a gist triton sits behind a crown-of-thorns starfish, both on the floor of a grey. There are more shells in the backkground

Innovative approaches to controlling crown-of-thorns starfish

Thinking differently about a decades-old problem

Crown-of-thorns starfish (aka COTS) contribute to large losses of hard coral on the Great Barrier Reef. Disturbances such as marine heatwaves and more severe cyclones because of climate change are placing increased pressures on the Reef. With little relief in sight, this makes efforts to control the starfish outbreaks at the local or regional level even more important.

Starfish control strategies currently include manual control through a program operated by the Great Barrier Reef Marine Park Authority as well as efforts to improve the water quality entering the Great Barrier Reef.

Studying crown-of-thorns takes place in the field and in the National Sea Simulator (pictured). Image: Christian Miller

AIMS scientists are developing innovative approaches to improve starfish control methods. This work is part of the Crown-of-thorns starfish Control Innovation Program (CCIP), funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.

Natural chemical cues can lure or disperse starfish

Crown-of-thorns starfish control programs currently rely on divers searching for the starfish and then manually injecting with bile salts or vinegar. When in outbreak proportions, starfish on individual reefs sometimes number in the tens of thousands, making this task labour intensive. This task is made even more challenging by their cryptic nature - many more starfish remain hidden within the reef’s structure, making them difficult to find and cull.

AIMS scientists are working to make this process more efficient and effective by developing a complementary approach that exploits the starfish’s keen sense of smell.

Even though crown-of-thorns starfish have an eye at the end of each of their many arms, they do not have good eyesight. Instead, they rely on detecting chemical cues in the water. This keen sense of smell can help them find coral prey, mates in spring, or even sense danger. For example, just a sniff of their natural predator the giant triton can send them fleeing.

How a crown-of-thorns starfish reacts to the smell of a giant triton snail

Luring the starfish

AIMS scientists collaborate with other research organisations to identify the chemical compounds and proteins which trigger an attraction response in the starfish. By isolating and characterising these chemical cues, scientists are working towards developing a starfish bait, similar to cockroach bait. These could be deployed onto the Reef to attract starfish to one location, making control easier and more effective.

We are using hydrodynamic models to help us identify the best time and place to release the baits on a reef to make sure starfish in the area will smell it and move in the direction we want them to.

AIMS leads this research as part of the COTS Control Innovation Program.

Snail vs starfish

The AIMS team are also investigating starfish deterrents and repellents. Repellents can come from sources such as injured or dead starfish, or predators such as the giant triton snail.

A giant triton slowly eats a crown-or-thorns starfish, despite the spines and toxic slime. Image: Christian Miller

We are exploring the potential role of these predatory snails and their chemistry to deter starfish from an area. We are also developing methods to map the distribution of giant tritons on the Great Barrier Reef to assist in their conservation in an effort to naturally and sustainably suppress crown-of-thorns starfish populations.