Scientists Plan to Use Pheromones to Trap Coral-Eating Starfish

The crown-of-thorn starfish is probably the Great Barrier Reef's most serious threat, perhaps only rivalled by the Australian Government's apathetic approach to climate change. The species is indigenous, but due to a range of human-led changes in the environment it's seasonally breeding in vast numbers and ingesting large sections of the reef. Attempts to reduce numbers have so far been unsuccessful but marine scientists from the University of Queensland think they've now got a solution. They're going to lure them to their deaths with pheromones.

The plan, published in Nature journal today, comes from husband and wife duo Dr Sandie and Dr Bernard Degnan. "Crown-of-thorns is one of the biggest threats to not only the Great Barrier Reef but other reefs throughout the Indo-Pacific," the latter tells VICE. "The idea we came up with is to trick the crown-of-thorns so that we could trap them. Basically we let them do all the work. We set the bait and the traps, and they'll come to us. Rather than having to swim around and kill them each individually."

So what's luring the starfish into the traps? Through their research, the Degnans discovered that the crown-of-thorns' greatest strength is also its greatest weakness. The starfish breeds by releasing large amounts of pheromones that attract crowds of other starfish, which then all spawn en masse. The Degnans were able to identify the genetic code producing the starfish pheromones, and replicate them, creating a synthetic version to use as bait.

The Degnans

"We wondered how they attracted each other into these aggregates. We thought, 'There must be some chemical they're releasing to attract each other.' So we proved that in the aquarium, and used some pretty fancy tools to characterise the proteins they were putting in the sea water, and then mapped the whole genome," Bernard explains.

Now that the research is complete, the traps need to be designed and placed around the reef.  "The next phase is to engineer some traps so the starfish can get in but can't get out," says Bernard. "I guess the thing that's really different is that we can put these traps out and make them really big and put them in good locations, then just go away and come back a few days later to harvest the traps, basically like a commercial fisherman does."

"Harvesting" for the Degnans means diving down to the traps with syringes filled with poison. They then inject starfish individually to kill them. It's a very targeted procedure, which along with the environmentally-friendly nature of the pheromones is the benefits of the plan. "The starfish are making this chemical already. It's their secret communication system, so we don't think any other animals will be attracted to it. It's specific to these starfish," Bernard says.

Unfortunately, the crown-of-thorns is but one of many threats to the Great Barrier Reef's future. Still, Degnan is confident that this research will make a big difference to coral health. "The reef is under a lot of different stresses, but the crown-of-thorns is definitely up there as one of the major ones," he says. "What we're really excited about is that what we're proposing is solving a problem, instead of just identifying it."

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