The Crown Of Thorns Starfish (Acanthaster Planci)

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Acanthaster planci, also known as the crown of thorns starfish, is one of the largest sea stars in the world, growing up to 3 feet in diameter and 10 pounds in weight. Despite its name, it’s actually not a true starfish, but rather a sea star of the Asteriidae family (along with over 2,000 other species of sea stars).

Also referred to as crown of thorns sea star, Crown of Thorns Starfish use their flexible arms to move along the ocean floor and hunt prey. They are typically found living in coral reefs and rocky seabeds at depths of 2,000 feet or more.

The Crown of Thorns Starfish belongs to the phylum Echinodermata, the same phylum that coral and sea urchins belong to. It may look like something out of your nightmares, but despite its spiky exterior, it poses no threat to humans if precautions are followed!

Acanthaster planci was accidentally introduced to the Hawaiian Islands by humans. Its natural range is the Indo-Pacific Ocean, and it preys on coral polyps by destroying their exoskeletons with its poisonous spikes and then consuming them. It’s called a crown of thorns starfish because it has knobby protrusions that resemble the thorns of a crown on its body surface.

They may look cute and cuddly, but don’t be fooled! This spiny sea star can wreak havoc on coral reefs by feeding on the animal tissue that gives coral its color and structural support.

Origin and descriptions

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The crown-of-thorns starfish is native to both Indo-Pacific and Pacific oceans. The scientific name is Acanthaster planci, and it is also referred to as a cactus star. It can grow up to 14 inches in diameter (the size of a dinner plate) and weigh as much as 5 kilograms (about 11 pounds).

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This gives them enough size and weight to cause problems for coral reefs when they eat their prey. Crown-of-thorns starfish are generally found in shallow water near coral reefs; however, they can be found at depths of over 100 meters (328 feet). They are nocturnal predators that prefer to feed on hard corals; however, if hard corals aren’t available, then soft corals will do. When hungry, crown-of-thorns starfish will attack stony corals as well.

Species profile

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The crown of thorns starfish belongs to the family Acanthasteridae. These animals are also commonly referred to as sea stars, but they are not related to true sea stars (which are echinoderms belonging to another phylum). There are around thirty species in existence, with two being particularly well known: Acanthaster planci and Acanthaster brevispinus.

They can be found throughout tropical waters in various parts of the world. They have been introduced into a number of other regions via human intervention, including Hawaii and Australia. They are voracious predators that feed on coral polyps and sponges.

Although they do play an important role in reef ecosystems by keeping populations of these organisms under control, their numbers sometimes grow out of control due to overfishing or pollution. When this happens, the crown of thorns starfish will feed on coral indiscriminately until it is all gone. This causes large-scale destruction for marine ecosystems that rely on healthy coral reefs for survival.

Scientific name

The scientific name of the crown of thorns starfish is Acanthaster planci

Where did the crown of thorns starfish come from?

Crown-of-thorns starfish are found in tropical and subtropical waters throughout Indo-Pacific, Atlantic and Caribbean regions. These marine invertebrates have been observed from low tide to 150 meters depth, and inhabit seagrass beds, coral reefs, rocky shores and mangroves.

While they’re typically found in warm, tropical waters in places like the Great Barrier Reef, crown of thorns starfish have been spotted as far north as South Africa and as far south as New Zealand, where they feast on corals that have more resistance to cold temperatures.

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Crown of thorns starfish size

Crown-of-thorns starfish size is generally 10-14 inches (25-35 cm) in diameter. Although they can grow up to a maximum size of 31.5 inches (80 cm).

Crown-of-thorns starfish facts

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The crown-of-thorns starfish (Acanthaster planci) is a venomous sea star that has been observed to cause serious harm to coral reefs. The impact of these marine invertebrates has been devastating, leaving large areas of reefs dead or destroyed. Learn more about these notorious creatures and how they affect coral reefs in our Crown-of-Thorns Starfish facts sheet explained below.

What do crown of thorns starfish eat?

Crown-of-thorns starfish, or cot stars, are coral predators that get their name from a crown of thorns surrounding their mouths. The species preys on coral polyps and can devour them in a matter of hours if left unchecked. While most other starfish species have five-pointed crowns, a cot star’s is more like six or seven points to allow for easy prey consumption.

Crown of thorns starfish life cycle

The crown of thorns starfish reproduces sexually by broadcast spawning, like most echinoderms. There is no evidence Acanthaster planci reproduces asexually. This means that it cannot reproduce via somatic fission or arm autonomy as other starfish species do.

Females release millions of eggs into the water column, and males fertilize them with sperm. Planktonic larvae are formed from fertilized eggs, and they rely upon phytoplankton for nutrition while passing through multiple developmental stages, from gastrula to bipinnaria to brachiolaria.

The larva settles onto a hard surface near the end of the brachiolaria stage and metamorphoses into a juvenile starfish. As it matures, its arms begin to form. When a starfish is a juvenile, it has five arms, which increase to 21 when it is an adult.

According to researchers, there are three age classes for crown of thorns starfish: juveniles, sub-adults, and adults. The rate of growth is age-specific: Juveniles grow rapidly (16.7 mm per month) while adult growth slows down to 4.5 mm per month.

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In summer, Acanthaster planci speckles seasonally according to the location of each population. During the northern hemisphere’s breeding season, spawning takes place between May and August, while in the southern hemisphere, spawning takes place between November and February.

There has been a correlation between these seasons and periods of warmer water temperature in the respective habitat. A vigorous female may contain between 12 and 24 million eggs, and may produce up to 60 million eggs in a single season.

Crown-of-thorns starfish predators

The crown-of-thorns starfish (Acanthaster planci) is a species that eats coral polyps. Their numbers are kept in check through natural predation and competition, and by diseases and parasites like dinoflagellates, algae, mollusks, worms, and crustaceans.

One of the biggest predators of adult crown-of-thorns starfish is the giant triton snail, followed by Humphead Maori wrasse, starry pufferfish, and titan triggerfish. Shrimps, crabs, and polychaetes worms are predators of juvenile starfish.

Crown-of-thorns starfish venom

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The crown-of-thorns starfish venomous spines can inject stings that produce a variety of symptoms, such as pain and prolonged vomiting, as well as symptoms like erythema and swelling. Despite some improvements in skin surface lesions of spine-sting patients, subcutaneous induration and pain persist in the majority of lesions.

On radiographs of victims, several spines can usually be seen. Therefore, surgical excision of the spines is usually necessary to alleviate the symptoms, which is followed by remission of the symptoms.

Are crown-of-thorns starfish poisonous to humans?

In short, yes. Divers will soon discover that the crown of thorns starfish isn’t just protected by sharp spines – their spines contain poisons that can be deadly to humans as well as to marine life.

What toxins are in crown of thorns starfish?

Spines of the crown of thorns starfish contain saponin toxins that cause irritation to puncture wounds (a considerable issue when working with the starfish).

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Can you touch crown-of-thorns starfish?

Definitely not. You should avoid touching these starfish if you encounter them. It may cause severe stinging, swelling, and pain that can last for days.