Starfish that prey on corals early in life become more destructive

A new study reveals that crown-of-thorns starfish can significantly enhance their growth by shifting their diets at a younger age.

Crown-of-thorns starfish (COTS) feed heavily on coral polyps, and outbreaks can be extremely detrimental to coral reefs. 

When the juvenile COTS first settle into a reef, they feed on eating rock-hard coralline algae. Researchers have found that the sooner the young starfish get a taste for coral polyps, the larger and more destructive they ultimately become.

A team led by Jennifer Wilmes of the ARC Centre of Excellence for Coral Reef Studies compared the growth of juvenile COTS who switch their diets within six months of settlement and those that continue to feed on coralline algae for up to a year.

The researchers found that juveniles which shift to eating corals earlier grow much faster and larger. The bigger COTS have higher reproductive success and consume coral at higher rates. 

“Here we demonstrate, based on extensive field sampling of juvenile starfish, that marked variation in body size among juvenile starfish is linked to an ontogenetic diet shift from coralline algae to coral,” wrote the study authors.

“This transition in diet leads to exponential growth in juveniles and is essential for individuals to reach maturity. Because smaller individuals experience higher mortality and growth is stunted on an algal diet, the ontogenetic shift to corallivory enhances individual fitness and replenishment success.” 

“Our findings suggest that the availability of coral prey facilitates early ontogenetic diet shifts and may be fundamental in initiating population irruptions.”

By preventing COTS outbreaks, experts can help to protect coral reefs from irreparable damage.

“Understanding the mechanisms that determine population replenishment is essential to develop effective early management intervention strategies,” wrote the researchers. 

“Failing to develop well-informed decision tools risks to produce counterproductive management outcomes and could in the worst case contribute to the collapse of the system itself, with potentially devastating and irreversible impacts on reef ecosystems.”

The study is published in the Proceedings of the Royal Society B.

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By Chrissy Sexton, Earth.com Staff Writer