Crown-of-thorns starfish

spineless obliterate
yet, ecological keystone
allegro agitato


Once upon a time there was a starfish. She was a rather beastly organism with over a dozen arms covered in toxin-riddled thorns. Hence her name, crown-of-thorns starfish (Acanthaster planci). She had an insatiable appetite that rivaled that of Cookie Monster’s. Her meal of choice: coral. Living in the waters of the Great Barrier Reef, she fed on fast-growing corals allowing slow-poke corals to grow, diversifying the spectacular reef. The starfish and the corals lived happily ever after.

Except, they most definitely did not.

Also known as COTS, when populations of this starfish explode the reef succumbs to a ravenous “plague”. Swarms of COTS devour corals at alarming rates. Vibrant reefs rich in diversity are converted to abysmal, colourless masses. COTS can be as damaging as cyclones, and thought to be responsible for ~40% of coral decline.

What causes a COTS outbreak?

There is no smoking gun. Maybe a perfect storm of factors. First, fluctuations in COTS population size occur naturally. But there has been over-harvesting of COTS’ natural predators including the Triton’s trumpet. Then there is urban and agricultural run-off increasing the nutrient-richness of river water entering the reefs, which could enhance larval COTS survival.

What can be done to mitigate outbreaks?

Physically removing COTS is tedious and getting pricked by the venomous spines is not ideal. A single injection of the chemical goop thiosulfate-citrate-bile-sucrose causes an allergic reaction and 24 hours later you’ve got dead COTS. The smell of their triton enemy causes COTS to run scared. Predator odour could be used to push COTS out of reefs. [update: injection of lime juice or vinegar also kills COTS!]

It remains a challenge predicting what conditions will cause an outbreak, and when and where an outbreak will occur.

This starfish and coral story is to be continued.

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