The beautiful Great Barrier Reef is the largest coral reef system in the world, and it's in trouble. One of its biggest threats is a nasty marine predator called the crown-of-thorns starfish, which can devastate reefs by feeding upon the coral. But scientists at the Australian Institute of Marine Science may have discovered a way to hold off this attacker – because just like any big bully, deep down the starfish is a scaredy-cat.

Crown Of Thorns 2016 07 29
Thanks to its big appetite for coral, the crown-of-thorns starfish is a major enemy of the Great Barrier Reef. Image: John Turnbull, Flickr

Okay, it might be unfair to call the starfish a bully. After all, it's only trying to survive. The problem is that it's just so good at it. The crown-of-thorns starfish (COTS) gets its name from the hundreds of sharp, toxic spines covering its body, which make any ocean-goer think twice before messing with it. On top of that, these starfish are super-reproducers. According to Dr Mike Hall, they can have the highest fertilisation rate of any known marine invertebrate. And for all those hungry COTS, coral is at the top of the menu.

Population outbreaks of the starfish are a major problem for coral in the Great Barrier Reef. In fact, they rank #2 on the list of reasons the iconic reef system is in decline, just below tropical cyclones and just above bleaching due to warming ocean waters. But unlike storms and global warming, the starfish have natural enemies, and chief among them is the Pacific triton. This snail may be key to protecting the reef. 

The Pacific triton is also called the "giant triton" because it can grow to a whopping two feet long. They live in Indo-Pacific coral reefs, and feed upon a variety of starfish and sea cucumbers, but they seem to have a particular liking for crown-of-thorns starfish. They don’t even seem to be bothered by all those needle-like spines!

Unfortunately, years of overhunting have taken their toll on the tritons' numbers. And since they eat perhaps just one starfish a week, they aren’t able to keep outbreaks in check through predation. But maybe they don't have to actually eat the starfish to control their numbers.

Hall and his team carried out some simple experiments where they introduced a crown-of-thorns starfish to seawater from a Pacific triton's tank – and just the scent of the snail in the water was enough to send the starfish into a bit of a frenzy, frantically (for a starfish anyway) scrambling at the sides of its tank. The starfish was positively terrified of these snails.

So here's the brilliant plan: by strategically planting tritons across the reef, researchers might be able to spread enough of that scary smell around to keep the starfish away from those areas. This tactic might even work to disperse COTS spawning aggregations, preventing them from multiplying like underwater bunnies. The scientists will also try to identify exactly what chemicals the starfish are reacting to. If that scent can be extracted or produced in the lab, it could then be used like oceanic bug spray, and the snails won't need to be present at all! 

There are still some obstacles in the way, of course. Most importantly, Pacific tritons are extremely rare, and not much is known about them. If this plan is going to work, researchers will need to study them more thoroughly, and probably establish a breeding programme to boost their numbers. In the end, a bit of snail stink might be a step towards preserving the beauty of the world's most famous reef system.


Top header image: Patrick Randall, Flickr