While climate change remains the greatest long-term threat to coral reefs, local pressures such as coral-eating species can also have a major impact – especially when predator populations become unnaturally high. Native species like Crown-of-Thorns Starfish (COTS) and Drupella snails naturally feed on coral, but when their numbers get out of balance, they can cause widespread damage.

Outbreaks of these predators are often linked to human-driven pressures like poor water quality, the loss of natural predators, and potentially climate change. Warmer seas and increased nutrient runoff can create conditions that allow their numbers to explode, with devastating impacts on coral communities.

Meet the Culprits

Crown-of-Thorns Starfish (Acanthaster planci)

A large, spiny sea star that feeds by spreading its stomach over live coral and digesting it. In small numbers, COTS are part of a healthy reef, slowing down fast-growing coral and increasing diversity. But in outbreaks, they can devastate large areas of coral in a matter of days.

• One adult can consume up to 13 square metres of coral per year.
• They reach maturity within 2–3 years and live up to 8 years.
• Each female can release between 20–60 million eggs per spawning season, allowing populations to boom rapidly.

Drupella Snails (Drupella rugosa, Cornus, and Fragum)

These small, unassuming sea snails feed on live coral by scraping away the living tissue. Like COTS, their populations have increased due to changes in water quality and the decline of their natural predators.

• In large numbers, they can strip the living tissue from coral colonies quickly, leaving behind dead, eroded skeletons.
• One snail can consume several square centimetres of coral in a day, and outbreaks often involve tens of thousands of individuals.

Why Are They a Problem?

When coral-eating predator populations explode, they can wipe out fragile coral communities already struggling with heat stress, bleaching, and storms. This leaves reefs more vulnerable to erosion and slows down recovery.

What Are We Doing About It?

Lady Elliot Island’s Reef Protection Program actively monitors coral health and predator outbreaks and responds swiftly to reduce damage. Controlling coral predators at a local level gives coral communities the best chance of surviving in a rapidly changing climate.

This work is gratefully supported by the Great Barrier Reef Marine Park Authority’s Tourism Reef Protection Initiative, which empowers Reef operators with the infrastructure already in place – such as boats, dive teams, and on-site capacity – to become site stewards. By providing targeted funding and resources, the program enables operators like us to protect our local reefs in a practical, cost-effective way.

Fast Stats – Reef Protection Program (2017–2025)

• Crown-of-Thorns Starfish culled: 4,500+
• Drupella Snails culled: 126,000+