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30 Surprising Crown of Thorns Starfish Facts

by Sankalan Baidya
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One predator can destroy 42% of a certain species in a certain location. How does that sound? Terrible enough? Well, that is the story of corals in Great Barrier Reef – the prey of the Crown of Thorns Starfish. Sounds weird but yes, today, Great Barrier Reef is threatened to a great extent by these voracious coral eaters. In this article, we are going to learn some surprising Crown of Thorns Starfish facts and find what these animals do, where they live and how they look.

Before we start…

Name Crown of Thorn Starfish (usually referred to as COTS)
Kingdom Animalia
Phylum Echinodermata
Subphylum Asterozoa
Class Asteroidea
Superorder Valvatacea
Order Valvatida
Family Acanthasteridae
Genus Acanthaster
Species Acanthaster planci

Okay, now that we have a basic info piled up in a table, we can move on with out Crown of Thorns Starfish facts list. Be ready to be surprised!

Surprising Crown of Thorns Starfish Facts: 1-5

1. If there is any animal in this world that eats seemingly lifeless, stony and hard coral polyps, it is none other than the Crown of Thorns Starfish.

2. This starfish is massive and in fact, it is one of the most massive starfish in world. Just how big? Well, they can have a diameter of 3 feet! However, they can be as small as only 9 inches in diameter.

3. This starfish can have up to 23 arms! Yes, you read it right. They can have 23 arms each. However, the minimum number of arms that COTS can have is 7.

4. Why such weird name? Well, why don’t you take a look at the creature? This starfish is covered on its upper body surface with thorns or spines which grow up to 2 inches in length.

5. These spines or thorns are really bad. They can not only pierce through the wet suit and give a nasty puncture wound but also laced with venom, which can cause vomiting, nausea and severe pain.

Surprising Crown of Thorns Starfish Facts: 6-10

6. Crown of Thorns Starfish look like the proverbial and Biblical ‘Crown of Thorns’. That explains why the name was give to this creature in the first place.

7. Scientists have studied the fossils of COTS and have come to understand that these creatures have been residing in Earth’s oceans for several million years now.

8. Crown of Thorns Starfish outbreaks or infestation occurs at times and that’s not a good thing because when the infestation occurs, its usually bad news for coral reefs across the globe provided the outbreaks are taking place in quick intervals.

9. COTS outbreaks have taken place a number of times but the first one that was recorded was in 1950s in Ryukyu Islands, Japan. In 1962, Green Island, Australia, recorded the first COTS outbreak in Australia.

10. While it is a known fact that COTS outbreaks are not good for coral reefs, it is also true that when coral reefs become unhealthy and lose balance, such outbreaks are good.

Surprising Crown of Thorns Starfish Facts: 11-15

11. Okay, how is COTS outbreak good and how is it bad? Good only when the outbreak takes places at a gap of minimum 15 years. They just infest the areas and feed on corals that grow faster and provide the opportunity for the slow-growing corals to regenerate. This allows proper balance.

12. The problem occurs when these outbreaks happen in quick successions (that is, in less than 15 years). Since the corals do not get ample time to regenerate, coral reefs become endangered. This is precisely what is happening at Great Barrier Reef of Australia.

13. To make the situation even grimmer for the coral reefs, other factors like coral bleaching and cyclones pitch in. These factors are also known for destroying and killing the corals. These factors make food supply short for the Crown of Thorns Starfish.

14. What happens when food becomes scarce for COTS? Crown of Thorns Starfish are known to usually feed on corals that are stony and hard but grow relatively fast. For instance, the Staghorn Corals are their primary food source. However, when the food source is depleted, they start feeding on other corals which are not so fast growing. This creates a massive threat for the coral reefs.

15. Talking of feeding, did you ever wonder how the Crown of Thorns Starfish feed? They are known to extrude their stomachs out from their bodies and cover the corals. Once that is done, they will release some enzymes and digest the coral polyps.

Surprising Crown of Thorns Starfish Facts: 16-20

16. It may take hours to fully digest the coral polyps. However, once the process is completed, they will simply move on to the next coral polyps. What they leave behind is white skeleton of the corals.

17. Several measures have been taken by humans to control the outbreak of the Crown of Thorns Starfish. One of the commonest methods used by humans is to kill these starfish. The easiest way to do so is to inject bile salt in their bodies while they lay down on the corals for feeding.

18. The big question that we need to ask for now is what really is causing frequent COTS outbreak. Scientists say that there are basically two very important factors. First is the problem of overfishing, which removes the natural predators or COTS.

19. The second problem is that of excessive nutrients in the sea water. These excess nutrients come from dumped sewage and fertilizers that lead to quick outbreaks of these starfish.

20. Did you know that the adult or grown up Crown of Thorns Starfish can live up to 9 months without eating? Isn’t that incredible?

Surprising Crown of Thorns Starfish Facts: 21-25

21. The spines or thorns that are present on the Crown of Thorns Starfish are all covered with epidermis. The toxin resides in this epidermis.

22. The toxin is known by the name plancitoxin and it is known to be toxic for both humans and marine lives.

23. Now here is one really surprising fact about Crown of Thorns Starfish – it can lose one of its arms when it gets hurt or comes under stress. However, this creature has the ability of regrowing its arm within a span of 6 months.

24. When it comes to reproduction, these COTS take the external route. This means that the males release sperms while females release eggs right in the water column.

25. Sperms fertilize the eggs in water and the larvae hatch out. They stay planktonic for a maximum of 4 weeks and a minimum of 2 weeks. After that period, they will simply settle down on the floor of the ocean.

Surprising Crown of Thorns Starfish Facts: 26-30

26. Once on the ocean floor the Crown of Thorns Starfish will coralline algae. This will take place for a few months and eventually, they will change their diet and move on to feed on the coral polyps.

27. Now here is perhaps one of the weirdest Crown of Thorns Starfish facts you will ever come across. The adult and large females can produce up to 65,000,000 (65 million) eggs during one season!

28. Talking of season, wondering when do they spawn? They do so when the water temperatures are maximum. That’s between the period October and March.

29. This starfish is world’s second largest starfish. The first spot is taken by Sunflower Starfish.

30. These creatures are nocturnal by nature and they have the ability to move at a speed of 12.5 miles an hour or 20 kilometers an hour.

Some Bonus Facts About Crown of Thorns Starfish

Eating frenzy One Crown of Thorns Starfish is capable of eating 6 square meters of corals in a single year.
Natural predators of grown up Crown of Thorns Starfish Titan trigger fish, starry pufferfish, humphead Maori wrasse, giant triton snail, yellow margin trigger fish, harlequin shrimp and lined worm.
Natural predators of juvenile Crown of Thorns Starfish (before spines are formed) Parrot fish, spangled emperor and red emperor, annelid worms, crabs, shrimps etc.
Larvae survival rate 0.00000001 %.
Outbreak mark If 30 Crown of Thorns Starfish are found in 1 hectare area, it is called outbreak. In 1970s, northern Great Barrier Reef saw an outbreak of the scale of 1,000 COTS per hectare.
Range Across Indian Ocean and Pacific Ocean.

Sources: 1, 2, 3, 4, 5, 6, 7, 8

Image Credits: 1, 2, 3, 4, 5

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