Crown-of-thorns starfish thrive in degraded coral

Researchers in Queensland might have discovered why attempts to eradicate crown-of-thorns starfish is so difficult. And it’s not just because they are prolific breeders.

Outbreaks of crown-of-thorns starfish, which can decimate coral populations and lead to widespread reef degradation, are among the most significant challenges facing coral reefs.

Now, new research reveals these coral predators appear to thrive in the very conditions of coral degradation they help create.

The study, published in the journal Marine Environmental Research, proposes a “degraded reef hypothesis” to better understand how crown-of-thorn starfish (COTS) remain so persistent, despite extensive efforts to manage their impact.

It outlines how the loss of live coral, which COTS feed off, actually benefits them by providing rubble habitats which serve as nurseries for juvenile COTS.

When corals start to recover it results in a pulsed emergence of COTS as juveniles transition into coral-eating adults,  exacerbating the cycle of coral loss and reef degradation.

“Our previous research has shown that juvenile COTS can wait for just the right moment to emerge in large numbers; sometimes up to six years,” says co-author Professor Maria Byrne of the University of Sydney.

The findings indicate that other conditions that lead to coral degradation – such as heatwaves, cyclones and pollution – can create favourable environments for COTS to thrive.

“Our findings reveal a critical feedback loop in reef ecosystems,” adds co-author Dr Kennedy Wolfe of the University of Queensland.

“COTS populations may thrive as coral reefs degrade, leading to further coral loss. This cycle not only threatens corals but also the range of species that depend on healthy reefs for survival.”

The researchers say this feedback loop explains repeated COTS outbreaks on the Great Barrier Reef, despite exhaustive management through manual culling.

“Effective management strategies must account for the resilience of crown-of-thorns starfish and their ability to exploit degraded habitats. These coral predators are a symptom of ongoing environmental impact,” says Byrne.