Mat Trueman

Crown of Thorns Starfish (COTS) Control Program

Mat Trueman
COTS Diver
Outbreak Locations - The Great Barrier Reef, Queensland, Australia

Mat works out on the Reef to tackle the Crown of Thorns Starfish (COTS), which is devastating the Reef. He and his team are real life aquatic superheros who spend weeks at a time hunting COTS. They’ve culled over 600,000 COTS at over 80 reefs since 2012.

What are COTS?

COTS are a native, coral-eating starfish found on reefs throughout the Indo-Pacific. COTS climb onto live coral, digesting the tissue off their skeleton with their stomachs. They prefer faster growing species like branching staghorns, but they will also eat slower growing species and soft coral. COTS spawn millions of eggs, which can travel up to 200km on ocean currents, easily moving from one part of the Reef to another.

Impact on the Reef

When starfish numbers are low, healthy coral can easily recover from their small-scale attacks, but outbreaks pose a severe threat to the Reef. During an outbreak, COTS eat coral tissue faster than it can grow, resulting in a significant decline in coral cover. In fact, it is estimated that COTS have been responsible for almost half of the coral loss seen over the last 30 years. Outbreaks typically last for 12 to 15 years and impact hundreds of kilometres of reef.

Action being taken

Two dedicated and highly trained dive teams from the Association of Marine Park Tourism Operators (AMPTO) travel the Great Barrier Reef in teams of 10-12 divers, manually culling starfish to protect coral cover on priority reefs, particularly prime tourism and conservation sites. This is done with a single injection that produces an allergic reaction in the starfish, causing it to break apart and die within 24 hours. Indigenous rangers play a key role through the “Working on Sea Country” program.

  • 3,000 – 4,000
    COTS can be removed in a 10 day expedition
  • 600,000
    COTS have been removed from 80 reefs
  • 27,000 COTS
    were removed in just 8 days at Arlington Reef
At times it feels like we are at war, but we are definitely winning; we are seeing coral regenerating, we can see the difference.
Col McKenzie, Executive Director, AMPTO

The project urgently needs support to:

  • Fund more boats and dive teams who can make an impact on the wider Reef
  • Train tourism operators in how to control COTS
  • Continue research into why outbreaks occur and how to prevent them in the future
  • Support other nations in their fight against COTS with education and equipment

Related actions

Unite for the reef.

Together, we can ease the pressures that the reef faces - but we need your support to do it. Because it’s only when we’re united as Citizens, that our individual actions can come together to make a real, physical impact on the Great Barrier Reef.