New research from the University of Sydney is reshaping the understanding of Crown-of-thorns starfish (COTS), commonly seen as a major threat to coral reefs. While COTS are known for their ability to destroy large areas of coral, this study suggests that in controlled numbers, they may actually contribute to coral diversity and resilience. The research focuses on the Great Barrier Reef, where COTS have caused significant damage in four major outbreaks since the 1960s, typically occurring every 15 years. These outbreaks are often linked to the decline of COTS predators, such as tritons and certain reef fish, which are essential in keeping COTS populations in check. The study, published in the journal Ecology and Evolution, examined the effects of COTS on coral at the University's One Tree Island Research Station, located on the Great Barrier Reef. The research team, led by Dr. Shawna Foo, observed coral feeding scars and surviving coral tissue after COTS predation. These sites are in protected areas where healthy fish populations naturally regulate COTS numbers, preventing the large-scale destruction seen in other parts of the reef. The researchers found that after nearly 75% of the COTS feeding events, living coral tissue remained, indicating that COTS may play a role in maintaining reef biodiversity. The findings suggest that at low densities, COTS can help prevent dominant coral species from taking over the reef. Fast-growing corals like Acroporidae, which are commonly found on reefs, did not regenerate after being fed upon by COTS. However, slower-growing corals such as Montipora and Porites were able to regenerate. This process allows for a more diverse coral community by creating space for slower-growing species to thrive. The study does not downplay the damage caused by large COTS outbreaks, but it highlights the potential benefits of maintaining a balanced COTS population in a healthy marine ecosystem. The research supports the intermediate disturbance hypothesis, a concept in ecology that suggests moderate disturbances can promote biodiversity. This insight may influence future culling strategies for COTS outbreaks, helping to determine when and how to manage COTS populations. According to Professor Maria Byrne, a co-author of the study, the findings emphasize the importance of maintaining a balance between COTS and their predators. Effective marine management, including protecting COTS predators, is crucial to keeping COTS populations in check and ensuring the long-term health of coral reefs.