![]() While its efficacy is supported by independent modelling exercises 14, 21, catchment and water quality improvement efforts, implemented since the early 2000s 22, are unlikely to have acted to suppress CoTS population dynamics and cannot yet be relied upon to contribute to CoTS control on the GBR 15. the terrestrial run-off hypothesis) 11 has become a central argument for policy and investment to improve water quality of the Great Barrier Reef (GBR) World Heritage Area 20. In Australia, the purported role of nutrient enrichment from land-based run-off (i.e. The nutrient enrichment hypothesis states that high nutrient availability increases phytoplankton biomass and enhances CoTS larval growth and survival leading to mass recruitment events and outbreaks. The role of water quality improvement programmes in CoTS control are predicated on the hypothesized link between nutrient enrichment and CoTS outbreaks 11. ![]() Recent improvements in single-injection methods to cull individual CoTS 18, combined with strategic deployment of manual control 19, have significantly improved the efficacy of manual control programmes to reduce CoTS impacts on coral reefs 14, 15. Manual control programmes have been implemented since the 1960s 7, 16, killing or removing an estimated 17 million CoTS across the Indo-Pacific by 2014 2, but with limited success in reducing either CoTS densities or coral loss 17. Given that CoTS outbreaks continue to be one of the major drivers of coral loss 12, including during recent mass bleaching events 13, new pathways for CoTS control at large scale have become increasingly important to halt further declines in coral cover and support reef restoration and resilience in a warming climate across the Indo-Pacific 14.Ĭontemporary management to reduce the detrimental impact of CoTS population outbreaks on coral reefs centres around a combination of direct manual control and water quality improvement 12, 15. While neither hypothesis has received universal or unequivocal support 2, their contributions to causing or propagating CoTS outbreaks are also not mutually exclusive. Whether human interference has exacerbated CoTS outbreaks, through increasing nutrient levels enhancing larval recruitment 11 or harvesting of natural predators that would limit CoTS abundance 9, remains a contentious topic 2. Destructive impacts of CoTS outbreaks on Indo-Pacific coral reefs were first documented in the 1950s s 8, 9, though anecdotal reports suggest that CoTS population densities have long varied widely 10. Phenomenal fluctuations in CoTS abundance within periods of a few years 2 can result in increased CoTS densities that cause extensive coral mortality 4, suppressing coral recruitment and recovery 5, and fundamentally altering the form and structure of coral reefs and their biological communities 6. Predation by native Crown-of-Thorns Starfish (CoTS, Acanthaster spp.) during periodic population outbreaks is a major contributor to sustained declines in coral cover across Indo-Pacific coral reefs 1, 2, 3. Designing targeted fisheries management with consideration of CoTS population dynamics may offer a tangible and promising contribution to effectively reduce the detrimental impacts of CoTS outbreaks across the Indo-Pacific. Moreover, the biomass of fish species and families that influence CoTS densities are 1.4 to 2.1-fold higher on reefs within no-take marine reserves, while CoTS densities are 2.8-fold higher on reefs that are open to fishing, indicating the applicability of fisheries-based management to prevent CoTS outbreaks. CoTS densities increase systematically with increasing fish biomass removal, including for known CoTS predators. Here, we show that fish biomass removal through commercial and recreational fisheries may be a major driver of CoTS population outbreaks. The potential drivers of these outbreaks have been debated for more than 50 years, hindering effective management to limit their destructive impacts. Outbreaks of corallivorous Crown-of-Thorns Starfish (CoTS, Acanthaster spp.) have caused persistent and widespread loss of coral cover across Indo-Pacific coral reefs.
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