Control efforts of crown‐of‐thorns starfish outbreaks to limit future coral decline across the Great Barrier Reef

Abstract

Crown‐of‐thorns starfish (CoTS) naturally occur on coral reefs throughout the Indo‐Pacific region. On Australia's Great Barrier Reef (GBR), outbreaks of CoTS populations are responsible for ecologically significant losses of corals, and while they have been documented for decades, they now undermine coral recovery from multiple stressors, especially anthropogenic warming. Culling interventions are currently the best approach to control CoTS outbreaks on the GBR, but assessing control effectiveness under multiple stressors is complicated. Using an ensemble of two reef community models simulating the temporal and spatial dynamics of CoTS and corals under future climate scenarios, we evaluate the present‐day and future effectiveness of the current implementation of the GBR CoTS Control Program. Specifically, we determine the culling effort needed (i.e., number of vessels) to achieve the maximum ecological benefits as predicted by the models under possible warming futures. Benefits were measured by comparing projections of coral cover and CoTS densities under scenarios of increasing control effort and baseline scenarios where no control was simulated. Projections of present‐day control efforts (five vessels) show that the number of individual reefs subject to CoTS outbreaks is reduced by 50%–65% annually, yielding a benefit of 5%–7% of healthy GBR coral area per decade, equivalent to gaining 104–150 km2 of live corals by 2035. A threefold increase in current control efforts is sufficient to reach more than 80% of the maximum coral benefits predicted by each model, but the future amount of effort required to control CoTS effectively depends on the intensity of warming and the early detection of CoTS outbreaks. While culling CoTS across the entire GBR is unfeasible, we provide a framework for maximizing ecosystem‐wide benefits of CoTS control and guide management decisions on the required culling effort needed to reduce CoTS outbreaks to levels that may ensure coral persistence in the face of future climate change impacts.

Protecting Great Barrier Reef resilience through effective management of crown-of-thorns starfish outbreaks

“…Our findings of regional scale outcomes align with recent modelling that a fleet of 10–15 vessels could deliver significant regional COTS outbreak suppression and coral growth and recovery effects under projected climate futures [ 51 – 53 ]. Our analyses estimate increases in coral cover consistent with previous predictions [ 13 ] in sectors where COTS have been effectively managed (e.g.…”

“…While COTS control has been shown to effectively protect coral cover at the site scales [ 37 , 55 ], this research provides the first published empirical evidence for reef and sector-level COTS outbreak suppression and coral protection. These findings support, and in some cases exceed, the estimated regional benefits of targeted COTS control [ 51 – 53 ] verify the benefit of early and sustained culling effort at large spatial scales.…”

Vinegar injections can be used safely to control outbreaks of crown-of-thorns starfish (Acanthaster solaris) during the peak spawning season

“…Despite extensive scientific research over the past half-century -a simple search for Acanthaster or crown-of-thorns on the Web of Science currently returns over 1000 scientific articles -, significant gaps persist in our understanding of crown-of-thorns starfish biology and ecology (Pratchett et al 2014(Pratchett et al , 2021. Beyond theoretical considerations, this severely hampers our ability to effectively predict and manage sporadic population outbreaks, and prevent widespread coral degradation at the Pacific scale (Mellin et al 2016, Castro-Sanguino et al 2023. In this paper, we investigated whether injections of household vinegar, a control method increasingly used in some Pacific island territories, could have detrimental effects by triggering massive spawning among aggregations of mature COTS.…”

Mapping the susceptibility of reefs to rubble accumulation across the Great Barrier Reef

“…Coral reefs are experiencing accelerating disturbance (Hughes et al, 2017 ; McWhorter et al, 2022 ), and while management can mitigate some types of damage, such as predation from crown-of-thorns starfish (Castro-Sanguino et al, 2023 ), major events like heatwaves (“coral bleaching”) and cyclones cannot be mitigated directly. Thus, management tends to focus on facilitating the process of coral recovery, whether through improving conditions for coral recruitment and survival (Gove et al, 2023 ; Mumby et al, 2021 ) or restoration (Doropoulos & Babcock, 2018 ).…”