What is the crown-of-thorns starfish?
The crown-of-thorns starfish is a large, spiny coral-eating starfish. Outbreaks of millions of them have caused major coral loss on the Great Barrier Reef, so divers work to control their numbers.
The starfish can grow wider than 50 centimetres and is covered in sharp, venomous spines. It feeds by pushing its stomach out over coral and digesting the living tissue, leaving white skeletons behind.
In normal numbers the starfish is part of the reef ecosystem. But during outbreaks, numbers explode and they can strip whole reefs of coral. Outbreaks have occurred in waves since the 1960s.
Why outbreaks happen
Scientists think nutrient runoff from farmland may help starfish larvae survive by feeding the plankton they eat. Overfishing of predators may also play a role.
Control divers inject the starfish with a solution such as bile salts or vinegar, which kills them without harming the reef. Teams target high-value reefs for tourism and biodiversity.
Researchers are also developing robots and other tools to find and control the starfish.
Did You Know?
A single female crown-of-thorns starfish can release tens of millions of eggs in a spawning season.