Crown-of-Thorns Starfish Can Boost Coral Reef Diversity, Study Finds
- Crown-of-thorns starfish (COTS) can play a surprisingly constructive role in maintaining coral reef diversity when their numbers remain low, according to new research.
- To understand how low-density populations interact with living reefs, a research team led by Dr.
- At One Tree Reef, COTS appear to consume a relatively consistent amount of coral during each meal and move on, rather than demolishing the entire coral colony.
Crown-of-thorns starfish (COTS) can play a surprisingly constructive role in maintaining coral reef diversity when their numbers remain low, according to new research. The study, conducted by researchers at the University of Sydney and published in the journal Ecology and Evolution, challenges the long-held perception that the coral-eating marine predators are exclusively destructive to environments like Australia’s Great Barrier Reef.
Tracking COTS Predation at One Tree Island
To understand how low-density populations interact with living reefs, a research team led by Dr. Shawna Foo tracked coral feeding scars and surviving tissue at the University’s One Tree Island Research Station. The surveyed sites sit inside protected marine areas boasting healthy fish populations that naturally keep starfish numbers in check, preventing the massive destructive outbreaks seen elsewhere on the reef. Researchers found that living coral tissue remained after almost 75 percent of the examined COTS feeding events. According to Dr. Foo, a University of Sydney Horizon Fellow from the School of Life and Environmental Sciences, the starfish consume a relatively consistent amount of coral during each meal and then move on rather than demolishing entire colonies.
At One Tree Reef, COTS appear to consume a relatively consistent amount of coral during each meal and move on, rather than demolishing the entire coral colony. This meant live coral tissue remnants were frequently left behind.
How Low-Density Starfish Support Coral Biodiversity
The study suggests that at low densities, crown-of-thorns starfish support coral biodiversity by preventing dominant, fast-growing coral species from monopolizing available reef space. The survey revealed that remnants of fast-growing Acroporidae corals did not regenerate over feeding scars, leaving regeneration to occur mostly among much slower-growing Montipora and Porites corals. By targeting dominant fast growers, low-density populations create vital space for slower-growing species to persist and diversify the ecosystem. Research co-author Professor Maria Byrne noted that these results align closely with the intermediate disturbance hypothesis, a conservation framework proposing that occasional, moderate ecosystem disturbance helps maintain biodiversity.
Implications for Future Reef Management and Culling
While the findings highlight ecological upside, the study’s authors emphasized they do not diminish the severity of major COTS outbreaks, which have struck the Great Barrier Reef four times since the 1960s with eruptions occurring roughly every 15 years. Diminishing populations of natural predators—such as tritons and multiple coral reef fishes—continue to heighten the vulnerability of marine environments worldwide to destructive outbreaks. Researchers stress the importance of distinguishing between starfish performing their natural predatory role and outbreaks causing sustained reef decline. Consequently, the findings suggest that once an outbreak is suppressed, culling programs should not necessarily aim to eliminate COTS entirely, but rather pair culling with strong marine management to protect predators and keep populations in check.
