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Five fascinating facts about crown-of-thorns starfish

Crown-of-thorns starfish, or COTS, are a native species on the Great Barrier Reef, but pose a major threat to coral populations. They eat up to 10 square metres of coral a year and, with long needle-sharp spines covering their body, they’ve got built-in protection from predators.

Five fascinating facts about crown-of-thorns starfish

They’re also super-spawners: millions of eggs are produced each season.

Our Reef is experiencing its fourth major COTS outbreak since the 1960s. With our partners, we’re working to advance the technology that helps us decide when and where to intervene to best protect coral reefs. 

Here are five fascinating facts about crown-of-thorns starfish.  

1. COTS are thorny in name and nature  

Crown-of-thorns starfish received their common name from the needle-sharp spines that cover their arms and body that supposedly resemble the biblical crown of thorns. Their scientific family name – Acanthaster - means almost the same thing. In Latin, Acanth means thorny and aster means star. 

2. COTS have lots of predators  

Despite their toxic spines, lots of animals on the Reef eat COTS. Until very recently, scientists believed only the giant Pacific triton snail could digest them, but we now know many fish and crustaceans dine on these starfish, particularly while they are young and don’t have as many toxic spines.  

3. COTS have eyes in their arms  

In the dark of night, you might spot COTS crawling across the reef at a whopping 30cm a minute. That’s relatively fast for a starfish. Like all starfish, COTS have tiny water-powered tube feet underneath their bodies that inflate, extend and walk them forward. A special light-sensitive eye spot located in the end of each arm helps the starfish to orientate themselves and find their feeding grounds.  

Credit: GBRMPA

4. COTS are supersized starfish  

Starfish are famous for their “arms” that give them their star-like shape. Of the 2,000 species that inhabit our oceans, the classic five-armed starfish are the most common. But some, like the crown-of-thorns, take it to a whole new level. They’re one of the largest of all starfish, growing more than 20 spine-covered arms in their lifetime and reaching 50cm in diameter.