Early detection of renewed population irruptions of Pacific crown-of-thorns starfish (Acanthaster cf. solaris) on Australia’s Great Barrier Reef

Recurrent population irruptions of the Pacific crown-of-thorns starfish (COTS; Acanthaster cf. solaris) remain one of the foremost causes of coral mortality on Australia’s Great Barrer Reef (GBR), contributing to substantial declines in coral cover and reef health. Preventing or minimising coral loss due to current and future population irruptions of COTS is critical for improving the status and outlook of coral reef ecosystems across the GBR. Establishing when, where, and why these population irruptions start is fundamental to effective largescale and long-term management. Previous population irruptions of COTS on the GBR are purported to have started on reefs between Lizard Island (14.6oS) and Cairns (17oS), an area commonly referred to as the initiation area. However, in previous outbreaks there were detectable increases in the abundance of adult COTS in the far northern GBR well ahead of similar reports for reefs within the putative initiation area (e.g. Lizard Island). This study used new and effective sampling methods to assess inter-annual variation in the abundance and size of COTS across the northern GBR from 2021–2024, testing for increasing densities of COTS that might represent the precursor of impending population irruptions.

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