-of-thorns starfish can regenerate its own body parts if they become injured or detached from its body.

Q9. What are some examples of food chains involving the crown-of-thorns starfish?

The crowns can be at both ends of a food chain or just somewhere in between, depending on what they eat. An example would be if they were eating shrimp, crabs, and fish then those species would ultimately be eaten by something else, so you could have a little food chain within another food chain.

Q10. How big is Crown Of Thorns Sea Stars?

When they reach adulthood, the average size of these sea stars is 25 cm. However, some can grow up to 35 cm in diameter. The size depends on the age as well as the availability of food and water in their habitats. An adult specimen can have 20 to 23 arms.


A crown-of-thorns sea star is one of the most realistic and natural-looking aquarium decorations that you will find. Crown of Thorns Sea Star, or COTS for short, is one of the most important reef organisms. It helps in controlling the number of uneaten algae or coral polyps that lie on the corals and kill them. As a result, their population is decreasing day by day.

The crown of thorns, however, is harder than we know, and they require very basic care to stay alive and healthy in aquariums. Again, with proper care, the crown of thorns is not difficult at all and will adapt and well adjust to any home aquarium tank. It’s a robust animal and will get on well with other invertebrates and fish provided that they have enough space to move and grow. So, if you are looking forward to having an ideal pet with lots of color and beautiful characteristics, then go for the COTS.

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