© Commonwealth of Australia (Reef Authority). Photographer: Braden Smith, 2019.

A crown-of-thorns starfish feeding on a coral colony.

Tackling a thorny problem to protect the reef

The Reef Authority’s Crown-of-thorns Starfish (COTS) Control Program is a proven, effective and scalable management action that protects coral and supports the Great Barrier Reef’s health and resilience.

The challenge

Pacific crown-of-thorns starfish (Acanthaster cf. solaris) are native to Australian waters. They can be found across much of the Indo-Pacific Region, including the entire 2,300km stretch of the Great Barrier Reef Marine Park.

They feed exclusively on live coral and can consume an area equivalent to half of their dinner-plate-sized bodies every day. When numbers are low, their presence helps maintain the diversity of coral communities and the ecosystem’s natural balance.

However, under certain conditions — including low numbers of their natural predators and plentiful nutrients in the water — crown-of-thorns starfish numbers can increase to outbreak levels, often in the hundreds of thousands, leading to large-scale coral loss. Fishers target fish species that eat the juveniles, and by reducing predatory fish numbers, more crown-of-thorns starfish can make it to adulthood, potentially contributing to population outbreaks.

At outbreak levels, crown-of-thorns starfish have caused equal, if not greater, declines in coral cover as other major Reef disturbances, including mass coral bleaching events and severe tropical cyclones.

Outcomes

Working collaboratively with government and industry partners, the COTS Control Program uses the best available science and field intelligence to strategically deploy systematic surveillance and culling operations to target reefs throughout the Great Barrier Reef Marine Park. The program effectively protects coral across hundreds of reefs and supports reef resilience.

Since the program’s expansion in 2012, the Reef Authority has invested more than 130,000 diver hours to protect more than 800,000 hectares of coral reef habitats from crown-of-thorns starfish predation. Moreover, the COTS Control Program provides over 140 reef jobs and employment and training opportunities for Traditional Owners.

Future initiatives

A $161.5 million funding commitment from the Australian Government will sustain the COTS Control Program until June 2030. The program has recently partnered with four companies, including an Indigenous-owned business, to deliver on-water operations through to 2027.

Over the next three years, the COTS Control Program aims to deliver more than 3,370 days at sea and 55,117 diver hours, targeting up to 200 reefs annually to protect coral from starfish predation and support the Reef’s natural resilience in the face of a rapidly changing climate.

© Rickard Abom, Reef & Rainforest Research Centre 2021.

A scuba diver uses a tool to cull a crown-of-thorns starfish that has eaten several coral colonies, which are bright white in the image.