Crown-of-thorns starfish are widely known for consuming coral and causing severe damage during population outbreaks. However, research from the University of Sydney indicates that these predators may also contribute to healthier coral communities when their numbers remain under control.
The study examined feeding scars and surviving coral tissue at the university’s One Tree Island Research Station on Australia’s Great Barrier Reef. The research sites were protected areas with healthy fish populations and relatively low numbers of crown-of-thorns starfish, unlike reef areas affected by major outbreaks.
Researchers found that living coral tissue remained after nearly 75% of the observed feeding events. According to lead researcher Shawna Foo, the starfish generally consumed a consistent amount of coral before moving on, rather than destroying entire colonies.
The findings suggest that this feeding behavior may influence competition among coral species. Fast-growing Acroporidae corals can spread quickly and limit space for slower-growing varieties. When crown-of-thorns starfish feed on these dominant corals, they may open areas where other species can persist.
The study found that surviving fragments of fast-growing Acroporidae corals did not regenerate across the damaged areas. Regrowth was instead concentrated among slower-growing Montipora and Porites corals. The researchers said this pattern could help increase coral diversity when starfish populations are kept at low densities.
The results do not lessen the threat posed by large outbreaks. Since the 1960s, the Great Barrier Reef has experienced four major crown-of-thorns starfish outbreaks, occurring roughly every 15 years. During these events, high numbers of starfish can destroy extensive areas of coral. The researchers linked the vulnerability of reefs to the decline of natural predators, including tritons and several reef fish species.
The study’s authors said conservation efforts should distinguish between starfish populations performing a natural ecological role and outbreaks that cause prolonged reef decline. They suggested that removing every starfish may not be necessary after an outbreak has been suppressed, provided marine management protects natural predators and keeps the population in check.
The researchers connected their findings with the intermediate disturbance hypothesis, which proposes that occasional, moderate disturbances can prevent one species from becoming too dominant. In this case, limited predation by crown-of-thorns starfish may help maintain a more diverse coral community, while uncontrolled population growth remains a serious conservation concern.
The research was published in Ecology and Evolution by Shawna Andrea Foo, Matthew Clements, Adi Zweifler, Georgie Eggleton, Hayden Millican and Maria Byrne.
Sources: ScienceDaily.